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The combination of aluminum and steel materials in hybrid structures shows promising applications in the automotive, marine, and aerospace sectors. The present study investigates how the tool–pin offset impacts the microstructural, mechanical, and electrochemical characteristics of friction stir-welded joints between dissimilar AA2024-T3 and SS304 materials. The optimum conditions were achieved at a tool rotation of 560 r/min, a traverse speed of 25 mm/min, and a tool–pin offset of 1 mm towards the Al side. Upon increasing the tool–pin offset to 1.5 mm, insufficient heat input resulted in inadequate plastic deformation and material flow, leading to the creation of flaws like voids, tunnels, and interfacial gaps. However, under optimal conditions, the joint exhibited a well-defined and serrated interface, with fine steel fragments securely embedded in the Al matrix. Additionally, thin intermetallic compounds were observed around the steel fragments within the Al matrix. This favorable combination resulted in enhanced tensile strength and increased ductility in the joint. The Vickers hardness test revealed that the stir zone exhibited the highest hardness values, primarily attributed to the ultra-refinement of grains. Furthermore, the potentiodynamic test revealed that the welded samples show improved corrosion resistance against the base material AA2024-T3, although BM-SS304 exhibited the highest corrosion resistance among all the samples, likely due to its higher chromium content. [ABSTRACT FROM AUTHOR]

With the elimination of solidification defects, friction stir welding becomes the most effective process for joining flat and curved surfaces. Tool geometry (tool pin profile, shoulder diameter) and tool rotation speed mainly contribute to the overall weld quality. The study evaluates the simultaneous effect of tool geometry, rotational speed, base offset and double pass Friction Stir Welding (DP-FSW) on the defect formation and the mechanical properties. Micro-structure and macro-structure have been analysed for weld strength and hardness characterisation, and found, at high tool rotation speed maximum hardness is achieved in the Stir Zone (SZ). A small tunnel present near the middle proved to be more detrimental than the large one at the bottom. Grain refinement in the SZ was 87.2% while augmentation in hardness was 21.3 HV. Maximum tensile strength of approximately 103% with decent bead profile is obtained, using taper cylindrical tool at 710 rpm with 14 mm shoulder diameter. Fractography of the fractured surface revealed a pure ductile failure. It has been discovered that with base offset the strength of the weld is increased. However, reduction of 4.8% was obtained with DP-FSW. Better weld profile gives better strength. With DP-FSW, a significant improvement in bead surface is obtained. [ABSTRACT FROM AUTHOR]

Aluminium matrix composites are one of the most important classes of materials and have become a major focus of attention in aerospace, aeronautical, defense, and automotive industries. Aluminium matrix composites when compared to conventional alloys offer various promising properties like excellent strength-to-weight ratio, higher stiffness, lower coefficient of thermal expansion, better dimensional stability, and tribological behavior. The properties of aluminium matrix composites are highly influenced by the appropriate selection of metal matrix, processing routes, and reinforcement. Various ceramic particles (oxides, carbides, nitrides, borides, etc.) are used as reinforcements for aluminium matrix composites. Significantly different properties may be obtained using various reinforced particles and matrix material, which makes it difficult for the traditional fusion welding techniques to meet the joining requirements of these composites and is restricted to certain grades of materials. Solid-state welding process offers greater advantages over the conventional fusion welding. As a solid-state joining process, friction stir welding has proven to be a better and promising technique for joining aluminium matrix composites. However, it is still subjected to various challenges to join aluminium matrix composites even with considerable progress has been made in recent years. The current review provides an overview of state-of-the-art of friction stir welding of aluminium matrix composite materials. Specific attention and critical assessment have been given to weldability, the macrostructure and microstructure of aluminium matrix composite joints, mechanical properties of joints, fractography, and the wear of friction stir welding tool during welding of aluminium matrix composite. Furthermore, the various existing challenges of friction stir welding of aluminium matrix composites are summarized and the recommendations for future research are proposed. [ABSTRACT FROM AUTHOR]