Calculation of the effective solidification range and its relationship with hot brittleness of alloys based on Mg–Al and Mg–Zn systems

Magnesium alloys of the Mg–Al and Mg–Zn systems have a wide effective solidification range (ESR), and as a result, have the tendency to hot brittleness during casting. There are several methods for analyzing and calculating the hot brittleness of magnesium alloys, but they are very labor-intensive. In this regard, the objective of the study is to develop a model for calculating the hot brittleness index (HBI) based on the value of the calculated effective solidification range, identifying and analyzing their relationship in binary and multicomponent alloys based on the Mg–Al and Mg–Zn systems. The ESR was calculated using the Thermo-Calc program (TTMG3 database). The ESR was calculated as the difference between the temperature of formation of a given amount of solid phases and the nonequilibrium solidus temperature. The study showed a good correlation between the calculated values of ESR and hot brittleness index in both binary and multicomponent magnesium alloys. In the Mg–Al system alloys, the calculated dependences of the ESR at 90 % of solid phases (ESR90) show the best correlation with the experimental values of HBI. In the binary alloys of the Mg–Zn system, a qualitatively similar dependence is observed. However, no clear correlation was noted between the ESR and HBI. The ESR65 and ESR80 dependences demonstrate the closest nature. According to the relationship between HBI and ESR, the considered multicomponent alloys are divided into two groups as a first approximation: the first one is the Mg–Al–Zn system alloys; the second one is the Mg–Zn–Zr and Mg–Nd–Zr alloys. Within these groups, the dependence of hot brittleness index and ESR has a nature close to a linear one. To describe the dependence of all alloys, a single equation can be applied if ESR65 is used in the calculations for Mg–Al–Zn alloys and ESR90 – for Mg–Zn–Zr and Mg–Nd–Zr alloys. The proposed model will allow for easy and quick calculation of the HBI, which is very important in the development of new high-tech magnesium alloys.