Unified Understanding of Strengthening Mechanisms Acting in Mg/LPSO Two-Phase Extruded Alloys with Varying LPSO Phase Volume Fraction

The influence of the volume fraction of the long-period stacking ordered (LPSO) phase on the strengthening mechanisms acting in Mg/LPSO two-phase extruded alloys is discussed by focusing on compression tests of Mg94Zn2Y4 and Mg92Zn3Y5 alloys. An increase in the LPSO phase volume fraction increases the yield stress of these alloys, but the magnitude of the increase is not monotonic with the volume fraction. For deformation parallel to the extrusion direction, the rate of increase in the yield stress shows two large gaps between the Mg99.2Zn0.2Y0.6/Mg97Zn1Y2 and Mg92Zn3Y5/Mg89Zn4Y7 alloys. This is derived from the change in strengthening mechanisms. The upper gap between Mg92Zn3Y5/Mg89Zn4Y7 is derived from the change in the strengthening mechanism between short-fiber reinforcement and the simple rule of mixtures. The lower gap between Mg99.2Zn0.2Y0.6/Mg97Zn1Y2 corresponds to the existence of a short-fiber strengthening mechanism or not. As the volume fraction of the LPSO phase decreases, the magnitude of kink-band strengthening to the yield stress decreases; however, it is still effective even in alloys with a low volume fraction of the LPSO phase.