Analysis the effect of tool pin profile on elongation, macro-micro structure, thermal and mechanical characteristics of Friction stir welded  2050-T84-Al-Cu-Li alloy plates

This study explores the impact of various tool pin profiles—cylindrical, conical, threaded, non-threaded, and a novel hybrid (square + threaded)—on the elongation, macro/microstructure, thermal, and mechanical properties of friction stir welded (FSW) 2050- T84 Al-Cu-Li alloy plates. The results reveal that the tool pin profile significantly affects weld quality, particularly elongation and bead structure. The hybrid pin profile, at 1400 rpm and 4 mm/s, achieved the best performance with a tensile strength of 404.2 MPa, elongation of 7.56%, and joint efficiency of 76.4%. It generated the highest heat input (1180 KJ/m) with optimal flow characteristics and lower axial force. Localized heat at the tip (25 KJ/m) and pin side (330 KJ/m) promoted refined equiaxed grains in the nugget zone and elongated grains in the TMAZ. SEM analysis confirmed ductile fracture surfaces. This work provides valuable guidance for optimizing FSW tool design and process parameters to enhance weld quality.