Influence of Al addition on solidification path and hot tearing susceptibility of Mg-2Zn-(3+0.5x)Y-xAl alloys

Hot tearing susceptibility (HTS) of Mg-2Zn-(3+0.5x)Y-xAl (x = 0, 2 and 3 at%) alloys is predicted by using modified Clyne-Davies' model (CSC*). The solidification path, solidification characteristic temperatures and dendritic coherency solid fraction have been studied by double-thermocouple thermal analysis. The solidification contraction stress vs. temperature (and time) curves are measured by using a T type hot tearing permanent-mold. The results reveal that the CSC* prediction values are in good agreement with the experimental results. Moreover, Al2Y phase acts as the heterogeneous nucleation core of alpha-Mg and significantly influences the grain size. It has been observed that minimum grain size, optimal dendritic coherency and minimum HTS are exhibited by Mg-2Zn-(3 +0.5x)Y-xAl alloy (x = 2). Furthermore, when Al content was increased to 3 at%, Al2Y phase exhibited a peritectic reaction and transformed into a mixed structure of Al2Y and Al + Al3Y phases, which increased the HTS of the alloy due to reduced fine-grained Al2Y content. (C) 2019 Published by Elsevier B.V. on behalf of Chongqing University.