Composition Profiles within Al3Li and Al3Sc/Al3Li Nanoscale Precipitates in Aluminum

An Al-11.3Li-0.11Sc (at. %) alloy was double-aged to induce first alpha'-Al3Sc and then delta'-Al3Li precipitates. Atom-probe tomography revealed both single-phase delta'-precipitates and core-shell alpha'/delta'-precipitates (with respective average radii of 16 and 27 nm, and respective volume fractions of 12 and 9%) conferring a high strength to the alloy. Although the delta'-shells contain little Sc (~0.027 at. %), the alpha'-cores have a high Li content, with an average composition of Al0.72(Sc0.17 Li0.11). The Li concentrations within the delta'-phase and the Li interfacial excess at the delta'/alpha'-interface both exhibit wide precipitate-to-precipitate variations.