Features and classification of solid solution behavior of ternary Mg alloys

The performance of Mg alloys is significantly influenced by the concentrations and solid solution behavior of the alloying elements. In this work, the solid solution behavior of 20 alloying elements in 190 ternary Mg alloy systems at 500 °C are systematically investigated. The solid solution behavior of a set of two different alloying elements in Mg alloy systems are suggested to be classified into three categories: inclusivity, exclusivity and proportionality. Inclusivity classification indicates that the two alloying elements are inclusive in α-Mg, increasing the joint solubility of both elements. Exclusivity classification suggests that the two alloying elements have a low joint solid solubility in α-Mg, since they prefer to form stable second phases. For the proportionality classification, the solubility curve of the ternary Mg alloy systems is a straight line connecting the solubility points of the two sub-binary systems. The proposed classification theory was validated by key experiments and the calculation of formation energies. The interaction effects between alloying elements and the preference of formation of second phases are the main factors determining the solid solution behavior classifications. Based on the observed solid solution features of multi-component Mg alloys, principles for alloy design of different types of high-performance Mg alloys were proposed in this work.