Study on the mechanism of dilute Mn addition in enhancing the creep resistance of hot-rolled Mg-1.5Y alloy sheet

Abstract

In this work, the compressive creep behaviors of Mg-1.5 wt%Y (0Mn alloy) and Mg-1.5 wt%Y-1wt.%Mn (1Mn alloy) were investigated. The compressive creep tests were performed along the rolling direction (RD), transverse direction (TD) and normal direction (ND) at 523 K under applied stresses ranging from 30 MPa to 80 MPa. It was shown that the 1Mn alloy exhibited a much higher creep resistance than the 0Mn alloy when crept along the same direction. The microstructure characterization indicated that the addition of dilute Mn barely changed the creep mechanisms crept along the RD and TD, including the dislocation cross-slip composed of basal <a > dislocations and prismatic <a > dislocations and {101‾2} twinning in both alloys. While the creep mechanisms crept along the ND changed from dislocation climb and pyramidal <c + a > slip in the 0Mn alloy to dislocation cross-slip and pyramidal <c + a > slip in the 1Mn alloy. The creep resistance enhancement by dilute Mn addition was closely related to the dynamic precipitation of α-Mn particles that strongly hindered the mobilities of dislocations and grain boundaries regardless of the loading direction. Moreover, the Mn atoms tended to segregate on the dislocations during creep, which effectively suppressed the continuous movement of dislocations and led to the excellent creep resistance of the 1Mn alloy. With increasing applied stress, the increased twin amounts crept along the RD and TD were responsible for the strong creep anisotropy in both alloys. Nevertheless, the dynamic precipitation of α-Mn particles evidently inhibited the thickening of twins, which was beneficial for the enhanced creep resistance and decreased creep anisotropy in the 1Mn alloy.