Effect of Multi-Pass Equal Channel Angular Pressing on the Microstructure and Mechanical Properties of a Heterogeneous Mg88Y8Zn4 Alloy

The microstructure evolutions and mechanical properties of a heterogeneous Mg88Y8Zn4 (in at.%) alloy during multi-pass equal channel angular pressing (ECAP) were systematically investigated in this work. The results show that four phases, i.e. α-Mg, 18R long period stacking ordered (LPSO) phase, Mg24Y5 and Y-rich phase, are present in cast alloy. During ECAP, dynamic recrystallization (DRX) occurs and the diameter of DRXed α-Mg grains decreases to 0.8 µm. Moreover, precipitation of lamellar 14H LPSO structure is developed within α-Mg phase. Both the refinement of α-Mg grains and precipitation of 14H LPSO contribute to the increase in micro-hardness from 98 HV to 135 HV for α-Mg. In addition, a simplified model describing the evolution of 18R LPSO phase is established, which illustrates that 18R undergoes a four-step morphological evolution with increasing strains during ECAP, i.e. original lath → bent lath → cracked lath → smaller particles. Compression test results indicate that the alloy has been markedly strengthened after multi-pass ECAP, and the main reason for the significantly enhanced mechanical properties could be ascribed to the DRXed α-Mg grains, newly precipitated 14H lamellas, 18R kinking and refined 18R particles.