Enhancing tribological properties via double-pass friction stir processing of novel Mg-Y-Nd-Zr/Ti/Al/Sn metal matrix composite

This comparative study investigates the effect of single-pass and double-pass friction stir processing on the tribological behaviour of Mg-Y-Nd-Zr based composite. A hybrid mixture of titanium, aluminium and tin powders in an equal atomic ratio was used as the reinforcement. A Si₃N₄ counter-body ball was used as the sliding material in the wear tests. The microstructural features evolved during single-pass FSP and double-pass FSP were analyzed and correlated with the tribological properties. Double-pass FSP led to a more homogenous distribution of reinforcement particles, particularly the uniform dispersion of Al/Ti particles, resulting in a substantial improvement in the wear resistance of the developed composite. Under dry sliding conditions, the coefficient of friction (COF) decreased by around 12.8 % and 10.5 % at applied loads of 15 N and 20 N, respectively, displaying notably better tribological characteristics compared to the base alloy. The average COF decreased from 0.145 (Mg-Y-Nd- Zr base alloy) to 0.126 in the double-pass friction stir processed (D-FSPed) composite. FESEM revealed that abrasive wear and delamination were the dominant mechanisms across all samples. Under lubricated conditions, all specimens exhibited significantly lower wear rate and COF values. Similar to dry sliding test, the D-FSPed specimen exhibited the lowest wear rate and COF, attributed to its refined microstructure and enhanced particle dispersion. The abrasive wear is corroborated by the material transfer from the developed composite on the surface of Si₃N₄ counter-body ball. The higher hardness and highly textured microstructure are the major contributors for the enhancement in wear resistance. This study demonstrates the potential of FSP in enhancing the wear performance and improving the service life of as-cast Mg alloys by developing metamaterial composites.