INFLUENCE OF MG AND SI ON CLUSTER FORMATION IN Al-Mg-Si ALLOYS STUDIED BY POSITRON ANNIHILATION LIFETIME SPECTROSCOPY

摘要

The change of positron lifetimes during natural ageing of binary Al-Mg and Al-Si alloys was characterized. The experiments show that for dilute alloys, the average lifetimes in Al-Si alloys decrease faster to a stable value during natural aging (NA) than in Al-Mg alloys and the vacancy-related lifetime components of Al-Si are also significantly higher than in Al-Mg alloys for equal solute content. For alloys with higher solute contents, the decrease of the lifetime becomes insignificant. This indicates that Si enhances the jump frequency of vacancy while Mg can trap vacancy and slow down the jump frequency of vacancy.