The Effect of Icosahedral Phase on Dynamic Recrystallization Evolution and Hot Workability of Mg-2.0Zn-0.3Zr-0.2Y Alloy

Abstract

The effect of Icosahedral phase (I-phase) on hot deformation behavior, dynamic recrystallization (DRX) evolution, and hot workability of Mg-2.0Zn-0.3Zr-0.2Y alloy has been investigated in the temperature range of 300-500 °C and strain rate range of 0.001-1 s−1 using Gleeble 3500D thermo-mechanical simulator. Based on regression analysis for Arrhenius-type equation of flow behavior, the average activation energy of deformation was determined as Q = 277.8 kJ/mol. The model of DRX evolution is \( \mathop X\nolimits_{\text{DRX}} = 1 - \exp [ - 1.8082(\frac{{\upvarepsilon - \upvarepsilon_{c} }}{{\upvarepsilon^{*} }})^{1.7904} ] \). The DRX model agreed well with the microstructure evolution of the alloy at all deformation conditions. At lower strain rates (0.001-0.01 s−1), continuous DRX (CDRX) is the main DRX mechanism that occurred near the original grain boundaries. Twin-dynamic recrystallization (TDRX) began to occur at lower deformation temperatures and higher strain rates (0.1-1 s−1). At a deformation temperature range of 250 to 350 °C and a strain rate of 1 s−1, the main DRX mechanism is TDRX, and the density of twins decreased, and CDRX began to occur near the original grain boundaries. When the deformation temperature increased to 400 °C, TDRX disappeared and CDRX occurred near original grain boundaries and I-phase particles. According to the flow stress behavior and DRX model, the processing maps have exhibited the optimum deformation conditions to be 450 °C and the strain rate range of 0.01-0.001 s−1.