Double-sided Friction Stir Welding Research Articles

Effectiveness and efficiency of tool alignment and simultaneity factors on double-sided friction stir welding for joining heat-treatable aluminum alloys: a review

Effectiveness and efficiency of tool alignment and simultaneity factors on double-sided friction stir welding for joining heat-treatable aluminum alloys: a review

Effect of Process Parameters on the Mechanical Properties of Simultaneous Double-Sided Friction Stir Welding Joints

Currently, conventional single-sided friction stir welding is primarily suitable for joining thin plate aluminum alloys, and its application to thick plates is still challenging in terms of welding efficiency and joint mechanical properties. Simultaneous double-sided friction stir welding (SDS-FSW) is a high-efficiency joining technique specifically developed for welding thick plates. However, there is little research on the influence of SDS-FSW process parameters on the joint mechanical properties. In this study, a 12 mm thick AA6061-T6 aluminum alloy and dual robot welding equipment are used to conduct SDS-FSW experiments exploring the influence of rotational speed ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} and welding speed v on the mechanical properties and microstructure. The results show that when the welding parameters are ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} = 800 r/min and v = 60–80 mm/min, smooth and defect-free thick plate aluminum alloy SDS-FSW joints can be obtained, and the macroscopic morphology of the joints is distributed in a “dumbbell” shape. The grain size in the weld nugget zone increases with increasing welding heat input. The microhardness distribution in the joint displays a “W” shape, and the hardness value of the weld nugget zone can reach 67% to 86% of that of the base metal (BM). The junction between the thermo-mechanically affected zone and the heat affected zone is the weakest region of the joint, with the lowest hardness being approximately 51% of that of the BM. When the welding parameters are ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} = 800 r/min and v = 140 mm/min, the SDS-FSW joint has the highest tensile strength, reaching 78.43% of the BM strength and exhibiting ductile fracture characteristics. This research indicates that acceptable weld strength in thick aluminum alloys can be achieved via the SDS-FSW joining mechanism, highlighting its significant potential for industrial applications.

Stepwise double-sided friction stir welding: an alternative for root defect mitigation in aluminium plates with lower gauge numbers

Penetration-induced fractional unbonded defects and flow-induced root flaws are part of the discontinuities of the conventional friction stir welded (FSW’ed) aluminium alloys with limited impact assessment/clarification in literature. The novelty of this study lies in the attempt to eliminate penetration-aided root defect via a stepwise double-sided welding process as well as identify its impact on loadbearing. As a result, the stepwise double-sided FSW welding of a thick aluminium plate (6 mm) was carried out while the microstructure, strength, and fracture modes of the ensuing welds were compared with the conventional (single-sided) friction stir welded counterparts. The stepwise double-sided FSW-welded joint demonstrated better tensile strength relative to the single-sided FSW-welded counterparts owing to its material flow consolidation (two-side deformation) and elimination of penetration-induced fractional unbonded region/root defect. The welding processes do not have a noteworthy influence on the fracture location of the welds as failure ensued via the stir zones of the respective welds. Transient breaking/brittle appearance, and ductile fracture modes were noticed in the single-sided and stepwise double-sided FSW-welded samples respectively. The stepwise double-sided FSW process is recommended as a better choice for thick workpieces relative to conventional FSW to improve the weld’s loadbearing resistance.

Microstructural, texture, and crystallographic analysis of SiC particle incorporation in double-sided friction stir welding of dissimilar aluminium alloys

This paper investigates the impact of incorporating SiC nanoparticles into the welded interface joint of dissimilar aluminium alloys 2024 and 7075. Double-sided friction stir welding (DS-FSW) was performed to investigate the impact of added nanoparticles on the joint's mechanical properties and crack growth rate. Microstructural analysis of the fractured surface was conducted to assess the influence of nanoparticles on crack propagation, while field emission scanning electron microscopy (FESEM) was utilized to examine the grain size distribution across different weld zones. On analyzing the DS-FSW joint with SiC-reinforced particles using electron backscattered diffraction (EBSD), predominant shear texture components such as B/B̅ and C are observed. Additionally, there are deformed textures like Rotating cube (H) {001} <110> and F {111} <112>, along with recrystallization texture elements such as Goss {110} <001>, P {011} <112>, and Cube {001} <101>. Mechanical properties, determined through hardness and tensile tests, were compared between nanocomposite weldments and base metal to assess the improvement in mechanical properties following the inclusion of SiC particles. Crack growth tests were performed using compact test (CT) specimens at a maximum load of 5 kN and a stress ratio of R = 0.1. The addition of SiC nanoparticles to the joint area led to a significant decrease in grain size and an increase in hardness within the stir zone, compared to the base metal and samples without the powder. The tests revealed an approximately 62 % increase in tensile strength and a notable increase in microhardness of the weld zone of the aluminium alloy metal matrix composite (AAMMCs).

Improving bonding strength of medium-thick Al-Cu dissimilar joint by a novel splat cooling assisted double side friction stir welding

To obtain a high-strength medium-thick Al-Cu dissimilar joint, a novel splat cooling assisted double side friction stir welding (SDS-FSW) is proposed. The microstructure and tensile properties of conventional double-side friction stir welding (DS-FSW) and the novel SDS-FSW joints under optimal welding parameters are systematically compared, it shows that the utilization of in-process splat cooling significantly reduces the welding peak temperature and the high-temperature dwell time. The in-process splat cooling causes significant grain refinement in the welding nugget zone (WNZ) of the Al-Cu dissimilar SDS-FSWed joint, it exists the lower recrystallization fraction and the higher KAM value. Although both DS-FSW and SDS-FSW joints fracture at the Al-Cu interface, the DS-FSW joint represents a brittle fracture characteristic, while the SDS-FSW joint represents a mixed ductile-brittle fracture mode. Under the drive of the mechanical stirring of the tool and the welding thermal cycle, the aluminium atoms and copper atoms diffuse to the copper base material and aluminium base material, respectively. Since copper diffuses in aluminium at a higher diffusion rate than aluminium diffuses in copper, and the solubility of copper in aluminium is much smaller than that of aluminium in copper, thus the Al2Cu becomes the first phase with the nucleation and growth. As the welding temperature and time continue to increase, Al2Cu reaches the supersaturation state, and the Al4Cu9 phase is produced between the Cu (Al) and the Al2Cu phase. In the end, the interface forms the stable double-layer IMCs structure (Al2Cu/Al4Cu9). The optimal tensile strength of the SDS-FSWed joint is 159 MPa, which is increased by 42% compared to the DS-FSWed joint at the same welding parameter. This was mainly because in-process splat cooling contributed to forming a thinner IMCs layer at the A-Al-Cu interface. It reveals that the application of in-process splat cooling is a versatile method to thin the IMCs layer at the Al-Cu medium-thick DS-FSW process.

Strategy for double-side friction stir welding of thick Mg4Y3Gd alloy joints

Strategy for double-side friction stir welding of thick Mg4Y3Gd alloy joints

Fatigue crack growth rate and mechanical properties of one-step double-side friction stir welded AA6061-T6

Friction Stir Welding (FSW) is commonly used in transportation industries but faces challenges when joining thick plates. To address this, double-side FSW (DFSW) has been introduced, involving two steps: FSW on one side, flipping the plate, and then FSW on the opposite side. However, this process is time-consuming. To overcome this, a one-step DFSW technique was developed, where two tools simultaneously operate on both sides. This study aimed to investigate the impact of tool rotation speed on the fatigue crack growth rate of AA6061-T6 in one-step DFSW. One-step DFSW was performed at different upper and lower tool rotational speeds: 1500/900 rpm, 1500/1200 rpm, and 1500/1500 rpm. Tensile and fatigue crack growth tests were conducted on the joined specimens. The microstructure of the welded joint and the surface fractures resulting from the tests were analyzed using a scanning electron microscope (SEM). Results showed that the specimen welded at 1500/1500 rpm exhibited the lowest fatigue crack growth rate. The Paris constants (C and n) were determined as 4.348E-08 and 4.16, respectively.

Double side friction stir Z shape butt lap welding of dissimilar titanium aluminum alloys

Achieving excellent mechanical performance of medium-thick Ti/Al dissimilar joints is important in many industrial applications. However, due to the inherent heat generation mode associated with conventional friction stir welding (FSW), it is impossible to achieve sound medium-thick Ti/Al dissimilar joints. Although double side friction stir welding (DS-FSW) has been reported to solve the problems of conventional FSW. The inherent problems of forming hook structure and interface cracking in the center of the DS-FSW joints significantly weaken the joint performance. Therefore, an innovative double-side friction stir Z shape butt-lap welding (DS-FSZW) process was proposed to eliminate the inherent problems of conventional DS-FSW. The research objective of this work was to reveal the physical mechanisms of the novel DS-FSZW by the combination of numerical simulation and experimental characterization for optimizing the welding parameters. The influence of tool shoulder diameter on the heat generation, heat transfer, plastic material flow, microstructure evolution and mechanical properties of medium-thick dissimilar Ti/Al DS-FSZW joint has been systematically studied. The results indicate that the innovative DS-FSZW process lowers the axial force compared to the conventional DS-FSW, and the centerlines of the first and the second sides welds are staggered. Those are beneficial to inhibiting the cracking of the first-side weld at the interface. In addition, the DS-FSZW method eliminates the hook structures and cracks at the center of the conventional DS-FSW joint and also adds a lap joining interface, which significantly enhances the tensile strength of the joint from 150.7 MPa to 262.5 MPa, which is increased by 74%. Optimization of the shoulder diameter of DS-FSZW from 18 mm to 12 mm reduces the welding heat input and significantly thins the thickness of the IMCs layers at the Ti/Al interface. This helps to suppress the cracking at the Ti/Al lap interface and refine the grains. As a result, thus the tensile strength of the DS-FSZW joint increases from 262.5 MPa to 312.5 MPa, which is increased by 19%. The medium-thick Ti/Al dissimilar DS-FSZW joint at the tool shoulder diameter of 12 mm fracture at the SZ. It proves that the novel DS-FSZW is a suitable welding method for joining medium-thick dissimilar Ti to Al alloys.

Microstructure and mechanical properties of double side friction stir welded AA 7075 aluminum alloy

Friction stir welding of aluminum alloys is, nowadays, widely used in several industries and the welded joints are expected to exhibit adequate weld characteristics. In fact, normal single side friction stir welds, particularly thick section joints, are prone to reductions in weld properties due to higher heat inputs. Double side friction stir welding (DS FSW) is considered to be one of the possible solutions to address the problem of weld property reductions. Hence, the present work aims at investigating the possibility of improving the joint properties of welds by welding from both sides. Double side friction stir welds were made using 10 mm thick AA7075 plates and the welds were investigated for mechanical properties using hardness, tensile, impact and bend tests. Microstructure, precipitate morphology and fracture surface of the samples were also studied by optical (OM), transmission electron (TEM) and scanning electron microscopies (SEM), respectively. The results showed that the weld nugget exhibits fine equiaxed grains and severe dissolution of strengthening precipitates. In addition, the hardness of the double side welds improved by about 20 HV compared with that of single side welds due to increased survival rate of strengthening precipitates in the WN and reduced PFZ's width in the HAZ. The results of tensile and impact tests showed that in DS FSW samples, the yield strength increased by about 30 MPa and impact toughness increased by 4.83 J compared with single side welds. By and large, it was observed that the better microstructural and mechanical properties can be achieved by double side friction stir welding.

Achieving an improved performance in double-sided friction stir weld joints by adjusting the welding conditions during the passes of AA6061-T6 aluminium alloy

The present study aims at investigating the effect of interaction between the process parameters of each weld pass (1st pass and 2nd pass) to improve the joint performance during the double-sided friction stir welded joints of AA6061-T6 aluminium alloy. Experimental designs were conducted following a design matrix developed using response surface methodology to investigate the impact on the microstructural changes and tensile properties. Pronounced interaction between the process parameters of each weld pass of the joint was observed and indicated a strong interdependency between them. The detailed microstructural study conducted through EBSD insights into the extent of homogenization, and abnormal grain refinement and reflects a vast transformation of low-angle grain boundaries into high-angle grain boundaries within the stir zone. The profound examination through scanning electron microscopy and transmission electron microscopy analysis validated the uniform homogeneous distribution of Al-Fe and Al-Si-rich precipitates. The significant improvement in the grain refinement and distribution of the strengthening precipitates within the stir zone led to a substantial enhancement in the microhardness, along with achieving a maximum ultimate tensile strength of 223 MPa and a percentage elongation of 14%. A study of the fracture morphology ensures the ductile fracture behavior of the tensile fracture specimen by observing the presence of numerous dimples within a well-bonded joint.

High-speed friction stir butt welding of 25.4 mm thick 7175-T79 aluminum alloy

This study presents the first experimental demonstration of high-speed friction stir butt welding of 25.4 mm thick AA7175-T79 aluminum alloy. The utilization of friction stir welding (FSW) tool pin threads that terminate away from the shoulder region reduced stress concentration during tool traversing. This tool design enabled a welding speed above 500 mm/min and a penetration depth greater than 10 mm without pin fracture near the shoulder. Two types of welds were performed: one-sided with full penetration and double-sided with partial penetration of the plate thickness. The junction of the double-sided friction stir welding (FSW) exhibited significant grain refinement (grain size 1.3 ± 0.8 μm) compared to other regions. Cross-weld tensile testing revealed high local strains at the double-sided FSW junction, which improved the yield strength by 20–24% compared to slower one-sided FSW. The joint efficiency of the as-welded, high-speed double-sided FSW was approximately 76% of the base material's ultimate tensile strength.

Improving joint performance of friction stir welded AZ31/ AM60 dissimilar Mg alloys by double-sided welding

Two types of welding processes，with double-side friction stir welding (DS-FSW) and single-side friction stir welding (SS-FSW)，were used for dissimilar welding between AM60 and AZ31 Mg alloys in this study. The evolution of texture and microstructure, deformation behavior and mechanical properties of both joints were investigated. The microstructure observation indicated that the microstructure of the joint nugget zone (NZ) under both processes was refined after welding and their grain size was relatively close. The two joints exhibited approximately symmetrical local strong texture distribution characteristics from the advancing side to the retreating side. However, the DS-FSW joint had a larger processing volume and a symmetrical macroscopic weld structure. Due to the symmetry distribution characteristics of texture in NZ, the Schmidt factors for basal slip of the joints from the vicinity of the NZ side to the NZ center showed a decreasing trend, resulting in severe strain localization in both DS-FSW and SS-FSW joints during the tensile process. The tensile tests revealed that the DS-FSW joint exhibited excellent mechanical.properties compared with the SS-FSW joint. This was attributed to its large processing volume, lower volume proportion of the stirring zone and symmetrically distributed weld zone structure improved the deformation coordination of the joint, thereby delaying its premature fracture and exhibiting better mechanical properties.

A comparative study of microstructure and mechanical properties of conventional and synergistic double-sided FSW joints of 6061 zxaluminium alloy

In this study, synergistic double-sided friction stir welding (DS-FSW) is proposed to solve the problems of large deformation and the time-consuming of traditional DS-FSW. The microstructure, mechanical properties, and fracture paths of novel and conventional joints are studied under different welding parameters. Results show that defects in novel joints have been improved. However, the grain size in the stir zone of novel joints is larger than that of conventional joints. The microhardness map of the novel joint shows a more uniform distribution compared to that of the conventional joint. At a rotational speed of 1800 rpm and transverse speed of 1000 mm min−1, the distortion of the novel joint and conventional joint is 0.1 and 1 mm, respectively. The tensile force of novel joints is higher than that of conventional joints for the same welding parameters. The maximum tensile force of novel and conventional joints is 36.8 and 34.9 kN, respectively.

Apparatus Design of One-Step Double-Side Friction Stir Welding for Aluminum Plates

Aluminum alloys emerged as one of the materials used in manufacturing automotive car bodies due to their advantageous properties such as high strength-to-weight ratio, relatively low cost, high ductility, and high corrosion resistance. However, joining aluminum alloys using fusion welding poses serious problems due to the high solubility of hydrogen gas, which causes porosity in welding metal. Subsequently, solid-state welding, such as friction stir welding (FSW), has been considered a porosity-free aluminum joining method. However, the method has limitations, such as low flexibility and the need for a complex clamping system. It is particularly problematic when welding plates. It causes the welding process to be carried out twice on opposite sides, resulting in longer production times. This study designed and assembled a one-step double-side FSW apparatus to address this challenge and conducted welding trials with various welding parameters. During the welding trial, the upper and lower tool rotation varied at 900/900 rpm and 1500/1500 rpm. As a result, one-step double-side FSW was successfully used for welding 6 mm aluminum without any porosity defects. Faster tool rotation results in a wider heat-affected area and higher tensile strength. In addition, the hard test showed that the one-step double-side FSW process had a lower hardness compared to the hardness of the base metal.

Effect of exfoliation corrosion on the efficient hybrid joint of AA2024-T3 and AA2198-T8 formed by friction stir welding

The third-generation alloy, AA2198-T8, is highly recommended for the aerospace industry. However, it has come under scrutiny due to its high cost. This study aims to decrease the cost of manufacturing through a hybrid design that uses AA2198-T8 alloys for the crucial parts and AA2024-T3 alloys for the remaining structure. The two main techniques for joining AA2024-T3 to AA2198-T8 are reversed double-sided friction stir welding (DS-FSW) and traditional single-sided friction welding (SS-FSW). They were carried out under unaltered tool rotation speed followed by five different welding speeds. The mechanical properties of the joints were explored, and the maximum joining efficiency of the welding process was 96% for reversed DS-FSW at 102 mm/min welding speed. The hybrid joint was tested for compliance with ASTM G34 standards to examine the welding joint's exfoliation corrosion (EXCO) for eight exposure times. The findings showed that joint efficiency decreased relative to as-welded joints, and mechanical property deterioration increased with EXCO exposure duration, reaching 40% for specimens exposed for 120 h to the corroding solution. It has been noted that morphology and grain size changes significantly impact EXCO.

Optimizing the shoulder diameter for double side friction stir welding of medium-thick TC4/AA2024 dissimilar alloys by Taguchi optimization technique

Optimizing the shoulder diameter for double side friction stir welding of medium-thick TC4/AA2024 dissimilar alloys by Taguchi optimization technique

Enhancing the mechanical performance of medium-thick Ti/Al dissimilar joints by an innovative double side friction stir Z shape butt-lap welding process

An innovative double-side friction stir Z shape butt-lap welding (DS-FSZW) process was proposed for welding medium-thick Ti/Al dissimilar metals. It suggests that the DS-FSZW joint eliminates the weak bonding zone and adds a lap joining surface compared to the traditional double side friction stir welding (DS-FSW) joint. The DS-FSZW joint also forms a thinner IMCs layer between the Ti/Al interface, and this increases the effective bonding strength of the interface. In addition, the DS-FSZW reduces the axial force during the DS-FSW of the second-side weld. The tensile strength of the DS-FSZW joint is 313 MPa, reaching about 70% of the AA2024-T4, which is increased by more than 18% compared to the DS-FSW joint. This indicates that the innovative DS-FSZW enhances the joint performance.

Double-sided friction stir welding of Nitronic-40 stainless steel for application in tokamak devices

Nitrogen containing austenitic stainless steels (N-ASS) are widely utilized to fabricate various structural components in tokamak type fusion reactors owing to their suitable mechanical and functional properties. These components are exposed to a range of temperatures (4–500 K) and interact closely with the magnetic fields that are used to control and contain the plasma within the tokamak systems. Nitronic-40 (N40) or XM-11 stainless steel is one such N-ASS used for fabricating structural components in the magnetic and vacuum vessel systems in tokamak devices. Fabrication of most of the larger components in the magnetic and vacuum vessel systems typically involves some type of fusion-based welding process. This study presents a double-sided friction stir welding (FSW) approach as an alternative to fusion welding processes to join 12 mm thick N40 plates to obtain joints with a low fraction of δ ferrite (a detrimental ferromagnetic phase), high joint efficiency, no sensitization and loss of hardness in the heat affected zone, and minimal nitrogen desorption from the weld nugget. The double-sided FSW approach yielded superior weldments when compared to similar joints accomplished by fusion welding for application in tokamak devices.

An Experimental Study On Friction Stir Welding Of Aluminum-Magnesium Alloys For Improved Mechanical Properties Of Tailor Welded Blanks.

Tailor welded blanks (TWB) are used in automotive and aerospace industries as they offer weight saving followed by cost saving and improved fuel economy. Being light in weight and having low cost, Aluminum alloys have piqued the interest of scientists. Friction Stir Welding (FSW) is a well-known accepted technique used since 1991 worldwide for Aluminum and its alloys. Due to friction stir welding, mechanical changes occur due to stirring action at the joint. Also the inter-metallic compounds, kissing bond formation, onion ring formation etc. are defects encountered in the nugget zone of welding. Hence, a novel technique is suggested to carry out the friction stir welding using a blend of techniques viz. double sided friction stir welding and multi objective optimization of process parameters. For experimentation, AA 5182 and AA 5754-Aluminum Magnesium alloys of 5000 series are used with sheet size of 1.5 mm thickness. Experimentation was carried out on a vertical machining center, with circular, square, and triangular tool pin profiles with a tool rotational speed range between 1500 -1800 rpm and a welding speed range of 40 mm/min.-60 mm/min. For the analysis purpose, L9 orthogonal array was used and Grey Relational Analysis(GRA) was employed and ASTM standards were used for tensile testing. Base sample materials of AA 5182 and AA5754 are having ultimate tensile strengths of 289.58 N/mm2 and 220.75N/mm2respectively. The designed welded blank of the two materials recorded maximum ultimate tensile strength of 268.11N/mm2which was remarkable for FSW. Welded joint efficiency was found to be 92.73% and percentage elongation of TWB was found to be 44% as compared to the base metals.

Friction Stir Welding of Non-Heat Treatable Al Alloys: Challenges and Improvements Opportunities

Friction stir welding (FSW) is an effective solid-state joining process that has the potential to overcome common problems correlated with conventional fusion welding processes. FSW is used for the joining of metallic materials, in particular Al alloys (non-heat-treatable and heat-treatable). The heat produced by the friction between the rotating tool and the workpiece material generates a softened region near the FSW tool. Although the heat input plays a crucial role in producing a defect-free weld metal, it is a serious concern in the FSW of work-hardened non-heat-treatable Al alloys. In this group of alloys, the mechanical properties, including hardness, tensile properties, and fatigue life, are adversely affected by the softening effect because of grain growth and reduced dislocation density. Considering this challenge, work-hardened Al alloys have been limited in their industrial use, which includes aerospace, shipbuilding, automotive, and railway industries. The current comprehensive review presents the various approaches of available studies for improving the quality of FSW joints and expanding their use. First, the optimization of welding parameters, including the tool rotational and traverse speeds, tool design, plunge depth, and the tilt angle is discussed. Second, the incorporation of reinforcement particles and then underwater FSW are stated as other effective strategies to strengthen the joint. Finally, some supplementary techniques containing surface modification, bobbin tool FSW, copper backing, and double-sided FSW in relation to strain-hardened Al alloys are considered.