Effect of Zn content on hot tearing susceptibility of LPSO enhanced Mg–Znx–Y2–Zr0.06 alloys with different initial mold temperatures

Abstract

The critical temperature (Thci) corresponding to the load relaxation measured during the solidification of alloy in a ‘T′-shaped mold is introduced into the Clyne-Davies’ model, so that it can be used to predict the hot tearing susceptibility (HTS) of alloy under non-equilibrium cooling. Then, the improved model is applied to study the HTS of Mg–Znx–Y2–Zr0.06 (x = 0.5, 1 and 1.5 at%) alloys under two initial mold temperatures, i.e., two cooling rates. It is found that HTS is very sensitive to both Zn content and initial mold temperature, and the increase in Zn content or initial mold temperature can reduce HTS of the alloy. However, their micro mechanisms are different. The reason for the decrease in HTS with the increase in Zn content is the decrease in the dendrite coherency temperature. Specifically, the ratio of unconstrained feeding stage to intergranular feeding stage increases, and the intergranular liquid phase with eutectic composition increases in the later stage of solidification. The HTS decreases with the increase in the initial mold temperature because the solidification shrinkage stress is relieved. Consequently, the residual liquid phase between the grains can be fed in a more timely manner.