Study of intergrown L and Q′ precipitates in Al-Mg-Si-Cu alloys

Intergrown Q' and L precipitates formed in an overaged Al-Mg-Si-Cu alloy were studied by transmission electron microscopy and atom probe tomography. The composition of the ordered Q' phase was measured to be Al3.8Mg8.6Si7.0Cu1.0, while less Mg was found in the disordered L phase. Compared to the equilibrium Q phase, Q' contained less Cu and more Al. Similar Si concentrations were found in the Q' and L precipitates, consistent with the presence of a common Si arrangement in both structures. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.