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Friction Stir Welding and Processing II
Abstract
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.
... Meanwhile, the rotating action of the pin induces metal from each section to flow and form the processed area [15]. This results in a refined microstructure within the workpiece, offering opportunities for enhancing its properties to suit various applications [16,17]. As technology becomes more reliable and mature, industrial applications rise up, so new aspects of the process need to be studied: tool wear, energy consumption and sustainability of the process, and monitoring of the process [18][19][20][21][22]. ...
... Looking at Fig. 8, it is possible to appreciate that all the treated tracks appear free from superficial defects, such as grooves or cracks [17]. Furthermore, the width of the tracks is also quite regular, indicating effective processing and adequate tool-to-sheet contact [2]. ...
... Looking at the diagram, two considerations can be highlighted: i) the temperature increased with the TRS; ii) the temperature decreased with the increase of the tool usage. While the former is an expected outcome, as higher TRS [17], the latter deserves a more detailed explanation. In friction stir processes, heat generation is due to two mechanisms: the friction between the tool's shoulder and the top surfaces of the plates, and the friction between the tool's pin and the stirred material, it is generally agreed that most of the heat is generated by the tool [17,54]. ...
Friction Stir Welding (FSW) and Friction Stir Processing (FSP) are solid-state joining and material processing techniques that have garnered considerable attention for their versatility and industrial applicability. In the present work, FSP was performed on AA 6056 T4, dealing with the issue of monitoring tool wear and assessing its impact on the process. The impact of tool wear on power requirements was analyzed, and it was expanded the understanding of tool behavior and its implications for the overall process performance. Specifically, variations in energy consumption, temperatures, and vibrations are observed with changing tool conditions. Further insights are provided by analyzing the microhardness and the pin volume ratio, which show distinct trends as the tool wears. Two tool maintenance ways are proposed, that are cleaning the tool with a sodium hydroxide solution and increasing the tool’s rotational speed. Both the strategies exhibit the potential to partially restore the tool’s initial characteristics. This study highlights the critical importance of assessing tool condition, energy consumption, and process sustainability, particularly in industrial settings where material processing requires efficiency and quality assurance.
... Referring to Figure 6a, the movement of tool transfers the material being stirred across the front to the rear of the pin. The rate of thermal cycle heating during FSW is highly dependent on the tool feed rate [23]. Insufficient metal transport because of inadequate heat generation produces flaws in the weld zone at higher feed rates. ...
... The obtained tensile value for every parameter is typically greater for threaded tools than for unthreaded tools. This is a result of the tool thread's enhanced material mixing, which increases the grains' resistance to border dislocations [23]. ...
... Die Bilder 6a bis d zeigen, wie sich die Betriebsparameter beim Schweißen auf das Resultat, also die Zugfestigkeit (UTS) und die Mikrohärte auswirken.In Bild 6a wird deutlich, wie der gerührte Werkstoff durch die Bewegung des Werkzeugs vor dem Stift vorbei bis hin zur Rückseite des Stifts transportiert wird. Die Aufheizgeschwindigkeit des Wärmezyklus ist beim FSW stark abhängig von der Vorschubgeschwindigkeit des Werkzeugs[23]. Bei höheren Vorschubgeschwindigkeiten kommt es in der Schweißzone aufgrund eines auf eine ungenügende Wärmeentwicklung zurückzuführenden unzureichenden Metalltransports zu Fehlern. ...
Cast alloys find suitable applicability in aerospace sector owing to low porosity, high specific strength, corrosion resistance, fluidity and good machinability. The investigation focuses on friction stir welding (FSW) of cast A356 and A2014 alloys with varied range of process parameters, namely tool pin shape (cylinder, threaded cylinder, square, and conical), tool rotation speed (1800–2100 rpm) and welding speed (10–25 mm × min ⁻¹ ). Experimentation on stirwelding was performed based on selected tool pin shape between varied tool rotation and welding speed. The output responses, namely Ultimate tensile strength (UTS) and micro hardness, have been evaluated to study the effect of each tool. The microstructural characteristics of the weld samples were analyzed using optical microscope and scanning electron microscope (SEM) technique. The microstructural observation unveiled that complete fusion prevails between the parent alloys devoid of micro porosities and segregations. The re-crystallization effect resulted in the finer grains. The cylinder-shaped tool with a thread and square shaped tool rendered better strength and hardness properties of 136.6 MPa and 109.4 HV, respectively.
... Additionally, FSW causes intense plastic deformation in correspondence to the welding line, resulting in a microstructure composed of small and equiaxed grains that preserve the mechanical properties of the weld, including hardness, better than fusion welds. The single-pass capability of FSW makes it suitable for high-rate production systems, and it also enables the welding of dissimilar materials, leading to a reduction in both weight and cost [2]. ...
... The welding parameters windows were carefully determined based on an extensive review of relevant literature, aiming to maximize the mechanical properties of the welded joints for each alloy [2,31,32]. ...
This paper compares two predictive methodologies for optimizing friction stir welding process and predicting mechanical properties in the welding zone. The first approach combines finite element method (FEM) with artificial neural network (ANN) techniques to forecast hardness variations, reducing reliance on extensive experiments. The second approach integrates ANN and particle swarm optimization (PSO) to predict properties and optimal FSW parameters, particularly emphasizing hardness maximization. Results indicate the superior predictive accuracy of the combined ANN-PSO approach, offering streamlined implementation suitable for practical applications. Indeed, in the FEM-ANN approach, the average error is around 16.50%, while the ANN-PSO approach predicts hardness with an average error of about 4.80%. Moreover, error increases closer to the center line in both approaches, more prominently in the FEM-ANN approach. However, it should be noted that successful implementation of the ANN-PSO model requires a substantial historical dataset for ANN training. On the other hand, the FEM-ANN approach demands relatively less experimental effort but entails longer computational times. Overall, these comparative insights guide the selection of the most suitable approach based on resource availability and project-specific requirements, providing valuable guidance for optimizing FSW process and predicting properties while considering resource constraints.
... Hex-Dominant meshing was chosen because it offers advantages in terms of accuracy, convergence speed, and computational efficiency. 17,18 Table 2 provides information regarding the discretization of the computing domain ...
... The graph shown in Figure 5, which is taken from the machine during the experiment, shows that when the tool fails during plunging, the z-axis load suddenly drops down. 12,17 The maximum load at which the tool fails is noted down, and it is applied to the solid model for the analysis. Tool failure occurred during the process (without pre-hole condition) at a maximum load of 7 kN, whereas for the pre-hole condition, the maximum load is 11.2 kN. ...
The research focuses on examining the impact of utilizing a tungsten carbide tool on the friction-stir welding procedure used to join two stainless steel plates. This investigation examines the effects of traversal speed and rotation on microstructural alterations in a tungsten carbide tool, with a specific emphasis on weld resistance and creep strength. Stress analysis is used to understand fluctuations in stress levels during the welding process on a stainless-steel workpiece. The investigation aims to determine the impact of welding parameters, specifically welding speed, on the microstructure, hardness distribution, and tensile strength of welded joints. The effectiveness of the friction-stir welding is determined by the correlation between pin diameter and tool shoulder. A Numerical model and analysis of the experiments to understand tool behaviour, considering lateral bearing loads and viscous frictional torsion loads by using ANSYS. The finite element method is used to find stress distribution in stir welding, considering tool parameters. A tungsten carbide tool with a conical pin tool was used under constant conditions: a rotational speed of 325 r/min, a maximum axial load of 11.2 kN, and a welding speed of 10 mm/min. The results showed that the maximum equivalent stress reached 500 MPa when the tool had traversed a distance of 25 mm. These findings provide valuable insights into the stress dynamics of the tool under these specific operating conditions. Different tests are conducted with varying design parameters and pre-hole conditions to understand the stress distribution on the tungsten carbide tool.
... To create a smooth, accurate, and very strong junction, Apple's iMac recently employed friction stir welding to combine the particles of the two aluminium edges. The front suspension of the 2013 Honda Accord uses friction stir welding to connect steel and aluminium 5 . Typically, this method is used to replace procedures like GMAW, MIG, rivets, etc. in a variety of sectors, including aerospace, automobile, and naval 5 . ...
... The nuggets region often has the following patterns: elongated nuggets (a) and basinshaped nuggets (b) that widen at the upper surface (b). Numerous variables, including process variables, cutting parameters, work material temperature, and heat capacity, will affect the nugget's form 5 . Typically, the nugget zone is a little bigger than the pin radius. ...
To combine extra-strong aircraft aluminium alloys that are typically difficult to fuse using standard fusing methods of welding, a unique sustainable solid-state combining method known as Friction Stir Welding (FSW) is used. In contrast to certain other solid-state combining techniques, friction stir welding involves a third intimate contact with the tools, which creates extra interfacing areas. Ultimately, all of these areas merge under the application of heat and pressure to produce a solid-state joint. This systematic review discusses the fundamental principles of friction stir welding and processing on AA3000 series material, the creation of microstructures, the sensible processing conditions, frequent FSW flaws, as well as some application fields. Additionally, the article will cover a few FSW process variations; including friction stir processing and friction stir spot welding. The processing parameters were determined to be at their best using the Taguchi Technique (TT). The research also examined the microstructures on FSW specimens at the optimum point, welding zone hardness, and union effectiveness of the FSW joint. The efficiency and dependability of welded joints for operations in the shipbuilding industry may be shown by joint reliability. That was examined under ideal circumstances, and it turned out to be 85%.
... Friction stir welding (FSW) is attracting attention as a method of joining materials at low temperature in the solid state [14][15][16][17][18][19][20][21][22]. The FSW was initially used for joining aluminum, and it is now also being used for joining steel and aluminum. ...
The use of multi-materials, in which a wide variety of materials are used in the appropriate places, is being promoted to reduce carbon dioxide emissions. In the multi-materialization of automobiles, steel-aluminum joints are widely used. Friction stir welding (FSW) is used for joining steel and aluminum. Because of the solid state and short joining time of the FSW, the thickness of the brittle intermetallic compound layer can be minimized and high-strength joining can be achieved. Meanwhile, since recycling aluminum greatly reduces carbon dioxide emissions compared to the production of new ingots, easy disassembly technology is required. In this study, fabrication of thin foaming agent sheet was attempted. Then, we attempted to realize easy disassembly of steel/aluminum joints by FSW, which can realize strong joints, by using foaming agent sheets that can easily introduce foaming agent on joining interface during FSW. It was shown that foaming agent sheet can be prepared by solidifying foaming agent and pore morphology stabilizer powders using spark plasma sintering. It was also shown that even if a foaming agent sheet was introduced at the joining interface and FSW was performed, good jointing can be achieved. In addition, it was found that the introduction of a foaming agent sheet and foaming at the joining interface can significantly reduce the maximum disassembly load with fracturing at the joining interface. The above results indicate that the use of a foaming agent sheet can easily add an easy-disassembly characteristic to the area near the joining interface in the FSW process.
... As modern technology advances, traditional welding techniques have gradually revealed their limitations in contemporary manufacturing, particularly in the production of lightweight structures for aerospace vehicles, high-speed ships and boats, and high-speed rail trains. Friction stir welding is an innovative method of joining materials, known for its exceptional joint quality, minimal stress and deformation, increased efficiency in production, as well as the conservation of energy and materials [1][2][3][4]. To produce the joint connection, this technology utilizes the intense friction between a rapidly rotating tool and the workpiece to generate heat, thermoplasticizing the material. ...
Friction stir welding of aluminum alloy offers excellent joint quality, less residual stress and deformation, and high production efficiency when compared to conventional welding techniques. It is possible to optimize the welding process and raise the quality and efficiency of the welds by researching their nonlinear dynamic properties. In this study, a nonlinear dynamic model of friction stir welding of aluminum alloy was constructed by taking into account the flow of thermoplastic materials, time-varying upsetting force, and plastic metal friction model. The nonlinear behavior of the system was described by using bifurcation diagrams, Lyapunov exponent, time domain, fast Fourier transform (FFT) spectrum, phase plot and Poincare map. Moreover, the superharmonic resonance characteristics of the system were investigated using a multi-scale methodology, and the impact of displacement delay, displacement control, speed control, and system damping on the aluminum alloy friction stir welding system's oscillation mode were examined. According to the findings, the friction stir welding system of aluminum alloy possesses complex non-linear properties with the change of stirring pin rotation speed, feed speed and support stiffness. Furthermore, by choosing the right time delay parameters and boosting the damping, the system's stability can be enhanced.
... The aviation industries have recently focused on hybrid structures due to their excellent properties and unique characteristics [1]. These industries prioritize aluminum (Al) and magnesium (Mg) hybrid structures due to their excellent strength-to-weight ratio [2,3]. ...
The trade-off between welding and strength loss during dissimilar metals joining has been important for decades. Strength loss minimization is essential for industries. The current study investigates the microstructure clarification in the nugget zone (NZ) of AA7075/AZ31B dissimilar friction stir welded joints with or without ultrasonic vibration (UV) at different tool offset conditions. The reduction of incomplete dynamic recrystallization towards the AA7075 side and its transformation into complete dynamic recrystallization (DRX) were observed through the analysis of the grain microstructure, which showed that ultrasonic vibration improved dislocations and grain boundaries. Texture analysis discloses high-strain texture towards the AA7075 side, whereas less complex stresses texture for the AZ31 side under UV. Moreover, the grain refinement on both sides of the interface also affects the joint tensile strength. The maximum strength was obtained with ultrasonic vibration. The Schmid factor results reveal that the UV has a minor influence on the slip system towards the Al side. Conversely, it activates the twining system towards the AZ31 side.
... EBSD results are shown in Fig. 6 to better highlight the refinement of grain size, phase map evolution, and misorientation analyses of the grain with and without the distribution of TiB 2 . Equiaxed grains with uniform size and random crystallographic orientation were observed in the processing zone of all three samples, which are typical of friction-stir based processes resulting in dynamic recrystallization of the matrix [65]. Phase maps for TiB 2 show the distribution and densification of particles across the matrix for 12 vol% (Fig. 6, mid-left) and 24 vol% TiB 2 (Fig. 6, bottom-left) samples. ...
... During SPD processes, severe strain is applied to the deformed alloy to produce UFG (100-1000 nm) or nano-materials (NS) (˂ 100 nm) (Valiev et al., 2000). Nowadays, there are lots of techniques and methods used to achieve SPD, such as high-pressure torsion (HPT) (Lugo et al., 2008), accumulate roll bonding (ARB) (Jang et al., 2008), hydrostatic extrusion (HE) (Garbacz et al., 2007), cryorolling (Sarma et al., 2008), constrained groove pressing (CGP) (Ebrahimi et al., 2014), surface mechanical attrition treatment (SMAT) (Wang et al., 2003), friction stir processing (FSP) (Mishra and Ma, 2005) and ECAP (Neishi et al., 2001;Zhang et al., 2011). ECAP is a cost-effective approach with several advantages over other SPD techniques. ...
In the present study, the microstructure, mechanical and wear characteristics of commercial Cu-30Zn brass alloy were developed by an equal channel-angular process (ECAP) using a particular die in constant dimensions. The ECAP process was experimentally conducted at room temperature using (1-4) passes in route C with lubricating conditions. Also, the post-annealing treatment at 350 oC has been done for some brass samples, which were deformed with four passes. Findings revealed that by conducting the ECAP, a significant reduction in the grain size of the deformed brass samples is achieved compared to the as-received alloy. The grain refinement increased with the increasing number of ECAP passes. However, the post-annealing treatment increased the grain size of the deformed brass alloy, but still it was lower than the as-received alloy. Moreover, the mechanical performance, i.e. micro-hardness and strength, was significantly enhanced after the ECAP. The samples processed with three passes presented the highest hardness value (237 HV) and mechanical strength (UTS= 692 MPa, and YS= 542 MPa) due to the homogeneous strain hardening and substantial grain refinement throughout the ECAP process. However, the micro-hardness and mechanical strength of brass alloy decreased after post-annealing treatment compared to those of the ECAP deformed samples. The elongation to failure also decreased greatly with increasing the number of passes of ECAP. Additionally, the wear resistance of the investigated samples increased significantly after increasing the number of ECAP passes compared to the as-received alloy. The highest wear resistance has been achieved for samples deformed by three and four passes of ECAP due to the considerable grain size refinement and higher hardness. However, a slight increase in the wear rate occurred after post-annealing treatment on a brass alloy sample processed with four passes due to the increase in grain size.
... Therefore, it is necessary to consider the effect of the cooling rate. The approximate formula for the peak temperature during FSW is [39] (3) where T p is the peak temperature (°C) of the weld, T m is the melting point (°C) of the metal, ω is the rotation speed of the tool, υ is the welding speed, and α and K are the constants. Since the welding parameters are consistent, the peak weld temperature is theoretically approximated. ...
Friction stir welding (FSW) of galvanized steel offers unique advantages as it can avoid the extensive metallurgical problems associated with fusion welding. However, conventional FSW still leads to a higher temperature in the stir zone, which deteriorates the microstructure. To obtain a satisfactory weld, the welded joints of galvanized steel were created by FSW with different cooling rates employing a W–Re rotary tool with a large-diameter needle. The correlation between the microstructure evolution and mechanical behavior of joints at different cooling rates was systematically studied. The results demonstrate that the rapid cooling rate favors the refinement of ferrite and diffuse distribution of Fe3C. In addition, weakening of the texture and dispersion of dislocations were also observed after fast cooling FSW. It can be concluded that the microstructural evolution mechanism of the stirring zone (SZ) is continuous dynamic recrystallization at a slow cooling rate, while the microstructure has discontinuous dynamic recrystallization as the primary evolution mechanism at a fast cooling rate. Based on these advantages, the tensile specimens with fast cooling FSW obtained a synergistic improvement in strength-ductility, even surpassing the base material. This work provides new ideas for welding galvanized steel.
... The kind of heat input also matters since laser welding, which uses a concentrated heat input, tends to result in smaller zones of enhanced hardness when compared to the welding method known as MIG, which uses a less concentrated heat flow (Gaied et al. 2009). Both heat-treatable (precipitation-hardened) and nonheat-treatable (solid solution-hardened) aluminum alloys can be characterized (Mishra and Ma 2005). These alloys respond differently to welding in terms of their hardness. ...
The automotive industry is a prominent user of tailor-welded blanks (TWBs) for sheet metal components, as they offer numerous advantages such as weight reduction, cost savings, noise reduction, improved crashworthiness, dimensional accuracy, and corrosion resistance. Steel types commonly used in the automotive industry for TWBs include interstitial free (IF) steel, dual-phase (DP) steel, austenitic stainless steel (ASS), and aluminum alloys (AA) chosen for their crashworthiness and good formability. However, the welding process can introduce formability challenges. This work discusses the benefits and drawbacks of TWBs in the automotive industry, covering forming methods, welding processes, numerical modeling, and materials. It particularly focuses on the formability analysis of different sheet metals used in TWBs, their forming limits, and their applications. The aim is to provide valuable insights for researchers new to this field, shedding light on the formability aspects of TWBs. This review paper aims to provide a comprehensive understanding of the topic.
... A relatively new solution is modification of the surface layer using the modern FSP method. FSP technology was developed by R.S. Mishra et al. [4,5], although the essence of this method comes from the FSW technology developed in the early 1990s by W.M. Thomas from the Welding Institute (TWI) in Cambridge, UK [6], and is based on the same principles as FSP. The difference between FSW and FSP technology lies in the purpose of these methods. ...
The article presents an assessment of the possibility of using ashes from the combustion of coal and biomass as a reinforcing phase in metal matrix composites. The composite surface layer was produced by means of the FSP (friction stir processing) method, using an original hole solution with a shifted working zone of the pin. The composite matrix was AA7075 alloy. The obtained composite was subjected to microscopic observations, tribological tests, and hardness measurements. The microscopic examinations revealed favorable changes in the microstructure, in particular, strong refinement of the grains, uniform distribution of the reinforcing phase, and good bonding of the particles of this phase with the matrix material. Changes in the microstructure resulted in a significant increase in the hardness (from 36 to 41% depending on the type of reinforcing phase) and wear resistance (from 24.1 to 32.9%), despite partial dissolution of the intermetallic phases. It was found that the effect of strengthening the matrix and the uniformity of the distribution of the reinforcing phase depend on the physicochemical properties of the used powders, especially on the shape and size of the particles. The research shows that the use of ashes as a reinforcing phase in composites is fully justified.
... Each welding method has its inherent strengths and limitations, and the selection of the most suitable approach should hinge on factors like the materials involved, the application's demands, and the desired joint properties. Consequently, it is vital to consider the specific necessities of each application when opting for the appropriate welding process [33][34][35][36]. The detailed list of SSW techniques encompasses EW (explosion welding), DB, FSW, UW, CW (cold welding), and FW (forge welding) [37]. ...
The implementation of artificial intelligence (AI) techniques in industrial applications, especially solid-state welding (SSW), has transformed modeling, optimization, forecasting, and controlling sophisticated systems. SSW is a better method for joining due to the least melting of material thus maintaining Nugget region integrity. This study investigates thoroughly how AI-based predictions have impacted SSW by looking at methods like Artificial Neural Networks (ANN), Fuzzy Logic (FL), Machine Learning (ML), Meta-Heuristic Algorithms, and Hybrid Methods (HM) as applied to Friction Stir Welding (FSW), Ultrasonic Welding (UW), and Diffusion Bonding (DB). Studies on Diffusion Bonding reveal that ANN and Generic Algorithms can predict outcomes with an accuracy range of 85 – 99%, while Response Surface Methodology such as Optimization Strategy can achieve up to 95 percent confidence levels in improving bonding strength and optimizing process parameters. Using ANNs for FSW gives an average percentage error of about 95%, but using metaheuristics refined it at an incrementally improved accuracy rate of about 2%. In UW, ANN, Hybrid ANN, and ML models predict output parameters with accuracy levels ranging from 85 to 96%. Integrating AI techniques with optimization algorithms, for instance, GA and Particle Swarm Optimization (PSO) significantly improves accuracy, enhancing parameter prediction and optimizing UW processes. ANN’s high accuracy of nearly 95% compared to other techniques like FL and ML in predicting welding parameters. HM exhibits superior precision, showcasing their potential to enhance weld quality, minimize trial welds, and reduce costs and time. Various emerging hybrid methods offer better prediction accuracy.
... The relationships between process parameters-heat production-grain size formation are already explained in the present study, and were further accounted for the observed surface hardness. Similar results have also been reported [38][39][40]. In case of WE43 substrates, mitigation of dislocation density and resultant compressive stress in substrates caused by annealing could held responsible for decreasing surface hardness. ...
Magnesium matrix surface composites have been garnering attention due to their superior mechanical and corrosion resistance properties. An idea of facile fabrication of surface composite composed of nano-SiC reinforced WE43 matrix through friction stir processing was explored in this study. Also, the effects of tool geometries, tool rotations, and tool feeds on resultant properties were comprehensively investigated. Uniform dispersion of SiC nanoparticles within stir zone was evident. Square tool demonstrated the most promising results. Processing at 1700 rev min⁻¹ and 60 mm min⁻¹ with a square tool produced finest grains in surface composites exhibited exceptional microhardness (180.8 HV), nanohardness (1.867 GPa), elastic modulus (41.69 GPa), and wear resistance (0.0254 mm³ min⁻¹). Besides it, WE43 substrates also exhibited superior mechanical properties when processed with a square tool at 800 rev min⁻¹ and 60 mm min⁻¹. This research opens up new possibilities for the development of reliable magnesium matrix surface composites for multifunctional applications.
... However, due to its high melting temperature, low thermal conductivity, and tendency to form voids and defects, joining nylon-6 using traditional welding techniques has proven difficult [2]. Friction stir welding (FSW) is a solid-state joining process that has gained significant attention in recent years due to its ability to join a wide range of materials, including thermoplastics [3]. FSW is a promising technique for joining nylon-6 because it can avoid these issues, resulting in high-quality welds with minimal thermal damage [4]. ...
Nylon-6 is one of the most extensively used engineering thermoplastics. Due to its durability, reduced weight, low coefficient of friction, and abrasion resistance, this polymer is an excellent substitute for various materials, including metals and rubber. Despite being those, nylon-6 materials are joined together utilizing multiple welding processes. The current work examined the viability of the friction stir welding (FSW) method on nylon 6 plates that were 4 mm thick to investigate the effect of tool diameter ratio and feed rate on nylon-6 sheets with the FSW method on the tensile properties of the joints. The 4 mm thickness of the nylon-6 plate was cut into the dimensions of 115 mm x 100 mm. The sliced plates were then joined through the FSW process using ST80-based tools with various parameters in the shoulder to pin diameter ratio (D/r ratio) of 10/3, 15/3, and 20/3 and feed rates (FR) of 4 mm/minute, 6 mm/minute, and 8 mm/minute at a rotational speed (RS) of 5800 RPM. Afterward, the weld joint is cut using water jet cutting according to the tensile testing standard ASTM D638 type IV. Following this, characterization of the speci-mens, including macrograph examination, hardness testing, and tensile testing, was carried out. The results show that the highest tensile strength was obtained at a tool diameter ratio of 10/3 mm with a feed rate of 6 mm/minute, with a tensile strength value of 19 MPa reaching up to circa 90% of joint efficiency. The strength of the welded joint then decreases as the diameter ratio of the tool increases with each feed rate. Some defects appeared at the higher tool diameter ratios welded joint, including incomplete fusion, flash, thinning, and lack of bonding. In conclusision the combination of a D/d ratio of 10/3 and a FR of 6 mm/min at RS 5800 RPM can provide the optimal conditions for a strong nylon-6 friction stir welded joint.
... FSW. The welding is done by utilizing adiabatic plastic deformation due to the heat of friction between the rotating tool and the workpiece [1]. FSW parameters include travel speed, rotation speed, tilt angle, pin offset, and plunge depth. ...
Micro friction stir spot welding (mFSSW) is a type of solid-state spot welding of nonconsumable tools using friction and force to join material of thickness less than 1 mm. This research aimed to investigate the shape of the tools for best welding results among the proposed tool’s profile. The material specimen was aluminum alloy AA1100, with a thickness of 0.42 mm. This study aims to measure the temperature and RPM of the welding process with thermocouples and tachometers. And then investigate the mechanical properties using the tensile shear test, microhardness, and macrostructural observation to find the welding zone and hook profile. Four tools’ profiles are named tool 1, tool 2, tool 3, and tool 4. The result of this study was that tool 3 (Shoulder 450μm) had the highest temperature, around 428˚ C, and the shear tensile test was 450 N (the highest). The macrostructural observation used to define the zone on the welding result there are stir zone (SZ), thermos-mechanically affected zone (TMAZ), and heat affected zone (HAZ).
... The schematic diagram of FSP has been shown in Figure 1. Many researchers have contributed to Aluminium-MMCs through the FSP route, precisely [23][24][25][26][27][28][29][30][31][32] and others. FSP consists of significant input parameters at optimum levels to achieve desired properties and surface characteristics [33,34]. ...
This study explores the optimization of Micro Friction Stir Spot Welding (mFSSW) by investigating the influence of tool profiles on welding outcomes, using aluminum alloy AA1100 with a 0.42 mm thickness as the specimen material. Monitoring temperature and RPM during welding with thermocouples and tachometers, mechanical properties are assessed through tensile shear tests, microhardness measurements, and macrostructural observations. The findings serve as the basis for developing Neural Network models using Rapidminer software, marking a transformative development that positions Neural Networks as potent tools for optimizing welding processes, potentially leading to achieving optimal weld quality. The investigation also delves into three welding tool configurations – the two-stage pin, one-stage pin, and pinless mFSSW probes – highlighting their distinct impacts on tensile shear test values and overall welding quality. Notably, the two-stage pin configuration emphasizes the significance of larger pin diameters and controlled heat generation for enhanced weld strength, while the one-stage pin configuration underscores the pivotal role of pin diameter and elevated temperatures in improving weld quality. The pinless mFSSW probe configuration, on the other hand, emphasizes the importance of shoulder diameter and temperature control for superior tensile shear test results. Leveraging Neural Network modeling for optimization, this study advances our understanding of parameter interactions and underscores the efficacy of Neural Networks in achieving superior tensile shear test values and welding quality in mFSSW, offering valuable insights for future endeavors in the field..
Friction stir welding (FSW) of AA2219-T87 plates have been investigated in this research work utilizing a square pin tool, and the effect of spherical steel balls in the shoulder of the square pin was examined. Microstructural characterizations were conducted through an optical microscope, SEM, and EBSD study on the FSW processed samples. In addition, mechanical properties including hardness and tensile behavior were evaluated, and fracture surfaces were studied with SEM. Significant refinement in the grain was noted in the WNZ due to intense plastic deformation, as confirmed by EBSD analysis showing finer grain sizes. Significantly lower grain size with an average grain size of 8.86 µm was noted in the WNZ compared to the BM, with an average grain size of 52.27 µm. Thermal cycling during FSW resulted in coarser grains in the HAZ. Additionally, samples processed with the spherical ball shoulder exhibited improved microstructural characteristics, including grain refinement and increased dislocation density in the TMAZ, leading to enhanced hardness values. Besides, alterations in the microstructure contributed to the improved tensile properties of the AA2219-T87 samples. The YS and UTS of the AA2219-T87 specimens processed with spherical ball shoulder were improved by 11.17% and 7.39% than the samples processed without spherical ball shoulder. Further, fractographic analysis revealed evidence of ductile fracture mechanisms, supported by the presence of dimples observed in the SEM fractography. Overall, the incorporation of spherical ball shoulders in the square pin tool profile for the FSW processes offers a promising avenue for enhancing microstructural refinement and mechanical performance in aluminum alloys.
The article examines the influence of energy characteristics on the process of formation of dissimilar metals of aluminum and copper alloys during friction stir welding. The relationship between machine engine power consumption and stir welding friction regimes for a dissimilar joint of technically pure aluminum AD1 and copper M1 is studied. The influence of production regimes on weld appearance and the possibility of stabilizing power consumption during friction stir welding due to formation of a welded metal superplastic state are revealed. A relationship between capabilities of the equipment used and the permissible geometrical parameters of the welding tool is estimated.
The aim of the research is to evaluate the 3-D temperature distribution in the friction stir welding (FSW) joints of AA1100 alloy plates by using Finite difference method. The theoretical results are correlated with experimental output in terms of temperature profiles of the weld zones. Microstructure analysis and tensile test have been conducted to determine the joint quality that strongly depends on the amount of heat generation which again is governed by the processing parameters. Microstructure of the weld samples clearly shows the grain refinement in the weld zone. The friction coefficient is also an important factor that totally depends on the tool pin design. More is the friction; sound welds are produced with minimum defects and an enhanced weld strength. This process finds its applications in the automotive industries as the demand for better performance in joining components for vehicles prompts the implementation of aluminium alloy FSW technology.
To fulfill the need to limit automotive emissions, reducing vehicle weight is widely recommended and achieved in many ways, both by the construction of individual elements of the vehicle and by the selection of light materials, including Al alloys. Connecting these elements with each other and with elements made of iron alloys can be realized, inter alia, by welding or stir welding. However, the quality of the welds obtained varies widely and depends on many design, operational, and environmental factors. The present study focused on a review of various welding techniques used to join both similar and dissimilar Al alloys utilized in the automotive industry, the effect of various process parameters on weld quality, and the phenomena observed in such welds. The research methodology was based on the analysis of the content of articles from main databases. Apart from capturing the current state of the art, this review evaluates reaching the possible highest joint quality and welding process disadvantages such as porosity, poor surface quality, a tendency toward hot cracking, and low ductility for the Al alloys applied in the automotive industry.
The article considers the force applied to the welding tool during friction stir welding of commercially pure copper M1 and aluminum AD1. A technique for measuring the axial force applied to the tool is presented. The results of the study show that the speed of rotation and feed (welding) of the tool affect the value of the axial force. While maintaining a constant feed rate of the tool, the axial force increases as the speed of its rotation decreases. The maximum value of the force was 28.75 kN at a rotation speed ω= 800 rpm. Increasing the tool speed to 900 and 1000 rpm leads to a decrease in axial force by 15% and 40% of the maximum that occurs at 800 rpm. At a fixed tool speed and increasing welding speed, the change in axial force is negligible.
The peak temperature range of the weld zones of the AZ61 alloy sheet during FSW varied from 450.1 to 569.4 °C depending on the welding conditions. The evaluation of FSW integrity suggests that both void defects and tunneling cavities observed at the conditions of 400 rpm-100 mm/min and 400 rpm-300 mm/min are caused by insufficient material fluidity because of the low temperature inside the welds. However, tunnel- and surface defects at the condition of 1600 rpm-100 mm/min are caused by a high peak temperature of 569.4 °C, which leads to mass loss at the outer boundary of the stir zone because of excessive flash and local melting during the rotation of the tool. To enhance the integrity and mechanical properties of the weld, the welding parameters should be controlled such that the peak temperature in the weld zones is in the range of 493.2–508.9 °C. The microstructure of the FSWed AZ61 joints was analyzed in terms of grain size and micro-texture by optical microscopy and Electron back-scattered diffraction. The fracture behaviors and mechanical properties of the FSWed AZ61 joints were closely related to the microstructure of the thermomechanical affected zone (TMAZ), and it was discussed based on the grain size and average Schmid factor in the TMAZ.
Aluminum alloy is one of the important materials in the field of automotive lightweight research; in order to meet the current demand for welding process of new energy power battery shell, this paper adopts static shoulder friction stir welding (SSFSW) on 3-mm-thick AA3003-H14 to conduct welding test; to explore the influence of welding process parameters on the forming quality, microstructure evolution and mechanical properties of the joint are investigated. The test results indicate that, at a constant welding speed of 500r/min, rotational speeds ranging from 2000 to 4000r/min yield defect-free welded joints with satisfactory forming quality. The cross section of SSFSW weld primarily consists of the weld nugget zone, the surrounding thermo-mechanically affected zone, and the heat-affected zone. The width of the weld seam and the overall grain size decrease as the welding speed increases. The distribution curve of joint microhardness exhibits a “W” shape, with the lowest hardness occurring in the backward side of the heat-affected zone and the highest hardness appearing in the forward side of the weld core area. Optimal tensile properties are observed when the welding speed is 1000 mm/min and the stirring head rotates at 4000r/min, resulting in a tensile strength of 157.79 MPa, which is equivalent to 92.8% of the base material's strength. A joint with favorable tensile properties can be achieved when the value of ω/v falls between 3 and 6. The fracture location corresponds to the region of lowest hardness in the joint, predominantly located at the junction of the thermo-mechanically affected zone and the heat-affected zone on the backward side of the joint. This fracture is characterized by evident toughness.
Friction stir processing: Nowadays, much more attention toward surface modification techniques impart enhanced surface properties without altering the properties of the substrate material. The field of surface engineering encompasses thermal spray techniques, namely plasma spraying, flame spraying, and many others widely used for surface modification applications in the past. One major limitation of the thermal spray process is the change of phase at higher temperatures interacting with intense heat, thereby deteriorating the coating properties. Friction sir processing (FSP) is emerging as a suitable method to eliminate the drawback associated with thermal spraying. In FSP, friction plays a vital role in generating appropriate heat at the tool–workpiece interface, causing the material to soften to join due to severe plastic deformation. FSP and its variations are hence solid-state by nature. FSP modifies the surface integrity such as toughness, ductility, wear, and corrosion resistance without altering the qualities of the underlying material. Recent advancements encompass the fabrication of surface alloys and metal matrix composites by inserting the reinforcement particles in order to change the material's surface properties by employing the FSP technique. As a result, FSP plays a significant role in surface engineering as a modification technique.
This chapter summarizes the fundamental of friction stir processing along with the process parameters that affect the surface integrity (wear and corrosion). Further, their role in surface engineering as a modification technique is also discussed. In the end, the inappropriate parameters that affect the surface modification technique have been assessed.
Introduction: Titanium and Hydroxyapatite (HA) are widely used in various industries, especially medicine and implants. The friction stir welding process (FSP) is one of the best methods for the fabrication of Ti/HA surface composites. Methods: This research specifically examines the effect of pin shape in FSP on the microstructure and mechanical properties of Ti/HA surface composites. Process parameters including pin shape (triangular, square, and conical pins), speeds of 1150 and 1250 rpm, and traverse speeds of 30 and 45 mm/min were used. Characterization of Ti/HA surface composites was performed with the help of FESEM, X-ray diffraction analysis, energy dispersive spectrometer (EDS) analysis, and tensile test. Findings: The results of the microstructure investigation showed that the triangular pin could not enter HA powder in the titanium substrate. At a higher rotational speed, fusion occurs to a greater extent in square and conical pins, reducing defects such as holes and cracks. The ultimate tensile strength values for the square pin with traverse speeds of 30 and 45 mm/min were 772 and 605 MPa, respectively. For the conical pin with traverse speeds of 30 and 45 mm/min, they were 894 and 747 MPa, respectively. Therefore, it was found that the ultimate tensile strength decreases with increasing traverse speed in both square and conical pins. Additionally, the ultimate tensile strength is always higher in samples processed with a conical pin than a square pin. These results show that process parameters significantly affect the mechanical properties of the specimens.
Aluminium alloys AA5083 and AA7075 were welded using friction stir welding (FSW) with three different welding speeds of 50, 100, and 150 mm/min at a constant rotation speed of 1000 rpm in a butt joint configuration. The microstructural characteristics were investigated utilizing scanning electron microscope (SEM), optical microscope (OM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction analysis (XRD). Mechanical properties were assessed through tensile and hardness tests, while the fracture surface of the tensile-tested samples was analysed using FE-SEM. Furthermore, corrosion behaviour was studied to comprehend the impact of intermetallic compounds (IMCs) on dissimilar joining. The examination of the microstructure in the base metals (BM) revealed a notable difference in the average grain size between AA7075 and AA5083, measuring 40 μm and 25 μm, respectively. Additionally, the types of precipitates differed between the two alloys. The stir zone (SZ) exhibited significant grain refinement, with an average grain size of 2 μm at a welding speed of 50 mm/min, which increased to 6 μm as the welding speed was raised to 150 mm/min. The dissimilar joints displayed ultimate tensile strengths ranging from 160 to 200 MPa and tensile strains ranging from 11.2 to 16.4%. The fracture surface of the dissimilar joints predominantly exhibited a brittle/ductile fracture mode. The sample S1 yielded the maximum hardness value of 200 Hv. Conversely, the lowest hardness value of 141 Hv was recorded for sample S2. As per the results of EIS plots and polarization curves the sample S1 showed the better corrosion resistance than other two samples i.e., S2 and S3.
This study aimed to investigate the detailed microstructure and mechanical characteristics of welded butt joints in dissimilar AA7075/AA6061. Three different welding methods were employed for the comparison: TIG (tungsten inert gas), FSW (friction stir welding) and TIG + FSP (FSP over TIG). Aluminum plates were welded using TIG along the rolling direction. The joint produced by FSW was created using a tool rotating at 931 rpm and a transverse speed of 40 mm/min. To characterize the microstructure evolution of the welded joints, we utilized optical microscopy (OM) and FE-SEM (field emission scanning electron microscopy) along with EBSD (electron backscattered diffraction). Additionally, FE-SEM with high magnification examined the fracture surface of tensile-tested specimens. The results of the study revealed valuable insights into the mechanical properties and microstructure evolution of the three welding methods. It was found that TIG + FSP exhibited superior mechanical strength (233 MPa). In contrast, TIG and FSW methods showed ultimate tensile strength of 195 MPa and 158 MPa, respectively. NZ maximum hardness in the nugget zone (128 HV) was found through TIG + FSP as compared to TIG (108 HV) and FSW (121 HV). This outcome can be attributed to refined grain (smallest grain 7.2 µm) structure with defect-free bonding achieved through TIG + FSP. The TEM analysis revealed valuable insights into the precipitate’s size. It revealed that the FSWed and TIG + FSPed samples show fine precipitates. Meanwhile, in the TIG welded sample, the coarse precipitates. The hybrid TIG + FSP approach leads to promising techniques for various industry applications.
Highlights A novel gradient pseudo-precipitates heterostructure (GPHS) is designed and fabricated for non-heat treatable 5xxx aluminum alloy; The proposed GPHS achieves enhanced strength-ductility synergy for Al-2.5%Mg alloy; The formation mechanism of the GPHS is revealed as an inter-diffusion mechanism activated and promoted by various sub-structures; HDI strengthening and strain hardening of GPHS are demonstrated as dominant effects in deformation mechanism. 2 Abstract Heterostructures of alloyed composites, comprising heterogeneous domains with dramatically different constitutive properties, hold remarkable potential to expand the realm of material design systems and resolve the trade-off between strength and ductility. This study introduces an innovative materials design method for synthesizing gradient pseudo-precipitates heterostructure (GPHS) in non-heat-treatable Al-2.5%Mg alloys. Utilizing cost-effective mild steel as both the diffusion source and protective layer, this heterostructure is achieved through pin-less friction stir-assisted cyclic localized deformation process. Exogenous Fe atoms diffuse across the interface by friction stir-induced heat conduction, forming Fe-Al second-phase particles in the Al alloy matrix. A rapid inter-diffusion mechanism is activated in conjunction with dense dislocation walls, grain boundaries, and sub-structures, resulting in the formation of pseudo-precipitates. These pseudo-precipitates are ultimately dispersed in a gradient distribution throughout the entire thickness of the Al alloy matrix induced by localized incremental deformation. The GPHSed Al-2.5%Mg alloy exhibits an enhanced synergy of strength and ductility, with a uniform elongation increase from 11% to 21.2%, while maintaining the strength. Multiple strengthening and hardening mechanisms, such as solid solution strengthening, dislocation hardening, and second phase strengthening, work synergistically to promote mechanical performance. Notably, the hetero-deformation between hard pseudo-precipitates and soft Al alloy matrix induces additional strain hardening, leading to high ductility. This work provides a fresh perspective on the design and fabrication of high-performance alloys with advanced heterostructures, especially for non-heat-treatable alloys. 4
The primary focus of this investigation is to examine the impact of friction stir processing (FSP) parameters on the tungsten inert gas (TIG) welded dissimilar AA6061-T6 and AA7075-T6 joints. Tool spindle speed, feed rate, tilt angle, and tool pin configuration were selected as input processing variables. A regression model was built using a central composite rotatable design matrix (CCRD) and response surface methodology (RSM) to forecast the mechanical features such as ultimate tensile strength (UTS), percentage elongation (PE), microhardness (MH), and residual stress (RS). Analysis of variance (ANOVA) was used to estimate the adequacy of the built-up models and identify significant terms. The results revealed that the tool pin configuration was found to be the most influential processing parameter relative to other parameters. The TIG + FSP joint fabricated with cylindrical threaded with triflat faces (THF) pin configuration has the highest mechanical properties and low residual stresses. The TIG + FSP joint showed an optimal UTS of 279.93 MPa, a PE of 20.92%, an MH of 115.42 HV, and a RS of 19.95 MPa when using a tool spindle speed of 1106.39 rpm, a feed rate of 45.79 mm/min, a tilt angle of 2.00 degrees, and a THF pin configuration. TIG joints exhibited brittle failure because of the rough cleavage facet and macro voids, while TIG + FSP joints exhibited brittle failure due to fine dimples and no voids. Electron backscatter diffraction showed that TIG + FSP welding produced ultrafine grains and significant grain boundary strengthening compared to TIG joints. Pole figures showed some recrystallization \({\text{A}}_{1}^{*}\)/\({\text{A}}_{2}^{*}\) and A/\(\stackrel{\mathrm{-}}{\text{A}}\) textures in the TIG joint at the FZ center, whereas the TIG + FSP joint exhibited significant shear deformation B/\(\overline{\text{B}}\) and C textures at the SZ center. Moreover, the intensity of texture in the TIG joint was only 3.02, while it was 10.34 in the TIG + FSP joint, indicating that significant texture strengthening occurred after FSP.
Friction stir welds were made in 6 mm thick plate in the mill annealed and β annealed conditions using a commercially pure tungsten pin-tool. A detailed characterization of the microstructure, using transmission and scanning electron microscopy, is presented here as a complement to previous texture analysis (using orientation imaging microscopy) with the aim of describing the evolution of microstructure during the FSW of titanium alloys. In both material conditions, the stir zone is characterized as a colony structure with a refined (10 μm) prior β grain size that developed during the relatively slow cooling from above the β transus temperature. The β grain size in the stir zone does not appear to be related to the microstructure prior to welding but rather to the extensive local deformation in this region and the relatively short dwell time above the β transus, both of these a factor in preventing β grain growth. The cooling rate from the β transus was slow enough to cause formation of grain boundary a along the prior β grain boundaries but rapid enough to cause stacking fault formation on basal planes in the α phase. The thermomechanically affected zone, TMAZ, contains a large amount of fine (1 μm) equiaxed α, the origin of which is still unknown and for which possible explanations will be presented. The thermo-mechanical history of the TMAZ of the mill annealed material caused the precipitation secondary α. Results will be presented with discussion focused on the combined effects of deformation and phase transformations.
The localized corrosion and environmentally assisted cracking of high strength aluminum alloys 7075-T651 and 7050-T7451 friction stir welds have been investigated in the weld transverse and longitudinal orientation by using conventional electrochemical measurements, corrosion immersion tests as well as constant extension rate testing. The weld micro-zones of both 7075-T651 and 7050-T7451 friction stir welds were found to be more susceptible to corrosion as compared to the unaffected parent metals. The heat affected zones of the weld were found to be the most susceptible to corrosion and environmental assisted cracking for the 7075-T651 FSW. An asymmetrical distribution of the' localized corrosion susceptibility (intergranular corrosion) correlated with the slightly different Cu depletion along the grain boundaries on both sides of the weld. In this alloy, fracture occurred constantly within the "soft" heat affected zones for samples tested in air and in 3.5 wt. % NaCl solution. In 7050-T7451, the TMAZ-nugget boundary exhibited the greatest corrosion susceptibility. In this alloy, the fracture position changed from the "soft" heat affected zones for samples tested in air to the TMAZ-nugget interface for samples tested in 3.5 wt. % NaCl solution. In this case a high environmentally susceptibility was found within the nugget and the TMAZ which exhibited grain boundaries heavily populated with Cu-enriched corrosion susceptible Mg (Zn, Cu)2. In constant extension rate tests, 7075-T651 FSW generally exhibited better environmental cracking resistance as compared to 7050-T7451 FSW, while 7075-T651 parent metal indicated lower resistance then the parent metal of 7050-T7451.
Friction stir welding (FSW) is a well established joining process for welding aluminum and other lower melting temperature metals. The application of this process to steels and stainless steels has primarily been limited by the availability of suitable tool materials. This paper will present the result of FSW in quench and tempered C-Mn steel. FSW were successfully made using polycrystalline cubic boron nitride (PCBN) tool material which exhibited negligible wear after 6 meters of weld. Transverse metallographic samples indicate excellent weld quality. Post weld transverse tensile properties were in excess of 70% of the base metal yield and tensile strengths. More detailed characterization of tool life along with weld microstructure and mechanical properties is presented.
An investigation has been carried out on the friction stir welding of four magnesium alloys. These consisted of three die-cast magnesium alloys and one wrought: AM50, AM60, AZ91 and AZ31 (wrought material). All of the alloys have each been successfully welded to themselves and also to each other, without any problems from the trapped gases in the cast materials, but the tolerance box of processing parameters to ensure that sound welds are produced has been found to be more restrictive than those seen in friction stir welding aluminium alloys.
Friction stir welding technology is described together with recent developments in tool technology for lap welding. The application of the process to tube welding is outlined.
The corrosion behavior of a friction stir welded Al-2.05Li-2.70Cu-0.6Mg-0.3Zn alloy AF/C458 has been characterized using several corrosion techniques. Vicker's hardness profiles collected transverse to the weld direction and optical microscopy helped distinguish different zones within the weld. Zones identified were the parent material, advancing heat affected zone (HAS), trailing heat affected zone (HTS), the thermo-mechanically affected sides on both sides of the weld (TMAZ) and nugget. The nugget and parent material were found to have Vicker's hardness values of 118 ± 4 HV and 170 ± 4 HV, respectively. The environmentally assisted cracking (EAC) and the corrosion behavior were investigated using constant extension rate testing (CERT), intergranular corrosion immersion test, and potentiodynamic scans. The CERT experiments were completed in air and 10mM NaCl solution on round tensile bar samples cut from within the weld micro-zones parallel to the weld and also transverse (perpendicular) to the weld direction. In samples from each of the micro-zones cut parallel to the weld, the ductility ratio (D.R.) was greatest for parent material (0.88), and lowest for the HTS (0.45), indicating higher corrosion susceptibility in this zone. The HAS had a slightly higher D.R. (0.72) than the nugget (0.62). From the metallography and fractography data of the weld transverse samples in air and 10mM NaCl solution, it appeared that the heat-affected zones were the most susceptible to intergranular and intersub-granular corrosion. Immersion testing conducted according to ASTM G110-92 standard revealed equiaxed pitting over the entire surface of the weld. Under high magnification, pitting, discontinuous sub-grain attack and borderline intergranular attack were observed in the HTS, HAS, TMAZ of the trailing and advancing sides as well as the parent material. The nugget displayed borderline intergranular attack and pitting only. Polarization scans showed that the pitting potentials in each micro-zone increased in the following manner: parent material (-506 ± 27 mV) > advancing and trailing HAZs (-522 ± 15 mV and -519 ± 19 mV, respectively) > nugget (-532 ± 5 mV). The repassivation and corrosion potentials did not show such a trend and were approximately the same for each weld zone.
Friction stir welding provides a new technology for solid state joining of a wide variety of aluminum alloys that cannot be joined with conventional fusion welds. However, recent work has shown that significant tensile residual stresses are developed in the stirred region with local tension maxima at the transition between the stir and heat-affected zones. Residual tension at the edges of the stir zone has been associated with stress corrosion cracking and corrosion fatigue crack growth initiation. This fatigue debit has been overcome using low plasticity burnishing (LPB) to introduce a deep surface layer of compressive residual stress. LPB processing after friction stir welding has increased the high cycle fatigue endurance of aluminum alloy FSW by 80%. However, the LPB processing parameters have not yet been optimized to produce the maximum achievable fatigue life. A linea r elastic fracture mechanics approach is applied to calculate the fatigue crack growth rates and fatigue lives of friction stir welded 2219-T8751 aluminum with initiation from salt fog pitting. The analysis is performed with and without the including of th e deep compressive residual stresses produced by low plasticity burnishing (LPB). Calculated fatigue lives are compared to fatigue data developed in four- point bending at R = 0.1 following 100 hr. salt fog pitting corrosion. The results indicate that the improved fatigue life achieved with LPB after friction stir welding can be explained by delayed crack initiation and retardation of growth in the deep compressive layer produced by LPB. The fatigue crack growth analysis provides a theoretical basis for understanding the improved fatigue life realized with LPB and for estimating the residual stress distribution that will provide the highest achievable fatigue strength.
The rapid thermal cycle generated during friction stir welding (FSW) produces a gradient of microstructures and precipitate distributions in the weld heat affected zone (HAZ) and the thermo mechanical affected zone (TMAZ). Metallurgical transformations associated with such heating and cooling become complex under these nonequilibrium conditions, producing unstable microstructures, which cause unpredictable changes in properties relative to the parent alloy. Our work has shown that the composition changes caused by the nucleation and coarsening of precipitates during FSW produce a sensitized microstructure in 7050 and 7075 aluminum alloys. This paper describes the deleterious effects on the corrosion behavior of 7050 and 7075 aluminum alloys resulting from FSW and the effects of pre- And post- Weld heat treatments on the corrosion properties of the welded material.
This paper investigates the potential of Laser Surface Melting (LSM), carried out using an excimer laser, to suppress the localised intergranular corrosion of friction stir welds (FSW) from the alloys 2024-T351 and 7010-T7651. The laser-melted surfaces have been characterised using optical microscopy, Scanning Electron Microscopy (SEM), immersion testing and atmospheric corrosion panels. A micro-electrochemical technique has also been used to obtain profiles of the anodic and cathodic reactivity across the width of each weld and laser treated surface. LSM treatment has been shown to produce a chemically homogeneous melt layer (∼10μm thick), which is more corrosion resistant than the untreated alloy. By laser-treating the surface of FS welds, it has been possible to suppress intergranular corrosion of the HAZ and nugget regions, displacing it instead into the surrounding untreated material where a more general pitting attack occurs.
The microstructure and hardness of a friction stir welded (FSW) 7075-T6 alloy has been correlated with mechanical properties, corrosion and environmental cracking behavior for transverse and longitudinal orientations. The strength and ductility of the weld micro-zones are controlled by grain size, the presence and size of the coherent intragranular precipitates, along with the degree of sensitization achieved during the weld process. The corrosion behavior is influenced by the intermetallic phases as well as the grain boundary phases and/or precipitate-free zones, although a discrimination on the intergranular susceptibility between the micro-zones could not be clearly achieved with conventional polarization techniques. The heat affected zone in the trailing side of the weld is the highest susceptible micro-zone to corrosion as well as environmental assisted cracking which correlate with the sensitization level i. e. with the extent of Cu depletion at grain boundary.
The grain structures formed during friction stir welding of a typical aluminium aerospace alloy have been studied by high resolution EBSD analysis. The grain structures reflect the local deformation conditions, and due to the high temperatures and strains show characteristics typical of different stages of dynamic recrystallisation. The large strains and high density of second phase particles in the nugget zone result in a very fine 2-3 μm equiaxed grain size. There is an abrupt transition in grain structure between the nugget and the TMAZ at the side of the weld. A very fine grain structure was also observed near to the top surface of the weld that was in contact with the tool shoulder. The nugget zone, 'onion ring' structure was attributed to bands of different densities of second phase particles, rather than any significant difference in the local grain structure or texture.
Volume 6 provides information on both the theory and practice of joining engineered materials and parts. It explains the underlying science of welding, brazing, and soldering, emphasizing how chemistry, physics, and metallurgy affect weldment properties and performance. The volume covers nearly 30 of the most common joining methods, describing process parameters, advantages and limitations, and equipment requirements. It also provides extensive information on specific materials, including selection criteria, application considerations, joining properties, and related data. Other topics covered include welding in special environments, corrosion, process modeling, evaluation, and quality control. For information on the print version of Volume 6, ISBN: 978-0-87170-382-8, follow this link.
Friction stir welding may enable higher strength and lower cost in the Advanced Amphibious Assault Vehicle under development, for the U.S. Marines.
The corrosion properties of high strength aluminum alloys are strongly dependent on grain boundary composition as well as the composition and morphology of the intermetallics. The recrystallized microstructure of the weld nugget usually has corrosion properties different from those of the parent material. In addition, the local temperature occurring during FSW is sufficiently high to cause dissolution, nucleation, and/or coarsening of the strengthening intermetallics in the weld heat affected zone (HAZ). Our investigations have shown that these transformations produce a sensitized microstructure increasing susceptibility to intergranular corrosion, pitting, and stress corrosion cracking (SCC). This work investigates post weld heat treatments of FSW and active cooling of AA7050-T7651 as corrective actions for restoring SCC resistance. Results using the slow strain rate (SSR) technique showed that an artificial aging treatment of 100°C for 1 week restored a significant amount of the SCC resistance. Other artificial aging treatments investigated, although they restored the SCC resistance, caused an unacceptable loss in mechanical properties under ambient conditions.
Friction stir welding (FSW) is a solid state joining technique. This makes it an attractive joining method for aluminum alloys and composites produced by a powder metallurgy route. In this study, the mechanical behavior of both a powder metallurgy monolithic aluminum alloy and composite were evaluated, i.e., IN 9052 and 7093 Al-SiC. Mini-tensile specimens were used to determine property variations in different FSW regions including the weld nugget, the thermo mechanically affected zone adjacent to the nugget, and the parent metal. A comparison of the microstructures and mechanical properties of these regions revealed no damage to the SiC particulates in the friction stirred region. The grain sizes in the nugget region of both materials also remained comparable to the fine-grained parent materials. These are significant advantages of FSW over fusion welding techniques.
The article reports on thermoanalysis measurements of the eutectic temperature of sodium- or strontium-modified cast alloys of the type of AlSi7Mg. The thermoanalysis was proved to be a usable, reliable means for rapid determination of the modification degree of molten metal ready for pouring.
The movement of material during friction stir welding is documented as a means of developing a conceptual model of the deformation process. Two new techniques for visualizing material flow patterns in friction stir welds are presented. Based on 7075 aluminum, material movement within friction stir welds is by either simple extrusion or chaotic mixing, depending on where within the weld zone the material originates.
Friction stir welding (FSW) was utilized to join three high-strength aluminum alloys, namely Al 7075, 2219 and 2195. In the present investigation, the stress corrosion cracking (SCC) behavior of these FSW alloys was studied by conducting two types of experiments: (i) four-point bending at three loading levels (50%, 65% and 85% of the ultimate tensile strength) under alternate immersion (AI) conditions in 3.5% NaCl solution for 90 days and (ii) slow extension rate testing (SERT) at 3.3×10-5 s-1 of specimens that were pre-exposed (PE) under AI in 3.5% NaCl solution. The latter set of experiments also involved testing of all specimens that survived the 90-day exposure under four-point bending. The results showed that all FSW alloys exhibited significantly lower strength compared to their parent alloy counterparts. Also, with respect to the corresponding parent alloys, FSW Al 7075 and 2195 exhibited lower ductility (∼50% reduction), whereas FSW Al 2219 exhibited comparable ductility. The four-point bending results revealed no SCC susceptibility for any of the FSW alloys for the given exposure period and loading levels. Significant ductility reductions were observed only for Al 7075 in the more severe SERT experiments. In this case susceptibility increased with increasing PE time. The present evidence suggests that the observed environmental susceptibility in FSW Al 7075 is due to hydrogen embrittlement.
The change of microstructures in Fe-24%Cr-7%Ni (ferrite (α) + austenite (γ) two-phase stainless steel during hot compressive deformation at the corresponding temperature of (α + γ) two phases was investigated. Two kinds of specimens with different microstructures are prepared for the hot compressive deformation. One has a microduplex structure which consists of fine α subgrains and γ grains. The other has an α single phase structure which was deformed to the reduction of 80% in thickness by cold rolling and compression. In the former case, high angle α grain boundaries appear in the early stages of compressive deformation at 1173 K under a strain rate of 1.1 × 10-3 s-1, due to local recrystallization of α subgrains. Misorientation angles among the α grains increase with increasing compressive deformation. Such a microduplex structure with high angle grain boundaries is presumed to be responsible for superplastic deformation at the high temperature.
In order to introduce different levels of microstructural heterogeneity into an experimental DRA material, three 6061/SiC/25p DRA extrusions were produced, using established P/M techniques. Each contained F-600 grade SiC particles (median diameter, d50 = 13.4 μm) however, the median matrix particle size was varied in a controlled manner, by careful screening of the 6061-Al powder stock. The range of matrix particle sizes that were chosen (26.4 μm, 42.0 μm and 108.6 μm) introduced increasing levels of spatial heterogeneity into the DRA microstructures, as quantified using the Multi-Scalar Analysis of Area Fractions (MSAAF) technique. The DRA materials were further processed, using FSP, in order to ascertain the effect of FSP on the homogeneity of the as-extruded microstructures. It was found that FSP introduces a significant amount of solid-state mixing which reduces the amount of microstructural spatial heterogeneity, even in the worst DRA specimens. In addition, minitensile tests were carried out on the as-extruded and as-processed DRA materials, and these results are presented in the context of the effects of microstructural heterogeneity on tensile mechanical properties.
The Friction Stir Joining process can be described in terms of five conventional metal working zones: a) preheat, b) initial deformation, c) extrusion, d) forging, and e) post heat/cool down. A simple approach to metal flow modeling of the extrusion zone using mass balance considerations reveals a relationship between pin tool geometry, operating parameters, and flow stress of the materials being joined. Analysis of the extrusion zone flow also provides for calculation of the width of the extrusion zone, strain rates, and x-direction pressure, Coupled with empirically determined relationships between processing parameters, maximum temperature, and material constitutive properties from Gleeble data, an understanding of the conditions necessary to produce an "optimum" weld emerge. Examples of this analysis approach to FSJ optimization for 2195 and 6061 aluminum with comparison to experimental observations are presented.
By any standard the industrial adoption of friction stir welding as the preferred joining technique for a range of aluminium alloys represents a remarkable progress of technical development. Furthermore, a range of non-ferrous and ferrous materials has also been shown to be readily welded by FSW in the laboratory. The design of the tool is the key to the successful application of the process to a greater range of materials and over a wider range of thickness. A number of different high performance tool designs have been investigated. This paper describes recent developments using these enhanced tools from the perspective of existing and potential applications.
The microtextures in a friction-stir-welded magnesium (Mg) alloy, AZ61, with a nugget-shaped stir zone were analyzed by orientation imaging microscopy (OIM). The base material had a (0002) texture ((0002) parallel to the sheet plane, parallel to the welding direction). Friction stir welding produced texture components different from those of the base material in the stir zone. Except for the upper surface of the plate, most of the stir zone had a texture with a strong tendency for the (0002) basal plane to align with the surface of the hard pin of the welding tool. Formation of this texture component was attributable to shear deformation arising from the rotation of the hard pin. The (0002) planes tended to align with an ellipsoidal surface in the nugget-shaped stir zone. The present study suggests that the nugget shape, which is a characteristic feature of the stir zone, is strongly related to formation of the ellipsoidal surface described by the (0002) basal plane.
Dynamic recovery (DRV) and recrystallization (DRX) are softening mechanisms that have distinctive effects on shaping the flow curve and retarding fissure formation to raise the hot ductility. DRV alone produces equiaxed subgrains in elongated original grains, whereas DRX gives rise to equiaxed grains containing a DRV substructure resulting from deformation during DRX. Confusion arises at very high strains (>10) when the elongated grain thickness is almost equal to the subgrain diameter. As a result of strong serrations in the original boundaries, one third of the perimeter of the average subgrain has a high misorientation. Moreover, serrations protruding into grains from above or below the observation plane may give the appearance of nuclei. The microscopic procedures for distinguishing DRV from DRX are discussed. Reinterpretation is made of several published results to show that DRX does not take place in Al alloys having less than 4% Mg.
Friction Stir Welding was used to join castings-to-castings and castings-to-wrought aluminum alloys for potentially expanding the usage of castings in airframe applications. Butt Joints of D357 castings to D357 castings had nearly parent metal strength after aging. However D357 castings to 2024 wrought plate joints had poor ductility. Butt joints in thin (0.080″) 2024-T3 sheets were evaluated as potential replacements for fastened, spliced joints in airframe fuselages. Joints in alclad material and hybrid joints (doubler concept) lacked ductility and had poor fatigue properties. In contrast, joints with bare material were found to have very attractive static and fatigue properties. The effects of weld surface roughness and intentionally introduced root-surface disbonds on properties were also assessed.
Friction stir welding (FSW) and friction stir processing (FSP) produce a fine grained 'nugget' region. The microstructural refinement and uniformity depends on processing parameters and tool design. During post-processing at high temperatures, friction stir processed 7050 and 2519 aluminum alloys show abnormal grain growth not reported previously. The locations for onset of abnormal grain growth are different for these two alloys. The nucleation and growth characteristics of abnormal grains have been investigated using differential scanning calorimetry, optical microscopy, and transmission electron microscopy. Precipitate distribution, precipitate stability, and microstructural non-uniformity in abnormal grain growth are discussed. The observation of abnormal grain growth has important implications for post-FSW heat treatment and superplastic properties of FSP material.
Friction stir welds were produced from 6.4 mm (1/4-inch) thick DH-36 steel and 304L stainless steel. Single-sided DH-36 welds and both single-sided and double-sided 304L welds were evaluated. During weld trials, the welding parameters were varied to develop a relationship between weld parameters and weld quality. As part of the friction stir welding process development, the microstructure and hardness profiles were evaluated as a function of weld energy. The microstructures of both DH-36 and 304L materials were observed using optical microscopy and scanning electron microscopy. Unlike 304L, DH-36 experiences readily observable solid-state phase transformations during FSW. The phase transformations were observed in four distinct zones with hardness values decreasing as one moved away from the stir zone. Results from mechanical property testing showed higher tensile strengths in the weld region than the base.
Direct joining of damage tolerant 2XXX alloys with high strength 7XXX alloys offers the promise of fabricating tailor-made structural components. Butt joints in 1" thick plates of 7075-T7351 and 2024-T351 were produced by friction stir joining. Joints were sound and free of voids and root surface disbands. The joints have a joint efficiency (Fty) that is 80% of the parent metal 2024-T351. Properties are consistent as functions of depth and position along the length of the weld. Tensile failures are always ductile; elongations are typically 5%, which is a consequence of the deformation being localized to the lower strength heat-affected zones. The fatigue response (Kt=1.5 and R=0.05) of these weldments was determined in the weld nugget; both heat affected zones, and parent material. The lifetimes were shortest in the heat-affected zones, but were at least 1/3 of the parent metal lifetimes.
Friction stir welding (FSW) is a solid state process that has been shown to successfully join high strength aluminum-lithium alloys. These Al-Li alloys have traditionally experienced difficulties in joining by plasma fusion welding processes (VPPA). Lockheed-Martin Michoud Space Systems (LMMSS) has developed hybrid microstructural enhancement (HFSW) and conventional autogenous (AFSW) friction stir welding processes for 2195 Al-Cu-Li plates. The cryogenic External Tank of the Space Transportation System is designed using fracture mechanics methodologies and proof test logic. The results of surface crack tension (SCT) and simulated service (SS) tests performed on AFSW and HFSW panels at various locations throughout the weld region are described. Comparisons are made to those results obtained from conventional VPPA welds.
The corrosion-fatigue crack propagation and corrosion-fatigue resistance (S-N) lives of friction stir welded (FSW) welded Al 2519 in air and in salt water were investigated. TEM studies reveal the presence of very fine θ' in the base metal, the coarsening of θ' in the HAZ, and the dissolution of the θ' in the weld nugget. Microhardness mapping was obtained for FSW weldments to illustrate the drop in hardness in both weld nugget and HAZ, and to help locate the HAZ positions. Fatigue crack growth rates in the weld and HAZ are significantly lower and fatigue crack growth thresholds significantly higher than those in the base metal. The better fatigue cracking resistance for cracks located in the FSW weld and HAZ may be attributed to the presence of compressive residual stresses at the crack tip. In air, FSW specimens exhibit shorter fatigue lives and lower fatigue thresholds than those of the base metal. In 3.5% NaCl solution, however, FSW and base metal specimens have similar fatigue lives and fatigue thresholds.
In Friction Stir Welding (FSW) a rotating pin-tool inserted into a weld seam literally stirs the edges of the seam together. The superposition of a rapidly rotating cylinder, a slowly rotating ring vortex, and a uniform translational flow generates a "wiping" flow that appears to model the plastic flow around the pin-tool. The wiping model is described and used to explain the results of a number of tracer experiments (traversed slab, line of shot, traversed wires). The wiping process model is compared to the metal cutting process and shown to have much in common, including very high strain rates. The model comprises a starting point for the rational design of the FSW pin-tool.
European and Japanese makers of railway rolling stock are revolutionizing the industry by applying an innovative welding process to the fabrication of trains and trams. In particular, modern railway carriages are increasingly produced from longitudinal aluminum extrusions with integrated stiffeners. This design approach can enhance the crashworthiness of vehicles because of the absence of transverse welds and the high buckling strength of the panels under longitudinal compression.
General Dynamics Land Systems, Inc. (GDLS), and Edison Welding Institute (EWI) have developed the friction stir welding (FSW) process to join 2519-T87 aluminum armor plate. Friction stir welded mechanical properties were found to have equivalent strength with increased ductility when compared to conventional arc weld properties. This is the first process to ballistically qualify 2519 aluminum in a butt joint weld configuration. Successful ballistic performance is believed to be associated with the increased ductility.
Experimental methods and results are presented illustrating metal flow during friction stir welding (FSW) of 6.35-mm thick plates of 7050 aluminum alloy. Composite marker materials (Al-30 vol.% SiC and Al-20 vol.% W) that are visible within the welded aluminum were positioned at the plate midplane either on the advancing side of the weld or at the weld centerline. Marker positions following welding were documented with metallographic and x-ray methodologies. The SiC and W particles were shown to flow readily with the 7050 Al during welding. The welding process pushes material ahead of the FSW pin upward significantly - markers were uplifted approximately 1.6 mm above the midplane in the 6.35-mm thick plate. Markers on the advancing side of the weld were distributed over a much wider region in the wake of the weld than markers that began at the weld centerline. Material is pushed downward in the plate by the action of the threads on the pin. In the wake of the welds, material beginning on the advancing side was shown to come back up to nearly the plate midplane. For material at the weld centerline, there was a slight rise in material above the midplane in the wake of the weld. Marker material thickness is reduced in the wake of the weld for material on the advancing side; this occurs much less for material starting at the weld centerline.
Friction stir welding (FSW) is a solid state welding process primarily for aluminum alloys and aerospace applications. However, there is also interest in using FSW for higher temperature aerospace materials such as titanium alloys. In light of this, FSW of Ti-6Al-4V was modeled and compared to aluminum alloys using a finite element model. The model was used to predict the tool and workpiece temperatures for various tool rpm's and plunge rates, as well as loads and deformation behavior. The effect of various tool materials was also examined with respect to tool and workpiece temperature response.
Friction stir processing (FSP) can be used to locally tailor the microstructure to enhance specific properties. In this work, FSP has been applied to cast aluminum plates to modify the microstructure to improve mechanical properties. The influence of FSP parameters on microstructural changes and microstructure-mechanical property correlations is described. FSP is shown to homogenize and refine the cast microstructure and completely eliminate porosity. This results in a significant increase in both tensile and yield strength. This concept can be used to locally enhance the properties of castings.
Friction-stir welding (FSW) has already been demonstrated to involve dynamic recrystallization as a mechanism for solid-state plastic deformation. Studies on aluminum alloys have also revealed complex flow patterns in the microstructure of the weld. However the flow characteristics remain somewhat unexplained. In this study, microstructural features of some friction-stir welded commercial aluminum alloys are being investigated involving light metallography (LM) and transmission electron microscopy (TEM). Similar (7075/7075, 2017/2017, 5052/5052) and dissimilar (7075/5052, 2017/5052, 7075/2017) aluminum plates of 3 mm thickness have been friction-stir welded at a rotational speed of 1250 rpm and traverse speed of 1 mm/sec. Complex vortex and swirl-like structures are observed to be more prominent in the dissimilar systems. Comparisons of microhardness profiles with microstructure for friction-stir welded aluminum alloys indicate that large differences in hardness may influence the complex spiral flow pattern at the weld zone. Microstructures of dissimilar systems have been observed to be different when two dissimilar plates change their sides while the rotation convention remain constant. In other words, for a constant tool rotation direction, the weld flow pattern and weld efficiency change when the position of the base plate changes and especially when a very hard aluminum alloy (Al 7075: 140-160 VHN) is stirred with a very soft aluminum alloy (Al 1100: 30-60 VHN) or vice-versa.
Fundamental, science based modeling and understanding of the friction stir welding process can greatly reduce the cost and cycle time of its application in joining operations. Modeling and simulation were used in a comprehensive thermomechanical framework that includes all relevant mechanics and thermodynamics. The three-dimensional analysis captures the coupling between tool geometry, heat generation, and plastic flow of the material under complex asymmetric thermomechanical loading conditions present in friction stir welding processes. Model validation results with detailed marking and thermocouple experiments are outlined. Model predictions are crucial to be able to follow the complex evolution of material deformation and microstructure. The deformation and flow patterns are important in avoiding voids and weld defects in FSW design. Tracking changes in microstructure is necessary for optimization of specific properties such as mechanical and fatigue strength and determines the extent to which this process can be applied in aerospace joining and assembly operations.
Friction stir welding (FSW), a new solid-state joining technique, is probably the most remarkable joining process that has been invented in this decade. This process produces low-distortion, high-quality, low-cost welds on aluminum alloys, even those difficult to weld by traditional fusion processes. In this paper, a three-dimensional finite element model of the FSW process is presented. The modeling effort includes a de-coupled heat transfer and a subsequent thermo-mechanical analysis. The temperature fields during the welding, the residual stress distribution and distortion of the workpiece after the FSW process are studied. Two unique features in FSW, namely (1) the effect of the fixture used to clamp the workpiece to the support backing plate and (2) the reduction of yield strength near the weld nugget area of the heat-treatable aluminum in the FSW process, are incorporated into the modeling. The results from the modeling are consistent with the available experimental data and trends. The model is then used to study the fabrication process of the FSW. An example is given.
This paper presents a thermal model for overlap joints produced through Friction Stir Welding (FSW) process and comparison of the model with experimental results for 5454-O Al-Alloy. A comprehensive 3-D thermal model based on a finite element analysis is proposed to predict temperature distribution during overlap friction stir welding process. The model accounts for moving heat generation caused by the rotation and linear traverse of the shoulder and pin as well as the convective/diffusive heat transfer caused by the plastic flow of the material in the vicinity of the shoulder and the pin. The moving heat source includes heat generation due to friction at the interface between the tool shoulder and the work piece as well as the interface between the pin and the work piece. The contact pressure distribution and consequently the surface conductance at the contact surface between the sheets is modeled as varying with the highest pressure being applied directly underneath the shoulder area. Temperature dependent properties of the weld-material have been used for the numerical modeling. A reasonably good match was demonstrated between the simulated temperature profiles and experimental data obtained through 3-D measurement of temperatures during real overlap FSW process. Some parametric analyses based on the present model are also presented.
Al/Al–SiCp bi-layer composites were produced by plasma spraying the premixed Al (or Al alloy) and SiC powders onto a 6061Al substrate. The obtained composites can be used for electronic packaging and are easy to join with other packaging components by the unreinforced substrate. A transition zone of lowered SiC particle volume fraction in the sprayed layers near the substrate surface was often formed. It can be affected by several factors, such as the initial temperature of substrate. No interfacial reactions between Al and SiC, as well as oxidation reaction, were found in the sprayed layers of the composites. SiC particles remained intact after spraying impact.
During laser processing to create an Al–SiCp surface metal matrix composite (MMC) layer on AA6061 Al alloy, needle-shaped particles were formed when a high laser energy
input was used. Optical microscopy showed this phase to be similar to Al4C3 and Al4SiC4. Previous work was unable to identify the compound as one of those already known in the Al–Si–C system that included Al4C3, Al4SiC4, Al8SiC7, Al4Si2C5 and Al4Si3C6. Therefore, in the present work a phase identification was undertaken on the unknown, using transmission electron microscope
(TEM) and the associated energy dispersion analytical X-ray (EDAX) system, together with X-ray diffractometry (XRD). This
suggested that the phase was an aluminium silicon carbide having an hexagonal structure with a = 0.3316 and c = 2.1330 nm, which could be a metastable phase formed under the particular laser processing conditions used.
The susceptibility of welded and unwelded samples of Al 5454 (UNS A95454) in the -O and -H34 tempers to pitting corrosion and stress corrosion cracking (SCC) in chloride solutions was studied. Welded samples were fabricated using the relatively new friction stir welding (FSW) process as well as a standard gas-tungsten arc welding process for comparison. Pitting corrosion was assessed through potentiodynamic polarization experiments. U-bend and slow strain rate tests were used to determine SCC resistance. The FSW samples exhibited superior resistance to pitting corrosion compared to the base metal and arc-welded samples. U-bend tests indicated adequate SCC resistance for the FSW samples. However, the FSW samples exhibited discontinuities that probably were associated with remnant boundaries of the original plates. These defects resulted in intermittent increased susceptibility to pitting and, particularly for Al 5454-H34 samples, poor mechanical properties in general.
Friction stir welding (FSW), a relatively new solid-state joining process, is used to join Al alloys of all compositions, including alloys essentially considered unweldable. This study focused on microstructures in FSW Al alloy 7075-T651 (AA 7075-T651 [UNS 97075-T651]), an alloy not commonly fusion welded, and the resultant corrosion susceptibility. Although the heat input associated with FSW was relatively low and the time at temperature was short compared to fusion welding, localized microstructures, chemical segregation, and precipitate distributions were created that generally are not present in parent metal AA 7075-T651. Typically, in the weld and heat affected zone (HAZ), the times at peak temperature were short, cooling was relatively rapid, and peak temperatures were > â500 C. Accordingly, a corresponding microstructural gradient developed from the weld nugget into the unaffected parent metal with the precipitate distribution in and around grain boundaries reflecting this temperature excursion. Some of these microstructures, when exposed to a corrosive environment, showed selective grain boundary attack and a decrease in the pitting potential relative to the parent metal. A characterization of the microstructure and localized chemistry differences within the weld zones suggested that the decrease in corrosion resistance correlated with a depletion of Cu within the grain boundaries and precipitate-free zones. These results provided evidence that the lowered resistance to intergranular corrosion following FSW of AA 7075-T651 was caused by a difference in pitting potentials.