α-Mg/LPSO (Long-Period Stacking Ordered) phase interfaces as obstacles against dislocation slip in as-cast Mg-Zn-Y alloys

The influence of alpha-Mg/LPSO (Long-Period Stacking Ordered) phase interfaces on the flow stress of as-cast Mg-Zn-Y alloys was experimentally and numerically evaluated by compressive loading samples with different volume fractions of LPSO phase. The experimental results showed that the flow stresses of Mg-Zn-Y alloys with LPSO volume fractions ranging from 40 to 85% are clearly higher than those of single phase alpha-Mg or LPSO alloys. Comparison of deformation behavior between Mg-Zn-Y alloys and Mg-Zn-Y-Zr alloys, where Zr effectively decreases grain size of alpha-Mg phase, showed that the flow stresses of Mg-Zn-Y alloys with 25 and 40% of LPSO phase were insensitive to grain size whereas the flow stress of alpha-Mg single-phase alloy showed clear grain size dependence. By including the dependence of critical resolved shear stress (CRSS) on the average interface spacing, crystal plasticity analysis successfully reproduces the observed experimental stress-strain behavior, which suggests that alpha-Mg/LPSO phase interfaces are effective obstacles against dislocation slip in two-phase Mg alloys containing LPSO phase.