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FLAWS IN FRICTION STIR WELDS
Abstract
One of the major drivers for using friction stir welding for aluminium fabrication is the low incidence of weld flaws compared to that produced by conventional arc welding. However, the process does have its own characteristic flaws. A number of different process variables affect the quality of a joint produced by friction stir welding: tool design, tool rotation and travel speeds, tool heel plunge depth and tilt angle, welding gap, thickness mismatch and plate thickness variation. Successful, reproducible welds may be produced by operating within process "windows". However, problems may arise when the welding conditions deviate from the standard operating window. In such circumstances, flaws may be generated. In the current work, a number of flaws encountered in friction stir welds, in particular voids, joint line remnants and root flaws were generated in an Al-Cu-Mn-Si-Mg alloy by using welding parameters outside of the established tolerance box for producing flaw-free welds. The welds were characterised using X-ray and ultrasonic non-destructive testing techniques and by metallographic sectioning. The causes of such features are described and recommendations are made to prevent their occurrence.
... Insufficient specific pressure on the tool, high welding speed [1], low tool feed rate [2,3], and insufficient clearance between the parts to be welded [1,4] in the process of STP cause porosity of aluminum welds. Insufficient specific pressure on the tool and, as a consequence, insufficient mechanical action on the tool does not contribute to the structural heterogeneity of the welded samples [1,[5][6][7][8]. ...
... Insufficient specific pressure on the tool, high welding speed [1], low tool feed rate [2,3], and insufficient clearance between the parts to be welded [1,4] in the process of STP cause porosity of aluminum welds. Insufficient specific pressure on the tool and, as a consequence, insufficient mechanical action on the tool does not contribute to the structural heterogeneity of the welded samples [1,[5][6][7][8]. ...
... Insufficient specific pressure on the tool, high welding speed [1], low tool feed rate [2,3], and insufficient clearance between the parts to be welded [1,4] in the process of STP cause porosity of aluminum welds. Insufficient specific pressure on the tool and, as a consequence, insufficient mechanical action on the tool does not contribute to the structural heterogeneity of the welded samples [1,[5][6][7][8]. The inhomogeneity of the weld is caused by a smaller number of tool rotations per millimeter, less work, and the amount of heat per unit length of the weld, necessary for the plastically deformed material to reach a sufficiently high temperature [3,9]. ...
... AlZnMgCu (7XXX series) alloys [4,8,9]. The mechanical properties of the arc welded joint in these alloys can be seriously compromised by a dendritic structure formed in the fusion zone [9,10]. ...
... In contrast to traditional welding procedures, FSW can successfully avoid solidification flaws such as porosity and hot cracking in the weld region due to the solid-phase characteristics of the joining procedure [8,24]. However, other flaws, such as lack of penetration (LOP), wormholes (tunnel defects), kissing bonds and lazy S features (also called zigzag line defect, Joint Line Remnant (JLR) or entrapped oxide defect) are common in FSWs [3,25]. ...
... The latter mostly occurs due to the presence of a continuous oxide film in the weld zone coming from an initial oxide layer on the butt surfaces [26][27][28][29]. When the entrapped oxide film is connected to the root of the friction stir welded joints, the lazy S features are called kissing bonds, weak bonds or root-flaws [8,25,27,30,31]. Material properties, tool design [32,33] and critical operation parameters (including rotation and translation speed [34], tool plunge depth, spindle tilt angle, forge force and fixture clamping condition) play an important role in the formation of flaws and in the quality of the [8,25,27,[35][36][37][38]. Welding conditions such as insufficient tool plunge depth, low tilt angle and insufficient heat-input may result in the formation of kissing bond flaws at the weld root [8,25,27,30]. ...
... AlZnMgCu (7XXX series) alloys [4,8,9]. The mechanical properties of the arc welded joint in these alloys can be seriously compromised by a dendritic structure formed in the fusion zone [9,10]. ...
... In contrast to traditional welding procedures, FSW can successfully avoid solidification flaws such as porosity and hot cracking in the weld region due to the solid-phase characteristics of the joining procedure [8,24]. However, other flaws, such as lack of penetration (LOP), wormholes (tunnel defects), kissing bonds and lazy S features (also called zigzag line defect, Joint Line Remnant (JLR) or entrapped oxide defect) are common in FSWs [3,25]. ...
... The latter mostly occurs due to the presence of a continuous oxide film in the weld zone coming from an initial oxide layer on the butt surfaces [26][27][28][29]. When the entrapped oxide film is connected to the root of the friction stir welded joints, the lazy S features are called kissing bonds, weak bonds or root-flaws [8,25,27,30,31]. Material properties, tool design [32,33] and critical operation parameters (including rotation and translation speed [34], tool plunge depth, spindle tilt angle, forge force and fixture clamping condition) play an important role in the formation of flaws and in the quality of the [8,25,27,[35][36][37][38]. Welding conditions such as insufficient tool plunge depth, low tilt angle and insufficient heat-input may result in the formation of kissing bond flaws at the weld root [8,25,27,30]. ...
... Till now, numerical and empirical investigations to thoroughly understand the heat transfer and material flow phenomena in the FSW process are still ongoing [6,7]. FSW was initially used for aerospace aluminum alloys, because of their low arc weldability, e.g. on AlCu type (2XXX series) and AlZnMgCu (7XXX series) alloys [4,8,9]. The mechanical properties of the arc welded joint in these alloys can be seriously compromised by a dendritic structure formed in the fusion zone [9,10]. ...
... 1). In contrast to traditional welding procedures, FSW can successfully avoid solidification flaws such as porosity and hot cracking in the weld region due to the solid-phase characteristics of the joining procedure [8,24]. However, other flaws, such as lack of penetration (LOP), wormholes (tunnel defects), kissing bonds and lazy S features (also called zigzag line defect, Joint Line Remnant (JLR) or entrapped oxide defect) are common in FSWs [3,25] . ...
... The latter mostly occurs due to the presence of a continuous oxide film in the weld zone coming from an initial oxide layer on the butt surfaces26272829. When the entrapped oxide film is connected to the root of the friction stir welded joints, the lazy S features are called kissing bonds, weak bonds or root-flaws [8,25,27,30,31]. Material properties, tool design [32,33] and critical operation parameters (including rotation and translation speed [34], tool plunge depth, spindle tilt angle, forge force and fixture clamping condition) play an important role in the formation of flaws and in the quality of the [8,25,27,35363738. ...
Friction Stir Welding (FSW) is a relatively new solid state welding procedure developed at The Welding Institute (TWI-UK) and is widely considered for welding aluminum alloys in various applications. In order to inspect the quality of the welds and to detect a variety of welding flaws such as wormholes, Lack of Fusion (LOF) and Lack of Penetration (LOP) defects, it is required to develop a methodical examination technique that can be used for the identification and the localization of all such defects.
The most prevalent and risky defect in this type of welding is the unrevealed lack of penetration (also known as the root flaw with a length varying from 100-700 µm). Due to the characteristics of the flaw, conventional ultrasonic methods are not always able to readily detect such fine Lack of Penetration (LOP) defects.
Here, we propose a novel approach to characterize root flaws using an oblique incident ultrasonic C-scan backscattering analysis. The implementation consists of an immersion ultrasonic testing method in pulse echo (i.e. backscatter) mode with a 3.5 MHz transducer, and makes use of an empirical method to allow focusing and gating the received signal for root flaw examination. By scanning the surface above the welded component, a “slanted C-scan” image, displaying the backscattering response from the root surface of the nugget zone, can be obtained which allows a simple interpretation of the root flaw status of the weld.
... The tunnelling defect can be eliminated or minimized by adequate heat input and its distribution on either side of the weld zone and appropriate material flow intermixing behind the probe [217,218]. In addition to this voids and cavity defects are usually found at the advancing side of the weld and they may or may not break comprehensively to the weld surface as mentioned in Table 5 [219]. The formation of voids and cavities may occur due to the very low tool rotational speed. ...
... The presence of voids strongly leads to reduction in ductility and somewhat the weld strength also. Higher traverse speed and lower rotational speed results in insufficient material flow and heat generation [210,219]. To eliminate such defects, an optimum welding and rotational speed should be selected. ...
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.
... The voids were on the advancing side of the weld between the stirred zone and the TMAZ. It is due to the fast rotation rate causes anomalous viscoplastic form of the material with lack of accommodation of the material interface between two zones [9]. It is assumed that the forging pressure should be increased in this condition to prevent this type of defects. ...
... The voids were on the advancing side of the weld between the stirred zone and the TMAZ. It is due to the fast rotation rate causes anomalous viscoplastic form of the material with lack of accommodation of the material interface between two zones[9]. It is assumed that the forging pressure should be increased in this condition to prevent this type of defects. ...
... Characteristics of the weld depend strongly on welding parameters such as tool rotating speed and tool travel speed. High strength joints without defects such as voids or lack of penetration (LOP) can be produced when using appropriate welding parameters [2,3]. However, other types of weld imperfections or weld flaws can arise even under the optimized welding conditions, that may or may not compromise the integrity of the welded join. ...
... welding speed) and tool configuration. "Root flaw" (sometimes "kissing bond") is a weld defect with partially unwelded or only weakly bonded butt surfaces on the root side of the weld due to insufficient plunging of the tool, poor joint to tool alignment or inappropriate welding parameters [2,7,8,9]. JLR can be formed accompanying root flaws depending on the welding conditions. These insufficient bonds at the bottom part of the JLR (i.e. ...
The influence of the joint line remnant (JLR) on tensile and fatigue fracture behaviour has been
investigated in a friction stir welded Al-Mg-Sc alloy. JLR is one of the microstructural features formed in
friction stir welds depending on welding conditions and alloy systems. It is attributed to initial oxide layer on
butting surfaces to be welded. In this study, two different tool travel speeds were used. JLR was formed in both
welds but its spatial distribution was different depending on the tool travel speeds. Under the tensile test, the
weld with the higher heat input fractured partially along JLR, since strong microstructural inhomogeneity
existed in the vicinity of JLR in this weld and JLR had weak bonding. Resultantly, the mechanical properties of
this weld were deteriorated compared with the other weld. Fatigue crack initiation was not affected by the
existence of JLR in all welds. But the crack propagated preferentially along JLR in the weld of the higher heat
input, when it initiated on the retreating side. Consequently, such crack propagation behaviour along JLR could
bring about shorter fatigue lives in larger components in which crack growth phase is dominant.
... The JLR may be connected for some particular welding conditions to the weld root and induce fracture during severe bending of the weld. In this particular case, it is referred to as Kissing Bond (KB), weak bond or root flaw [16][17][18][19][20][21]. It will be referred to as KB hereafter. ...
... In [25] it was found that so-called wormholes may appear in the weld when an initial gap wider than 0.5 mm is left. Some defects can be remediated by increasing the heat input energy [17,26]. Little data is available about the consequences of such a gap on the mechanical properties of the welded joint, and in particular its fatigue strength. ...
The fatigue strength and failure mechanisms of defect-free (“sound”) and flaw bearing friction stir butt-welds of 3.1 mm-thick AA2198-T8 Al–Li–Cu alloy have been investigated via S–N curves at R = 0.1 using cross weld specimens. The fatigue strength of sound welds is only reduced by 10–15% at the aimed lifetime of 105 cycles compared to the base material. Joint Line Remnant (JLR) bearing welds have a similar fatigue strength as sound welds and the JLR is not the crack initiation site. Kissing Bond (KB) bearing welds that have undergone a weld root polishing show a reduction in fatigue strength by 17% compared to sound welds. For specimens loaded at or above yield strength of the weld nugget the crack systematically initiates from the KB during the first cycle, which is interpreted further using fracture mechanics. The strongest reduction, about 28% in fatigue strength, is found for welds with an initial gap between the parent sheets (GAP welds) along with initiation at intergranular surface microcracks. Kahn tear tests show a reduction in tearing resistance for the flaw bearing welds with a similar ranking as for the fatigue strength.
... Thus, understanding the characteristics and formation mechanisms of welding defects are of critical importance for obtaining high-quality FSW joints. For normal FSW of aluminum alloys, a considerable amount of information is available on welding defects, and the defects are commonly considered to occur due to inadequate or excess heat input19202122 . When less frictional heat is generated at the tool/work piece interface, the lower plasticity of material does not permit complete filling of the hole produced by the pin rotation, which consequently leads to defect formation [10, 16, 17,192021. ...
... For normal FSW of aluminum alloys, a considerable amount of information is available on welding defects, and the defects are commonly considered to occur due to inadequate or excess heat input19202122 . When less frictional heat is generated at the tool/work piece interface, the lower plasticity of material does not permit complete filling of the hole produced by the pin rotation, which consequently leads to defect formation [10, 16, 17,192021. Conversely, when excess heat is generated by using improper parameters (e.g., higher rotation speeds), the formation mechanisms of defects are not quite clear. In the FSW of ADC12 aluminum alloy, it was found that voids were formed in the joint when the rotation speed was increased up to a certain value, and the size of the defect increased with increasing the welding speed [20]. ...
Underwater friction stir welding (FSW) has been demonstrated to be a promising method for strength improvement of heat-treatable aluminum alloy joints. However, when improper welding parameters are utilized, welding defects, such as voids can be produced in the joints, leading to dramatically deteriorated mechanical properties. Thus to obtain high-quality underwater joints, it is necessary to understand the variables that promote the formation of these defects. In this study, the characteristics of welding defects in underwater joints were examined, and the formation mechanisms of the defects were investigated by analyzing the material flow patterns during underwater FSW. The results indicated that welding defects can occur at both low- and high-rotation speeds (HRS). The defects formed at HRS can be divided into two types according to the welding speed. When a HRS and a low welding speed are chosen, the material beneath the tool shoulder tends to be extruded into the pin stirred zone (PSZ) after flowing back to the advancing side. This results in a turbulent flow condition, creating void defects in the PSZ. When a high welding speed is coupled with the HRS, a large amount of material from the thermo-mechanically affected zone is dragged into the pin hole, which causes the material of the shoulder stirred zone to fill the pin hole in a downward flow direction. This leads to turbulent flow in PSZ, and creates voids or even groove defects in the as-welded joints.
... Researchers have investigated the formation of defects in FSW joints which deteriorates its mechanical properties. Improper process parameters, excess or insufficient heat input are some of the reasons for the defect formation [2][3][4]. FSW is currently used in aerospace and shipbuilding industries and is found in a wide range of material including aluminium, steel and titanium alloys. ...
... LOP, as the name implies, arises when the tool probe is too short or when the plunge depth is too shallow. 42,43 Increasing probe length amplifies material flow, ensuring better mixing near weld root. 32 Finally, voids appear as empty regions within NZ. ...
Friction stir welding (FSW) has matured considerably since its introduction in 1991. Over the last decades, it has indeed branched and been applied in different fields, such as automotive, aerospace, railway, and shipbuilding. This article aims to survey the basic knowledge related to the conventional FSW of aluminum alloys in order to provide a tool for understanding the friction stir processes. The review covers the five basic process parameters: rotational
speed, welding speed, tool geometry, tilt angle, and plunge depth. Furthermore, it presents the related equations and recommended ranges of those parameters to facilitate the process design step for industrial implementation. A sample of 30
published articles was drawn for that purpose. The current article also discusses the main five properties most researchers are interested in, namely, microstructure, microhardness, tensile strength, residual stresses, and distortion.
... The plunge depth was found to be important in void formation. Leonard and Lockyer,20 too, observed inadequate plunge depth and higher tool travel speed resulted in the poor consolidation of the weld. They reported that voids are generally located on the advancing side (AS) of the weld and below the crown surface if Department of Mechanical Engineering, Indian Institute of Science, Bangalore, India the weld is made under these circumstances. ...
The reduction of agglomeration of particulate reinforcement in friction stir processing and elimination of joint line remnant in friction stir welding depends on stirring ability of friction stir tool. The magnitude of stirring is indicated by the intensity of material inter-mixing in tool interacted region. Present investigations analyse the influence of geometrical aspects of classical friction stir tool on the intensity of material intermixing, location of high stir regions and void formation during the steady-state phase of friction stir welding. The classical tool was chosen as its geometrical features undergo minimal wear in the harsher processing environment. Investigating material mixing using metallic inserts have their shortcomings due to different flow properties of insert/marker and parent material. Therefore, bi-colour plasticine configuration possessing primary colours was adopted to understand the level of intermixing. The hue attribute of the generated secondary colour was utilised to identify and quantify material mixing. Experimental results revealed that the pin diameter positively influenced mixing and negatively affected void formation. Shoulder size and pin taper angle aided in the closure of void with inferior mixing. The intensity of mixing enhances on selection of tools possessing a shoulder to pin diameter ratio of 2.5. Finite element simulation studies were conducted to understand the reasons for mixing under certain tooling conditions. Since material subjected to stirring is concentrated primarily on a portion of advancing side, components of shear strain, shear strain rates, shear stress and velocity were tracked for this portion of processed material during its interaction with tool pin for one complete rotation.
... This can also be due to a misalignment of the tool center relative to the weld joint. A few of the more common defects for linear butt welds are shown in Figure 2-11 (Leonard and Lochyer [90]). In the upper left corner is a lazy S or kissing bond defect. ...
Friction stir welding, FSW, is a solid-state joining method that is ideally suited for welding aluminum alloys. Welding of the aluminum is accomplished by way of a hardened steel tool that rotates and is pushed with great force into the work pieces. Friction between the tool and the aluminum causes heat to be generated, which softens the aluminum, rendering it easy to deform plastically. In recent years, the FSW process has steadily gained interest in various fabrication industries. However, wide spread acceptance has not yet been attained. Some of the main reasons for this are due to the complexity of the process and the capital cost to procure the required welding equipment and infrastructure. To date, little attention has been paid towards finding optimal process parameters that will increase the economic viability of the FSW process, thus offsetting the high initial investment most. In this research project, a robust and efficient numerical simulation code called SPHriction-3D is developed that can be used to find optimal FSW process parameters. The numerical method is meshfree, allowing for all of the phases of the FSW process to be simulated with a phenomenological approach. The dissertation starts with a focus on the current state of art. Next an in-depth development of the proposed meshfree formulation is presented. Then, the emphasis turns towards the presentation of various test cases along with experimental validation (the focus is on temperature, defects, and tool forces). The remainder of the thesis is dedicated to the development of a robust approach to find the optimal weld quality, and the associated tool rpm and advancing speed. The presented results are of engineering precision and are obtained with low calculation times (hours as opposed to days or weeks). This is possible, since the meshfree code is developed to run in parallel entirely on the GPU. The overall outcome is a cutting edge simulation approach for the entire FSW process.
... To avoid any change in the heat sink during the welding process, the horizontal plane containing the workpieces was free of bolts and their holes (Fig. 1c). As per the results presented in the works of Christner and Sylva [42] and Leonard and Lockyer [43], the formation of a gap between specimens up to 33%-36% of the plate thickness does not affect the joint strength and could be [44] observed that a lesser distortion and more consistent distribution of the residual stresses through the weld thickness can be achieved by applying higher clamping forces. It has been demonstrated that the possibility of defects could also be minimized by preventing any creation of gaps between the abutting edges of the welding plates. ...
Friction stir welding of dissimilar aluminum alloys has become an important application in the modern industries. Joint strength is a major consideration in this advanced technology. This paper presents an attempt made to improve the weld tensile strength by controlling the temperature distribution during the joining process. High-strength AA7075-T651 and AA2024-T351 aluminum alloys were friction stir welded using different backing and clamping materials. The tool rotation rate was preliminarily investigated to estimate the optimal spindle speed. Next, three composite backing plates and clamping systems were tested in conjunction with varying levels of traverse speeds and materials position. The transient temperatures were experimentally measured at different distances from the welding line. Asymmetric temperature distributions were observed with maximum records on the advancing side of the weld. Moreover, the influence of backing and cover materials on the joint strength was found to be varied with the applied level of the welding traverse speed. Based on these results, an idea to use asymmetric system of backing and cover materials was inspired. This system assisted to improve the temperature distribution and resulted in a sound weld with higher tensile strength. The detailed results of this work were discussed and the main outputs were outlined in the conclusions.
... Frictional heat generated between the welding tool and the workpieces makes the material softened, and an FSW joint was formed [4]. Owing to the more environmental-friendly welding process and better joint with higher mechanical properties, FSW has achieved rapid development in joining of aluminium alloys [5]. ...
The 5 mm thick Al–Mg–Si alloy was self-reacting friction stir welded using the specially designed tool at a constant rotation speed of 400 rev min⁻¹ with various welding speeds. Defect-free welds were successfully obtained with welding speeds ranging from 150 to 350 mm min⁻¹, while pore defects were formed in the weld nugget zone (WNZ) at a welding speed of 450 mm min⁻¹. Band patterns were observed at the advancing side of WNZ. Grain size and distribution of the precipitated phase in different regions of the joints varied depending on the welding speed. The hardness of the weld was obviously lower than that of the base metal, and the lowest hardness location was in the heat affected zone (HAZ). Results of transverse tensile tests indicated that the defective joint fractured in the WNZ with the lowest tensile strength, while the fracture location of the defect-free joints changed to the HAZ.
... Hence, a kind of chip or hole appeared in RS section Table 3Alteration width of weld against tool rotational rate at depths of 0.5, 1, and 1.5 mm from weld surface (mm). which is so called tunnel defect [16]. The higher magnification micrograph from tunnel defect of Fig. 2cis shown in Fig. 3a . ...
... In FSW, Christner and Sylva [17] recorded that the formation of gap between specimens up to 36% of the plate thickness does not affect the joint strength. In a similar work, Leonard and Lockyer [18] noted that a gap presence up to 33% of the workpiece thickness could be tolerated without the existence of weld flaws. On the other hand, Richter and his group of researchers [19] observed that lesser distortion and a more consistent residual stresses distribution through the thickness can be achieved by applying higher clamping forces. ...
Sound friction stir welds could be attained by using an active design of backing/clamping system with a proper selection of the welding parameters. This work presented a simplified design of fixtures and backing plates to be used for friction stir welding of aluminum alloys. The test-rig was constructed to prevent dispersal or lifting of the specimens throughout the joining process and to ensure uniform distribution of temperature along the plates. The workpieces were subjected to uniform lateral and vertical pressures by means of bolts and nuts. Compound backing plates and pressure bars with additional side plates were included to increase the heat sink. Several coupons of dissimilar aluminum alloys AA7075 and AA6061 were joined to inspect the validity of this design. The tests showed promising results with defects-free welds, good strength and smooth surface finish without geometric imperfection and gap creation between the welded specimens. Efficiency of the joint reached its maximum value of about 82% with respect to the ultimate strength of the AA6061 alloy at 1100 rpm rotation speed and 300 mm/min feed. These results encourage using and improving the present design for future studies of friction stir welding.
... Entrapped oxide is very difficult to detect using NDT methods. (Leonard and Lockyer 2003) It was noticed earlier that entrapped oxide particles make pure copper susceptible to hydrogen sickness, while an addition of phosphorus diminishes it or even prevents it (Savolainen et al. 2004). Jene et al. (2006) studied oxide particles and their distribution in AlMg3Mn alloy. ...
Some aspects of entrapped oxide particles in friction stir welds have been documented, for example that the oxides form patterns depending on the base material, tool geometry, and welding parameters. It has been also noticed that the presence of entrapped oxide particles may lead to a decrease of mechanical properties and that they are difficult to detect using NDT methods. This study combines the prior knowledge with new information about the origin and effects of entrapped oxide particles in friction stir welds of copper. The base material was 20 mm thick oxygen-free copper with 40 ppm of phosphorus (Cu-OFEP), the type planned to be used in corrosion barrier capsules for final disposal of spent nuclear fuel. A triflat tool with a concave shoulder and a 5.5 mm long tool pin was used. Welding parameters were: rotation speed 750 rpm; traverse speed 70 mm/min; tilt angle 2.5˚; and plunge depth 5.7 mm. Narrow grooves of varying depths (0, 2, 5, and 8 mm) were made to the work pieces using electric discharge machining. The effect of oxide removal (immersion in nitric acid for 30 s) prior to welding and shielding gas (argon) during welding was studied using different combinations of them: 1) no oxide removal, no shielding gas; 2) oxide removal, no shielding gas; 3) no oxide removal, using shielding gas; and 4) oxide removal, using shielding gas. Two transverse cross-sections were taken from each combination, the cross-sections being mirror images of each other. One sample of each pair was hydrogen annealed at 850˚C for 30 min, and the other one not. The samples were studied using hardness measurements, light optical microscopy, scanning electron microscopy, and electron back-scatter diffraction. Samples with no grooves (0 mm) showed no evidence of entrapped oxide particles. It was noticed that the samples contained the least amount of entrapped oxide particles when using simultaneously both oxide removal and shielding gas. During welding without shielding gas the surface of copper oxidizes readily. An oxidation zone was seen in front of the tool during welding. The appearance of the welded samples is greatly influenced by the use of shielding gas. Using shielding gas the surface remains clear and bright, and without it, the surface oxidizes strongly and becomes dark. An interesting microstructural feature is the pinning effect of the entrapped oxide particles. After annealing the samples for 30 min at 850˚C the general grain size was considerably larger, but the grains near the entrapped oxide particles remained small. Grain growth is suppressed by pinning of the grain boundaries caused by the entrapped oxide particles. In some applications the need for very high weld integrity may be necessary and possibilities of reducing the amount of entrapped oxide particles can be important. Local oxide particle pinning of the grain boundaries during annealing is very important in enhancing the formation of a nonhomogeneous microstructure.
... Tabatabaeipour et al. [22] inspected the root flaws in the friction stir welds by conventional ultrasonic C-scan. Though it is still unclear whether the conventional ultrasonic inspection is able to depict the bonding behavior in atomic scale due to the fact that the ultrasonic wave length is much greater than the atomic length scale [8,23,24], it has been demonstrated that the ultrasonic inspection had the capability to evaluate the interfacial voids in a wide range from the macro-scale down to the grain scale (8–10 μm [20,21] ). This capacity makes the ultrasonic inspection a viable approach to provide quantitative insight Materials ...
... c o m / l o c a t e / j m a d was introduced by the insufficient pin depth or poor tool to joint alignment. Similarly, the other type of JLR was the distribution of oxide particles through the thickness of the weld [12]. Sato et al. evaluated the behavior of an oxide layer on the initial butt surface during FSW. ...
Effects of various initial surface oxide films on microstructural and mechanical properties of friction stir welded (FSW) joints have been studied in the present paper. Anodizing was adopted to produce oxidation on AA2219-T62 surface. A series of friction stir welded joints were produced with various initial surface oxidations to study the effects on microstructural and mechanical properties of the joints. X-ray radiography inspection was conducted to determine the existence of welding defects. Optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize stir zone features and microstructure. Tensile test was employed to obtain FSW joint mechanical properties. Results show that initial surface oxide film has pronounced effect on the joint line remnant (JLR) distribution, microcosmic appearance and mechanical properties. Further analysis of the JLR particles suggests that the dispersed particles are Al2O3 oxide with the characteristics of polycrystalline structure because of the effect of the thermo-mechanical cycles. In addition, tensile strength of FSW joints with JLR inside the stir zone only reached about 60% of a sound FSW joint. Fractography analysis of broken tensile specimens exposed a series of severe “scalloping” correlated with JLR flaw, while sound weld exhibits fine dimples on the fracture surface.
... Hence, the analysis of the weld surface could also provide various other details. The reasons for number of defects encountered in FSW were described by Leonard et al. [4] using ultrasonic nondestructive techniques and X-ray analysis. It was also found that the bands of texture or texture patterns of FSW influenced the mechanical strength of the welded joints [5]. ...
Online monitoring of friction stir welding (FSW) is inevitable due to the increasing demand of this process. Also the machine vision system has industrial importance for monitoring of manufacturing processes due to its non-invasiveness and flexibility. Therefore, in this research, an attempt has been made to monitor friction stir welding process by analyzing the weld surface images. Here, discrete wavelet transform has been applied on FSW images to extract useful features for describing the good and defective weld. These obtained features have been fed to support vector machine based classification model for classifying good and defective weld with 99% and 97% accuracy with Gaussian and polynomial kernel, respectively.
... The amount of oxide inclusion can be reduced by increasing the weld speed, resulting in low oxide layer disruption per millimetre. 21 Another new modification is laser-assisted FSW (in which the laser is mainly used for preheating) which has the additional advantage of using more simple and inexpensive machines, in addition to the reduction in tool wear and higher attainable welding speeds. 22 Low-energy arc (MIG) welding methods such as cold metal arc transfer (CMT) are a recent development of the MIG process. ...
The use in motor vehicles of lightweight metals such as aluminium and titanium provides a high strength-to-weight ratio, thereby lowering overall weight and reducing energy consumption and CO2 emissions. Aluminium alloys have thus become an important structural material especially high strength and ultra-high strength alloys such as AW 7020. Many studies have shown that the presence of an aluminium oxide (Al2O3) thin film formed naturally on aluminium alloys is detrimental to welding. This article further investigates the specific effect of the Al2O3 thin film on welding AW 7020 alloy. An analytical experiment of welded AW 7020 alloy using a pulsed metal inert gas (MIG) robotic weld machine is carried out. Four specimens were cut, butt welded, and examined. The weld parameters included pre-weld cleaning of the Al2O3, pre-, and post-weld heat treatment. Al2O3 was removed by wire brushing; preheating was conducted at a temperature of 130 °C; and natural ageing was conducted by post-weld heating at 480 °C for 2 h, followed by quenching in water at 90 °C for 8 h, reheated, and sustained at 145 °C for 15 h. The result shows that the presence of Al2O3 layer appears not to be detrimental to the weld with new welding technologies, therefore suggesting that it is not necessary to grind off the Al2O3 layer before welding. This finding implies that welding costs can be lowered and weld quality improved when new welding technologies are applied in the welding of high-strength aluminium alloys.
... If the ratio of speed of advance to speed of rotation is not within an acceptable range, there is a high risk of causing welding defects. Leonard and Lochyer [5] provide a description of a few of the most common defects found in a joint created by the FSW process. ...
Recognition of the friction stir welding process is growing in the aeronautical and aero-space industries. To make the process more available to the structural fabrication industry (buildings and bridges), being able to model the process to determine the highest speed of advance possible that will not cause unwanted welding defects is desirable. A numerical solution to the transient two-dimensional heat diffusion equation for the friction stir welding process is presented. A non-linear heat generation term based on an arbitrary piecewise linear model of friction as a function of temperature is used. The solution is used to solve for the temperature distribution in the Al 6061-T6 work pieces. The finite difference solution of the non-linear problem is used to perform a Monte-Carlo simulation (MCS). A polynomial response surface (maximum welding temperature as a function of advancing and rotational speed) is constructed from the MCS results. The response surface is used to determine the optimum tool speed of advance and rotational speed. The exterior penalty method is used to find the highest speed of advance and the associated rotational speed of the tool for the FSW process considered. We show that good agreement with experimental optimization work is possible with this simplified model. Using our approach an optimal weld pitch of 0.52 mm/rev is obtained for 3.18 mm thick AA6061-T6 plate. Our method provides an estimate of the optimal welding parameters in less than 30 min of calculation time.
... This prevents the material from flowing out of the weld cavity producing sufficient amount of friction heat and hydrostatic pressure, which attributes compactness to the weld leading to elimination of weld defects normally caused by inadequate compactness. Fig.1 Schematic diagram of friction-stir welding process and terminology A J Leonard and S A Lockyer [9] described the causes for number of flaws encountered in FSW by characterizing the welds using X-ray and ultrasonic non-destructive testing techniques. A void is a flaw encountered along the advancing side between the weld nugget and the reminder of thermomechanically affected zone and small voids were also observed below the top of the weld. ...
... This defect is not considerable and has a little effect on the mechanical properties. This defect appears in retreating side near the weld line [7,8] .The welded sample (B3) is free from defects when examined by this technique. ...
... This defect is not considerable and has a little effect on the mechanical properties. This defect appears in retreating side near the weld line [7,8] .The welded sample (B3) is free from defects when examined by this technique. ...
The aim of the present work is to investigate the fatigue behavior of friction stir welded joints for dissimilar aluminum alloys (2024 -T3 and 7020-T6). Friction stir welding (FSW) had been done for 6.6 mm thick plate by using NC milling machine with R18 tool steel of 18mm with shoulder diameter and 6mm pin diameter with different tool designs; threaded cone with double bevel, threaded cylinder with concave shoulder of 4°, and beveled cone with concave shoulder of 4°. FSW were carried out under various welding parameters, travel speed of 40, 50, 75 mm/min, rotation speed range (275-1250) rpm and tilt angle of (Ɵ = 3°) with counterclockwise revolution. Many non-destructive inspections and mechanical tests were performed to evaluate welded joints to determine the best welding parameters. Fatigue test has been done at constant stress amplitude cantilever with stress ratio of (R= -1). The results showed that maximum tensile strength and joint efficiency were 360MPa and 86% respectively for dissimilar joints which were welded at 40mm/min travel speed and 550 rpm rotation speed by using threaded cone with double bevels. اﻟﺧﻼﺻﺔ ط اﻟﺧﻠ ﺔ ﺑطرﯾﻘ ﺔ ﻣﻠﺣوﻣ ﺎﺑﮭﺔ ﻣﺗﺷ ر ﻏﯾ ﻼت ﻟوﺻ ﻼل اﻟﻛ ﻠوك ﺳ ﺔ دراﺳ ﻰ اﻟ ث اﻟﺑﺣ دف ﯾﮭ وم اﻷﻟﻣﻧﯾ ﺑﺎﺋك ﺳ ن ﻣ ﺎﻛﻲ اﻷﺣﺗﻛ) (2024 -T3 and 7020-T6 . و ﺎﻟﺧﻠط ﺑ ﺎم اﻟﻠﺣ ﺔ ﻋﻣﻠﯾ ت أﺟرﯾ اﻷﺣﺗﻛﺎ ﺑﺳﻣك ﻟﺻﻔﺋﺢ ﻛﻲ 6.6 ﻣﺎﻛﻧﺔ ﻋﻠﻰ ﻣﻠم دة اﻟﻌ ﻓوﻻذ ﻣن ﻟﺣﺎم اداة ﺑﺎﺳﺗﻌﻣﺎل اﻟﻣﺑرﻣﺟﺔ اﻟﺗﻔرﯾز وع ﻧ) R18 (و ره ﻗط ف ذوﻛﺗ 18 ره ﻗط ﻣﺎر وﻣﺳ م ﻣﻠ 6 اﻷداة ﻣﯾم ﺗﺻ ر ﺗﻐﯾﯾ ﻊ ﻣ م ﻣﻠ . د وﻗ ﺗﺻﺎﻣﯾم ﺛﻼث اﺳﺗﻌﻣﻠت ﻣﺧﺗﻠﻔﺔ ھﻲ ﻟﻸداة ﺎﻧﺑﯾن اﻟﺟ طوف ﻣﺷ ﻣﺳﻧن ﻣﺧروط , ﻊ ﻣ ﻧن ﻣﺳ طواﻧﻲ اﺳ ﺑزاوﯾﺔ ﻟﻠداﺧل ﻣﻘﻌر ﻛﺗف 0 4 و ﺔ ﺑزاوﯾ داﺧل ﻟﻠ ر ﻣﻘﻌ ف ﻛﺗ ﻊ ﻣ طوف ﻣﺷ ﻣﺧروط 4 0
... Channel defects, which are often associated with an incorrect tool angle, may seriously affect tensile properties and elongation percentage, while 'kissing' bonds are the consequence of poor adhesion, service loading or impact damage. These are typical defects in friction stir welding [31]. This sample was ultrasonically stimulated in a point located at 70 mm from the weld. ...
Ultrasound-stimulated IR thermography, thanks to its large-area imaging capability, high test productivity and safety, is a powerful tool for the inspection of cracks in heavy aluminum structures. In thick aluminum parts, the most important defect detection parameters are the differential temperature signal and signal-to-noise ratio (SNR), which typically reach their maximums at shortly (under 1 s) after the beginning of the ultrasonic excitation. In the IR inspection of non-metals, the ultrasonic excitation may be relatively long, while in the case of highly-conductive aluminum, short-pulse (burst) stimulation (from 0.4 to 1 s) is sufficient The crack detectability can be improved by evaluating temperature images at the times when maximum SNR values occur. Further enhancement of test results can be achieved by applying some data processing algorithms which can be 1D, i.e. applied to temperature evolutions in time, or 2D, i.e. applied to spatial coordinates, or a single image.
... The presence of poor fit-up, like poor weld parameter selection, is not a fault in and of itself, but rather a fault causing condition. In Leonard and Lockyer (2003), gaps are listed as a potential cause of void (worm-hole) formation. ...
Purpose – This paper aims to investigate methods of implementing in-process fault avoidance in robotic friction stir welding (FSW). Design/methodology/approach – Investigations into the possibilities for automatically detecting gap-faults in a friction stir lap weld were conducted. Force signals were collected from a number of lap welds containing differing degrees of gap faults. Statistical analysis was carried out to determine whether these signals could be used to develop an automatic fault detector/classifier. Findings – The results demonstrate that the frequency spectra of collected force signals can be mapped to a lower dimension through discovered discriminant functions where the faulty welds and control welds are linearly separable. This implies that a robust and precise classifier is very plausible, given force signals. Research limitations/implications – Future research should focus on a complete controller using the information reported in this paper. This should allow for a robotic friction stir welder to detect and avoid faults in real time. This would improve manufacturing safety and yield. Practical implications – This paper is applicable to the rapidly expanding robotic FSW industry. A great advantage of heavy machine tool versus robotic FSW is that the robot cannot supply the same amount of rigidity. Future work must strive to overcome this lack of mechanical rigidity with intelligent control, as has been examined in this paper. Originality/value – This paper investigates fault detection in robotic FSW. Fault detection and avoidance are essential for the increased robustness of robotic FSW. The paper's results describe very promising directions for such implementation.
... The fracture position in the welds reflects the position of minimum hardness, which means that the strength of the joints is only function of microhardness distribution and the joints can be considered defect free. Furthermore, during the transverse tensile tests of the welded specimens, the plastic deformation was mainly restricted to the hardness valley; consequently, the low plastic strain at failure value of the standardized test was due to this localization of plastic deformation [40,41]. ...
The tool geometry is a crucial characteristic of the friction stir welding (FSW) process; its design is the key to the successful
FSW application for a wide range of materials and thicknesses improving the weld strength and fatigue life. The present study
investigates the influence of three shoulder geometries on the FSW joint performance, in terms of residual stresses state,
microhardness profile and mechanical properties of 1.5 mm thick AA 6082-T6 FSW joints in the butt-joint configuration. The
three tool geometries are characterized by three different shoulders: a shoulder with scroll, a shoulder with a shallow cavity,
and a flat shoulder. Transverse and longitudinal tensile tests at room temperature were performed in order to evaluate the
mechanical properties, respectively, of the joints and of the stirred zone, while the fatigue tests were performed transversally
to the joint line.
Friction stir welding (FSW) exhibit high rate of plastic deformation thereby microstructure modification through intense coarsening and grain boundary precipitation found in the weld zone. The microstructure and microchemistry of the weld can be controlled by cooling assisted friction stir welding (CFSW) with minimizing peak temperature and heat input thereby better efficiency and performance of joint produced. This becomes more considerable especially during dissimilar material joining due to variations in thermo-mechanical properties and chemical compositions of material. The joint efficiency can also be enhanced by suppressing the intermetallic compounds (IMCs) formation and controlling the grain growth by applying cooling medium (i.e. compressed air, water, carbon dioxide (CO2) and liquid nitrogen). This article reviews the current status of on-going research in CFSW. The particular attention has been paid to process parameters, phase transformation, texture evolution, recrystallization mechanism, microstructural behaviour, and the influence of these factors on the joint tensile strength, hardness, fatigue properties, residual stresses as well as corrosion behaviour. And also, new research directions in this field have been proposed for upcoming research.
Friction stir-welding (FSW) is a prominent solid-state welding process widely used in different industries to join similar and dissimilar light-weight and low-strength metals and alloys made feasible by a fusion-welding process. In the present investigation, AA6061 aluminum alloy plates of 6-mm thick are FSW with three distinct types of tool pin geometry, namely circular, equilateral triangular, and square pin. Rotational speed of tool, transverse speed, and tool pin geometry are taken as process parameters to investigate the effect on mechanical and microstructural properties of the joint. Taguchi’s L9 orthogonal array was used to design the experimental layout for different experiments. Tensile test and microhardness test were carried out to examine the strength of the FSW sample. Fractographic analysis of fracture surface by scanning electron microscope (SEM) shows the ductile mode of fracture. Microstructural analysis by optical microscope shows various types of defects in the FSW joint due to a change in input process parameters. To find the best level of parameters setting for maximum strength of joint, Taguchi design of experiment was used. The maximum strength was found at the square pin profile of tool, tool rotational speed of 710 rpm, and welding speed of 20 mm/min. The ANOVA result shows that tool pin profile is a significant parameter that affects the strength of FSW joint.
Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implemented in the transport industry today. Fracture surfaces of AA5083-H111 specimens, which were friction-stir-welded using different parameters, were studied with a scanning electron microscope (SEM). The changes in the microstructure of the weld, the location and type of defects that accompanied each stirring process determined the magnitude of reduction in strength and soundness of joints for flawed samples. The paths of crack propagation and modes of fast fracture under static loads were also determined. The sharp edges of the defects were stress concentrators which aided crack initiation. Understanding of the effect of microstructure and defect on the failure of FSW joints will aid optimization of the process variables, tool design, weld quality assurance and decision making. On the long run, it will boost the confidence of medium-scale manufacturers in the adoption and implementation of this fairly new technology.
The zigzag line has significant and complicated effects on the mechanical properties of friction-stir-welded aluminum alloys. The zigzag line feature and its affecting characteristic on joint property are largely related to welding speed. In this paper, an Al-Zn-Mg aluminum alloy was butt friction-stir-welded, and the effects of welding speed on zigzag line feature and joint property were studied in detail in order to reveal the intrinsic correlations between the critical process parameter and the weld quality and, consequently, to provide guidance for the process optimization. The results indicate that at high welding speed of 300 mm/min, the loose and dilute distribution of the oxide layer fragments induces the relatively ambiguous zigzag line feature; the joint does not fail through the zigzag line during tensile test and shows superior tensile properties. With decreasing welding speed to 175 and 50 mm/min, the zigzag line feature is not weakened by the severer tool stirring action, as widely reported by previous studies, but is strengthened gradually due to the enhancement of the collective flow and more concentrated redistribution of broken oxide particles, leading to joint failure at zigzag lines and the degradation of tensile properties of joints.
Linear friction welding (LFW) is an innovative solid-state welding technique that allows to manufacture joints with high mechanical properties. This technology has various applications in the aerospace field; in particular it is used to weld massive structural components made of Ti6Al4V. This paper deals with the experimental study of Ti6Al4V T-joints welded through LFW, with particular focus on the effectiveness of ultrasonic control in detecting and distinguishing welding defects within the joints. Aiming to this scope, joints with different properties were manufactured and tested: some were free from defects but with different metallurgy, and some had different types of defects. The results obtained proved that the ultrasonic control was an effective method to detect and identify defects in linear friction welded titanium joints, moreover it was possible to get information regarding the microstructure and in particular the extension of the different metallurgical zones induced by the welding process.
The manuscript reports on detection of defect that arises during friction stir welding using continuous wavelet transform (CWT) on force signal. The vertical force during welding undergoes sudden change due to presence of defects. These localized defects are detected accurately with the help of continuous wavelet transform scalogram (CWT coefficients’ gray scale image). Statistical feature of variance is used on scale of 1 of transformed signal to localize the defects. The experiments of welding are conducted on the work piece of AA 1100 with varying tool rotational speed (1000, 2000, 3000 rpm) and transverse velocity (50, 75 and 125 mm/min). The manuscript also presents the comparison of results obtained using discrete wavelet transform and CWT of force signals and shows better localization and determination of degree of defect are possible through CWT analysis.
A 30–40 μm thick oxide layer was prefabricated on the top, butt or bottom surfaces of AA2024 sheets by micro-arc oxidation, which were then friction stir welded. Sheets without oxide layer were also welded with blowing oxygen along the weldline during welding for comparison purposes. Results reveal that the tensile properties depend on the amount and distribution of the residual oxide impurities in the joints. The oxide layer on the butt surface leads to continuously distributed oxide impurities in the shoulder-affected zone near the advancing side, and a 159 MPa maximum degradation in tensile strength was noticed. Moreover, the oxygen blowing during welding has a little influence on the joint tensile strength and no oxide was detected in the joint.
In this work, the mechanical properties of butt joints of AA1100 Aluminum alloy obtained through FSW in a conventional milling machine and a friction stir welding machine were compared. The joints were obtained using the same tool geometry and welding parameters. The milling machine was adapted to ensure position control during the welding process and the friction stir welding machine was operated under force and position control modes. Mechanical properties of the beads were evaluated through tensile tests and microhardness measurements. Defects generated in the joints were analyzed using optical and scanning electron microscopy. Results showed that mechanical properties were strongly affected by the welding parameters, whereas the kind of machine influenced the presence of defects in the joints. It was found that the tensile properties were more appropriate to compare the results between sets of parameters and level of defects than the hardness test. Higher mechanical properties and a lower level of defects were obtained in the FSW machine by position control mode, with tensile strength around 130MPa, whereas the highest tensile strength obtained in the conventional milling machine was 109 MPa.
Metal matrix composites (MMCs) reinforced with SiC particles combine the matrix properties with those of the ceramic reinforcement, leading to higher stiffness and superior thermal stability with respect to the corresponding unreinforced alloys. However, their wide application as structural material needs proper development of a suitable joining process. In this investigation, an attempt was made to study the effect of heat input on the evolution of microstructure in weld region of friction stir welded AA6061-10% SiCp MMCs. The tensile properties of the joints were evaluated and they are related with microstructure and heat input of the process. The microstructure characterization of the weld zone shows evidence of a substantial grain refinement of the aluminum matrix and fracturing of reinforcement particles due to dynamic recrystallization induced by the plastic deformation and frictional heating during welding.
The groove defect formed in the friction stir welding dramatically deteriorates weld appearances and mechanical properties of the joints owing to its larger size and penetration. Therefore, the friction stir repair welding was utilized to remove such a groove defect, and the focus was placed on the mechanical properties and microstructural characteristics of the repair joints so as to obtain an optimum repair welding process. The experimental results indicate that the groove defect can be removed by friction stir repair welding, and the offset repair welding process is superior to the symmetrical repair welding process. In the symmetrical repair welding process, a large number of fine cavity defects and an obvious aggregation of hard-brittle phase Al2Cu occur, accordingly the mechanical properties of the repair joint are weakened, and the fracture feature of repair joint is partially brittle and partially plastic. A good-quality repair joint can be obtained by the offset repair welding process, and the repair joint is fractured near the interface between the weld nugget zone and thermal-mechanically affected zone.
This paper describes a technique for determining the position of a friction stir welding (FSW) tool with respect to the weld seam during welding. Forces are used as a feedback signal, and a general regression neural network is trained to predict offset position given weld forces. Experimental results demonstrate the accuracy of the developed position predictor. This technique is proposed for online misalignment detection or as a position estimator for in-process tracking of the weld seam for FSW and robotic FSW.
With the industrial use of FSW growing steadily, non-destructive testing methods that can detect the impending formation of flaws during welding must be developed. The present work accomplished two goals. First, the distribution of oxide fragments within aluminium welds could be correlated with certain welding process variables. Consequently, an approach was suggested to prevent the conglomeration of oxide fragments in the weld by reducing the surface roughness of the abutted edges. Second, welding forces can be used to predict the formation of elongated cavities inside the weld. This project showed that by monitoring the welding forces, the ability to change the welding variables in real time could prevent the formation of flaws in friction stir welds.
This paper established a model about the flow process of softened material around rotational tool during friction stir welding. According to the flow pattern of different parts of softened material, the flow process was divided into three parts: flow process near the shoulder, near the pin top and near the pin end. The softened material near the shoulder firstly flew into the cavum behind the pin, and the residual material rotated around the shoulder side slowly, forming the arc crest of arc corrugation on friction-stir weld. The softened material near the pin top flew to retreating side from advancing side in a shear way. The softened material near the pin end flew to the retreating side from the advancing side in an extrusion way.
The effects of welding conditions, tool rotation speed, Rt and plate traveling speed, V on weld joints formation and mechanical properties have been investigated on Friction Stir Welding joints of high strength aluminum alloys of 2024-T6 and 7075-T6 in comparison with 5083-O of 4 mm thick plates. Rt/V, Welding parameter, which is closely related to welding heat input per unit length of the welded joint affected joint qualities. Peak temperature of FSW joints near stir zone during welding increased with increasing Rt/V, but lower than solidus temperature for each alloy. As weld defects, lack of bonding and inner defect occurred at low Rt/V for each alloy, and excess high Rt/V caused surface tearing as defect both for 2024-T6 and 7075-T6. As to a range of optimum welding condition, 5083-O was wider than those of 2024-T6 and 7075-T6, and optimum Rt/V range common to three alloys was 3.3 to 5.0. In case of any aluminum alloy, tensile strength of the welded joints increased with increasing Rt/V, and weld defects caused low tensile strength. The maximum tensile strengths for 2024-T6, 7075-T6 and 5083-O were 373, 444 and 296 MPa in as-welded condition, which were almost 76, 83 and 100% to base metal strength. Post-weld artificial aging increased the tensile strength of 7075-T6 joint to 512 MPa, 90 % to base metal strength, but in 2024-T6 decresed it slightly.
Review of factors influencing porosity in aluminium arc welds
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