Tension-compression asymmetry and the grain-scale slip behavior in untextured Mg-10Gd-3Y-0.5Zr (wt.%)

Abstract

Mg-10Gd-3Y-0.5Zr (wt.%) is a recently developed high-performance cast Mg alloy with random texture. The present work found that both strength and ductility of this alloy were significantly larger for compression than that for tension, i.e. the mechanical properties exhibited tension-compression asymmetry (TCA), although no twins were observed. To understand this uncommon behavior, the relative activity of individual slip modes and slip-slip interactions during deformation were analyzed in detail at grain scale, based on quasi-in-situ experiments, combined with slip trace analysis and EBSD technique. Significantly asymmetric slip behavior was observed. Although basal slip always dominated for both tension and compression, the relative activity of pyramidal II <c+a> (PyrIICA) slip for tension was 2.6 times higher than that for compression. Statistical analysis of the angle between the active slip plane normal and the loading direction implied that the PyrIICA slip was more easily activated when the slip plane under tension. The asymmetric activity of PyrIICA slip was believed to contribute to the observed yield strength TCA. What’s more, almost all possible combinations of cross slip and slip transfer for total 30 slip systems were observed and analyzed in detail only during compression, while such behavior was not observed under tension. The strong slip-slip interactions induced by massive cross slips and effectively accommodated intergranular deformation by slip transfer were consistent with the well-balanced strain hardening, which resulted in improved ultimate strength and ductility for compression.