Small additions of Ag and Mg stimulated nucleation of the Ω phase in artificially aged Al–Cu alloys, after which these elements segregated to the Ω/matrix interfaces. Here, positron spectroscopy results showed that vacancies accompanied the Ag (and Mg) atoms at the interface during precipitate formation, after which they were released back into the matrix and facilitated secondary ageing at ambient temperatures.

Vacancy–Solute Interactions during Multiple-Step Ageing of an Al–Cu–Mg–Ag Alloy. R.Ferragut, A.Dupasquier, C.E.Macchi, A.Somoza, R.N.Lumley, I.J.Polmear: Scripta Materialia, 2009, 60[3], 137-40