Roles of dislocation slip and twinning in the creep performance of a wrought Mg-Zn-Mn alloy sheet

Abstract

In this work, the tensile creep performance of a wrought Mg-1Zn-1Mn (wt%) alloy sheet with a strong basal texture was investigated based on the mechanism analysis relating to various dislocation slip and twinning activities. Tensile creep tests were conducted at 120 ℃∼180 ℃ along the extrusion direction (ED), transverse direction (TD) and normal direction (ND) under applied stresses ranging from 30 MPa to 90 MPa. The creep performance exhibited obvious dependence on loading direction, and the best creep resistance was obtained along the ED while the worst creep resistance was obtained along the ND. When crept along the ED and TD, the creep mechanisms were dislocation climb at 120 ℃, while dislocation cross-slip and pyramidal <c+a> slip were dominant at 150 ℃ and 180 ℃. When crept along the ND, the creep was constantly dominated by {101̅2} twinning, basal slip and dislocation cross-slip, which resulted in the unsatisfied creep resistance. With increasing temperature, the dislocation cross-slip along the ED and TD was active and the {101̅2} twinning along the ND was inhibited, leading to the decreased creep difference. In addition, the stress exponent and activation energy indicated that the dislocation slip was separately assisted by the pipe diffusion mechanism under low applied stresses and the lattice diffusion mechanism under high applied stresses regardless of loading direction. This investigation on the roles of dislocation slip and twinning activities in the creep difference of wrought Mg alloys sheet along different directions hopefully contributes to the fabrication of high-performance Mg alloys under various utilization conditions.