A comprehensive analysis on microstructure evolution of Mg-5.65Zn-0.66Zr alloy during hot deformation

Abstract

The microstructure evolution of Mg-5.65Zn-0.66Zr (wt.%) alloy was studied based on the hot compression tests. The results indicated that the flow stress increased rapidly to a peak point at the initial stage, and then it gradually decreased. Moreover, high temperature and low strain rate resulted in the decreasing of flow stress. All samples exhibited a necklace grain structure because of the occurrence of partial dynamic recrystallization (DRX). High temperature increased both the size and fraction of DRXed grains, while high strain rate showed an opposite tendency. At the conditions of 350 °C/0.001 s−1 and 350 °C/0.1 s−1, the twins were not exhibited and DRX played a dominant role. Importantly, the obvious split of basal texture was observed. The pyramidal <c+a> slip with high value of Schmid factor was active in large deformed grains, which corresponded to the peak split point in (0001) pole figure. A mechanism about the grain rotation was proposed to explain the relationship between the pyramidal slip and the split of basal texture. Finally, it was found that large number of {10–12} extension twins were formed during the initial stage at condition of 300 °C/1 s−1, and the number of twins decreased with the increase of strain. The twins greatly contributed to the fast formation of basal texture and grain rotation. Moreover, the non-basal slips were active in twining region, which could facilitate the nucleation of DRX.