Composition profiles within Al₃Li and Al₃ScAl ₃Li nanoscale precipitates in aluminum

An Al-11.3Li-0.11Sc (at. %) alloy was double aged to induce first α′ - Al3 Sc and then δ′ - Al3 Li precipitates. Atom-probe tomography revealed both single-phase δ′ -precipitates and core-shell α′ δ′ -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 δ′ -shells contain little Sc (∼0.027 at. %), the α′ -cores have a high Li content, with an average composition of Al0.72 (Sc0.17 Li0.11). The Li concentrations within the δ′ -phase and the Li interfacial excess at the δ′ α′ -interface both exhibit wide precipitate-to-precipitate variations.