Hot compression behavior of the ignition-resistant Mg-5Y-2.5Zn-1.2Ca alloy with long-period stacking ordered structures

The effect of addition of Ca to the hot compressive deformation and dynamic recrystallization (DRX) behaviors of the Mg-5Y-2.5Zn alloy was studied for the development of Mg alloys with long-period stacking ordered (LPSO) structures that have high ignition-resistance and good forgeability. The addition of Ca by 1.2 wt.% markedly increased the ignition temperature (by 323 K), from the baseline value of 1150 to 1473 K. Most of the Ca in the alloy was in the form of Mg2Ca, which coexists preferentially with the LPSO phase. Due to the brittleness of Mg2Ca and the occurrence of eutectic melting of α-Mg/Mg2Ca, the temperature and strain rate ranges for hot deformation of the Mg-5Y-2.5Zn-1.2Ca alloy were narrower compared with those for the Mg-5Y-2.5Zn alloy. Analyses and comparison of the DRX behavior and processing maps of the two alloys, however, indicated that there is a window (650-723 K and 1 × 10−3-1 s−1) within which the addition of Ca promotes workability. This result can be attributed to the formation of a higher DRX fraction by the presence of Mg2Ca phase that causes more effective breaking of LPSO phase during hot deformation and thereby provides more sites for nucleation of DRXed grains.