Effect of ultrasonic surface rolling process on microstructure, mechanical properties, and wear resistance of Mg-1.9Mn-0.3Ce alloy

Abstract

This study investigated the effects of ultrasonic surface rolling process (USRP) on the microstructure characteristics, mechanical properties, and wear behavior of Mg-1.9Mn-0.3Ce alloy. The results show that a typical gradient microstructure with refined grains and twins was formed in the cross-sectional plane of Mg-1.9Mn-0.3Ce alloy after USRP. As set pressure increases during USRP, the depth of the severe deformation (SD) layer, the density of twins and refined grains increase near the surface of samples. Significant enhancements in microhardness and yield strength were achieved, though ductility was slightly reduced due to a shift in the fracture mechanism in the SD layer. The enhanced yield strength of USRPed samples can be attributed to several mechanisms, including grain boundary strengthening, dislocation strengthening and twin strengthening. The results of friction and wear tests reveal that the wear resistance of samples is significantly improved after USRP. The friction coefficient and wear rate of USRPed samples decreased with increasing set pressure, which were related to the formation of the harder surface and the modified microstructure. As the set pressure increases to 0.3 MPa, the primary wear mechanism of worn surface transitioned from abrasion and delamination wear to fatigue wear, indicating a shift toward more stable wear behavior. The optimal balance of minimal surface roughness, superior mechanical properties, and improved wear resistance was achieved in Mg-1.9Mn-0.3Ce alloy after USRP with 0.2 MPa.