Microstructural evolution during ageing of Al–Cu–Li–x alloys

In this study atom probe tomography was used to investigate the microstructure of AA2198 (Al-1.35Cu-3.55Li-0.29Mg-0.08Ag) over a range of ageing conditions to examine the evolution of phases in the alloy, in particular aiming to reveal the nucleation mechanism of the strengthening T1 phase, which has been under debate for decades. T1 precursor phases were observed from early ageing, a significant number of which were connected to solute-enriched dislocations. Ag and Mg segregation to T1 interfaces was convincingly observed when the plates were oriented perpendicular to the probing direction, which is the condition under which the spatial resolution of the atom probe data is highest.