The behaviour of vacancies during isothermal aging, following quenching of an Al-1.7Mg-1.1at%Cu alloy, was studied by means of positron annihilation lifetime spectroscopy. The positron lifetime parameters varied in parallel with the Vickers hardness; thus suggesting the occurrence of a simultaneous migration of vacancies, plus changes in the size and concentration of clusters and dislocation loops. The results could also explain a long hardness plateau, which had been observed during aging experiments between 100 and 240C, in terms of the continuous growth of Mg-Cu vacancy clusters during aging. The vacancy concentration of the clusters increased gradually up to the onset of a cluster to Guinier-Preston-Bagaryatsky zone transformation.

Positron Lifetime Study of an Al-1.7Mg-1.1at%Cu Alloy. L.Reich, K.Svegh, J.Lendvai, A.Vertes: Philosophical Magazine Letters, 2001, 81[3], 145-51