A statistical analysis of compressive deformation mechanisms in an extruded Mg–3Y sheet

Abstract

A statistical analysis of plastic deformation mechanisms was performed on an extruded Mg-3 wt%Y sheet during room temperature uniaxial compression along the extrusion direction. Grain-scale slip trace analysis and twin variant analysis were performed grain-by-grain to reveal the active slip/twinning systems based on quasi-in-situ SEM and EBSD. The initial microstructure was fully recrystallized exhibiting typical rare-earth texture characteristics. The true stress-true plastic strain curve showed a sigmoidal shape indicating a profuse twinning activity which was consistent with the twin analysis. After 10% strain, there were 78 out of ~700 grains exhibited slip trace. In addition to the dominated basal <a> slip (79.5%), considerable non-basal slips including 2nd pyramidal <c + a> slip (11.5%) following prismatic <a> slip (9%) were active. For twinning activity, among the ~250 grains analyzed at 10% strain, all the identified ~150 twins were tension twins with an area fraction of 19%. The twin variant selection did not solely follow the Schmid law, i.e. 42.3% twins exhibited low Schmid factor values (m<0.2) and 5.4% m values was negative. However, the proposed normalized m (mnor) can correlate the variant selection more effectively, and over 80% twins exhibited large mnor values. Twin transmission at grain boundary was observed for over 50% twins, and only 43.6% of them had high Luster-Morris parameter values (m’>0.75). However, the transmitted pairs with both large mnor sum and normalized m’ were preferred, and the fraction was over 64%. The twined number fraction was closely related to the maximum m values of prismatic slip. The present work implied that the twinning behavior is greatly dependent on the local conditions, and slip and twinning are closely related.