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

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A rolled AZ31 alloy was tensile tested in a scanning electron microscope at 323K (50°C), 423K (150°C), and 523K (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 323K (50°C) extension twinning, basal, prismatic 〈a〉, and pyramidal 〈c+a〉 slip were active. Twinning disappeared above 323K (50°C), suggesting that the critical resolved shear stress (CRSS) of non-basal systems becomes less than that of twinning at T<423K (150°C). Plasticity was controlled at high temperature by a combination of basal and prismatic 〈a〉 slip. From 423K (150°C) to 523K (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 423K (150°C), indicated that less slip and more grain boundary cracking occurs during creep deformation compared with the higher-stress tensile experiments.