Effect of Alloying Elements on the Stacking Fault Energy and Ductility in Mg2Si Intermetallic Compounds.

Alloying elements can pronouncedly change the mechanical properties of intermetallic compounds. However, the effect mechanism of this in Mg2Si alloys is not clear yet. In this paper, systematic first-principles calculations were performed to investigate the effect of alloying elements on the ductility of Mg-Si alloys. It was found that some alloying elements such as In, Cu, Pd, etc. could improve the ductility of Mg2Si alloys. Moreover, the interatomic bonding mechanisms were analyzed through the electron localization functional. Simultaneously, the machine-learning method was employed to help identify the most important features associated with the toughening mechanisms. It shows that the ground state atomic volume (V GS) is strongly related to the stacking fault energy (γus) of Mg2Si alloys. Interestingly, the alloying elements with appropriate V GS and higher Allred-Rochow electronegativity (En) would reduce the γus in the Mg-Si-X system and yield a better ductility. This work demonstrates how a fundamental theoretical understanding at the atomic and electronic levels can rationalize the mechanical properties of Mg2Si alloys at a macroscopic scale.