Tension-compression asymmetry in hot-rolled Mg-3wt%Gd alloy under creep loading

Abstract

Creep stress including tensile loading and compressive loading was carried out on hot-rolled Mg-3wt%Gd alloy at 473 K along the rolling direction (RD) and the normal direction (ND) separately. For briefness, T-RD was applied to representing the sample under tensile creep loading along the RD. The other three samples were named C-RD, T-ND and C-ND, respectively. The results of creep tests showed an obvious tension-compression asymmetry along both the RD and the ND. Twinning deteriorated the creep resistance of the C-RD and the T-ND samples, and caused the resultant asymmetrical behavior. The T-RD sample had the best creep resistance, followed by the C-ND sample, and the last two samples with similarly poor creep resistance were the C-RD and the T-ND. During creep loading, the T-RD sample was controlled by cross-slip containing a-dislocations. The C-ND sample were dominated by basal slip and pyramidal <c+a> slip. Both the C-RD and the T-ND samples were dominated by cross-slip and twinning. Furthermore, compared to the asymmetrical behavior along the RD, pyramidal <c+a> slip in the C-ND sample weakened the asymmetrical behavior along the ND. However, basal slip deteriorated the creep resistance of the C-ND sample. Therefore, future researches for developing dilute Mg-RE based alloys with high creep resistance should be inducing pyramidal <c+a> slip, inhibiting twinning and impairing basal slip.