In situ analysis of the tensile and tensile-creep deformation mechanisms in rolled AZ31

A rolled AZ31 alloy was tensile tested in a scanning electron microscope at 323 K (50 °C), 423 K (150 °C), and 523 K (250 °C) in order to analyze the deformation mechanisms in situ. Electron backscatter diffraction was performed both before and after straining. There was a significant difference in the activity of the various deformation modes at the three test temperatures and the mechanical anisotropy was considerably reduced with temperature. At 323 K (50 °C) extension twinning, basal, prismatic 〈a〉, and pyramidal 〈c+a〉 slip were active. Twinning disappeared above 323 K (50 °C), suggesting that the critical resolved shear stress (CRSS) of non-basal systems becomes less than that of twinning at T < 423 K (150 °C). Plasticity was controlled at high temperature by a combination of basal and prismatic 〈a〉 slip. From 423 K (150 °C) to 523 K (250 °C), a transition occurs in the dominant deformation mechanism from basal + prismatic 〈a〉 to mainly prismatic 〈a〉 slip. This is consistent with a decrease of the CRSS of non-basal slip systems with increasing temperature. These results suggest that the observed drop in normal anisotropy with increasing temperature is likely to be the consequence of an increase in non-basal slip activity. In situ tensile-creep experiments, performed at approximately the yield stress at 423 K (150 °C), indicated that less slip and more grain boundary cracking occurs during creep deformation compared with the higher-stress tensile experiments.