A viscoplastic self-consistent analysis of tensile anisotropy and tension-compression asymmetry in rare-earth magnesium alloy

Abstract

The anisotropy and tension-compression asymmetry of rare-earth magnesium (Mg-RE) alloys have attracted significant attention. In this study, the room-temperature tensile anisotropy and tension-compression asymmetry of the extruded Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy were investigated utilizing techniques such as optical microscopy (OM), electron backscatter diffraction (EBSD), and viscoplastic self-consistent (VPSC) modeling. Among the tensile samples, the T0 sample (with axis parallel to extrusion direction) exhibits the greatest tensile yield strength (TYS) of 270 MPa and ultimate tensile strength (UTS) of 336 MPa, the T45 sample (with axis inclined at a 45° angle to extrusion direction) and T90 sample (with axis perpendicular to extrusion direction) exhibit lower TYS and UTS. The C0 sample shows a slightly greater compressive yield strength (CYS) of 290 MPa. The ratio of TYS/CYS is approximately 1.07. This study significantly adjusts the VPSC hardening parameters through the Schmid factor of deformation mechanisms in Mg-RE alloy, particularly increasing the τ0 (critical resolved shear stress, CRSS) and τ1 values for basal <a> slip and {10-12} twinning. The ratios of CRSS for other deformation mechanisms to basal <a> slip are approximately as follows: CRSSTwin/CRSSBas = 2, CRSSPri/CRSSBas ≈ 2.7 and CRSSPyr/CRSSBas ≈ 3.3, while these ratios in traditional alloys are generally higher. The stress-strain curves and pole figures obtained from the modified VPSC model demonstrate excellent agreement with experimental results. According to the VPSC simulation results, the primary factor contributing to tensile anisotropy is the disparity in the activation levels of slip systems. The inclusion of rare-earth elements mitigates the tension-compression asymmetry by reducing the difference of CRSS between different deformation mechanisms.