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 (γ_us) of Mg₂Si alloys. Interestingly, the alloying elements with appropriate V _GS and higher Allred-Rochow electronegativity (En) would reduce the γ_us 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.