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

Abstract

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 Mg_99.2Zn_0.2Y_0.6/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 Mg_99.2Zn_0.2Y_0.6/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.

Fig. 9 Variations in the strengthening factors affecting the yield stresses of Mg/LPSO two-phase extruded alloys, in the various R10 extruded alloys deformed in the 0° orientation at (a) RT, (b) 200 and (c) 300°C.