Microstructural evolution of AZ31 magnesium alloy after high strain rate expanding rings tests

The majority of the magnesium used in industrial applications is in the form of cast alloys, due to its low ductility. AZ31 is one of the most formable Mg alloys, exhibiting tensile elongation of 0.14. In the present work, expansion of rings was performed at a high strain rate and observed to enhance the elongation of the material. The strain before failure was 0.18 and the strain at failure increased up to 0.34. Increasing the strain rate increased the strain to failure. The enhanced strain ensued from intense deformation along the whole ring and from multiple necking. Immediately after expansion the material contained a high density of twins. The local twin density determined the rates of nucleation and growth of new grains. The recrystallized grain size depends on the strain rate and the proximity to a neck or a fracture. It was shown that the recrystallization occur after the deformation ended.