Microstructure and tribological properties of LPSO-structured Mg alloys processed through ultrasound assisted ECAP

Ultrasonic vibration-assisted processing technology is an advantageous method to improve processing efficiency and material performance, and has been widely applied to various alloys. This study systematically investigates the effects of ultrasonic vibration-assisted equal channel angular pressing (UVA-ECAP) on the microstructure and friction properties of Mg_98.5Zn_0.5Y₁ alloy. The study finds that the microstructure of the sample subjected to UVA-ECAP is more uniform and refined, with a grain size of approximately 10 μm. The introduction of ultrasonic vibration facilitates the dispersion of dislocations and promotes the thickening of twins, makes the formation of secondary twins more favorable. During the UVA-ECAP process, the bending angle of the long-period stacking ordered (LPSO) phase is gentler compared to that in conventional equal channel angular pressing (ECAP), which to some extent reduces stress concentration and improves the mechanical properties of the alloy. After UVA-ECAP, the yield stress of the alloy decreases, but its plasticity shows a certain degree of improvement, with an elongation rate of 16.6%. Additionally, the surface roughness of the specimens processed by ultrasonic vibration-assisted extrusion is lower than that of surfaces processed by conventional ECAP, resulting in improved surface finish. Compared to specimens without ultrasonic vibration, the alloy exhibits a friction coefficient of 0.2, which is reduced by 23% compared to conventional ECAP. The wear scar depth is 62 μm, representing an 11% reduction compared to conventional ECAP.