Effects of Local Bonding between Solute Atoms and Vacancy on Formation of Nanoclusters in Al–Mg–Si Alloys

Nanoclusters formed in Al–Mg–Si alloys affect the aging behavior of the alloys depending on the formation temperature. In the present study, first-principles calculations were carried out to evaluate the two- and three-body interactions between Mg, Si atoms and vacancies in the Al matrix and estimate the effect of local bonding on the formation of nanoclusters. Monte Carlo simulations were subsequently performed to investigate the stable structure of the nanocluster formed in Al–0.95 mass pct Mg–0.81 mass pct Si alloy. We found that the Mg–Si and Si–Vac pairs are stable in the Al matrix. The result shows that the solute atoms easily aggregate with different types of solute atoms and that the Si atom has a strong attractive interaction with a vacancy. Furthermore, Mg–Si–vacancy triplets are more stable than Mg–Si and Si–vacancy pairs in the Al matrix. The nanoclusters in the Al matrix were thermally stabilized by the stable configurations between solute atoms and vacancy. Thus, the electronic structure calculations suggested that the local bondings within a nanocluster play a significant role in not only the thermal stability but also the formation and growth behavior of nanoclusters during aging at low temperatures.