Microstructure evolution and fracture behavior in superplastic deformation of hot-rolled AZ31 Mg alloy

Fine-grained AZ31 magnesium alloy sheets were prepared through hot rolling process. The super-plastic deformation behavior of hot-rolled AZ31 magnesium alloy was investigated at a temperature range 250 - 450°C and an initial strain rate range 0.7 × 10^-3 - 1.4 × 10^-1 s^-1. Optical microscope and scanning electronic microscope (SEM) were employed to observe the microstructure evolution and fracture behavior in superplastic deformation of AZ31 Mg alloy and the values of deformation activation energy at various temperatures were calculated. It is shown that the hot-rolled AZ31 Mg alloy begins to exhibit superplasticity from 300°C and the maximum elongation of 362.5% is obtained at 400°C and an initial strain rate of 0.7 × 10^-3 s^-1. In the temperature range 300 - 400°C for super-plastic deformation of AZ31 Mg alloy, the predominate deformation mechanism is grain boundary sliding (GBS) controlled by grain boundary diffusion and the influences of strain rates and temperatures on the fracture behavior of AZ31 Mg alloy are embodied by the transformation of deformation mechanism from intracrystalline slip to GBS.