Twinning and dynamic recrystallization of Mg–7Sn–3Zn alloy under high strain rate hot compression

In this study, we investigate the twinning behavior and dynamic recrystallization (DRX) of Mg–7Sn–3Zn alloy under a high strain rate (10 s−1) during hot compression deformation. At a relatively low temperature (300 °C) and high strain rate (10 s−1), the preferential occurrence of multiple {101‾2} tension twin variant at the initial compressed stage is attributed to the Schmid factor (SF) criterion, and the following {101‾2} tension twin variants nucleate because of the geometric compatibility factor mʹ of the ortho-position twin pair. Because of the growth and interaction between the ortho-position {101‾2} tension twin pairs, the volume fraction of 60° boundaries evidently increases. Moreover, as the logarithmic strain increases, the volume fraction of {101‾2} tension twins and 60° boundaries significantly decreases, and a few {101‾1} compression twins and {101‾2}–{101‾1} double twins form. Then, twinning-induced dynamic recrystallization (TDRX) as a primary DRX mechanism occurs in {101‾1} compression twins and {101‾2}–{101‾1} double twins. These results indicate that at a high temperature (400 °C) and 10 s−1, certain {101‾2} tension twins form during the early stage compression in accordance with the SF criterion, and discontinuous DRX (DDRX) occurs along the original grain boundaries because of the higher deformation temperature, which increases the nucleation rate and promotes the migration of grain boundaries. With the accumulation of logarithmic strain, continuous DRX (CDRX) occurs. The recrystallization grains consume the twin boundaries, which causes the {101‾2} tension twins to merge. Under the same logarithmic strain, when the deformation temperature increases from 300 °C to 400 °C, the DRX process is significantly improved.