Plastic deformation behavior of Mg89Zn4Y7 extruded alloy composed of long-period stacking ordered phase

The deformation behavior of an Mg89Zn4Y7 (at.%) extruded alloy composed mostly of the long-period stacking ordered (LPSO) phases, was investigated at room temperature. Several heat-treatments were conducted for the extruded alloy in the temperature range between 400 and 525 °C, and the correlation between the microstructure and the mechanical properties were quantitatively examined. The yield stress of the as-extruded alloy showed extremely high value of ∼480 MPa. The deformation of the as-extruded alloy proceeded accompanied by the formation of deformation kinks and small amounts of non-basal slips. The microstructure of the extruded alloy was highly thermally stable and the yield stress showed little change by heat-treatments below 400 °C. However, the yield stress was gradually decreased by annealing above 400 °C. The yield stress of the alloys annealed at and above 475 °C showed discontinuous decreases with increasing annealing temperature. The yield stress of the annealed specimens could be estimated by the Hall-Petch relationship by regarding the length of the long-axis of plate-like grains as the grain size. This suggests that the basal (0001) slip governed the plastic behavior of the LPSO-phase alloy composed of randomly oriented grains.