HOT DEFMATION BEHAVIOR AND HOT WORKABILITY OF Mg-Zn-Zr-Ce Alloy

The hot deformation behavior of the T4-treated Mg-6Zn-0.5Zr-0.5Ce alloy was investigated by compressive test using Gleeble 3800 thermal-simulator in the temperature range of 523-673 K and strain rate range of 0.001-1.0 s(-1). The results show that the flow stress is significantly affected by both deformation temperature and strain rate. The flow stress increases with either decreasing deformation temperature or increasing strain rate. The flow stress value tends to be constant after a peak value appearing at high deformation temperature and low strain rate. In the present work, the average activation energy for the hot deformation has been determinded to be 145.76 kJ/mol using the hyperbolic sine constitutive equation. A feed-forward back-propagation artificial neural network (ANN) has been established and used to investigate the flow behaviors of the alloy. The predicted data by the ANN is in good agreement with the experimental ones. Combing microstructure observation, the processing map for this alloy established on the basis of a dynamic material model indicates that the dynamic recrystallization (DRX) would take place in the range of 648-673 K and 0.1-1.0 s(-1), while under the same strain rate the flow instability would occur due to mechanical twinning when the temperature below 573 K. The formation of interfaces depends on the process of mechanical recovery caused by cross slip of screw dislocations. The DRX model indicates that DRX of this alloy is controlled by interface migration.