Atom probe tomography and transmission electron microscopy characterisation of precipitation in an Al-Cu-Li-Mg-Ag alloy

► The peak-age microstructure at 200 °C consists of a very intricate network of T1 (Al2CuLi), θ′ (Al2Cu) and GPB/S (Al2CuMg), which are often touching or crossing. ► S and GPB zones, formed at earlier stages of ageing appear in the form of lath and needles, respectively. Some are still present in the peak-aged state, and they are mostly found linked to plate-shaped precipitates. ► Mg and Ag are partitioned inside the T1 phase but do not segregate at the interface of the plate-shaped precipitate with the matrix. ► Mg and Ag seem to exhibit a catalytic behaviour-although they help in the formation of T1, their matrix content show that they are consumed very early in the reaction, but are then progressively released in the matrix as the reaction reaches the peak age. ► Although δ′ Al3Li was not observed to precipitate as spheres in the matrix, a thin layer of δ′ at the interface θ′/matrix was observed.