Hot deformation behavior and microstructure evolution of as-cast AZ91D magnesium alloy without pre-homogenization treatment

The deformation behavior and the microstructure evolution of as-cast AZ91D magnesium alloy without pre-homogenization treatment were systematically investigated. The flow stress behavior was studied by compression tests in strain rate range of 0.001–1.000 s⁻¹ and deformation temperature range of 220–380 °C with a maximum deformation strain of 60 %. The dependence of flow stress on deformation temperature and strain rate was described by hyperbolic sine constitutive equation. Through regression analysis, the average apparent activation energy and coefficient of strain rate sensitivity were estimated to be 181.98 kJ·mol⁻¹ and 0.14, respectively. The results also reveal that the variation of peak stress depends on strain rate and deformation temperature. Microstructure observation shows that, at temperatures higher than 300 °C and strain rates lower than 0.01 s⁻¹, DRX developed extensively at the grain boundaries and in the core of coarse grains, resulting in a more homogeneous microstructure. Furthermore, the effects of strain, deformation temperature, strain rate, and eutectic β phase on the microstructure evolution of as-cast AZ91D magnesium alloy were discussed.