Understanding the Reversed Tension–Compression Asymmetry of an Extruded Mg-10Y Sheet from the Perspective of Slip Activity and Plastic Heterogeneity

To understand the reversed tension–compression asymmetry (TCA), i.e. compressive yield strength > tensile yield strength, in an extruded Mg-10Y sheet, quasi-in-situ grain-scale slip activity and plastic heterogeneity were studied statistically using slip trace analysis and EBSD. No twins were found in present study, while notable TCA slip behavior was observed and analyzed in detail. The overall slip activity, in terms of the fraction of the grains exhibiting slip traces, for compression (79.5 pct) was higher than that of tension (64.6 pct). Besides, basal < a > and prismatic < a > slips always exhibited higher activity during tension than compression, while the opposite was true for pyramidal slips. Further analysis of the critical resolved shear stress (CRSS) ratio, based on 1185 sets of observed slip traces, revealed that CRSS_{pyr II}/CRSS_bas and CRSS_{pyr I}/CRSS_bas for tension was ~ 3 times larger than that for compression, while CRSS_pri/CRSS_bas was symmetric. Statistical investigation on the angle between active pyramidal slip plane normal and loading direction indicated that pyramidal slip was more active when the slip plane was under tension compared to compression, which was consistent with the asymmetric CRSS ratios. More inhomogeneous deformation, in terms of higher intragranular misorientation angle (IGM) and geometrically necessary dislocation (GND) density, was found during compression.