First-principles study of generalized-stacking-fault (GSF) energy in Mg with Al and Zn alloyings

Influences of Al and Zn contents on the GSF energies in Mg-Al-Zn alloys (Mg141Al2Zn1, Mg139Al4Zn1 and Mg135Al8Zn1; Mg142Al1Zn1 and Mg141Al1Zn2) are investigated by the first-principle methods. With an increase in Al or Zn contents, the unstable stacking fault energy (γus) continuously decreases and more slip positions with a low γus emerge in the Mg matrix for the {0001}〈112¯0〉,{101¯0}〈112¯0〉,{101¯1}〈112¯0〉 and {112¯2}〈112¯3〉 slip systems, which both facilitate the formation of basal , prismatic , pyramidal and stacking faults. More importantly, a criterion for predicting the location with the highest probability to form stacking faults in different slip systems is proposed, which contributes to predicting the ductility of Mg alloys on the atomic scale. The decrease in GSF energies with Al and Zn additions is presumably attributed to the enhanced charge flow and the weakened Mg-Mg bonds on slip planes.