Study on solid-solution interaction and existing forms of alloying elements in Mg–Al–Zn-Gd alloy

Mg–9Al-0.7Zn-0.9Gd(wt%) alloy was prepared by die casting. The solid solution amount of alloy elements was determined. The solid solution ability of alloy elements was analyzed by using the first principle. The activity interaction coefficient was calculated by using the relevant thermodynamic model to explore the effect of solid solution between elements. Determine and calculate the content of alloy elements in each phase, and analyze the specific role of alloy elements in the alloy. The results show that Al has the largest amount of solid solution in the alloy, while Zn and Gd have relatively small amounts of solid solution. The reason for the small amount of Gd solid solution is that chemical reaction between Gd and Al took place before α-Mg was formed, consuming most of Gd. The solid-soluble Al has repulsive effect on Zn, which leads to the decrease of the solid-soluble ability of Zn. Therefore, the solid-soluble amount of Zn in α-Mg is very small, and most of Zn is solid-soluble in Mg17Al12. Al plays the role of solid solution strengthening and second phase strengthening in the alloy, while Zn plays the role of grain refinement and solid solution strengthening of Mg17Al12 in the alloy. Gd mainly exists in the form of Al2Gd, which plays a role in strengthening the second phase, but Al2Gd can be used as heterogeneous nucleation particles to play a role in grain refinement.