Improving the mechanical and tribological properties of AA2024/YSZ composites through tool design in friction stir processing

The surface composites of AA2024-T3 aluminum alloy were produced using friction stir processing (FSP), incorporating Yttria-Stabilized Zirconia (YSZ) particles, commercially known as Metco 204NS as reinforcement. The high hardness and thermal stability of YSZ enhanced the load-bearing capacity and tribological resistance of the composites. The tool pin configuration played a decisive role: using a protruding cylindrical pin (PCP) led to more uniform particle dissemination and reduced the mean grain size from ∼6.87 μm to ∼ 4.12 μm compared with a conventional cylindrical pin (CCP). The PCP-processed composites exhibited significant enhancements, including an ∼20 % increase in hardness (from 109 to 131 HV), a ∼27 % improvement in shear strength (from ∼145 to ∼186 MPa), and an ∼18 % reduction in wear rate (from 0.45 to 0.38 mm³/N·m) than CCP-processed composites. These improvements are attributed to the combined effects of reinforcement characteristics, refined microstructure, and stable tribolayer formation. The results highlight that the synergy between tool design and reinforcement addition is critical for tailoring high-performance aluminum matrix composites.