Loading-direction dependence of non-basal slip activity in a pre-twinned AZ31 magnesium alloy

Abstract

In Mg alloys, basal 〈a〉 dislocation slip is the preferential slip system that is activated at room temperature, while non-basal slips are typically difficult to activate owing to their high critical resolved shear stress. Until now, minimal focus has been directed towards the influence of loading direction on slip behavior in pre-twinned AZ31 (Mg-3Al-1Zn-0.3Mn, wt%) Mg alloys. This study employed transmission electron microscopy to demonstrate that non-basal 〈a〉 slips, specifically prismatic and pyramidal I slips, are activated under deformation conditions where de-twinning is difficult in a pre-twinned AZ31 Mg alloy. When the tensile loading direction is parallel to the precompression direction, de-twinning and basal 〈a〉 slip are the primary deformation modes. Conversely, when the tensile loading direction is perpendicular to the precompression direction, where de-twinning is challenging to activate, both basal 〈a〉 and non-basal 〈a〉 slips, such as prismatic and pyramidal I slips, emerge as the primary deformation modes. These results indicate that the pre-twinned AZ31 Mg alloy cannot deform solely through basal 〈a〉 slips, and the activation of either de-twinning or non-basal 〈a〉 slips is necessary to satisfy the von Mises criterion. Our findings in this study demonstrate the impact of non-basal slip activity on macroscopic yield stress and overall deformation, hence enhancing the understanding of magnesium alloy deformation mechanisms.