Hot deformation behavior and microstructure evolution of ZK21 magnesium alloy

The hot compression deformation behavior and microstructure evolution of the homogenized ZK21 magnesium alloy were investigated in the temperature range of 250-400 °C and at the strain rate range of 0.1-50 s−1. The dynamic recrystallization (DRX) extent at the grain boundaries and twins played a determinant role on the hot workability of ZK21. At the lower temperature range (250-300 °C) and the lower strain rate (<1 s−1), DRX could hardly occur and microcracks emerged at the grain boundaries due to the large stress concentration. At the higher temperature (350-400 °C) and the lower strain rate (≤1 s−1), DRX developed mainly at the grain boundaries. At all the temperature range (250-400 °C) and the higher strain rate (≥10 s−1), DRX developed extensively at the grain boundaries and twins, resulting in a more homogeneous microstructure than the other conditions. The hot deformation characteristics of ZK21 exhibited an abnormal relationship with the strain rate, namely the hot workability increased with the strain rate increasing. However, the DRX grain size was almost the same with the temperature increasing at the strain rate of 10 s−1, while that increased obviously at the strain rate of 50 s−1. Therefore, hot deformation at the strain rate of 10 s−1 around and at the temperature range of 250-400 °C was desirable and feasible for the ZK21 alloy.