Compressive deformation behavior of Mg-Zn-Ca alloy at elevated temperature

The compressive deformation behavior at elevated temperature of the as-extruded and as-ECAPed Mg-5.3Zn-0.6Ca (wt%) alloys was investigated in the current study. The flow stress in the as-ECAPed alloy was lower than that of the as-extruded alloy when the compressive temperature was above 200 °C, due to the grain boundary softening effect. The strain rate sensitivity (SRS) was remarkably enhanced with the decrease of grain size or the increase of test temperature, and the corresponding m-value was calculated as 0.06-0.13, which indicated that the deformation was mainly dominated by the climb-controlled dislocation creep. Furthermore, the grain boundary sliding (GBS) mechanism might also be activated, which contributed to the higher SRS in the as-ECAPed alloy. The true deformation activation energy (Q') modified by threshold stress was calculated as 92-98 and 70-76 kJ/mol in the as-extruded and as-ECAPed alloy, respectively, which was close to the activation energy for grain boundary diffusion, and the lower Q'-value in the as-ECAPed alloy might be derived from the non-equilibrium grain boundaries.