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 {0001} 11 (2) over bar0 , prismatic {10 (1) over bar0} 11 (2) over bar0 and pyramidal {11 (2) over bar2} 11 (2) over bar3 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 (gamma(us)) of the basal and prismatic slip systems are decreased compared with that of Mg-144. 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 gamma(us) lower than that of pure Mg. The atomic radius of element X has a significant impact on the gamma(us) value of Mg142Sn1X1, and also indirectly affects the gamma(us) by affecting the relative substitution positions of Sn and X atoms in the structure. Accordingly, the plastic formability parameters chi have been analyzed based on the calculated stacking fault energy (SFE) values. The effects of second-alloying-elements on GSF energies and chi provide a guidance for the design of high-performance multi-elements-alloying Mg alloys.