Effect of tool rotational speed on thermal and mechanical behaviour in friction stir welding of AA6092/17.5 SiCp-T6 composites

This study investigates the FSW of AA6092 reinforced with 17.5% SiC p in T6 condition, focusing on the effect of TRS (1000 rpm to 1750 rpm) on the thermal profiles, force-torque behaviour, microstructure, and mechanical characteristics. The results reveal that peak temperature increases with TRS, reaching ∼487°C, while a reversal in temperature trend along the weld direction is observed at higher TRS. A distinct AS-RS asymmetry is noted, with higher temperatures consistently on the advancing side. Increasing TRS significantly reduced spindle torque (14.7 to 10.6 Nm) and axial force (9715 to 7126 N), indicating enhanced material softening. Microstructural analysis reveals particle fragmentation and grain refinement up to 1500 rpm, with minimum grain size of 9.16 µm and particle size of 6.86 µm, followed by coarsening at 1750 rpm. Tool wear debris (Fe-rich particles) and oxide-rich phases are observed at higher TRS. The welds exhibit a characteristic ‘W’-shaped hardness profile, with maximum hardness of 121 HV 0.1 at 1500 rpm. The highest tensile strength (358 MPa) and joint efficiency (87%) are achieved at this condition, while further increase in TRS leads to strength degradation (308 MPa). Fractographic analysis confirms predominantly ductile fracture with dimple features up to 1500 rpm, transitioning to mixed-mode fracture at 1750 rpm.