Abstract
In this study, the effect of Cu addition on the structures of atomic clusters and Guinier-Preston zones in Al-Mg-Si alloys and their connection to age-hardenability were studied by atomic-resolution scanning transmission electron microscopy. Cu addition promoted the formation of 1β” zones consisting of single structural units (eyes) of the β”-phase, as well as extended ‘Disordered Frank-Kasper’ (DFK) atomic clusters, in both naturally- and 90 °C pre-aged conditions. During a subsequent artificial aging at 175 °C, the DFK clusters dissolved, while β”-based precipitates were formed having Cu enrichment at several atomic sites. A refined precipitate distribution was achieved by Cu addition, suggesting that enhanced formation and thermal stabilization of β” structural units by Cu incorporation contributed to the enhanced age-hardenability in Cu-added alloys.