Improved plastic anisotropy of Mg–Zn–Ca alloys exhibiting high-stretch formability: A first-principles study

First-principles shear and tensile tests were performed on pure Mg, Mg–Zn–Ca, Mg–Ca and Mg–Zn models, and the generalized stacking fault energy for basal and prismatic slip systems and the surface energy of the {0 0 0 1} plane were investigated to understand the origins of the high-stretch formability of Mg–Zn–Ca alloys. The calculations showed that the plastic anisotropy is reduced by the addition of Ca and Zn due to the non-linear nature of the unstable stacking fault energy for basal slip in higher-order alloying. Therefore, it is suggested that the improved plastic anisotropy gives rise to the reduced basal plane texture, resulting in the high formability of Mg–Zn–Ca alloys. The improved plastic anisotropy is caused by the charge transferred from Mg to Zn atoms, thereby compensating for the decreased charge density around the Ca atoms in the basal slip system, while no such compensation takes place in the prismatic slip system.