Optimization of hardness and wear behavior in AA6061/(Al2O3-TiC-MoS2) hybrid composites fabricated by friction stir processing

This study investigated the microstructure, hardness, and tribological properties of friction stir processed (FSPed) AA6061 aluminum alloy-based hybrid surface composites reinforced with various combinations of Al 2 O 3 , TiC, and MoS 2 particles. Three FSP passes were performed at a rotational speed of 950 rpm and a traverse speed of 30 mm min -1 . Microstructural characterization revealed pronounced grain refinement, relatively uniform particle dispersion, and extensive fragmentation of the reinforcing particles. In the C/(33Al 2 O 3 -33TiC-33MoS 2 ) composite, the average particle sizes of Al 2 O 3 , TiC, and MoS 2 decreased from 4.7, 16.9, and 11.9 μm (as-received powders) to 0.25, 0.41, and 0.48 μm, respectively. The maximum microhardness of 119 HV was obtained for C/(50Al 2 O 3 -50TiC), representing an approximately 27% increase relative to the base material (BM). The highest wear resistance was achieved by the C/(50Al 2 O 3 -50MoS 2 ) composite, with a volume loss of approximately 0.59 , corresponding to a decrease of about 62% compared with the BM. This improvement was attributed to the load-bearing and strengthening effects of Al 2 O 3 and the solid-lubricating effect of MoS 2 . The average friction coefficient (AFC) of this composite was approximately 30% lower than that of the FSPed alloy. The C/(33Al 2 O 3 -33TiC-33MoS 2 ) and C/(50Al 2 O 3 -25TiC-25MoS 2 ) composites exhibited the most balanced improvements, with hardness increases of at least 20% and volume-loss decrease of at least 40% compared with the BM. Examination of worn surfaces indicated a transition from severe plastic deformation (SPD), extensive delamination, and abrasive wear in the BM to mild delamination and abrasive wear in the C/(50Al 2 O 3 -25TiC-25MoS 2 ) composite.