The role of solute clusters in the nucleation of precipitates in Al–Mg–Si–Cu alloys

In this work the precipitation behaviour of both high and low Cu variants of a Al-6xxx alloy were investigated with and without natural ageing. The material yield strength was greater in the high Cu alloy and without natural ageing. The strength was seen to correspond to changes in precipitate number density and a mechanism of dislocation bowing around these precipitates. In the samples without natural ageing, Cu was seen to increase the number density of nuclei and hence the final precipitate number density. In the samples with natural ageing, solute clusters were observed to dissolve during subsequent artificial ageing, but a higher proportion remained in the high Cu alloy and acted as nucleation sites for further precipitation.