Stationary Shoulder Friction Stir Welding Research Articles

Influence of a Stationary Shoulder Friction Stir Welding Tool on the Mechanical and Corrosion Properties of AA2024 Aluminum Alloy Joints at Different Parameter Values

Influence of a Stationary Shoulder Friction Stir Welding Tool on the Mechanical and Corrosion Properties of AA2024 Aluminum Alloy Joints at Different Parameter Values

Robotic friction stir welding in lightweight battery assembly of extrusion-cast aluminium alloys

The present study focuses on developing lightweight assembly of two different aluminium alloys extruded and high pressure die cast (HPDC) for battery frame assembly in BEV. The goal is to produce defect-free welds in lap configuration with smooth surface finish. Stationary shoulder friction stir welding (SSFSW) was employed with welding speeds of 3–15 mm/s. EBSD analysis revealed two groups of grains in the stir zone (SZ) due to dynamic recrystallization. Moreover, the grain size of the SZ significantly decreased compared to both alloys. The cast alloy contains large iron particles, and that were broken by the rotating probe, and the stirred material consisted of fine dispersed precipitates. Tensile-shear test found the fracture location at the hook area near to cast, and a model representing fracture behavior is also discussed. With increasing welding speed from 3 to 5 mm/s, the tensile strength found ∼95 and ∼100 MPa, respectively without any significance difference in the fracture behavior and location. Overall, this study provides valuable insights such as materials mixing, grain refinement, and joint strength in dissimilar joining using SSFSW. The findings could be useful in developing optimized welding parameters and improving the overall quality and productivity of the SSFSW process for battery pack assembly in BEV.

Effects of different friction stir welding processes on residual stress and deformation of Ti62A alloy joints

Residual stress induced by welding easily causes deformation and even fracture failure in welded structures. In this paper, a three-dimensional thermal-mechanical coupling finite element model of friction stir welding (FSW) was developed. The effects of different welding processes, namely conventional friction stir welding (C-FSW), stationary shoulder friction stir welding (SS-FSW), and bobbin tool friction stir welding (BT-FSW), on the temperature, residual stress, and deformation of welded joints were investigated by employing a heat source model and a force model to the welding analysis. The results reveal that a discernible disparity in temperature gradient is observed in the region ahead of the tool and behind it among various welding processes. The peak values of longitudinal residual stress along the surface and bottom paths of SS-FSW are reduced by 35.7% and 34.1%, respectively. In addition, the deformation at the initial end of the weld is slightly larger than that at the final end along the welding direction in three welding processes. Compared with other FSW processes, SS-FSW exhibits the smallest deformation, which is advantageous for improving assembly accuracy and enhancing the load-bearing capacity of weldments. The above results provide an important theoretical reference for the FSW process optimization of Ti62A alloy.

Computational Modelling and Comparative Analysis of Friction Stir Welding and Stationary Shoulder Friction Stir Welding on AA6061

This research focuses on the computational modelling and comparative analysis of friction stir welding (FSW) and stationary shoulder friction stir welding (SSFSW) applied to AA6061-T6 aluminium alloy. SSFSW, an FSW variant, employs a stationary shoulder and a rotating pin. This study introduces a numerical model for both processes, using the innovative Smoothed Particle Hydrodynamics (SPH) technique to capture their distinct thermo-mechanical characteristics. The aim is to unravel its mechanics and multi-physics in SSFSW and compare it with conventional FSW. The temperatures predicted by the model exhibited a close agreement between the advancing side (AS) and retreating side (RS). Plastic strain patterns show that regular FSW is different from SSFSW. In SSFSW, the strain is less, and the plastic area is comparatively slightly narrower. The distinct “ironing effect” resulting from the stationary shoulder in SSFSW reduces the heat-affected zone (HAZ). Yet, it maintains efficient plasticisation and material flow within the pin-affected zone (PAZ). This research emphasises the significant impact of temperature, strain, material flow, and thermo-mechanical characteristics on the quality of joints. Future suggestions include exploring process parameters more broadly, examining dissimilar welding techniques and hybrid approaches, and comprehensively investigating the diverse effects of SSFSW under various configurations and joint angles.

Determining the mechanism of defect formation and material flow characteristics in underwater stationary shoulder friction stir welding using coupled Eulerian-Lagrangian simulation

Determining the mechanism of defect formation and material flow characteristics in underwater stationary shoulder friction stir welding using coupled Eulerian-Lagrangian simulation

Friction Stir Welding of Aluminum in the Aerospace Industry: The Current Progress and State-of-the-Art Review.

The use of the friction stir welding (FSW) process as a relatively new solid-state welding technology in the aerospace industry has pushed forward several developments in different related aspects of this strategic industry. In terms of the FSW process itself, due to the geometric limitations involved in the conventional FSW process, many variants have been required over time to suit the different types of geometries and structures, which has resulted in the development of numerous variants such as refill friction stir spot welding (RFSSW), stationary shoulder friction stir welding (SSFSW), and bobbin tool friction stir welding (BTFSW). In terms of FSW machines, significant development has occurred in the new design and adaptation of the existing machining equipment through the use of their structures or the new and specially designed FSW heads. In terms of the most used materials in the aerospace industry, there has been development of new high strength-to-weight ratios such as the 3rd generation aluminum-lithium alloys that have become successfully weldable by FSW with fewer welding defects and a significant improvement in the weld quality and geometric accuracy. The purpose of this article is to summarize the state of knowledge regarding the application of the FSW process to join materials used in the aerospace industry and to identify gaps in the state of the art. This work describes the fundamental techniques and tools necessary to make soundly welded joints. Typical applications of FSW processes are surveyed, including friction stir spot welding, RFSSW, SSFSW, BTFSW, and underwater FSW. Conclusions and suggestions for future development are proposed.

Effect of post-weld heat treatment on the microstructure and mechanical properties of SSFSW HVDC AlSiMgMnCu alloy

The high vacuum die casting (HVDC) AlSiMgMnCu alloy sheets were successfully welded by stationary shoulder friction stir welding (SSFSW) technique, and a post-weld heat treatment (PWHT) was also performed to enhance the mechanical properties of the joints. The microstructure and maximum texture intensity obviously change in different zones before and after the heat treatment. In the as-SSFSW joint, the microstructure in nugget zone (NZ) and thermal mechanically zone (TMAZ) possessed stronger texture of brass components than the heat affect zone (HAZ). After the T6 PWHT, the joints of the alloy showed continuous recrystallization. The texture type is still brass texture in NZ and TMAZ, while the texture intensity in the NZ and TMAZ significant increased. Some grains in NZ and TMAZ rotate 20° towards the <111>. The nano-precipitation β'', Q′ and θ′ phases formed in the Al matrix after the T6 PWHT. The yield strength, ultimate strength and elongation of PWHT joints are 252 MPa, 297 MPa and 4.1%, respectively. The joint welding coefficient of PWHT joint is 96.1%, which was ascribed to dislocation and precipitation strengthening.

Effect of cube texture on local softening of stationary shoulder friction stir welding for thick-plate Al-Li alloy

• Impacts of Cube texture on local softening of the joint are investigated. • High shares of maximum Schmid factor in 0.4–0.5 cause softening of the joint. • A higher fraction of Cube expresses higher softening tendencies. Based on stationary shoulder friction stir welding (SSFSW) tests results on a 12-mm-thick plate of 2195-T8 Al-Li alloy, the influence of Cube on the softening tendencies in different regions of the weld is explored by calculating the average (SF avg ) of the five maximum schmid factors (SF max ) for different crystal orientations. The interface (HAZ-TMAZ) between heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ), the bottom of welding nugget zone (WNZ-B), and TMAZ have significantly higher proportions of SF max in 0.4–0.5. It indicates that quantities of grains with softening orientations in these regions are much larger and the softening tendencies are much serious. SF avg in the 12 groups of slip systems for Cube reaches 0.4082 and expresses the higher softening tendency. The fractions of Cube in HAZ-TMAZ, TMAZ and WNZ-B reach up to 4.0%, 3.3% and 13.0%, respectively. Therefore, these regions have more seriously softening tendencies. The hardness, yield strength, and ultimate tensile strength of these areas are 54%-58%, 46%-48%, and 63%-70% of the base metal (BM), respectively.

Softening behavior of stationary shoulder friction stir welded joint for thick-plate Al–Li–Cu alloy

12-mm-thick Al–Li–Cu alloy plates were fabricated by stationary shoulder friction stir welding (SSFSW) to evaluate the softening behavior of the whole joint under a given rotational speed of 400 rpm and a welding speed of 60 mm/min. Continuous dynamic recrystallization, discontinuous dynamic recrystallization, and geometric dynamic recrystallization are the main dynamic recrystallization mechanisms in SSFSWed joints. Such mechanisms help to gradually change rolling grains of base material (BM) into equiaxed grains of welding nugget zone (WNZ) and significantly lower dislocation density. The decrease in dislocation density is the main reason for joint softening. Continuous coarsening of T1/θ′ in heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ) weakens the strengthening effect. The development of precipitate-free zones and re-precipitation of TB primarily contribute to severe softening at the interface between HAZ and TMAZ on the advancing side (AS-HAZ-TMAZ). The serious softening behavior at the bottom of WNZ is attributed to the re-precipitation of TB and the complete dissolution of T1/θ′. Hardness profiles and tensile strength distribution of SSFSWed joint exhibit a “W” pattern, while a “U” pattern appears at the bottom. The hardness profile and tensile strength of WNZ are significantly poorer at 8–12 mm from the weld surface compared to those at 0–8 mm. Softening behavior also results from the higher fractions of the maximum Schmid factor (in 0.4–0.5) and Cube. From BM to WNZ, fracture mode transitions from quasi-cleavage fracture to plastic fracture.

Texture features and strengthening mechanisms in welding nugget zone of SSFSWed thick-plate Al–Li alloy joint

In order to investigate the microstructure evolution, texture features, and strengthening mechanisms at different positions in the welding nugget zone (WNZ) of thick-plate joints in depth, stationary shoulder friction stir welding (SSFSW) tests were conducted on a 12-mm thick 2195-T8 Al–Li alloy with rotating speeds of 300–500 rpm. At 300 rpm, the results demonstrate that WNZ is mostly made up of equiaxed grains orientated in <111> and <101>//TD, with a homogeneous grain size distribution along the plate thickness. In contrast, at 500 rpm, the crystal orientations convert to <001> and <101>//TD, and the grain size at the bottom of WNZ reaches only 39.3% of that at the top. At 300 rpm, WNZ is predominantly composed of shear textures and remains a large number of needle-like precipitates T1 and θ′, both of which contribute to the improvement in mechanical properties. The weld zone exhibits higher microhardness and tensile strength along the plate thickness at a lower rotating speed, retaining a high level within 8 mm from the weld surface but gradually decreasing from 8 to 12 mm as the rotating speed increases. In addition, the strengthening mechanism of the whole WNZ is dominated by precipitation strengthening at 300 rpm, which is replaced by dislocation strengthening at 400 rpm. As the rotating speed increases to 500 rpm, grain refinement strengthening takes over as the dominant strengthening mechanism in the WNZ.

Microstructure evaluation of dissimilar AA2024 and AA7050 aluminum joints made by corner stationary-shoulder friction stir welding

Fillet welds made by the corner stationary-shoulder friction stir welding process between AA7050-T7451 and AA2024-T4 sheets were characterized using different metallographic techniques and mechanical testing. Robotic welds of an aircraft’s skin-to-internal stiffeners were examined using Barker’s electrolytic and Keller’s etching techniques and correlated with electron backscattered diffraction results and energy-dispersive microprobe analysis. The composition and grain orientation maps and material flow lines demonstrated excellent weld quality in spite of the apparent inhomogeneities in the stir zone where mechanical mixing was complete. Welded joint efficiencies were in the 85–92% of the base metals and were acceptable in terms of resistance to crack initiation and propagation and corrosion resistance, even with softening of the heat-affected zones. It was concluded that several optical and electron microscopy techniques are needed to characterize these dissimilar aluminum welds fully and that post-weld mechanical and thermal treatments could even further improve their quality.

Numerical Simulation and Experimental Studies on Stationary Shoulder Friction Stir Welding of Aluminum Alloy T-Joint

The application of the corner stationary shoulder friction stir welding (CSSFSW) on T-shaped structures is exceptional, and adequate research is still required for the related theory. In this paper, taking 5,083 aluminum alloy as the workpiece, based on the Arbitrary Lagrangian Eulerian (ALE) method, a three-dimensional thermomechanical coupled model of the CSSFSW process was established. The temperature field and material flow were simulated and analyzed during the welding process. The friction heat formed an elliptical temperature gradient range, and expanded with the progress of the welding. The highest temperature of up to 575°C was recorded on the advanced side, which is higher than that on the retreating side (about 532°C). The forward and backward material flow directions were found to be opposite to each other. In the traverse direction, the material on both sides flowed upward along the pin and downward under the action of the stationary shoulder at the top. The difference between the simulated and the measured temperature lies within 7%, and the material flow also has good agreement with the experimental results.

Effect of Microstructure and Mechanical Properties of Al 3003 Alloy Weld by Stationary Shoulder Friction Stir Welding Process

Effect of Microstructure and Mechanical Properties of Al 3003 Alloy Weld by Stationary Shoulder Friction Stir Welding Process

Material flow and viscous slips during stationary shoulder friction stir welding of Ti6Al4V

The flow and slip rate of material in friction stir welding mainly determined the weld quality, flow rate depended not only on the shape of pin and welding parameters but also on slip, and an instantaneous centre of speed was generated by rotating speed and welding speed. The relative speed of contact interface is generally an important factor in material flow. The material experienced different viscous slips when rotating around the pin, which disengaged pin at a larger slip and adhered to pin at a smaller slip, resulting in large differences in two sides. The first derivative of the dividing line at the boundary of SZ was extracted to investigate material flow.

Numerical simulation of the stationary shoulder friction stir welding of Ti-6Al-4V

Numerical simulation of the stationary shoulder friction stir welding of Ti-6Al-4V

An investigation on mechanical and microstructural evolution of stationary shoulder friction stir welded aluminum alloy AA7075-T651

The stationary shoulder friction stir welding (SSFSW) technique promotes new opportunities for welding material. In the current work, a special setup of SSFSW was designed and manufactured in only three parts according to the homemade friction stir welding (FSW) machine dimensions and specifications. This setup with minimum parts is easily adjustable beside it facilitates fast control of the tool pin length. This gives the design more advantages than the previous designs published for the same purpose. Two different parameters were used with the SSFSW setup to butt weld samples of AA7075-T6 of 5 mm thick. Various welding travel speeds of 25, 50 mm/min, and 75 mm/min and different values of Z-force of 20, 25 KN, and 50 KN were used to evaluate the effect of the SSFSW parameters on the joints’ quality and properties. The results confirmed that sound joints were produced without internal or surface defects. In addition, the joints are characterized with a smooth surface finish compared to the conventional FSW joints. A narrow heat affected zone around the nugget due to the elimination of heat generation by the shoulder. The tensile strength of welded samples increases with increasing the vertical force with the maximum tensile strength of 418.7 MPa at a rotational speed of 600 r/min, a welding speed of 50 mm/min, and 50 KN Z-force. This implies that the vertical applied force upon SSFSW is an important parameter in controlling the joint properties. Analysis of the hardness distribution across the weld cross-section shows slight reduction in the heat affected zone.

Stationary shoulder friction stir welding of Al–Cu dissimilar materials and its mechanism for improving the microstructures and mechanical properties of joint

The fundamental reasons for the poor mechanical properties of the Al–Cu conventional friction stir welding (CFSW) joints are serious material mixing and excessively thick intermetallic compounds (IMCs). In this study, stationary shoulder friction stir welding (SSFSW) was innovatively applied to join the Al–Cu dissimilar materials. The results indicated that the material mixing and the IMCs growth were successfully suppressed. Compared with the CFSW, the grains in the SZ of the SSFSW joint were refined and the plastic deformation in the SZ was enhanced. This was attributed to the frictional driving force of SSFSW was higher than that of CFSW. The mutual diffusion reaction of Al and Cu elements was inhibited owing to the lower heat input of the SSFSW. The mechanical properties of the joints were significantly improved by the SSFSW. The tensile strength of the optimal SSFSW joint was found to be 211.4 MPa which is 15.1% higher than that of the optimal CFSW joint. Moreover, the fracture occurred in the Al matrix. Reducing the stress concentration in the SZ caused by materials mixing was shown to be the main mechanism for SSFSW to improve the tensile performance of the joint.

Summary of Research Progress on Friction Stir Welding of Dissimilar Metals

Background: Friction stir welding technology is widely applied in the welding of dissimilar metal materials because of its high welding efficiency, low welding process cost, high welding joint strength and reliability, and green environmental protection. The research on the processing methods and working principle of friction stir welding of dissimilar metals is beneficial to improve the mechanical properties of the joint and reduce weld defects. Therefore, the development of reliable friction stir welding technologies for dissimilar metals joining has been paid increasing attention in recent years. Objective: The study aims to satisfy the processing of various dissimilar metals and improve the joint performance and weld defects. Friction stir welding has developed into bobbin tool friction stir welding and stationary shoulder friction stir welding. Methods: This paper retraces various current representative patents relative to friction stir welding, bobbin tool friction stir welding, and stationary shoulder friction stir welding. Results: Through the investigation of a large number of patents on friction stir welding, the main current existing problems, such as poor mechanical properties of the joints and defects in the welds, are summarized and analyzed. In addition, the development trend of friction stir welding in dissimilar metal welding is also discussed. Conclusion: The research on friction stir welding methods and devices is beneficial to improve the mechanical properties of welded joints and reduce weld defects. More correlative patents will be invented in the future.

Microstructure and Mechanical Property of Fillet Welded Joint by Stationary Shoulder Friction Stir Welding for 2A14 Aluminum Alloy Thick-plate

Microstructure and Mechanical Property of Fillet Welded Joint by Stationary Shoulder Friction Stir Welding for 2A14 Aluminum Alloy Thick-plate

Microstructure characterization and evaluation of mechanical properties in 2A97 aluminum-lithium alloys welded by stationary shoulder friction stir welding

2A97 Al–Li alloy joints with the thickness of 1.5 mm were fabricated by stationary shoulder friction stir welding (SSFSW) under rotational speeds of 600–1000 rpm and a fixed welding speed of 200 mm/min. As the rotational speeds increased, the grain sizes of the nugget zone (NZ) kept almost constant with the presence of zigzag defects. The electron backscattered diffraction (EBSD) analysis suggested that the initial crystal orientation with near <001>‖TD and <001>‖WD textural components exhibited weaker anisotropy induced by the severe shearing deformation. The dynamic recrystallization (DRX) mechanisms were clarified in the transition from low-angle grain boundaries (LAGBs) to high-angle grain boundaries (HAGBs). In contrast to the conventional FSW joints of Al–Li alloys, the dispersions were indexed as Al11Cu5Mn3, Al2Cu within the grains, and Al–Cu–Mn–Zn phase at the grain boundaries in the SSFSW joints. The T1, δ′/β' and θ′ precipitates were detected in the base metal (BM), and the θ′ precipitates were dissolved in the heat affected zone (HAZ). However, those strengthening precipitates were absent in the NZ. The variation of the ultimate tensile strength first increased and then decreased with the increasing rotational speeds. Moreover, the joint obtained at a rotational speed of 1000 rpm exhibited the best combination of strength and ductility. The defect-free joints failed in the thermo-mechanically affected zone (TMAZ), which corresponded to the hardness minima positions (HMP). However, an abnormal fracture occurred in the NZ due to the presence of weak-bonding areas and curved band structures.