Effect of friction stir processing on microstructural evolution and tribological behaviour of UASC AA2024–SiC composites

AA2024-SiC composites with SiC contents of 0,3,6,9, and 12 wt% were fabricated by ultrasonic-assisted stir casting (UASC) and then subjected to two passes of friction stir processing to examine the effects of processing on their microstructure, hardness, tensile, and wear performance. The as-cast composite exhibited a coarse dendritic microstructure, uneven particle distribution, and various casting defects. FSP significantly improved the microstructure by refining the grains through intense plastic deformation and dynamic recrystallization. FSP also increased hardness, raising it from 82.7 HV in the as-cast sample to 108.24 HV (∼30.9%). The highest hardness, ∼140.9 HV, was recorded for the 6 wt.% SiC composite. The 9 wt% SiC stir cast composite achieved the highest tensile and yield strengths of 158.85 MPa and 108.02 MPa, respectively. The wear behaviour showed a noticeable improvement in tribological performance after FSP; a wear rate (∼1.92 × 10−4 mm3/Nm) was observed in the FSPed 9 wt% SiC sample. Overall, the composite containing 6 wt% SiC exhibited the best hardness, whereas 9 wt% SiC exhibited the best tensile and wear characteristics owing to the combination of grain refinement, uniform reinforcement distribution, and enhanced interfacial bonding.