Dynamic mechanical response and microstructural evolution of extruded Mg AZ31B plate over a wide range of strain rates

Abstract

In this research, the mechanical behaviors of extruded AZ31B Mg plate along normal direction (ND) were investigated over a wide range of strain rates. High strain rate tests were carried out using a split Hopkinson pressure bar at room temperature. The corresponding deformation mechanisms, texture evolution and microstructure changes were analyzed by utilizing optical microscope (OM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). It is found that the mechanical responses exhibit both sigmoidal hardening and power-law hardening behaviors under compression at high strain rate ranges of 1068–5647 s−1. The prismatic type textures of the skin layer and center layer of the AZ31B plate determine its mechanical behaviors. The sigmoidal hardening behaviors are resulted from the formation and development of {10-12} extension twinning at the initial stage of deformation. Whereas the power-law hardening behaviors are resulted from non-basal 〈c+a〉 dislocation slip dominated the deformation at the initial deformation stage. Experimental results indicate the critical resolved shear stress (CRSS) for extension twinning and non-basal 〈c+a〉 dislocation slip are insensitive to strain rate, but the latter CRSS is significantly higher than the former CRSS. The flow stress is insensitive to strain rate if plastic deformation is dominated by extension twinning, while it increases with the increase of strain rate if plastic deformation is dominated by non-basal 〈c+a〉 dislocation slip. Dynamic recrystallization (DRX) took place if the AZ31B plate was compressed at strain ranges of 4737–5647 s−1, resulting in a decrease in flow stress and a significant increase in ductility.