The effects of second-alloying-element on the formability of Mg-Sn alloys in respect of the stacking fault energies of slip systems

Generalized stacking fault (GSF) energies of the basal 0001112̅0，prismatic 101̅0112̅0 and pyramidal 112̅2112̅3 slip systems in the primary phase of Mg-Sn based-alloys have been studied using first-principles calculations in this work, where twenty-one third elements (X) have been taken in to consideration for their solution in primary (Mg, Sn) phase. The relative positions of Sn and X in Mg₁₄₂Sn₁X₁ supercell have been determined by searching the minimum formation energies points. It is shown that, with alloying-elements of Sn and X, the unstable stacking fault energy (γ_us) of the basal and prismatic slip systems are decreased compared with that of Mg₁₄₄. For the pyramidal slip system, only certain second-alloying-elements, namely Ag, Al, Cd, Ga, In, Li and Zn, soluted into the Mg-Sn alloys, make the γ_us lower than that of pure Mg. The atomic radius of element X has a significant impact on the γ_us value of Mg₁₄₂Sn₁X₁, and also indirectly affects the γ_us by affecting the relative substitution positions of Sn and X atoms in the structure. Accordingly, the plastic formability parameters χ have been analyzed based on the calculated stacking fault energy (SFE) values. The effects of second-alloying-elements on GSF energies and χ provide a guidance for the design of high-performance multi-elements-alloying Mg alloys.