A Review on Friction Stir Welding and Processing Techniques for Lightweight and High-Strength Alloys

Friction Stir Welding (FSW) and Friction Stir Processing (FSP) are solid-state joining and microstructure modification techniques that have revolutionized the welding of lightweight and high-strength materials, particularly aluminum, magnesium, and titanium alloys. This review comprehensively examines the fundamental principles, process parameters, tool geometries, material flow mechanisms, and microstructural evolution in FSW/FSP. Key factors such as heat generation, tool rotation speed, traverse speed, plunge depth, and tilt angle are critically analyzed for their influence on weld quality. The study highlights the significance of tool design (shoulder profiles, pin shapes, and materials) in optimizing joint integrity and mechanical properties. Furthermore, the distinct microstructural zones—weld nugget zone (WNZ), thermo-mechanically affected zone (TMAZ), and heat-affected zone (HAZ)—are discussed in relation to their impact on hardness, tensile strength, and fatigue resistance. The paper also explores advancements in dissimilar material joining, metal matrix composite fabrication, and industrial applications in aerospace, automotive, and marine sectors. By addressing challenges such as tool wear and process optimization, this review provides insights into future directions for enhancing FSW/FSP efficiency and expanding its applicability to high-melting-point materials like steels and titanium alloys