Quantitative study on slip/twinning activity and theoretical critical shear strength of Mg alloy with Y addition

Slip/twinning activity and theoretical critical shear strengths (tau(max)) during room-temperature tensile deformation of as-extruded pure Mg and Mg-1 wt.%Y sheets were investigated quantitatively via electron back-scattered diffraction (EBSD), scanning electron microscope (SEM) and first-principles calculation. Slip trace analysis results indicated the relative frequency of the active slip modes transformed from basal slip (100%) for pure Mg, to basal slip (84.8%), prismatic slip (9.7%) and pyramidal slip (5.5%) for the alloy. The proportion of grains containing twins reduced significantly from 20.5% to 5.92% with Y addition. To explain the mechanism for the enhancement of the non-basal slip activity in Mg-Y alloy, the critical resolved shear stress of basal slip and pyramidal II slip were assessed by calculating tau(max). The calculated results showed that the tau(max) ratio of the pyramidal II slip to basal slip decreased from 13.7 to 7.5, which may be responsible for the observed enhanced activity of non-basal slip.