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Friction stir spot welding of AA 1050 Al alloy and hot stamped boron steel (22MnB5)
Abstract
The present study investigates the effect of joining parameters on the microstructural and mechanical characteristics of dissimilar friction stir spot welding (FSSW) between AA 1050 Al and 22MnB5 hot stamped boron steel. Mechanical performance has been evaluated by shear and microhardness testing. Optical microscopy has been used to investigate the microstructure generated in the different FSSW regions. A macrostructural examination has revealed the creation of mechanical interlocking in the Al steel connections. No volumetric defects or any other imperfection has been found in all FSSW connections. Shear failure load has increased with increasing both tool rotational speed and plunge depth for all FSSW connections. Higher plunge depth has improved the mechanical interlocking between lower and upper sheet due to the formation of a larger secondary flash. Encouraging results have been obtained using coated WC–Co tools in terms of durability and joint performance.
... While, in theory, solid-state welding based on friction effectively eliminates the challenges related to IMCs, numerous studies state that a thin Fe x Al y IMC layer is still formed at the dissimilar interface [17]. Furthermore, an Al-Si coating may serve as a filler material to promote better interfacial bonding between the aluminum and steel [18][19][20]. For instance, da Silva et al. [18] reported the possibility of welding an AA1050 aluminum alloy and 22MnB5 steel using FSSW. ...
... While, in theory, solid-state welding based on friction effectively eliminates the challenges related to IMCs, numerous studies state that a thin FexAly IMC layer is still formed at the dissimilar interface [17]. Furthermore, an Al-Si coating may serve as a filler material to promote better interfacial bonding between the aluminum and steel [18][19][20]. For instance, da Silva et al. [18] reported the possibility of welding an AA1050 aluminum alloy and 22MnB5 steel using FSSW. ...
... Furthermore, an Al-Si coating may serve as a filler material to promote better interfacial bonding between the aluminum and steel [18][19][20]. For instance, da Silva et al. [18] reported the possibility of welding an AA1050 aluminum alloy and 22MnB5 steel using FSSW. Based on the results of tensile tests, the authors concluded that the Al-Si coating could play an important role in the weldability of these materials since it could positively enhance the diffusion ability of Al into the coating. ...
Lap joining of an aluminum AA6082-T6 plate and a UHSS steel plate coated with an Al-Si layer was performed using Probeless Friction Stir Spot Welding (P-FSSW). The dwell time and rotational speed were controlled in the range of 10–15 s and 1000–1500 rpm, respectively. For all the samples, thermo-mechanical deformation occurred solely within the upper AA6082 plate. A refined grain structure was formed in the aluminum plate close to the surface. The dwell time was responsible for the intensity of the material flow, resulting in stirring between the Al-Si layer and the aluminum plate at 15 s. The microhardness distribution corresponded to the microstructure features.
... Conventional friction stir spot welding (FSSW) is a relatively new solid-state joining technology, which is a natural alternative to fusion welding due to that it avoids the problems of solidification and liquation cracking [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Mazda has used conventional FSSW to join Al alloy to coated steels in aluminum trunk lid [27], acceptable weld strength was achieved although keyhole significantly decreased effective bonded area [11][12][13][14][15]. ...
... Mazda has used conventional FSSW to join Al alloy to coated steels in aluminum trunk lid [27], acceptable weld strength was achieved although keyhole significantly decreased effective bonded area [11][12][13][14][15]. There are three main approaches of joining Al alloy to steel by conventional FSSW: (i) directly joining Al to uncoated steel through the formation of IMCs while avoiding plunging the tool pin into bottom steels [11][12][13][14][15][16], (ii) mechanical interlocking by displacing the bottom steel into the Al sheet [17][18][19][20][21][22][23], and (iii) adoption of coatings on steels to promote the interfacial bonding [24][25][26][27][28]. It is noted that a relatively longer welding cycle (5-15 s) needs to be applied to promote the IMCs layer formation when directly joining Al to uncoated steels [11,12,14], which is impractical for the mass production. ...
... It is noted that a relatively longer welding cycle (5-15 s) needs to be applied to promote the IMCs layer formation when directly joining Al to uncoated steels [11,12,14], which is impractical for the mass production. Meanwhile, advanced tool material such as WC-Co [19], WC [20,22], W25Re [17,18,21], tungsten carbide [22], or silicon nitride should Table 1 Chemical compositions of as-received materials and coated materials (wt%) [39,40]. be used to obtain interlocking mechanism by plunging tool pin into the bottom steels [23]. ...
Defect-free dissimilar Al/zinc coated steel and Al/AlSi coated steel welds were successfully fabricated by refill friction stir spot welding. However, Al alloy and uncoated steel could not be welded under the same welding condition. Al-Zn eutectic layer formed at the Al/zinc coated steel interface showed non-uniformity in thickness and nanoscale intermetallic (IMC) produced was discontinuous. The bonding formation between the Al-Zn layer and the surrounding materials was attributed to a liquid/solid reaction mechanism. Bonding formation at Al alloy and AlSi coated steel interface was attributed to a solid/solid reaction mechanism, as the joining process did not involve with melting of base metals or AlSi coating materials. Kissing bond formed at the weld boundary acted as a crack initiation and propagation site, and the present study showed that weld strength of Al 5754/AlSi coated steel was greatly influenced by properties of original IMC layer.
... Elrefaey et al. [1] argue that the Al-Fe bonding is promoted by a layered structure formed in a steel fine-grained zone, adjacent to the base materials interface, and constituted by Fe 2 Al 5 and Fe 4 Al 13 intermetallic compounds (IMC). Other IMC compounds, such as FeAl 3 and FeAl, were also detected by Shen et al. [6] and Kimapong and Watanabe [8], in welds performed with other base materials combinations. Those authors assumed that the presence of a IMC layer is the main bonding mechanism in Al-Fe lap welding. ...
... Beyond the IMC layer, other Al-Fe bonding mechanisms were already reported in dissimilar FSLW literature. Da Silva et al. [3] determined that a mechanical interlocking effect and diffusion bonding between the aluminium sheet and the Al-Si coating of a 22MnB5 steel were the main bonding mechanisms in AA1050-22MnB5 dissimilar Al-Fe joining. According to Chen and Nakata [14], the surface finish of the steel plate may influence the type of bonding mechanisms in FSLW of aluminium to steel. ...
... According to Shen et al. [6] as well as Da Silva et al. [3], the use of different pin plunge depths influences the bonding. In addition, the use of an excessive plunge depth was harmful due to the intense pin wear, caused by the tool penetration into the steel plate. ...
The use of a multipass welding strategy for increasing the bonding area in the dissimilar friction stir lap welding (FSLW) of aluminium to steel is analysed in current work. In order to minimize tool wear, the pin penetration into the lower plate, the steel plate, was set to a minimum. By performing partially overlapped welding passes it was possible to analyse the quality of the bonding across the multipass weld. The microstructural analysis of the bonding interface, after weld collapse in tensile-shear testing, enabled to conclude that by minimizing the pin penetration in the steel plate, the formation of intermetallics in the bonding interface is supressed and base materials joining results from mechanical bonding and solid state solution. However, for each welding pass, the bonding is not uniform/continuous across the pin trajectory. The deleterious effect of the bonding discontinuities on the monotonic weld strength may be limited by overlapping the successive weld passes, in order to maximize the bonding area. Improving the fatigue strength requires optimizing the welding parameters and/or pin positioning relative to the lower plate in order to avoid the occurrence of micro-cavities at the bonding interface.
... A recent study investigated the impact of various processing parameters on the quality and mechanical properties of joints made by FSW using AA1050 aluminum alloy. The study examined the effect of processing parameters such as rotational speed, traverse speed, plunge depth, and dwell time on the joint properties [1]. It is essential to recognize and comprehend the potential interactions that can take place between the welding parameters to maximize the performance of the FSW joint that is produced as a result of the welding process [2]. ...
... In general, there is an optimum range of traverse welding speeds for each material that produces optimal mechanical properties. For AA1050 Aluminium alloy welded using FSW process, studies have shown [1] that an optimum range of 20-28 mm/min produces good quality welds with high strength and ductility. ...
Friction stir welding (FSW) is gaining popularity in aluminum alloy joining due to its numerous advantages, such as creating high-quality joints with minimal heat input. This study examined the impact of different processing parameters, such as rotational and traverse speeds, on joints' quality and mechanical properties created through the FSW of AA1050 aluminum alloy. Various experiments were conducted to weld AA1050 aluminum alloy to investigate this, varying the rotational speeds (450-900 rpm) and traverse speeds (14-40 mm/min). The findings indicated that higher rotational speeds were associated with diminished joint quality, as indicated by heightened levels of porosity and the formation of intermetallic compounds. Moreover, an augmentation in traverse speed led to elevated tensile strength and hardness levels. The study determined that the processing parameters substantially impact the quality and mechanical properties of joints created through friction stir welding of AA1050 aluminum alloy. The study suggests that superior joints with favorable mechanical properties can be achieved by utilizing an intermediate rotational speed of 900 rpm and a traverse speed of 20 mm/min.
... A recent study investigated the impact of various processing parameters on the quality and mechanical properties of joints made by FSW using AA1050 aluminum alloy. The study examined the effect of processing parameters such as rotational speed, traverse speed, plunge depth, and dwell time on the joint properties [1]. It is essential to recognize and comprehend the potential interactions that can take place between the welding parameters to maximize the performance of the FSW joint that is produced as a result of the welding process [2]. ...
... In general, there is an optimum range of traverse welding speeds for each material that produces optimal mechanical properties. For AA1050 Aluminium alloy welded using FSW process, studies have shown [1] that an optimum range of 20-28 mm/min produces good quality welds with high strength and ductility. ...
... There have been few studies on the direct welding of Al to boron steel. Ding et al. [5] and Shen et al. [6] used refill friction stir spot welding whereas Silva et al. [7] applied friction stir spot welding to join 5XXX series Al alloys to Usibor 1500 Ò (abbreviated as Usibor from hereon). However, in the studies [5] and [7] the steel used was in a soft, prior hardened state with ultimate tensile strengths between 400 and 600 MPa. ...
... Ding et al. [5] and Shen et al. [6] used refill friction stir spot welding whereas Silva et al. [7] applied friction stir spot welding to join 5XXX series Al alloys to Usibor 1500 Ò (abbreviated as Usibor from hereon). However, in the studies [5] and [7] the steel used was in a soft, prior hardened state with ultimate tensile strengths between 400 and 600 MPa. A wide variety of joining techniques have been utilized to join 6XXX series Al alloys to boron steels including fric-tion element welding (FEW) [4,8], self-piercing riveting (SPR) [4], ultrasonic plus resistance spot welding (U+RSW) [2], mechanical clinching [4,9,10], resistance element welding (REW) [4,11], RIV-TAC Ò [4] and most recently resistance spot welding (RSW) [12]. ...
Direct welding of ultrahigh-strength boron steels to aluminum alloys is challenging but of great practical importance. The present study reports a new approach in vaporizing foil actuator welding to produce direct spot welds between 6022-T4 Al alloy and Usibor 1500®, a representative boron steel. Mechanical testing results revealed a strong joint with failure occurring at the Al base metal outside the weld nugget. Comparison of joint strengths with other joining techniques revealed performance on par if not better, opening prospects for development of more robust dissimilar welding pairs in the future.
... Santella et al. [19] investigated dissimilar friction stir joining of 780-MPa grade high-strength steel and HPF steel, and Hong et al. [20] evaluated failure mode and fatigue behavior of FSSW specimens. da Silva et al. [21] investigated FSSW of Al 1050 alloy and Al-Si-coated 22MnB5 boron steel using a WC tool. Sound FSSW joint without volumetric defects and reliable tool life were confirmed. ...
... Before HPF After HPF A straight hook shape was observed only when the Fe-Al-Si coating existed on the steel sheet, while bent hooks were found in both non-coated and pure Al-Si-coated specimens. For the pure Al-Si-coated steel sheet, non-HPF specimens were used, and a bent hook was confirmed on the crosssection of the weldment, which coincides with the results of a previous study by da Silva [21]. The formation of Fe-Al-Si coating layer during the HPF process is accompanied by quenching and hardening of the steel sheet. ...
In the automotive industry, the demand for ultra-high-strength steel is increasing due to the CO2 emission and safety regulations. Hot-press forming (HPF) steels are a type of boron-alloyed high-strength steel fabricated via hot-press forming, which enables both high strength and elongation. Because HPF is conducted at high temperatures (900–950 °C) for a few minutes, its surface is coated with Al–Si or Zn to prevent surface oxidation and decarburizing. However, the coating layer often influences the properties of the welds. In this study, friction stir spot welding (FSSW) is used to weld dissimilar metals, i.e., an Al alloy and Al–Si-coated HPF steel. The effects of Al–Si coating on the mechanical and metallurgical properties of the hook formation on the weld are investigated. The shape of the hook, which is formed during FSSW, changes from bent to straight shape due to the presence of Al–Si and the HPF process. The joint strength of the straight hook-shaped specimens is demonstrated to be lower than that of the bent hook-shaped specimens. This difference in strength is because the hard Fe–Al–Si intermetallic (IMC) layer on the outer surface of the hook disturbs the bending of the hook during the welding. On the outer surface of the hook, a Fe–Al–Si IMC layer of chemical composition similar to that of the coating layer formed during HPF is observed. This formation is different from the inner surface of the hook, wherein a thin Fe–Al IMC layer is reconstructed between aluminum and steel. Thus, the hard Fe–Al–Si intermetallic layer transformed during the HPF process is the primary cause of the straight hook shape.
... The increasing demands for energy saving and weight reduction in automotive and aerospace industry has led to replacing certain ferrous parts with lightweight alloys and advanced high strength steels (HSS). This interest has created the need to develop a reliable joining technology which can produce aluminum-steel dissimilar joints of high quality instead of conventional fusion welding processes [1,2]. The highly alloyed 2XXX series (aluminum-copper alloys) are used extensively in aerospace industries. ...
... These aluminum alloys are generally classified as non-weldable alloys due to the deterioration of their mechanical properties causes of the dissolution of strengthening precipitates during fusion welding [3,4]. Therefore, solid state welding processes, such as friction stir welding (FSW), were developed in order to overcome a variety of problems and weld defects in fusion welding of aluminum alloys [1,5]. During FSW, the maximum temperature of the welded plates is typically ranges from 70% to 80% of the melting temperature of the workpiece material [6,7]. ...
Friction stir spot welding (FSSW) is a solid state joining process derived from the linear friction stir welding as an alternative method for the single-point joining processes. Three tool rotational speeds of (535, 980, 1325rpm) and two types of tool-pin geometry (straight cylindrical and triangular) were used to fabricate the FSSW joints of similar AA2024-T3 aluminum alloy sheets with 2mm thickness. This study was aimed to investigate the effects of pin geometry and tool rotational speeds on the lap shear strength and microstructural characteristics of friction stir spot welds. In addition to that, temperature distribution during FSSW, using both tool-pin shapes at the best rotational speed, was evaluated by two thermocouples K-type which were positioned at two different locations within welded area. Three dimensional non-linear numerical models using ANSYS program were built to simulate the temperature distribution. Tensile-shear test results showed that the weld strength was improved in all FSSWed joints by changing the tool pin profile from cylindrical to triangular. Scanning electron microscopy of the failed specimens observed that the pin geometry influence fracture mode under tensile shear loading. Microscopic examinations revealed that grain size in the stir zone increased with increasing rotational speed in the welds made by the cylindrical pin. While, conversely, was occurring in the other welds fabricated by the triangular pin. Temperature distribution obtained from the experimental and numerical model results was directly affected by the pin geometry during the welding process. Index Term-Friction stir spot welding, AA2024-T3 aluminum alloy, Pin geometry, Temperature distribution, ANSYS, Fracture mode.
... For dissimilar metal joints in RFSSW, in order to obtain mechanical interlocking by displacing the bottom ferrous material into the upper lightweight material sheet, it is necessary to plunge the tool pin into the bottom sheet. This would require an advanced tool material, such as W-25 wt-%Re or WC-Co to be used [6,15]; however, such materials are not currently available for RFSSW tooling. Previous research has shown that acceptable joint strengths can be achieved by purely metallurgical or diffusion bonding mechanisms, with the lightweight alloy sheets set as the top sheet when joining to a harder material. ...
... However, micro-scale cracking was noted at the Al/steel interface. The current study does not provide the microstructure details of the top Al sheet, since the previous research showed that the upper sheet microstructure scarcely affects the weld strength when interfacial fracture dominates [15,16]. Figure 6b. ...
Sheet metal welding in the automotive manufacturing industry is encountering increasing challenges while joining light weight alloys. For some time, resistance spot welding (RSW) has been the method of choice to join the vast array of automotive structural steels based on the speed and low cost; however, new combinations of non-ferrous materials suffer from limited weldability by RSW. Specifically, aluminum sheet metals offer many desirable properties for use in sub critical components such as body skins or brackets and latches, and advanced high strength steels are becoming commonplace for components requiring extremely high strength for rigidity and crashworthiness. However, joining these two dissimilar metals to each other presents a challenge for manufacturing. The present work examines Refill Friction Stir Spot Welding (RFSSW) to join aluminum sheet to zinc coated steel. Joints were made without melting of either of the base materials utilizing the plastic flow of the aluminum sheet to generate pressure and heat during welding. Weld parameter testing along with metallography including SEM/EDX analysis was performed to investigate the joining mechanism and define an operational window which can meet overlap shear fracture load requirements of AWS standards.
... The increasing demands for energy saving and weight reduction in automotive and aerospace industry has leads to necessity of replacing certain ferrous parts with lightweight alloys and advanced high strength steels (HSS). This interest has created the need to develop a reliable joining technology which can able to produce aluminum-steel dissimilar joints of high quality instead of conventional fusion welding processes, because of dissimilar joining of these materials by a traditional fusion welding is rather complicated and difficult due to their different chemical and physical properties, particularly the difference in melting temperatures [1,2]. Aluminum alloys are difficult to be fusion welded due to the requirements of gas shielding of weld pool and removal of oxide layers before or during the welding process. ...
... These defects deteriorate the weld quality and mechanical properties of the welded joints. Therefore, solid state welding processes, such as friction welding, friction stir welding, explosion welding, hot pressure welding, etc. were developed in order to overcome a variety of problems and weld defects related to melting and solidification in fusion welding of aluminum alloys [1,5]. Friction stir welding (FSW) is a solid state welding process that was invented by Wayne Thomas at The Welding Institute (TWI), United Kingdom, in 1991 [6], and has emerged as a welding technique used in high strength alloys (2XXX, 6XXX, and 7XXX series) for aerospace, automotive and marine applications [7]. ...
Friction stir spot welding (FSSW) is a type of solid state joining processes, which was derived from the linear friction stir welding (FSW) as an alternative method for single-point joining processes like resistance spot welding and fastening. The main limitation of FSSW is the keyhole that remains at the center of the spot after welding process, which can be classified as a defect for the friction stir spot welding in its conventional method. In this work, a newly developed technique called friction stir spot welding with refilling by friction forming process (FSSW-FFP) was used to remove the keyhole from the conventional FSSW joints. Both of this new technique and conventional friction stir spot welding process were used to weld lap shear specimens of AA2024-T3 aluminum alloy sheets, thickness 2 mm, and the results were compared. Two types of tool pin geometry (straight cylindrical & triangular) and three rotational speeds (535, 980, and 1325) rpm were used to study the effect of these parameters on the mechanical and microstructural properties of friction stir spot welds. The keyhole was successfully refilled by the new refilling process. The tensile-shear test results showed that the refilled FSSW specimens are better than the specimens welded by the conventional FSSW process at all tool rotational speeds with using different tool pin profiles. The minimum tensile shear load obtained from the conventional friction stir spot welds was improved (to about 45%) by the refill FSSW process. Fracture modes under tensile shear tests were analyzed in detail using the scanning electron microscope (SEM). The variation of microhardness in different regions of the spot was evaluated.
... Therefore, there is a growing need for more cost-effective and innovative joining technologies particularly in the case of high-strength Al alloys and advanced high strength steels. Solid-state FSSW and its pinless variant as well as DeltaSpot RSW are being considered as promising techniques to be used in large-scale production when spot joining Al to steel is required [10][11][12][13][14]. ...
... As expected, the amount of flash increases as PD increases. Contrary to the FSSW process, there is no mechanical interlocking between the Al alloy and the steel [13]. The boundary between both materials is clearly defined with no material mixing/stirring at the interface. ...
The aim of this investigation is to evaluate and compare two spot joining processes suitable for dissimilar welding Al and steel for mass production applications in the automotive industry: pinless friction stir spot welding (FSSW) and DeltaSpot resistance spot welding (RSW). The effect of joining parameters on the mechanical and microstructural properties of dissimilar 1 mm-thick Al alloys (5754-H22 and 6082-T6) and 22MnB5 hot-stamped boron steel joints produced by both processes has been investigated. Microstructural features of FSSW and RSW connections have been analysed; while mechanical performance has been investigated in terms of shear testing. Failure modes of shear specimens have been also investigated. Maximum failure loads close to 3 kN have been obtained in RSW spots; while FSSW has shown lower failure loads. Interfacial failure mode has been observed in RSW conditions; while a mixture of interfacial and nugget pullout failure modes have been found for FSSW connections.
... There have been several works about dissimilar joining between Al and steel by FSSW. [1][2][3][4][5][6] However, the processing time of FSSW is generally longer than that of conventional resistance spot welding (RSW), where the dwell time of FSSW was ranging from 2 to 5 s. [1][2][3][4][5][6] If the RSW technique is efficiently used for the joining of Al and steel, the processing time could be shortened compared with FSSW (v1 s). ...
... [1][2][3][4][5][6] However, the processing time of FSSW is generally longer than that of conventional resistance spot welding (RSW), where the dwell time of FSSW was ranging from 2 to 5 s. [1][2][3][4][5][6] If the RSW technique is efficiently used for the joining of Al and steel, the processing time could be shortened compared with FSSW (v1 s). Furthermore, to integrate FSSW procedure into the assembly line of vehicle components, new FSSW machines have to be introduced, resulting in costly investment in plant and equipment. ...
Aluminium alloy sheets were joined to stainless steel ones by a resistance spot welding method using Al–Mg alloy interlayer. The interlayer exhibits a lower melting point than the Al alloy. Consequently, melted interlayer with a lower temperature filled the gap between the two sheets and resulted in effective joining. Subsequently, tensile shear fatigue tests had been conducted to evaluate fatigue strength and to determine the fatigue fracture mechanism. Resistance spot welding dissimilar welds exhibited higher fatigue strengths than friction stir spot welded dissimilar ones. Fatigue fracture modes were dependent on the load levels, where plug type fracture occurred at high load levels, shear fracture through the nugget at medium load levels and through thickness fatigue crack propagation in the Al sheet at low load levels. The fracture mode transition was attributed to the geometrical rotation around the nugget.
... Size. Te optical micrographs of the cross-sectional view of the welded joints revealed three clearly defned weld zones: the stirred/nugget zone (SZ), the thermomechanically afected zone (TMAZ), and the heat-afected zone (HAZ), as shown in Figures 8(a) and 8(b), similar to the descriptions by Silva et al. [32] and Ahmed et al. [33]. Te SZ is generally the equal diameter as the tool probe and particularly contains deeply deformed material due to elevated temperatures and extensive plastic deformation contains smaller grains than the base metal as Journal of Engineering 5 revealed in Figures 8(c) and 8(d). ...
The present study investigates the impact of varying process parameters on the mechanical properties of friction stir spot welding (FSSW) joints involving Al 5754 and Al 6111. Taguchi’s L16 design of experiment approach was employed to conduct experiments and optimize the process parameters. Key parameters, including tool pin profile, dwell time (5–30 sec), rotating speed (250–1400 rpm), and plunge depth (1.5–1.8 mm), were systematically considered. The results indicated that the optimized welding conditions for attaining higher tensile-shear strength are a spindle speed of 1400 rpm, dwell time of 10 sec, plunge depth of 1.7 mm, and a tool pin profile of a triangular pyramid. As for bending strength, the optimal conditions are a spindle speed of 250 rpm, dwell time of 30 sec, plunge depth of 1.8 mm, and a tool pin profile of a square pyramid, representing higher bending strength. The analysis of variance technique revealed that the tool pin profile and plunge depth significantly influenced the tensile-shear strength and bending strength of the developed FSSW joint, respectively. Regression analysis was employed to formulate mathematical models predicting tensile and bending strength, and the predicted values closely matched experimental results with 80% accuracy.
... Liyanage et al. [9] reported tool wear during FSSW of Al 6111 and low carbon steel DP600, though the tool is made of W-25Re alloy. Da Silva et al. [10] reported tool wear during FSSW of AA 1050 aluminum alloy and hot-stamped boron steel using the WC-Co cemented carbide tool. ...
A novel method, friction stir spot welding using a consumable sheet (FSSW-C), is introduced here with the aim of joining dissimilar sheets. In this process, faying surfaces of the base materials are kept at a specific gap, and a consumable sheet is placed on the top of the base materials. When the tool progresses into the consumable sheet, the plasticized consumable material gets extruded into the gap and joining occurs between the base materials. The tool never touches the steel base material overcoming the tool wear problem. In the present work, AA6063-T6 and CRCA/IS-513 are the base sheets, and AA6063-T6 is the consumable sheet. The effect of tool rotational speed on the joint formation, interface characteristics, microhardness, temperature evolution, lap shear strength, bend shear strength, and fracture modes have been analyzed. Microstructural zones are also revealed. The rotational speed of 900 rpm is the best choice for FSSW-C of AA6063-T6 and CRCA/IS-513 sheets, keeping 2-mm/min plunge speed, 2-mm plunge depth, 5-s dwell time, and 1.5-mm gap constant. However, additional case studies reveal a plunge depth of 1.5 mm (at 900 rpm) as a better choice due to further lap shear fracture load improvement.
... Even though this layer has been reported to result in achieving strong welds, an excessive thickness would weaken the strength of the bond, as the brittle IMC favors the initiation and propagation of cracks [7]. An alternative to conventional welding techniques which is environmentally friendlier and has demonstrated its potential to join different materials [8][9][10], and more concretely aluminum to steel [11][12][13][14], is friction stir spot welding (FSSW). ...
In this work, friction stir spot welding of 5754 aluminum alloy to dual phase steel was investigated using two different ratios of martensite and ferrite (0.38 and 0.61) for steel sheet initial microstructure and varying tool rotation speed (800, 1200 and 2000 rpm). The effect of these parameters on the joint formation was evaluated by studying the plunging force response during the process and the main characteristics of the joint at (i) macrolevel, i.e., hook morphology and bond width, and (ii) microlevel, i.e., steel hook and sheet microstructure and intermetallic compounds. The plunging force was reduced by increased tool rotation speed while there was no significant effect from the initial steel microstructure ratio of martensite and ferrite on the plunging force. The macrostructural characterization of the joints showed that the hook morphology and bond width were affected by the steel sheet initial microstructures as well as by the tool rotation speed and by the material flow driver; tool pin or shoulder. At microstructural level, a progressive variation in the ratio of martensite and ferrite was observed for the steel hook and sheet microstructure. The zones closer to the tool presented a fully martensitic microstructure while the zones away from the tool showed a gradual increase in the ferrite amount until reaching the ratio of ferrite and martensite of the steel sheet initial microstructure. Different types of FexAly intermetallic compounds were found in three zones of the joint; the hook tips, in the hooks close to the exit hole and in the corner of the exit hole. These compounds were characterized by a brittle behavior with hardness values varying from 456 to 937 HV01.
... During the joining of dissimilar materials like steel and Al alloy, tool wear is an important issue due to severe frictional conditions at the steel side. Hence, the refractory materials, i.e., polycrystalline cubic boron nitride (PCBN) [52,53], tungsten carbide [23,54], tungsten-rhenium [55], and Si 3 N 4 [56], are required for the tool. In this study, a tungsten carbide (WC-10wt. ...
In this study, an attempt was made to join one type of high-strength shipbuilding grade steel, i.e., DH36 steel with 6061aluminum alloy (AA6061), using the friction stir welding technique. The effect of tool offset on micro/macrostructure and mechanical properties of the welded joints was investigated. The intermetallic compound (IMC) formation in the various regions, such as aluminum/steel interface, stir zone (SZ), and mixed zone (MZ), was examined through energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis. It was observed that the ultimate tensile strength (UTS) increased with an increase in tool offset from 0.4 to 1.5 mm and then reduced with a further increase in tool offset from 1.5 to 2.5 mm. Sample S4 (i.e., tool offset of 1.5 mm) exhibited the maximum UTS of 207.6 MPa, which was about 76.16% of the AA6061 base material. The lower UTS at other tool offsets could be attributed to the cross-sectional defects, i.e., voids and cracks at the interface, inadequate IMC layer thickness, distribution of steel fragments, and IMCs inside the SZ. The AlFe and AlFe3 IMCs were observed in MZ at a tool offset of 0.4–1.5 mm. However, Al2Fe and AlFe were identified in MZ at a tool offset of 1.8 mm and 2.2 mm. The aluminum/steel interface exhibited the Al3Fe and Al5Fe2 IMCs. These IMCs significantly affected the mechanical properties of the welded joints. The irregular distribution of hardness was attributed to the scattering of steel fragments and Al3Fe IMCs inside the AA6061 matrix.
... Abundant studies have been conducted on the FSSW of aluminum to conventional steel, including the welding of aluminum alloy 6016 to IF steel [40], 6061 to low carbon steel [41], 6061 to AISI 1018 [42], 6111 to DC04 steel [43], 1050 to hot stamped born steel [44] and 5083 to St-12 steel [45]. More and more attention has been paid to the FSSW of dissimilar materials in recent years. ...
In recent years, growing amount of attention has been drawn to studies of reducing vehicle weights in automotive industry considering both economic and environmental factors. One of the effective methods to achieve this goal is to replace steel components with multi-material vehicle structures. Joining of dissimilar materials is therefore very important to meet this demand. It is generally difficult to join dissimilar materials with the conventional welding technologies, as they have quite different physical and chemical properties. In addition, the formation of large amount of brittle intermetallic compounds (IMCs) is highly detrimental to joint quality. Friction stir welding (FSW) is a solid state welding technique and can avoid bulk melting during the process. As a variant of friction stir welding, friction stir spot welding (FSSW) is a promising solution to make spot joints between dissimilar materials. However, limited studies have been conducted on the FSSW of dissimilar materials, specifically aluminum alloy to steel. When performing the FSSW, the keyhole left on the welding zone deteriorates the joint strength and the process requires a large plunge force to make a spot welding with the dissimilar materials. To solve the existing issues, the FSSW process has been successfully applied to join aluminum alloy 6061-T6 to TRIP 780 steel. Cross sections of weld specimens show the formation of a hook with a swirling structure. A higher magnified SEM view of the swirling structure with EDS analysis reveals that it is composed of alternating thin layers of steel and Al/Fe intermetallic compounds (IMCs). To evaluate the effects of different process parameters including tool plunge speed and dwell time on the weld strength, the design of experiments (DOE) and analysis of variance (ANOVA) is used. It shows that dwell time is a more dominant parameter in affecting the weld strength than plunge speed. Furthermore, the investigation of failure after applying lap shear tests reveals that the cross nugget failure is the only failure mode. A FSSW process model is developed in this study based on the Coupled Eulerian-Lagrangian (CEL) method, which considers the material flow at the dissimilar material interface and the interaction between the welding tool and workpiece. The force and thermal history generated by the numerical work also correspond well with the experimental data. In the experimental investigation of applying the proposed keyhole refilled FSSW process to join aluminum alloy 6061-T6 to TRIP 780 steel, it is shown that the original keyhole area is filled with the aluminum alloy and no obvious voids can be found at the Al/Fe interface. The lap shear force produced by the keyhole refilled FSSW increased by 55.98% when compared to the conventional FSSW. Three bonding mechanisms can be concluded according to the experimental observations: (1) the keyhole is refilled by the aluminum alloy; (2) the bonding area is increased between the steel and aluminum; and (3) the hooks developed from the conventional FSSW process generate bonding between the steel and aluminum. Finally, the electrically assisted FSSW process for joining aluminum alloy 6061-T6 to TRIP 780 steel is performed. The experimental results show that the application of electrical current reduces the axial plunge force and assists the material flow of the aluminum matrix during the welding process.
... It is typically used for chemical process plant equipment, food containers, architectural flashings, lamp reflectors, and cable sheathing [15,16]. Only a limited number of publications are available about the FSW of this alloy and are mainly in the dissimilar welding with other aluminum alloys [17] or with steel alloys [15,18]. Due to the very high ductility of the AA1050, it is highly affected by the heat generated during FSW and very sensitive to the FSW conditions. ...
In this work, three mathematical models for the heat generation during bobbin tool friction stir welding (BT-FSW) of aluminum using three tool pin geometries have been proposed. The models have utilized and updated the available models for the heat generation during the conventional tool friction stir welding (CT-FSW). For the validation of the models, BT-FSW experiments have been carried out for aluminum alloy AA1050 using three different pin geometries (cylindrical, square, and triangular), at different welding speeds of 200, 400, 600, 800, and 1000 mm/min and a constant tool rotation speed of 600 rpm. The welding temperatures during BT-FSW have been measured to be compared with that calculated from the models at the same parameters. It has been found that the calculated welding temperatures from the models and that measured during BT-FSW are in good agreement at all the investigated welding speeds especially in case of the square and cylindrical pins, proving the validity of the developed models for the predication of the heat generation as well as the welding temperatures. This will allow proper designing of the BT-FSW parameters and avoiding the conditions that can deteriorate the joint quality and properties.
... Material interlocking phenomenon in dissimilar FSW material joining is a bond formation mechanism that depends on complex material flow behaviour around the joint interface. This phenomenon has been described to be one of the best methodology in improving the weld strength especially in dissimilar material joining through FSW, such as Al-Mg [74], Al-steel [127,128], Al-Cu [129] and Mg-steel [128]. It can be seen from Fig. 9(a-c) that both aluminium and magnesium are intermixed in solid form in stir zone and mechanical interlocking take place [6]. ...
At present aluminium-magnesium alloys are widely used in various engineering applications due to its light weight and superior properties. Joining is considered as one of the most complex phenomenon in various precision industries like aerospace, railway, automotive and marine structures because inflexible tolerances are required during different product assembly. The friction stir welding (FSW) of aluminium-magnesium of various grade has incited substantial scientific and industrial importance since it has a potency to transform the product with a good quality joint. The fabrication of such alloys is a challenging task through conventional fusion welding due to its various metallurgical concerns. Therefore, the present work is intended to summarize the recent progress in FSW of aluminium-magnesium alloys. Particular attention has been paid to microstructural evolution, phase transformation, recrystallization mechanism, material flow behaviour and how the process parameters influence the various mechanical properties and associated defects during FSW. Various experimental and numerical simulation results have been mentioned for weld property comparison. Finally, this work not only points out the prominent conclusions of the preceding research but also recommends the upcoming guidance concerning to fabrication of aluminium-magnesium alloys through FSW.
... Si3N4, pCBN 등 고경도 재료가 개발되었으며, 이를 통해 툴의 마모를 최소화하려고 있다 8,9) . 고강도재료 중 가장 중요한 소재인 강 [10][11][12][13][14] 이나 Al/ Fe 이종재료조합 [15][16][17] 에 FSW를 적용하기 위하여 다양 한 연구가 수행되고 있다. 그러나 철강재료는 알루미늄에 비해 높은 온도에서 항복강도가 저하되므로 [18][19][20][21] , FSW 를 적용 시에 시스템의 변형이 크고 6) , 툴의 마모 혹은 파 손이 발생하기 용이하다 22) . ...
... A considerate amount of studies has been conducted on the FSSW of aluminum alloys, including aluminum alloys 5052 [30,31], 5083 [8], 5754 [32,33], 6061 [34][35][36][37][38][39], 6011 [40], 7050 [41] and 7075 [42]. In addition, increasing interests in the dissimilar material welding brings the attention to the FSSW, especially for the aluminum alloy to the conventional steel, which includes the welding of aluminum alloy 6016 to IF steel [43], 6061 to low-carbon steel [44], 6061 to AISI 1018 [45], 6111 to DC04 steel [46], 1050 to hot-stamped boron steel [47], and 5083 to St-12 steel [48]. ...
This paper covers a detailed study of friction stir–related processes with the focus on joining dissimilar materials. First, the effects of the process parameters and tool geometries on weld mechanical properties, defects, and weld microstructure along with the formation and growth of intermetallics are systematically reviewed. Process-structure-property relationships are discussed in details. Second, the paper summarizes different physical models that have been developed for friction stir–related process. A specific session on modeling dissimilar material joining is provided. The objective of these models is to determine the temperature profile, stress, and strain distribution along with material flow field based on the input process parameters and tool geometries. By further implementing these results into microstructure evolution and material property models, the dissimilar material weld mechanical performance can be predicted eventually. Third, recently developed friction stir variants for process improvement and joint quality enhancement are discussed. Finally, potential future research directions are recommended in conclusion.
... Mechanical bonding is another joining mechanism in aluminum/ steel joint besides metallurgical bonding (Silva et al., 2010). The mechanical bonding features, including hook (Liu et al., 2015), saw tooth interface (Mahto et al., 2016) and swirl-layered structure (Fereiduni et al., 2016), were beneficial to improve the joint strength. ...
High-quality aluminum /steel joint was achieved via self-riveting friction stir lap welding (SRFSLW) characterized by the prefabricated holes in steel sheet. According to the origination of filling materials, the prefabricated holes were filled with the plasticized aluminum materials in this order: the deformed aluminum ahead of a pin firstly, the stirred aluminum by the pin body secondly and the driven aluminum by the pin tip finally. The strength of the SRFSLW joint reached maximum value of 317 N/mm at the hole diameter of 3 mm, which was 23% higher than that by conventional friction stir welding (FSW). The optimized joints failed at both the aluminum/steel interface and the formed aluminum rivets. The synergistic effect of mechanical bonding induced by the riveting and metallurgical bonding induced by the Al/Fe IMC layer contributed to high strength of the SRFSLW joint.
... Mechanical interlocking is the mechanical bonding component in Al-Mg FSW that relies on forming a complicated geometry at the bonded surface to enhance mechanical strength. Due to the complex geometry formed through plasticization and shearing of base metals, mechanical interlocking has been reported to be one of the primary means in enhancing joint strength of other incompatible dissimilar welds, including welds involving Al-Mg [79], Al-steel [80], [81], Al-Cu [82] and Mg-steel [81]. Since low heat input is desired to maintain low temperature in order to impede IMC growth, formation of these mechanical interlocks between the intercalated layers is crucial to joint strength. ...
The paper critically assesses the research progress towards aluminium–magnesium dissimilar friction stir welding (FSW). First, the theoretical requirements are explored through the understanding of joining mechanism and heat generation in aluminium–magnesium FSW. Next, the observed trends in microstructural characterisation and mechanical properties are analysed. Finally, the effects of welding parameters and how it influences process variables and materials responses are discussed in detail, and several suggestions are made based on these discussions.
... Finally, the tool is drawn out of the sheets and protruded pin leaves a characteristic keyhole depression in the middle of the joint (see Fig. 30a and b). [242][243][244][245][246][247][248][249][250][251][252][253][254][255][256][257][258][259][260] Figure 30c and d shows schematic and typical micrograph of macrostructure of friction stir spot welds. The unique feature of the FSSW like friction stir welding process is that the transport of heat is aided by the plastic flow of the substrate close to the rotating tool. ...
... One of the technologies with potential to produce aluminum-steel dissimilar joints is Friction Stir Welding (FSW). Previous works have shown the potential of this and related techniques to produce dissimilar joints [4][5][6][7][8][9][10], based on its solid state nature and the possibilities to limit the generation of brittle intermetallic compounds that could reduce the quality of the joints. The present study was focused to the development of dissimilar aluminum-steel joint using AA6082-T6 as aluminum alloy and S355JR as steel. ...
The properties of dissimilar aluminum-steel lap joints performed by FSW were studied in this investigation, using AA6082-T6 aluminum alloy and S355JR steel. The effect of the bonded area on the mechanical and microstructural properties of the joints was analyzed combining different numbers of overlap passes. Microstructural features were analyzed by optical and scanning electron microscopy; while mechanical performance was investigated in terms of microhardness and shear tensile testing. Different fracture modes of shear tensile specimens such as interfacial failure and aluminum HAZ failure were observed, being related to the bonded interface section. No volumetric defects were found in the metallographic examination. The formation of intermetallic compounds was analyzed by SEM. Encouraging results were obtained regarding the wear and durability of FSW tools using WC-Co as probe material.
... Fusion joining involves RSW with a cover plate [7], RSW with an interlayer [8], and cold metal transfer spot plug welding [9]. Solid-state joining involves friction stir spot welding [10,11] and ultrasonic spot welding [12,13]. Mechanical joining involves self-piercing riveting (SPR) [14,15], clinching [16], and friction bit joining [17]. ...
A novel resistance element welding technology was applied to join 6061 Al alloy and uncoated 22MnMoB boron steel. To conduct the resistance element welding process, a technological hole was drilled in the Al sheet into which a Q235 steel rivet was inserted. Resistance spot welding was carried out at the rivet. The mechanical properties, fracture morphology, nugget formation process, dynamic resistance, microstructure, and hardness distribution of the resistance element welding were investigated. Traditional resistance spot weld joints were also prepared for comparison. Resistance spot welding could barely join Al 6061 and boron steel, and had a maximum tensile shear force of less than 1000 N. Novel resistance element welding could join the metals reliably with a maximum tensile shear force of over 7000 N and a relatively high toughness. Nugget formed at the interface of rivet and steel acted as loading position, and IMC interlayer connected rivet and aluminum.
... Thus, friction stir spot welding (FSSW) is also applicable to the dissimilar spot welding. The application of FSSW to Al/steel dissimilar welding had also been widely reported, [2][3][4][5][6][7][8] and revealed that the joining was achieved by the formation of very thin IMC layer. 2,3,5 Bozzi et al. 5 had reported that IMC layer thickness could be controlled by the process parameters and that tensile shear fracture load could be related to the IMC area fraction. ...
Al alloy sheet was friction stir spot welded (FSSW) to galvanised steel sheet by a scroll grooved tool without probe. Tensile and fatigue tests had been conducted using tensile shear specimens, and the results were discussed in comparison with Al/steel dissimilar FSSW joint, in which steel sheet was not galvanised. Energy dispersive X-ray analyses revealed that Zn coating was melted or softened and circumferentially resolidified around the nugget. Intermetallic compound between Al and Fe was formed along the interface resulting in the joining of Al to steel. Tensile shear strength of Al/galvanised steel weld was lower than that of Al/steel one without galvanising. However, Al/galvanised steel welds exhibited higher fatigue strengths. Finite element method analyses around the nugget revealed that circumferentially resolidified Zn brought about the stress relaxation at the edge of the nugget, resulting in the better fatigue performance of Al/galvanised steel welds.
... One of the technologies with potential to produce aluminum-steel dissimilar joints is Friction Stir Welding (FSW). Previous works have shown the potential of this and related techniques to produce dissimilar joints [4][5][6][7][8][9][10], based on its solid state nature and the possibilities to limit the generation of brittle intermetallic compounds that could reduce the quality of the joints. The present study was focused to the development of dissimilar aluminum-steel joint using AA6082-T6 as aluminum alloy and S355JR as steel. ...
The properties of dissimilar aluminum-steel lap joints performed by FSW were studied in this investigation, using AA6082-T6 aluminum alloy and S355JR steel. The effect of the bonded area on the mechanical and microstructural properties of the joints was analyzed combining different numbers of overlap passes. Microstructural features were analyzed by optical and scanning electron microscopy; while mechanical performance was investigated in terms of microhardness and shear tensile testing. Different fracture modes of shear tensile specimens such as interfacial failure and aluminum HAZ failure were observed, being related to the bonded interface section. No volumetric defects were found in the metallographic examination. The formation of intermetallic compounds was analyzed by SEM. Encouraging results were obtained regarding the wear and durability of FSW tools using WC-Co as probe material.
... As an effective solution of improving fuel economy and reducing carbon emissions, joining aluminum to steel for multimaterial vehicle structure is becoming more and more desirable in automotive industry. Traditional fusion welding could hardly achieve satisfactory joints between these two materials, which is due to the great differences in their physical and mechanical properties as well as formation of large amount of brittle intermetallic compounds (IMC) [1]. On the other hand, the solid state nature of FSW technique provides it with several superiorities [2,3]. ...
In this study, a coupled thermomechanical model has been developed for the plunge stage of friction-stir welding (FSW) for joining dissimilar Al 6061 to TRIP steel. Governing equations of mass, momentum, and energy have been formulated for the bulk material and the interface, respectively. Generalized material properties defined with the field variable α are introduced for material identification at different regions. Local instant formulation based on binary phase flow theories has been proposed for developing conservation equations at the interface. These analytical derivations are then implemented into a finite-element model for numerical simulations. In the early stage of plunging, the estimated axial force correlates well with the experimental results, where a short plateau can be observed before the final peak occurs. Discrepancies at the later stage can be attributed to different experimental configurations and related simplified model assumptions.
The present study concentrates on experimental characterization and finite element (FE) simulation of a novel friction stir spot welding (FSSW) of AA6063-T6 and CRCA/IS-513 alloys using a consumable sheet (FSSW-C) at varying tool plunge depth (TPD). In this method, the rotating tool does not plunge into the base sheets (AA6063-T6 and CRCA/IS-513) that are located at a specific distance between the edges. Rather, it plunges through the consumable sheet kept at the top of the base sheets. As the tool moves down during plunging, it plasticizes the consumable sheet material. The plasticized material helps in developing permanent joint between the base sheets. Due to this arrangement exorbitant tool wear is entirely avoided. Experimental characterization explores joint formation, interface traits, microhardness, temperature evolution, and bendability at different tool plunge depths (TPDs). DEFORM-3D FE simulations understand material flow, strain, and strain rate evolution during FSSW-C across varying TPDs. The joint macrograph reveals the complete merging of the consumable sheet with AA6063-T6 base metal, while it is predominantly mechanical bonding between the consumable sheet and steel base metal. Keeping other FSSW parameters constant, TPD of 1.8 mm is found to be the optimum level with a peak shear load of 0.5 to 0.8 kN during bend tests. At 2.2 mm TPD, 1.7-μm-thick IMC layer comprises of AlFe and FeAl3 exhibits hardness of 300 HV. Shear friction factor of 0.4 is the optimized value for accurate prediction of temperature during FSSW-C. 4-10% deviation is observed between the predicted and experimentally measured peak temperature. Strain rates between 3 and 127 s−1 are predicted at different locations during FSSW-C, closer to the range available in FSP literature. Material flow analysis reveals seamless merging of AA6063-T6 base sheet and consumable, forming a residual thin consumable layer atop the steel base sheet.
Hot press forming (HPF) steels with a full martensite structure and 2.0 GPa strength (HPF2.0) were friction stir welded as bead-on-plate using a WC–Co12% tool. The stir zone was composed of recrystallized grains of various sizes and had comparable to or higher hardness than the base material. However, the intercritical heat-affected zone (ICHAZ) and subcritical HAZ experience softening. During the tensile test, fractures consistently occurred at the softened HAZ. The minimum hardness of the ICHAZ in the friction stir welds was 300 HV, which was similar to that in the arc welds with polygonal ferrite (328 HV) and lower than that in the laser welds with needle-like ferrite (400 HV). Remarkably, the softened width of the friction stir welds was narrower than half that of the arc welds. These results confirm the possibility of expanding the application of friction stir welding to next-generation HPF steels.
In this study, it was aimed to join by friction stir welding the two dissimilar sheets made of AA5754 Al-Mg alloy and AA 1050 aluminium, which are intensely used in the automotive. The applied welding speed was 75 mm/min with different tool rotational speeds. The mechanical properties and the microstructure of the welded joint were investigated by the tensile test, the three-point bending test, the microhardness measurements, the optical microscopy, SEM and EDS. The best result in terms of tensile strength was obtained at 780 rpm with 80% performance. The optimum mixing was obtained in the joining process where the welding tool rotation speed was 2440 rpm. It was determined that the changes in microstructure had a significant effect on hardness and tensile strength of the welded dissimilar materials. The precipitate phases influenced the hardness of the nugget zone.
The AA6061 alloy and Q235 steel were well joined by refilled friction stir spot welding without stirring steel, as a 1 mm thick coating was deposited on the steel by friction surfacing before welding. The coating was composed of highly refined grains. The materials experienced shear deformation in the stir zones and the extrusion in hook and thermo-mechanical affected zones, resulting different predominant textures in the weld. A Fe-rich layer was depicted from the interface due to the enhanced atomic diffusion, and the layer's thickness increased as the sleeve plunged deeper during welding. Al-Fe intermetallics, including Al13Fe4, Al5Fe2, formed in the Fe-rich layer, since the solubility of Fe in Al was far lower than the measured content. The optimal shear strength reached 7.31 kN in this study. The welds fractured along the weld boundary and the Al/steel interface. The fracture initiated at the edge of the gap between AA6061 plate and coating, and propagated along the weld boundaries, resulting in the shear dimples and the faceted appearance. However, the spot weld with 2.9 mm penetration was fractured along the Al/steel interface mainly, which was attributed to the over formed intermetallics at the interface.
In this century, innovation and technology are required to fabricate the hybrid joint of metal and polymers. Due to their lightweight and anti-corrosion properties, the mixed components are increasingly used to produce lightweight hybrid structures such as aerospace and automobiles. It is essential to develop welding techniques for joining dissimilar materials and instead use them in engineering structures. The bonding mechanism of the weld joint has varied depending upon the welding process. In the present review, the bonding mechanism of various hybrid joints like Friction stir welding (FSW), Friction stir spot joining, Friction riveting, laser welding, ultrasonic welding and induction welding is discussed in detail. The defects observed in the different welding process is discussed in details. The mechanical properties and microstructure analysis of different hybrid joints are reviewed in detail for a different combination of hybrid joints.
Advanced High Strength Steels (AHSS) is a relatively novel family of steels different with high mechanical strength, ranging typically from 600 MPa to 1800 MPa. Dual Phase, Complex Phase, Transformation Induced Plasticity (TRIP), Hot Stamping and Quenching and Partitioning Steels are the more relevant materials of this family. It has been found particular interest for these materials in the automotive industry in the last years, being the welding of these steels a relevant issue. Among the welding processes more relevant to weld these materials are Laser Welding (LW), Gas Metal Arc Welding (GMAW), Resistance Spot Welding (RSW) and in the last years GMAW-Brazing and Friction Stir Welding (FSW) for similar and dissimilar materials. These materials are microstructurally designed to reach its high mechanical properties. In this sense, the welding thermal cycle could severely degrade the original microstructure, producing a drop in the local mechanical properties. Additionally, its high hardness requires, in thermomechanical processes like FSW or RSW, adjustments in the welding procedure in comparison with the conventional steels. As a consequence, the study of the effect of welding parameters in the microstructural evolution and the resulting mechanical properties is a challenge still open. This chapter addresses the state of the art in the welding of these materials oriented to automotive applications, remarking the main aspects to develop adequate welding procedures and the perspectives for the future.
Nineteen years ago, the automotive industry started using the friction stir spot welding (FSSW) process in joining metallic parts. The popularity of this welding process became higher every year. In this study, aluminum (Al) 1020 sheets of 2 mm thickness were joined with the FSSW process. The effects of FSSW parameters (plunge depth, tool rotation speed and dwell time) on the mechanical properties of weldments were investigated. The mechanical performance of the welds was evaluated by using the lap-shear tensile test. The optimization was done by using the Taguchi method. ‘The-higher-the-better’ quality control characteristic using the analysis of variance (Anova) method was applied to determine the optimum welding parameters. The signal-to-noise ratio was computed to calculate the optimal process parameters. The percentage contributions of each parameter were validated by using the Anova technique. The experimental results were analyzed by using the Minitab 17 software. The tool rotation speed was found as the dominant welding parameter on the weld strength of aluminum 1020 sheets for the FSSW process. The weld that had been produced with the optimum welding parameters gave a 23% higher fracture load than the initial welds.
Welding of dissimilar magnesium alloys and aluminum alloys is a critical issue because of their worldwide increasing applications. Dissimilar welding technology has touched new frontiers to take up the benefits of both metals simultaneously through their local demands. Friction Stir Welding (TWI, 1991) is rapidly blooming in the contemporary fields of aerospace, defence, marine, automotive, and railway industries as proven approach of solid state joining. Owing to its versatility, affability to environment and energy efficiency, it is widely getting acceptance as “green technology” in modern industries. FSW has facilitated joining of high-strength, lightweight aluminum and magnesium alloys which were earlier treated as unweldable by conventional fusion welding. Present article significantly appraises the review of growth of research towards joining of dissimilar aluminium–magnesium alloys by friction stir Processing (FSP). The investigative approach is addressed through the description of joining mechanism and hurdle faced in unification of Al-Mg. Formation of intermetallic compounds (IMCs) are inevitable during joining of such heterogeneous alloys (Al-Mg) irrespective of joining methods. So it becomes challenging to impede formation and growth of IMCs, hence research community always looks for novel techniques, a few of which are covered in this piece of writing. Present review also addresses responsible theories for IMCs and its correlation with process parameters through (categorized A, B, C) evolution of microstructures. Unlike fusion welding different sorts of defects have also been reported in literature originating through FSP. Moreover, influence and correlation of process variants have been covered through study of mechanical and metallurgical characterization mentioned in literature. Mainly literature advocates research involving optimization of process parameters and their compounding effects that eventually govern quality of weld and joint efficiency during FSP of Al-Mg. Finally, article throws light on summary of FSW developments by novel techniques and untouched future endeavours being potential area of research for Al-Mg
Press-hardened boron steels with ultrahigh strength (above 1500 MPa) are widely used in crash-sensitive safety components in automobiles. Joining such steels to aluminum alloys is challenging due to various factors including the steel’s tenacious Al-Si coating. A novel application of ultrasonic plus resistance spot welding was developed for such dissimilar metal joining. The nugget formation and the interface microstructure especially intermetallics formed were correlated to the joint strength, ductility and failure behavior.
Friction stir spot welding (FSSW) is a variation of linear Friction Stir Welding (FSW), which was invented to compete with resistance spot welding (RSW) and riveting of lightweight alloys in the automobile, shipbuilding and aerospace industries. Recently, the application of FSSW has rapidly extended to a variety of metals and non-metals. This article provides a comprehensive review of the recent progress on the process fundamentals, parameters optimization, microstructural evolution and mechanical properties, and relevant simulation and modeling of FSSW. The article also evaluates the energy generation, temperature distribution, plastic flow and joining mechanisms. The optimizations of tool design and welding parameters are obtained through experiments and modeling. Furthermore, a particular emphasis is given to microstructural characterization of the recovery, recrystallization and grain growth, and related annealing phenomena after in the welded alloys. The mechanisms of defect formation and liquidation cracking are discussed in detail. The mechanical properties, including hardness, static strength, fatigue performance and failure mechanisms and the relationship between mechanical properties and microstructures are also addressed along with residual stress and corrosion behavior.
In the present paper, mechanical and metallurgical characteristics of different dissimilar weldments fabricated by friction stir welding were investigated. Existence of lamellar composite structure within the stir zone in addition to observation of interfacial intermetallic compounds (IMCs) was the main characteristics that were investigated throughout this research. Results indicated that the optimum IMCs layers, resulting in enhanced mechanical properties, met three criteria, thinness, uniformity, and continuity.
The influence of welding flash on the corrosion resistance of friction stir spot welded (FSSW) AZ31B was examined by mass loss testing complimented with the scanning reference electrode and microcapillary polarization techniques. The microstructure of the flash was characterized by optical microscopy and the use of tungsten carbide tracer and correlated with the corrosion morphology of the joints. It was observed that the flash increased the corrosion rate of the welds, and its removal can reduce the corrosion rate by 20%. The increase in susceptibility for corrosion was explained by examining the electrochemical characteristics of the flash, and in particular to show the presence of a second stir zone (SZ) region in the flash. The electrochemical properties of the flash were correlated to second phase particle dissolution using a detailed microscopy analysis. The coupling of the two regions resulted in the formation of a local galvanic cell in the flash, leading to accelerated corrosion. Increases in dwell time and/or rotational speed of the tool during FSSW resulted in the formation of a larger SZ region in the flash, and produced a greater cathode to anode ratio.
Joining Al/Fe dissimilar metals is becoming a subject of special interest in the assembly of automotive parts as a trade-off between the weight lightening and the cost reduction. Although various studies have been introduced to join Al alloy with the steel sheet by fusion welding, weak joint strength and galvanic corrosion still remained as problems to be solved. As a solid state welding, friction stir welding has been preferred to fusion welding processes in the dissimilar metal joints. This study investigated friction stir spot welding (FSSW) of Al alloy to the thin steel sheet with a thickness of 0.65 mm. The conventional FSSW is a stationary spot welding process but new approach adopted an additional circumferential movement in company with high speed tool rotation. A full factorial experimental design was implemented, and the main and interaction effects of parameters were analysed on the failure load in the tensile shear test. The direction and radius of rotation were statistically significant parameters and these two parameters affected the joint width and the shape of the hook.
To achieve significant improvement in the shear strength of dissimilar joints between aluminum and mild steel sheets, four methods of friction stir multi-spot welding processes, were investigated. Initially, in all these methods, plasticized aluminum layer was deposited on the steel side by friction surfacing. Subsequently, the deposited aluminum was compacted by friction forming. After dressing, spot welding with different tool configurations was performed. Tool rotational speeds of 900, 1120, 1400 and 1800 rpm were used to analyze their effects on the weld nugget. Different mechanical and metallurgical characterizations were done on the welds thus made. The process with aluminum layer on grooved mild steel followed by friction stir multi-spot welding using concave tipped welding tool resulted in welds. These welds had better metallurgical bonding characteristics and higher shear strength, which at a rotational speed of 1120 rpm was more than twice that of the welds made with conventional friction stir spot welding.
This paper aims to present a study performed to produce lap joints of AA 1050-O over mild steel taking advantage of diffusion mechanisms induced by FSW. The pin length was set to fully process the aluminium plate, while slightly penetrating the steel. Influence of process parameters (axial load, rotation and travel speeds) on joining interface characteristics was studied. The diffusion layer was evaluated by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). An efficient defect-free bonding interface was produced extending beyond the region directly processed by the pin diameter. A diffusion layer with 8-10 μm thickness was observed.
The ultra high strength steel 22MnB5 before and after quenching were joined by tungsten inert gas (TIG) arc welding, the mechanical properties and microstructure of welded joints were studied by experiments, and the corrosion property of welded joints was analysis and compare with the base metal as well. The result shows that the ferrite and pearlite of non-quenched material were transformed to martensite after quenching treatment. The welded joints of the base metal have good mechanical property and microstructures, the tensile strength and hardness of the joints are slightly lower than the one of the base metal, the tensile strength of welded joints of quenched material reach 1 179.59 MPa, that is slightly lower than that of quenched material, but much higher than that of non-quenched base metal. The corrosion rates were rising after quenching heat treatment, the corrosion rate of the welding zone is much higher than the base metal, and the welding zone corrosion rate of the quenching material is highest.
One type of advanced high-strength steel, transformation-induced plasticity (TRIP) 780 steel, has been successfully welded to aluminum alloy Al 6061-T6 using friction stir welding (FSW) technique. The major Al-Fe interface in the steel side has been analyzed in detail under various welding conditions, where a thin layer of intermetallic compound (IMC) with a thickness of less than 1 μm can be generally observed and the composition was identified to be either FeAl or Fe3Al. This thin IMC layer can be shown to be beneficial for joint strength. Optical microscopy and scanning electron microscopy showed the weld nugget was distributed with sheared-off steel fragments encompassed IMC layers or simply IMC particles. Finally, a stirred-over steel strip embedded in the aluminum matrix was revealed, which would determine the failure mode and is crucial to joint quality based on tensile test results.
Friction stir spot welding (FSSW) has been applied to a dissimilar metal lap joint of an aluminium alloy and steel by stirring only the upper aluminium alloy sheet. Therefore, FSSW cannot be used to weld a lap joint composed of three or more sheets and a lap joint with an adhesive interlayer. In the present work, we propose a novel spot welding process for dissimilar metal lap joints using a new tool with the tip made of spherical ceramics. When this process is applied to the lap joint of the aluminium alloy and steel, the tool can be plunged into the lower steel sheet, then a steel projection is formed in the aluminium alloy sheet. The height of this steel projection increases with the plunge depth, and accordingly, the weld strength increases; the tensile shear strength and the cross tensile strength reached about 3.6 and 2.3 kN/point, respectively.
Sophisticated materials like high strength steel or even multi phase steel as well as aluminum require more efforts within the manufacturing process than conventional steel sheets as they have been used in the body in white recently. The manufacturing process itself as well as engineering of the parts, material of the forming tools as well as cold and warm joining technologies must be regarded separately. For forming tools coated steel inserts or sometimes even cooling is essential in terms of high-volume car series production. In mixed material solutions using steel in combination with aluminum, the common used resistance spot welding process does not work any more. To maintain high process stability of cold joining technologies combined with adhesive bonding a new process must have been developed. Other items for weight and cost savings are tailored rolled blanks or sophisticated joining technologies. Regarding the manufacturing costs, a cost effective combination of the mentioned high-sophisticated alloys with conventional material should be achieved. Developing a design concept due to crash, stiffness and driving performance, basic requirements have to be considered. This aims to check the high potential of cost intensive materials wherever high functional benefit is necessary under commercial aspects.
The magnetic pulse welding (MPW) is a cold weld process of conductive metals to the similar or dissimilar material. MPW uses magnetic pressure to drive the primary metal against the target metal sweeping away surface contaminants while forcing intimate metal-to-metal contact, thereby producing a solid-state weld. In this paper the MPW method and its application for several aluminium alloy (A1050, A2017, A3004, A5182, A5052, A6016, and A7075) and steel (SPCC) sheets joint were investigated and the process parameters and welding characteristics are reported.
Hybrid configurations between aluminium and steel are needed to meet today’s requirements for lightweight construction in the automotive industry. Different studies showed that Friction Stir Welding (FSW) as well as Friction Stir Spot Welding (FSSW) processes are suitable for joining aluminium to steel. In this work, dissimilar FSSW of aluminium AA5754 and galvanised steel HX 340LAD were examined. In particular the influence of different spindle speeds and dwell times on microstructure and the mechanical properties of the weld were analysed. In doing so, the cross-section microstructure of the weld interface was observed by light optical microscope (LOM) and scanning electron microscope (SEM). The strength of the welds was evaluated both by tensile shear and vibration fatigue tests. The influences of the individual parameters on the weld are presented in detail. The appearance of intermetallic phases (IMPs), a severe problem for conventional fusion welding processes between aluminium and steel, were investigated for the welded samples and a link to the mechanical properties is given.
We tried to join steel to Al-Mg alloy using a resistance spot welding method. The effect of Mg in Al-Mg alloy on the strength and the interfacial microstructure of the joint was investigated. Additionally, the effect of insert metal of commercially pure aluminum, which was put into the bonding interface, on the joint strength was examined. The obtained results were as follows. The cross-tensile strength of a joint between SS400 steel and commercially pure aluminum (SS400/Al) was high and fracture occurred in the aluminum base metal. However, the strength of a joint between SS400 and Al-Mg alloy was remarkably low and less than 30% of that of the SS400/Al joint. An intermetallic compound layer developed so thickly at the bonded interface of the SS400/Al-Mg alloy joint that the joint strength decreased. The intermetallic compound layer developed more thickly as Mg content in the Al-Mg alloy increased. Using insert metal of commercially pure aluminum containing little Mg successfully improved the strength of the SS400/Al-Mg alloy joint and the strength was equivalent to that of the base metal.
The magnetic pulse welding (MPW) is a cold weld process of conductive metals to the similar or dissimilar material. MPW uses magnetic pressure to drive the primary metal against the target metal sweeping away surface contaminants while forcing intimate metal-to- metal contact, thereby producing a solid-state weld. In this paper the MPW method and its application for several aluminium alloy (A1050, A2017, A3004, A5182, A5052, A6016, and A7075) and steel (SPCC) sheets joint were investigated and the process parameters and welding characteristics are reported.
The microstructural features and overlap shear strength properties of friction stir spot welds made between Al 6111 and low carbon steel, and between Mg alloy AM60 and DP600 dual phase steel, are investigated. When Al 6111 is the upper sheet in the dissimilar sandwich, completed spot welds show evidence of intermetallic layer formation and cracking. Increasing tool pin penetration into the lower sheet provided increased mechanical interlocking of the sheets due to clinching. However, increasing penetration also promoted intermetallic formation and cracking in completed welds. However, dissimilar AM60/DP600 steel friction stir spot welds produced with AM60 as the upper sheet in the dissimilar sandwich do not show evidence of intermetallic formation and cracking may be avoided by removing the zinc coating on the DP600 steel before the friction stir spot welding operation.
The structure and shear strength of brazed joints of aluminum to stainless steel are studied using a modification of the double lap joint configuration, which allows mechanical testing and joint microstructure examination on the same test piece. It is found that during furnace brazing of such joints at 600 C, using an Al-Si eutectic brazing alloy, the interfacial zone between the aluminum-rich braze and the stainless steel substrate features two intermetallic layers. The first is formed in the initial instants of the process and features an overall composition similar to that of the compound FeSiAl{sub 5}. The second appears after a 10-min hold time at the brazing temperature, and features an overall composition that parallels the FeAl{sub 3} intermetallic. Both layers are, however, more complex in structure than is suggested by these stoichiometric relations. The shear strength of the braze peaks at 21 MPa after a 10-min hold time at the brazing temperature. This peak is associated with nucleation of the second intermetallic layer, which is shown to fragilize the joint significantly. The presence of silicon in the brazing alloy would also seem to be beneficial by retarding formation of this second, more fragile Fe-Al intermetallic layer; however, more work is needed to substantiate this tentative conclusion.
Dissimilar metals joints of the galvanized steel (GI steel) and the pure aluminum (A1050) were produced using the laser pressure welding method. In this method, dissimilar metals sheets were set between the twin rolls. These sheets were opened to make up the wedge-shaped-gap. A 2 kW YAG laser beam was irradiated into a wedge-shaped-gap by a f:θ lens and scanned at various frequencies and patterns using two dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined.
The welding of the GI steel and A1050 were carried out. In order to investigate the effect of a zinc plated layer thickness on the weldability, the GI steel of plated layer thickness of two types were used, and plated layer thickness were about 1.7 µm and 2.6 µm.
The laser pressure welding experiments conducted by changing the laser power and the roller pressure indicated that welding is possible under except some conditions. The intermetallic compounds were observed by optical microscope, and the layer thicknesses were measured. The intermetallic compound layer thicknesses increased according to the increase in the laser power and the roller pressure, and the thicknesses of the compound layers were about 3 µm to 18 µm. The tensile shear strength and the peel strength of the welded joints were evaluated. In the tensile test, the strengths of the joints yielded in most welded conditions were so high that the fracture occurred in the aluminum base metal. In the peel test, the roller pressure of more than 1.96 kN, the specimen fracture occurred in the aluminum base metal. In order to investigate the joining mechanism of the welded joints of GI steel and A1050, the TEM observation of the compound layer was carried out to examine the reason why the high joint strength was obtained even if the compound layer was thick. From TEM observed results, the joints consisted of the intermetallic compounds mainly, and the Zn phases were formed between the intermetallic compounds. In this research, even if the mainly constitution phases were the intermetallic compounds, the high joint strengths were obtained because the Zn phases formed in the grain boundary of intermetallic compounds.
Dissimilar metals joints of Zn-coated steel sheets and pure aluminum were produced using the laser pressure welding method by changing the laser power and the roller pressure. In this method, dissimilar metals sheets were set between the twin rolls. These sheets were opened to make up the wedge-shaped-gap. A 2 kW YAG laser beam was irradiated into a wedge-shaped-gap by a f:θ lens and scanned at various frequencies and patterns using two dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined. The laser pressure welding experiments conducted by changing the laser power and the roller pressure indicated that welding is possible under all conditions. The intermetallic compounds were observed by optical microscope, and the layer thicknesses were measured. When the laser power was 1300 W, the intermetallic compounds layer thickness was about 15 μm. Very small voids were observed in the welded interface at the laser power of 1500 W, and the intermetallic compounds layer thickness was about 7 μm. The tensile shear strength and the peel strength of welded joints were evaluated. In the tensile test, the strengths of the joints yielded in most welded conditions were so high that the fracture occurred in the aluminum parent metal. In the peel test, at the laser power of 1200-1400 W and the roller pressure of 2.94 kN, the specimen fracture occurred in the aluminum parent metal. On the other hand, the specimen fracture occurred in the welded interface when the laser power was 1500 W. In the TEM observation results, the Zn phase was formed in the aluminum parent metal. Moreover, the intermetallic compound was identified as Fe4Al 13 phase by electron diffraction. The joint strength was high even if the intermetallic compound layer was thick. The reason for such high strength is attributed to an intermetallic compound dispersed finely in the (Al + Zn) phase.
The microstructure and bond strength of the friction-welded interface of Al-Mg alloy A5052 to carbon steel S45C have been investigated, to establish their dependence on C content of steel by comparison with those observed in the joint of A5052 alloy to low C steel S10C. TEM observations revealed that an intermetallic compound layer 100-1000 nm thick was formed at the interface, consisting of Fe2Al5 and Fe4Al13 similar to that observed at the A5052/S10C interface. The thickness of the intermetallic compound layer was increased almost in proportion to friction time in both joints, while that of the A5052/S45C joint grew at a lower rate than that of the A5052/S10C joint. In the intermetallic compound layer, granular Fe2Al5 and Fe4AI13 were distributed almost randomly, in contrast to those observed at the interface of the diffusion couple or diffusion-bonded joint, where intermetallic compounds formed as layers distributed in the order of their chemical compositions. This suggests that the formation of the intermetallic compound layer was significantly influenced by a factor other than the diffusion of Al and Fe. In the steel adjacent to the intermetallic compound layer, a very fine grain zone was observed, suggesting that the steel surface underwent heavy plastic deformation during the friction process. The thickness of the fine grain zone was also increased in proportion to friction time. It was found that the thickness of the intermetallic compound layer increased with that of the fine grain zone, obeying a relation almost independent of the C content of the steel and chemical composition of the Al alloy. These results suggest a significant contribution of mechanical intermingling of Fe with Al in the formation of the intermetallic compound layer. On tensile tests using specimens with a circumferential notch at the interface, the A5052/S45C joint was fractured at the interface region, showing higher fracture strengths than the A5052/S10C joint, probably because of the lesser thickness of the intermetallic compound layer.
A purpose of this review is to note the difficulties which remain to be overcome. After outlining the probable mechanisms of bond formation, work relating to bonding of aluminum to steel is summarized.
Ultrasonic welding between SS400 mild steel sheet and aluminum alloy sheet containing magnesium (A5052) was conducted. In this study, authors investigated the influence of ultrasonic welding conditions on the mechanical properties and the interface microstructure of a joint, and the effect of insert metal was examined to improve the joint strength. The main results obtained in this study are as follows.It was possible to weld ultrasonically SS400 mild steel sheet to A5052 aluminum alloy sheet containing magnesium. The strength of the joints welded using various clamping forces and constant welding time of 1.0s showed the maximum value at the clamping force of 588N and decreased with the clamping force over 588N because the excessively large clamping force reduced the frictional action at the interface. The strength of the joints welded using the constant clamping force of 588N and various welding times showed the maximum value at the welding time of 2.5s. However, the strength of the joint welded using the welding time of 3.0s decreased due to the formation of Fe2Al5 intermetallic compound at the interface. Using the insert metal of commercially pure aluminum, the joint strength was successfully improved and the strength of the welded using 3.0s welding time was about three times as large as that of the joint without the insert metal.
The authors tried to butt-weld an aluminum alloy plate to a mild steel plate by friction stir welding, and investigated the effects of a pin rotation speed, the position for the pin axis to be inserted on the tensile strength and the microstructure of the joint. The behavior of the oxide film on the faying surface of the steel during welding also was examined. The main results obtained are as follows. Butt-welding of an aluminum alloy plate to a steel plate was easily and successfully achieved by friction stir welding. The maximum tensile strength of the joint was about 86% of that of the aluminum alloy base metal. A small amount of intermetallic compounds was formed at the upper part of the steel/aluminum interface, while no intermetalic compounds were observed in the middle and bottom parts of the interface. The regions where the intermetallic compounds formed seemed to be fracture paths in the joint. Many fragments of the steel were scattered in the aluminum alloy matrix and the oxide film removed from the faying surface of the steel by the rubbing motion of a rotating pin was observed at the interface between the steel fragments and the aluminum alloy matrix.
Tool wear is a key issue for the friction stir spot welding (FSSW) of steel plates, especially in the automobile industry. In this study, steel plates were welded 500× using FSSW with WC–Co alloy tools of two different compositions. The effect of the weld number on the joint strength and the tool wear characteristics were analyzed by using a non-contact, D measurement system, scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). The experimental results indicated that the tool suffered extreme wear and that the joint strength was affected by the worn tool shape after welding. This tool wear was attributed to the formation of a ternary W–Fe–O compound, oxidative wear of WC and fatigue of the Co binder.
The microstructure of joints between an Al-alloy and a zinc coated ferritic steel sheet manufactured by the so-called CMT
joining method is investigated. The joint consists of a weld between the Al-alloy and Al 99.8 filler and a brazing of the
filler to the zinc coated steel. The morphology, the structure and the defects of the intermetallic phases that developed
at the interface between the steel and the Al 99.8 filler are characterised using scanning and transmission electron microscopy.
The intermetallic phase seam is only about 2.3 μm thick and consists of trapezoidal nearly equiaxial Fe2Al5 grains surrounded by finger-like remains of the steel and mostly elliptical FeAl3 grains extending into the Al 99.8 filler material. Both the Fe2Al5 and the FeAl3 grains contain crystal defects.
Dissimilar lap joints of low carbon steel and Al–Mg alloy were obtained by friction stir spot welding. Mechanically mixed layer between top and bottom plates was not formed at the weld nugget due to the limited tool penetration and the pin height of welding tool lower than the thickness of Al plate laid in top side. These welding conditions made it possible to weld steel plate using welding tools made out of a general tool steel. With increasing tool penetration depth (TPD), tensile shear force of joint increased and maximum value of 3·0 kN was obtained at the TPD of 0·5 mm, but excessive tool penetration beyond 0·5 mm was caused in a deformation of Al plate of top side. In the result of interface observation, interaction layer was formed between Fe and Al alloy, which was constituted by various intermetallic compounds (IMCs). Consequently, the size of strongly bonded area containing Fe3Al and Fe4Al13 IMCs increased with TPD, which resulted in the increase in joint strength under the limited TPD.
The joinability of aluminium alloy and mild steel sheets using a self piercing rivet is evaluated by a finite element simulation and experiment. The self piercing riveting has potential as a replacement for spot resistance welding generally used for steel sheets, because it is not easy to apply resistance welding to joining of aluminium and steel sheets which have very different melting points. Defects in the riveting are categorized into the penetration through the lower sheet, the necking of the lower sheet and the separation of sheets to obtain optimum joining conditions. The penetration, necking and separation are caused by the small total thickness, the small thickness of lower sheet and the large total thickness, respectively. The joinability for the combination of the upper sheet of steel and the lower sheet of aluminium is higher than that of the reverse combination.
Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships. # 2005 Elsevier B.V. All rights reserved.
Dissimilar metals TIG welding-brazing of aluminum alloy to galvanized steel was investigated, and the wettability and spreadability
of aluminum filler metal on the steel surface were analyzed. The resultant joint was characterized in order to determine the
brittle intermetallic compound (IMC) in the interfacial layer, and the mechanical property of the joint was tested. The results
show that the zinc coated layer can improve the wettability and spreadability of liquid aluminum filler metal on the surface
of the steel, and the wetting angle can reach less than 20°. The lap joint has a dual characteristic and can be divided into
a welding part on the aluminum side and a brazing part on the steel side. The interfacial IMC layer in the steel side is about
9.0 μm in thickness, which transfers from (α-Al + FeAl3) in the welded seam side to (Fe2Al5+ FeAl2) and (FeAl2+ FeAl) in the steel side. The crystal grain of the welded seam is obviously larger in size in the aluminum side. The local
incomplete brazing is found at the root of the lap joint, which weakens the property of the joint. The fracture of the joint
occurs at the root and the average tensile strength reaches 90 MPa.
Laser welding of low carbon steel to 5754 aluminum alloy was studied in keyhole welding mode in steel-on-aluminum overlap configuration. In order to decrease formation of intermetallic components during laser welding, effect of laser power, pulse duration and overlapping factor was investigated. Tensile test was performed to identify the effect of each parameter on the weld. The phase composition was characterized by energy dispersive spectrometry and Vickers microhardness test and microstructure by optical and scanning electronic microscopes. Results obtained show that increasing peak power (in constant pulse energy), pulse duration (in constant peak power) and overlapping factor (in constant pulse energy and peak power) will increase percentage of intermetallic components (PIC). On the other hand, decreasing the mentioned parameters will cause destructive effects such as inadequate penetration depth, spattering and cavity formation. Improvement in the tensile strength was attributed to low values of intermetallic components in weld metal. Finally, an optimized peak power, pulse duration and overlapping factor were reported.
The reaction layers of friction stir welded joints made from austenitic stainless steel and Al alloy consisted of mixed layers of elongated and ultra-fine grains and the intermetallic compound layer. The intermetallic compound layer was identified as Al4Fe with a hexagonal close-packed structure and a thickness of approximately 250 nm. The elongated grains were shown to consist of a ferrite phase because of their ferromagnetism and a body-centered cubic crystal structure. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
The microstructure and properties of aluminium–zinc coated steel lap joints made by a modified metal inert gas CMT welding–brazing process was investigated. It was found that the nature and the thickness of the high-hardness intermetallic compound layer which formed at the interface between the steel and the weld metal during the welding process varied with the heat inputs. From the results of tensile tests, the welding process is shown to be capable of providing sound aluminium–zinc coated steel joints.
The joining of a 6-mm thickness Al 6061 to AISI 1018 steel has been performed by the combined effects of fusion and solid state welding. The process is derived from friction stir welding (FSW) but with an adjustable offset of the probe location with respect to the butt line. Metallographic studies by optical microscopy, electron probe microscopy, and the utilization of the X-ray diffraction technique have been conducted. It was found that the intermetallic phases Al13Fe4 and Al5Fe2 exist in the weld zone. The tool was significantly worn during welding and is broken after traveling 100 mm at a rotational speed of 917 rpm. The wear of the tool significantly affects the structure of the weld, and the tool breakage was detected by the incorporated acoustic emission (AE) sensors. It appears that the joining of an Al 6061 alloy to AISI 1018 steel with a sound heterogeneous weld microstructure is feasible using this process, and the tool breakage can be detected by the AE sensing technique.
Post-weld properties of dissimilar friction stir welds of mild steel/A7075-T6 aluminum alloy were investigated. The joint strength increased with reduction in thickness of the intermetallic compound at the weld interface. During tensile tests of the composite weld, no weld failed in the aluminum base metal. Comprehensive analysis using the heat input parameter showed that the apparent interface strength between the steel and aluminum was lower than the joint strength of the friction-stir-welded A7075-T6 alloy.
The study of the metallurgy of the interface of metal/metal friction-welded components is essential for understanding the quality of bonding. We have studied, through optical and electron microscopy, and tensile strength measurements, the bonding properties of Al and interstitial free steel and Al and stainless steel friction-welded components. The samples were produced by varying the friction time and rotational speed, friction pressure, upsetting pressure, and upsetting time constant at optimized values reported earlier. The bonding occurs over an intermetallic phase, which, when too thick, influences the bonding properties adversely. The thickness of the intermetallic interlayer depends linearly of on the square root of the friction time, indicating that the growth is caused by diffusion. The effect of oxidation on the bonding is also studied on samples prepared under argon atmosphere and normal atmosphere.
Method and apparatus for joining
- T Iwashita
T. Iwashita: 'Method and apparatus for joining', EP patent no. 1
149 656 B1, 2005.
The parameters influencing the mechanical properties of friction stir spot welds between 6016 aluminum alloy and HSLA steel
- S Bozzi
- A L Etter
- T Baudin
- V Klosek
- B Criqui
- J G Kerbiguet
S. Bozzi, A. L. Etter, T. Baudin, V. Klosek, B. Criqui and J. G.
Kerbiguet: 'The parameters influencing the mechanical properties
of friction stir spot welds between 6016 aluminum alloy and HSLA
steel', Proc. 7th Int. Symp. on 'Friction stir welding', Awaji Island,
Japan, May 2008, TWI CD ROM.
Friction stir welding in automotive industry – recent developments
- T Weinberger
- G Figner
- N H Enzinger
- C Cerjak
- Kollbeck
T. Weinberger, G. Figner, N. Enzinger. H. Cerjak and C. Kollbeck: 'Friction stir welding in automotive industry – recent developments
Analysis of tool wear and failure mechanism during friction stir welding of steel
- T Weinberger
- S Khosa
- B Fuhrer
T. Weinberger, S. Khosa, B. Fuhrer and N. Enzinger: 'Analysis of
tool wear and failure mechanism during friction stir welding of
steel', Proc. 7th Int. Symp. on 'Friction stir welding', Awaji Island,
Japan, May 2008, TWI CD ROM.
Friction stir welding in automotive industry - recent developments and viable application
- T Weinberger
- G Figner
- N Enzinger
- H Cerjak
T. Weinberger, G. Figner, N. Enzinger. H. Cerjak and C. Kollbeck:
'Friction stir welding in automotive industry -recent developments
and viable application', IIW Doc. no. III-1532-2009, IIW,
Villepinte, France 2009.
Joining aluminium to steel. Part 1: Diffusion bonding
- S Elliot
- E R Walllach
Specimens dimensions and procedure for shear testing resistance spot, seam and embossed projection welds
- Iso