High-resolution transmission electron microscopy and tomographic atom probe studies of the hardening precipitation in an Al-Cu-Mg alloy
Résumé
The hardening precipitation of an Al-Cu-Mg aluminium alloy designed for aeronautics was investigated using high-resolution transmission electron microscopy (HREM) and tomographic atom probe techniques. The observed precipitates clearly belong either to the Guinier-Preston-Bagaryatskii (GPB) zones type or to the so-called S-Al2CuMg precipitation. We analysed a large number of precipitates in order to obtain statistical information on the precipitation. We focused on the structural and/or chemical composition of the different precipitates. It was found, in particular, that the very numerous GPB zones do not present a single chemical composition. Evidence is also given for the presence of two different kinds of S-precipitate/matrix orientation relationships, strongly linked to the morphology of the precipitate. The structure of the S precipitates was confirmed by direct comparison with simulated HREM images. Particular attention was paid to the nature of the S-precipitate/matrix interfaces.