Vacancy behavior during aging at 50 and 100°C in AlMgSi alloys with excess Si studied by positron annihilation spectroscopy

We have investigated the aging behavior of quenched-in vacancies in excess Si type AlMgSi-alloys by coincidence Doppler broadening of positron annihilation radiation and positron lifetime spectroscopy. The chemical composition around the quenched-in vacancies is initially rich in Si. For aging at both 50°C and 100°C, the Mg/Si composition ratio around the vacancies increases with aging time. The final Mg/Si composition ratio around the vacancies was found to be almost the same for aging at both 50 and 100°C. The difference of the aging time dependence of the chemical composition around the vacancies at 50 and 100°C was observed in the initial stage, i.e., the vacancy-Si-rich solute complexes was formed at 50°C, while the formation of the vacancy-Si-rich solute complexes was avoided at 100°C. Therefore, the avoidance of the formation of the vacancy-Si-rich solute complexes by pre-aging around 100°C before storage at room temperature may be a key to avoid negative effect of artificial aging in AlMgSi alloys.