In-situ analysis of microscopic plastic and failure behaviors of extruded magnesium alloy

Abstract

The microscopic plastic and failure behaviors of a hot-extruded magnesium alloy sheet under uniaxial tension along extrusion direction (ED) was studied by in-situ scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) techniques. Schmid factor (SF) and slip/twinning trace were analyzed to investigate the activities of various deformation modes. Basal and non-basal slips were found to be the dominated deformation modes, while both {101¯2} extension and {101¯1} contraction twinning contributed to the plastic deformation as a complementary. Basal slip and extension twinning with low SFs were also activated to help achieve strain-compatibility. Moreover, the relation between contraction twinning and cracks was focused on through the examination of traces and fracture surface. Isolated contraction twins were nucleated in the grains belonging to the ND component, acting as potential sites for the nucleation of local cracks. However, grains with c-axis inclined away from ND were free of cracks in spite of contraction twins nucleated inside. Either accompanied slip/twinning modes or adequate contraction twin lamellas in these grains can act as mechanisms of plastic relaxation and deformation homogenization, helping prevent premature failure. It can be further inferred that weakening basal texture should improve the formability of magnesium alloys.