Interaction between solute atoms and vacancies in Al-Mg-X (X＝Si, Ge) alloys

Al-Mg-Ge alloys are considered to exhibit similar aging behavior as Al-Mg-Si alloys, therefore, they have been alternatively used to analyze precipitates in Al-Mg-Si alloys. However, the interactions between solute atoms and vacancies in Al-Mg-Ge alloys are not clear. In this study, the binding energies between solute atoms and between solute atoms and vacancies in Al-Mg-Si and Al-Mg-Ge alloys were investigated using first-principles calculations, and the similarities and differences of biding energy in each alloy were analyzed. Comparing the three-body binding energy, the Mg-Ge-vacancy interaction in the Al matrix was stronger than the Mg-Si-vacancy interaction. The difference in the bond strength could be explained by the difference in the atomic radii against the Al atom. However, the binding energy change with different bond angles was consistent for the Si and Ge cases. These results indicate that similar interactions between solute atoms and vacancies are one of the reasons for the formation of similar precipitates in Al-Mg-Si and Al-Mg-Ge alloys. In addition, the strong interactions between solute atoms and vacancies in Al-Mg-Ge alloys suggest that the clustering occurs more rapidly than in Al-Mg-Si alloys, resulting in a rapid increase of hardness at the early stage of precipitation.