Double-sided Friction Stir Welding Research Articles

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.

Morphology Study of the Corrosion Rate on Weld Joint of Double Side Friction Stir Welding Aluminum Alloy AA6061

DSFSW welding uses the rotating of a tool in the workpiece to create heat owing to friction between workpiece and tool to be connected. Corrosion is influenced by the presence of high heat owing to friction and a non-uniform cooling rate. The heat transforms the metal in the Heat Affected Zone (HAZ) and Weld Metal (WM) region, which can result in flaws such porosity, kissing bond, fractures, voids (from welding penetration), and flash as well as changes to the microstructure. Changes in the microstructure of welded joints can affect the resistance of welded joints to corrosion. The purpose of this study is to experimentally analyze the main causes of failure of AA6061 DSFSW joints based on welding temperature, weld defects, microstructure, corrosion rate and morphology of the corroded surface. Temperature testing using thermocouple to analyze the temperature, welding joint defects using DSLR camera and radiography test, microstructure using optical microscope, corrosion rate using AUTOLAB PGSTAT and morphology of corroded surface using SEM. The temperature analysis results show that the advancing side has a higher temperature than the retreating side, due to friction between the tool and base metal accompanied by the opposite welding direction. Visual inspection shows that all specimens and welding positions produce flash that is quite rough on the top (1G) and bottom (4G) surfaces and radiographic test results show incomplete fusion in 4 specimens. Microstructure shows a change in shape and size resulting in recrystallization in the form of fine grains. The highest corrosion rate is found in specimen B 1G welding position of 0.63856mm/year and the lowest corrosion rate in specimen A of 0.058567mm/year. SEM test results show the type of corrosion that occurs in DSFSW welding joints is pitting corrosion.

Improving tensile properties by varying the welding conditions of the passes of the double-sided friction stir welding of AZ31B magnesium alloy

Improving tensile properties by varying the welding conditions of the passes of the double-sided friction stir welding of AZ31B magnesium alloy

Double side friction stir welding effect on mechanical properties and corrosion rate of aluminum alloy AA6061

Friction Stir Welding (FSW) is a solid-state welding method that has diffusion and different metal structures can blend well. Friction stir welding (FSW) has a weakness, one of which is the lack of flexibility the welding process is only carried out on one side of the plate being welded, so it is not applied on thick materials. Double side friction stir welding is a double working process in which the plate to be welded is subjected to friction from two tools on opposite sides. In the DS-FSW welding process, the dimensions and geometry of the tool and pin greatly affect the quality of the joint. This study to determine the mechanical properties and corrosion rate of Double side friction stir welding aluminum 6061 with variation rotation speed and axis of top and bottom tools. The results of this radiographic test can be seen that specimen 4 welded with variations in speed and tool position has defects in the form of incomplete fusion (IF). The results of microstructural observations showed that the heat caused by the welding process resulted in recrystallization in the form of fine grains in the stirring area and there was no phase change. The highest hardness value in the welding area is specimen B. The largest bending value at the 1G welding positions is specimen D, which is 41.86 MPa with a strain value of 13.23%, while the smallest value at the 4G welding position is specimen A, which is 38.18 MPa with a strain value of 5.03%. The fracture and crack surfaces showed that crack initiation, propagation and material stirring failure occurred in all test specimens, even though the impact test specimen was cut in a small area of Incomplete Fusion, but the test results showed that there was still a surface of the parent metal that had not been stirred. The corrosion test method uses three electrode cells with corrosion media as a substitute for seawater with a salinity of 3.5% NaCl, result of corrosion test is specimen B at the 1G welding position has the highest corrosion rate value of 0.63856 mm/year and specimen An at the 1G welding position has the lowest corrosion rate of 0.058567 mm/year.

Microstructure and toughness of thick-gauge pipeline steel joint via double-sided friction stir welding combined with preheating

Microstructure and toughness of thick-gauge pipeline steel joint via double-sided friction stir welding combined with preheating