Effect of multidirectional forging on microstructure and mechanical properties of micro-alloyed rare earth magnesium alloy

Abstract

In this work, the Mg-5Zn-1Gd-1Y (ZGW511) alloy was prepared and subjected to multidirectional forging (MDF) at 350 °C. The effects of cumulative strain on the microstructure, mechanical properties, work hardening and softening behavior of ZGW511 alloy were investigated. The results show that the Mg₂(Zn, Gd, Y) phase is precipitated in the grain at the initial stage of forging, and gradually changes from short rod to spherical W phase during the MDF forging process. With the increase of the cumulative strain, the W phase is refined and the deformation microstructure decreases, which weakens the promotion of DRX nucleation, but the DRX mechanism changes from DDRX mechanism to CDRX mechanism due to the gradual increase of DRX induced by cumulative strain. After MDF, the microstructure uniformity of ZGW511 alloy was significantly improved, the hardness difference was reduced, the ultimate tensile strength was increased from 196.77 MPa to 271 MPa, and the plasticity was increased from 7.7 % to 15.9 %, realizing the synergistic improvement of strength and plasticity. After MDF, the work hardening rate of ZGW511 alloy increases accompanied with the decrease of the softening rate in the early stage of deformation, both of which increase with the increasing cumulative strain. When the cumulative strain was increased from 2.4 to 4.8, the work hardening rate and softening rate decreased due to the increase of V_R/V_D (where, V_R is the volume occupied by DRXed grains and V_D is the volume occupied by deformed grains) value and the growth of DRXed grain.