The behaviour of vacancies during isothermal ageing following quenching of an Al-1.7at.% Mg-1.1 at.% Cu alloy has been studied by positron annihilation lifetime spectroscopy. The positron lifetime parameters vary in parallel with the Vickers hardness of the alloy, suggesting simultaneous migration of vacancies and changes in the size and concentration of vacancies containing clusters and dislocation loops. The results also explain the long hardness plateau observed previously in ageing experiments carried out between 100 and 240 °C in terms of a continuous growth of Mg-Cu-vacancy clusters during ageing. The vacancy concentration of the clusters increases gradually until the setting in of the cluster → Guinier-Preston-Bagaryatsky zone transformation.
ASJC Scopus subject areas
- Condensed Matter Physics