Recent Trends and Emerging Directions in Friction Stir Welding and Friction Stir-Based Technologies

Friction stir welding (FSW) is a solid-state joining technique widely recognized for producing high-quality joints with refined microstructures, low residual stresses, and minimal distortion, particularly in lightweight and high-strength materials. Since its invention by The Welding Institute in 1991, FSW has evolved into a broader class of friction stir welding-based technologies (FSWBTs), including friction stir processing (FSP), friction stir additive manufacturing (FSAM), friction stir spot welding, and various hybrid and assisted variants. Recent research has shifted from feasibility studies toward enhancing productivity, expanding material applicability, and enabling reliable industrial adoption. This review critically examines recent trends in FSW and FSWBTs, emphasizing advancements in process fundamentals, tool design innovations, and emerging process variants. Progress in joining advanced and dissimilar materials—such as steels, titanium alloys, metal matrix composites, and multi-material systems—is discussed, alongside challenges related to tool wear, intermetallic formation, and thermal management. Furthermore, developments in thermo-mechanical modeling, material-flow simulation, and microstructure–property correlation are highlighted, reflecting a transition toward science-based optimization. Recent integration of real-time process monitoring, sensor-based feedback, and data-driven approaches, including machine learning, is also reviewed. Finally, key challenges and future research directions toward intelligent, scalable solid-state manufacturing are identified.