A pat study of influences of precipitation on defects and electronic density in Al-Li-Cu-Mg-Zr alloys

The positron annihilation lifetime spectra of an Al-Li-Cu-Mg-Zr alloy in the conditions of under-ageing, peak-ageing and over-ageing were measured. The results showed that the precipitation and growth of delta' (Al3Li) phase particles increased the bulk electronic density, while the precipitation of S' (Al2CuMg) phase particles decreased the bulk electronic density. A large number of vacancies were recovered during the peak-ageing process, which made the number of defects decreased. However, the number of defects increased after the over-ageing process, which was related to the precipitation of S' phase particles.