On the diversity of the plastic response of magnesium in plane strain compression

Mg single crystals of selected 'hard' and 'soft' orientations were deformed at ambient temperature in channel-die compression. Specimens with a 'hard' basal starting orientation displayed a limited ductility and fractured along {112̅4} planes. Compression perpendicular to the c-axis of orientations well aligned for {101̅2} extension twinning revealed a very contrasting deformation behavior. Specimens compressed along the crystallographic 〈112̅0〉 direction exhibited an exceptionally high room temperature ductility, whereas compression along 〈101̅0〉 resulted in failure after an initial sigmoidal stress-strain response. In both cases {101̅2} extension twins were found to fully consume the matrix at low strains and convert the starting orientations into orientations corresponding to the respective high Schmid factor twin variants. High strains have also been attained for a prismatic starting orientation where the c-axis was constrained. In specimens, favorably oriented for basal slip, anomalous {101̅2} extension twins formed, clustered in bands parallel to the constraint direction. These twins produced a strain opposite to the imposed plane strain deformation and provided a pronounced dynamic grain boundary strengthening effect.