Effects of local bonding between solute atoms and vacancy on formation of nanoclusters in Al-Mg-Si alloys

Abstract

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 bond structures on the formation of nanoclusters. Monte Carlo simulations were subsequently performed to investigate the stable structure of nanocluster formed in Al-0.95 mass pct Mg-0.81 mass pct Si alloy. We found that the Mg-Si bond and SiVac bond were stable in the Al matrix. The result showed that the solute atoms are easy to aggregate with other types of solute atoms and that Si atom had a strong attractive interaction with a vacancy. Furthermore, Mg-Si-vacancy three-body bond was more stable than Mg-Si two-body bond and Si-vacancy two-body bond in the Al matrix. The results indicate that the nanoclusters in the Al matrix were thermally stabilized by the stable bonds between solute atoms and vacancy. Thus, the electronic structure calculations suggested that inner bonds within a nanocluster played a significant role in not only the thermal stability but also the formation and growth behavior of nanoclusters during aging at low temperatures.