Effects of Y on the Deformation Mechanisms of Extruded Mg-Y Sheets During Room-Temperature Compression

Abstract

The effects of yttrium (Y) contents on the slip/twinning activity in extruded Mg-xY (x = 0-5, wt pct) sheets during room temperature (RT) compression were investigated quantitatively and statistically using a quasi-in-situ scanning electron microscope (SEM), electron backscatter diffraction (EBSD) combined with slip trace analysis and twin boundary misorientation analysis. No observable slip trace was found in the pure Mg, while the fraction of grains exhibiting slip traces increased up to ~ 24 pct with increasing Y content. Grain-by-grain slip trace analysis showed that the relative activity of pyramidal 〈c + a〉 slips increased up to ~ 16 pct with increasing Y. Schmid factor analysis implied that increasing Y could promote basal 〈a〉 slip, while it had little effect on pyramidal 〈c + a〉 slips. Considering the observed opposite trends of the slip activity, it is reasonable to conclude that Y addition could lower the critical resolved shear stress (CRSS) ratio of pyramidal 〈c + a〉 slip/basal 〈a〉 slip. The dramatic texture change and twin boundary misorientation analysis revealed that almost all the grains twinned heavily in pure Mg after failure, and twinning was remarkably suppressed with increasing Y content. The dominant twinning mode was the {10$$ \bar{1} $$2} tensile twinning for all the samples studied. The present study clearly showed that Y alloying could significantly depress twinning and promote slip, especially for pyramidal slip, even at RT deformation.