An internal variable approach to high temperature deformation and superplasticity of Mg alloys

High temperature deformation behavior of pure Mg and Mg alloys has been investigated within the framework of an internal variable theory for inelastic deformation. To this end, a series of load relaxation tests has been performed for pure Mg single and poly crystals as well as the AZ31 Mg alloys. At 623 K, pure Mg single crystal exhibited a transition in deformation mechanism from dislocation climb at lower strain rates to plastic deformation at higher rates, while the polycrystal showed only the plastic deformation. The AZ31Mg alloy with the fine grain size of d = 10 μm revealed both the grain boundary sliding and plastic deformation under suitable test conditions in terms of temperature and strain rate, while the coarse grain with d = 20 μm exhibited only the plastic deformation. From the constitutive analysis based on the internal variable theory, the role of grain size refinement and process temperature on superplasticity has been clarified precisely as a dividend of present approach.