Tool geometry–driven microstructure, mechanical, and wear performance of TiC-reinforced AZ31 surface composites fabricated by friction stir processing

Magnesium alloys are promising for lightweight structural and tribological applications, but their low hardness and poor wear resistance limit performance. Friction stir processing (FSP) offers an effective route to develop particle-reinforced surface composites. In this study, AZ31 magnesium alloy was reinforced with 10 wt.% TiC using FSP with four tool pin geometries: square, hexagonal, tapered, and threaded, to evaluate their influence on material flow, microstructure, and properties. Significant grain refinement occurred in the stir zone due to dynamic recrystallization and particle pinning, with the threaded pin producing the finest grain size (18.2 µm). This resulted in the highest microhardness (113.36 HV) and superior tensile properties, achieving an ultimate tensile strength of 307.6 MPa and elongation of 0.105. Tribological results showed that the threaded pin composite exhibited the lowest wear rate of 1.9 × 10−4 g/m under a 10 N load. The enhanced performance is attributed to improved material flow and uniform TiC dispersion induced by the threaded geometry. Overall, the threaded pin configuration is most effective for producing high-strength, wear-resistant AZ31/TiC surface composites for lightweight tribological applications.