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

Abstract

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 α-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. Keywords: Mg–Zn–Y–Al alloys, Hot tearing susceptibility (HTS), Solidification path, Clyne–Davies’ model (CSC*), Dendritic coherency