Hot deformation behavior and processing map of as-cast AZ61 magnesium alloy

Isothermal compression tests were performed to investigate the hot deformation behavior of as-cast AZ61 magnesium alloy. True stress–true strain curves were obtained for deformation at temperature from 220 to 380 °C with the strain rate range from 10−3 to 1 s−1. Based on the flow stress data, the processing map at a strain of 0.6 for AZ61 magnesium alloy was developed using the dynamic materials model (DMM) theory. The processing map was found to be characterized by three dynamic recrystallization (DRX) domains. The values of apparent activation energy for domains I and II, falling in the low strain rate regime, were estimated to be 200 and 178 kJ/mol, respectively, suggesting that the cross-slip of screw dislocations may be the rate controlling process. At higher strain rates in domain III, dislocation climb is considered to be the rate controlling mechanism with the apparent activation energy being estimated as 152 kJ/mol. Furthermore, both the mechanisms for DRX and the deformation/microstructure stability in three domains were discussed with reference to the characteristics of the stress–strain curves and the processing map.