Positron annihilation spectroscopy was used to study the aging kinetics, and association of vacancies with solute elements, during precipitation in Al-Cu-Mg alloys having high Cu/Mg ratios. The results showed that isolated vacancy-Mg complexes existed in the alloy following quenching from the solution-treatment temperature. After aging at temperatures below 68C, the vacancies were associated with Cu and with Cu-Mg aggregates. The contribution of Cu-Mg aggregates decreased as the aging temperature was increased from 20 to 68C. Immediately after aging (180C, 15s to 10h), vacancies were present only in pure-Cu regions, but vacancies in Cu-Mg aggregates became observable when the sample was cooled and aged at room temperature. The formation kinetics of solute aggregates could be described, after scaling, by a temperature-independent function. An effective activation energy of 0.65eV was deduced from the temperature dependence of the scaling factors.

Positron-Annihilation Study of the Aging Kinetics of AlCu-Based Alloys - Al-Cu-Mg. A.Somoza, A.Dupasquier, I.J.Polmear, P.Folegati, R.Ferragut: Physical Review B, 2000, 61[21], 14454-63