Unveiling the microstructure evolution based on deformation mechanisms and dynamic recrystallization in as-extruded AZ31 Mg alloys during uniaxial compression

Abstract

A series of uniaxial compression experiments were carried out on the as-extruded AZ31 Mg alloy with<10–10>-<11–20>//ED (extrusion direction) double fiber texture at 200–350 ℃. The microstructure evolution during the work hardening and dynamic softening stages were systematically investigated based on deformation mechanisms and dynamic recrystallization (DRX), respectively. Experimental and simulation results demonstrated that in the work hardening stage, the dominant deformation mechanisms were the basal<a>slip and {10−12} twinning at 250 ℃, while the basal<a>slip and prismatic<a>slip 350 ℃. The appearance of profuse {10−12} twins at 250 ℃ not only effectively refined the microstructure but also quickly promoted the formation of strong<0001>//CD (compression direction) texture. Moreover, the activation of twin variants was mainly dependent on their own Schmid factor that was higher in<10–10>//CD grains, resulting in the earlier disappearance of the<10–10>//ED texture component than the<11–20>//ED texture component. In contrast, owing to the limited of {10−12} twins, the samples at 350 ℃ exhibited a weak fiber texture with diffusely distributed of basal plane along the CD. In the dynamic softening stage, high temperature increased both the grain size and proportion of DRXed grains, resulting in a more homogeneous microstructure. More importantly, the continuous DRX (CDRX) transformed into discontinuous DRX (DDRX) as the temperature increased from 250 °C to 350 °C. The similar orientation between the new CDRXed grains and parent grains at 250 ℃ preserved the strong<0001>//CD texture, while at 350 ℃ the basal texture was significantly weakened due to the random orientation DDRXed grains and higher activation of pyramidal<c + a>slip. These findings are beneficial for the optimization of the temperature range of the MDF process.