Vishvesh J. Badheka

A Review on Dissimilar Friction Stir Welding of Copper to Aluminum: Process, Properties, and Variants

Copper and aluminum materials are extensively used in different industries because of its great conductivities and corrosion resistant nature. It is important to join dissimilar materials such as copper and aluminum to permit maximum use of the special properties of both the materials. The joining of dissimilar materials is one of the most advanced topics, which researchers have found from last few years. Friction stir welding (FSW) technology is feasible to join dissimilar materials because of its solid state nature. Present article provides a comprehensive insight on dissimilar copper to aluminum materials joined by FSW technology. FSW parameters such as tool design, tool pin offset, rotational speed, welding speed, tool tilt angle, and position of workpiece material in fixture for dissimilar Cu–Al system are summarized in the present review article. Additionally, welding defects, microstructure, and intermetallic compound generation for Cu–Al FSW system have been also discussed in this article. Furthermore, the new developments and future scope of dissimilar Cu–Al FSW system have been addressed.

Effects of Tilt Angle on the Properties of Dissimilar Friction Stir Welding Copper to Aluminum

In the present investigation, dissimilar materials such as electrolytic tough pitch copper, and aluminum 6061-T651 were welded by friction stir welding technology. Effects of tool tilt angle on the mechanical and metallurgical properties were studied experimentally for dissimilar material systems. In the present study, the tool tilt angle was varied from 0° to 4° with an interval of 1°, while the other parameters such as rotational speed, welding speed, tool pin offset, and workpiece material position were kept constant. Macrostructure analysis, tensile test, macro hardness measurement, scanning electron microscopy, and energy dispersive x-ray spectrographic tests were performed to evaluate the weld properties of dissimilar copper–aluminum joints. The results revealed that a defect free dissimilar copper–aluminum friction stir welding was achieved by tilt angles 2°, 3°, and 4°. The maximum tensile strength was reported to be 117 MPa and the macro hardness was reported to be 181 VH (in the nugget zone) at a tilt angle of 4°. The macro hardness was increased as the tilt angle increases from 0° to 4°. In addition to this, the thermo-mechanically affected zone (at the copper side) was found to be the weakest zone for a dissimilar copper–aluminum friction stir welding system.

Influence of Friction Stir Processed Parameters on Superplasticity of Al-Zn-Mg-Cu Alloy

Friction stir processing (FSP) is a novel technique for refining the microstructure. In this study, the effect of FSP process parameters such as tool rotation, traverse speed and tool tilt on resulting grain size, microstructure and superplastic behavior of high-strength thick Al-Zn-Mg-Cu alloy is reported. The microstructure examination of the stir zone (SZ) was performed by optical as well as scanning electron microscope. Microstructure variation attributed to different process parameters is reflected in the SZ. It is observed that grain size increases with increasing tool rotation speed, and decreases with increasing traverse speed. However, tool tilt has no significant effect on grain size. Moreover, at higher tool tilt distorted grains were observed in microscopic images. The highest average value of hardness in the SZ is obtained for low heat input value corresponding to higher tool rotation and traverse speed. In this study, hardness has shown no dependency on the grain size of the SZ due to the strengthening of phase particles. Process parameter of 1500 rpm, 31.5 mm/min and 2° tool tilt (low heat input) only exhibited superplastic elongation of 225% at a superplastic condition of 400°C and 3 × 10−4 s−1 because of an appropriate material flow without any defect.

Friction Stir Processing as a Novel Technique to Achieve Superplasticity in Aluminum Alloys: Process Variables, Variants, and Applications

This article provides an overview of the potential for superplasticity of aluminum alloys using friction stir processing (FSP). FSP is a variant of friction stir welding (FSW), and FSP is an effective technique to alter the metallurgical and mechanical properties of the material, which results in superplastic properties at high strain rate and low temperature. This makes FSP as an attractive and cost-effective method to produce superplastic materials. A detailed summary of previously reported superplasticity in all aluminum alloys using FSP is tabulated in this review. It reveals the influence of tool design, machine variables, number of passes, active cooling, grain size, superplastic temperature, strain rate, and elongation on the superplastic properties of FSP aluminum alloys. Variants of FSP to achieve superplasticity at optimized conditions are proposed based on dual rotation of tool and additional cooing during the process. Applications of superplastic forming in aerospace and automotive are discussed. The direction of research in friction stir-processed superplasticity is covered in future scope.

Influence of tool pin design on properties of dissimilar copper to aluminum friction stir welding

Abstract Dissimilar friction stir welding (FSW) of copper and aluminum was investigated by nine different tool designs, while the rest of the process parameters were kept constant. Mechanical and metallurgical tests such as macrostructure, microstructure, tensile test, hardness, scanning electron microscope and electron X-ray spectrographs were performed to assess the properties of dissimilar joints. The results exhibited that, the maximum joint strength was achieved by the tool of cylindrical pin profile having 8 mm pin diameter. Besides, the fragmental defects increased as the number of polygonal edges decreased, hence the polygonal pin profiles were unsuitable for dissimilar FSW butt joints. Furthermore, the tensile strength increased as the number of polygonal edges increased. Stir zone of polygonal pin profiles was hard and brittle relative to cylindrical tool pin profiles for same shoulder surface. Maximum hardness of HV 283 was obtained at weld made by the polygonal square pin profile. The hard and brittle intermetallic compounds (IMCs) were prominently presented in the stir zone. Phases of IMCs such as CuAl, CuAl 2 , Cu 3 Al and Cu 9 Al 4 were presented in the stir zone of dissimilar Cu–Al joints.

Influence of heat input/multiple passes and post weld heat treatment on strength/electrochemical characteristics of friction stir weld joint

ABSTRACT The V-95 and D-19 precipitation hardened Russian aluminum alloys are widely used in the Russian aircraft industry and these alloys are not weldable by conventional fusion weld techniques. This paper intends to evaluate the effect of spindle and weld speed on joint strength characteristics of a single pass (SP) and double pass (DP) friction stir lap weld through a common heat index and to analyze the effect of retrogression and re-ageing treatment (RRA) on joint strength and corrosion characteristics. The strength characteristics were analyzed by welding and shear testing of specimens and corrosion susceptibility of joint through immersion in EXCO solution as per ASTM G34. The trials revealed that the joint strength of the welded alloy is inversely proportional to the heat index and the DP weld provided significantly higher strength than an SP weld. The heat affected zone of the joint was found most sensitized to corrosion. The RRA treatment was found to improve the strength of the joints welded with higher heat input while it slightly degraded the joint strength for low heat input welds. The corrosion characteristics of the welded joint is also significantly improved by the post weld RRA treatment.

Influence of Pin Profile on the Tool Plunge Stage in Friction Stir Processing of Al-Zn-Mg-Cu Alloy

Friction stir processing (FSP) is a solid state process for refining the microstructure. Though FSP has shown significant impact in manufacturing industry, a detailed investigation is needed for further development of the process. The current article presented an experimental investigation on tool plunge stage by using different pin profiles such as conical, square, pentagonal and hexagonal. Influence of pin profiles on the temperature distribution around the tool during plunge has been studied. Thermocouples were placed at two different locations around the tool in the workpiece of Al–Zn–Mg–Cu alloy and temperatures were measured simultaneously at both the locations. FSP tools with different pin profiles under same process parameters were used to study the effects of pin profile on the temperature of the workpiece. Temperature profile was found to be asymmetric around the tool. During plunging stage, it was observed that the temperature due to plastic deformation at pin was less than the temperature caused by friction on the workpiece. Compared to other pin profiles, pentagon pin generated more temperature during the plunging. Further, tool shoulder had significant influence on the workpiece temperature compared to tool pin.

Hybridization of filler wire in multi-pass gas metal arc welding of SA516 Gr70 carbon steel

ABSTRACT In the present investigation, multi-pass gas metal arc welding (GMAW) of SA516 Gr70 carbon steel was carried out by different filler wires such as solid, metal cored and flux cored, wherein, other process parameters were kept constant. The hybrid approach of multi-pass filler wires was applied to obtain three different welds. The root pass was filled by a solid wire for all three cases while the subsequent filler pass was applied through solid, flux-cored and metal cored filler wires, respectively. Metallographic, mechanical and metallurgical analyses such as macrograph study, optical microscopy, tensile testing and hardness variations were performed to address the quality of weld. The results revealed that defect-free sound welds were produced by the hybrid approach of different filler wires in multi-pass GMAW. Overall cost and time reduction can be achieved through hybrid filler welds, without affecting their mechanical strength. Angular distortion was reported minimum at hybrid weld of solid and metal cored filler wire. Maximum reinforcement with higher penetration was observed at weld of solid and metal cored filler wire. Impact toughness was reported higher in case of hybrid weld of solid and flux cored filler wire. Higher macro hardness was reported at weld of solid and flux cored filler wire.

Process parameters/material location affecting hooking in friction stir lap welding: Dissimilar aluminum alloys

ABSTRACT Influence of spindle and weld speeds, metal location, direction of spindle rotation, and tool pin length on hooking in lap FSW of dissimilar aluminum alloys and the effect of hook on tensile and fatigue weld strength was studied. Optical images of the cross-section of the specimen welded at different process parameters were analyzed. The results indicate that increased spindle speed, reduced weld speed, higher tool pin length, clockwise spindle rotation, and locating the stronger material at the bottom of the joint increased the size of the hooking defect. Higher weld speeds and very high spindle speeds resulted in lower hook size on the advancing side (AS) compared to the retreating side (RS) of the joint. Welding with low weld speed would result in higher advancing side hook size compared to the retreating side. Friction stir weld joints fabricated with anti-clockwise spindle rotation has been found to have extremely low hook both on the AS and the RS of the joint. The tensile and fatigue strengths of the weld joints and plates are degraded by the hook. The fatigue strength of welded alloys could be improved by a double pass weld, the second pass welded immediately adjacent to the first pass.

Friction stir welding of aluminium alloys: An overview of experimental findings – Process, variables, development and applications

The never ending appetite of the mankind to produce more and more competitive products results in continuous development of newer and newer manufacturing processes. One of such a kind, a solid state welding process highly appreciated for joining of a variety of aluminium and copper alloys, is friction stir welding. The process is also an accomplished method for joining dissimilar materials efficiently. The process finds its major application for joining hard-to-weld metals, especially the precipitation hardenable aluminium alloys and is widely adopted by industries for the welding of such aluminium alloys. However, the process has still not found an economical way for welding of steels and hence found limited applications in industries for welding steels. This paper aims at providing a comprehensive review of the work undertaken in the field of friction stir welding and provides an insight into the friction stir welding of aluminium alloys. The article pays critical attention and analytical evaluation of classification of aluminium alloys, friction stir welding process parameters, the mechanical testing and properties of the friction stir welding joints, macrostructure and microstructure evolution during friction stir welding, friction stir welding defects and industrial applications of the process. The friction stir welding process variants are discussed as well. Special accentuation has been given to (i) effect of friction stir welding parameters on the microstructure evolved and thus the ultimate mechanical properties (viz. tensile strength, hardness, fatigue strength, fracture toughness and residual stresses), (ii) the texture formation, microstructure refinement and the role of intermetallics. However, studies related to welding of dissimilar aluminium alloys, temperature, and heat transfer modeling and material flow are out of the scope of this paper. Finally, the directions of future research are examined.