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

Abstract

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 (γus) 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 γus lower than that of pure Mg. The atomic radius of element X has a significant impact on the γus value of Mg142Sn1X1, and also indirectly affects the γus 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.