Effect of minor Sc additions on precipitation and mechanical properties of a new Al-Cu-Li alloy under T8 temper

The effects of minor Sc additions on the formation of various precipitates and mechanical properties of a new Al-Cu-Li alloy have been experimentally investigated by scanning electron microscopy (SEM), trans-mission electron microscopy (TEM), three dimensional atomic probe (3DAP) analysis and tensile tests. Under T8 temper, the introduction of 0.092 wt% Sc accelerates the aging response of Al-Cu-Li alloy and induces a little reduction in the tensile and yield strength due to the decrease of solid solubility of Cu in Al alloy matrix and number density of T1 (Al2CuTi) strengthening phase, which are closely linked with the formation of insoluble Sc-containing W(AlCuSc) phase by consuming Cu solutes for the precipitation of T1 phase. Except for T1 and W phase, Nanoscale Al3(Sc,Zr) and S & PRIME; phases are also found after minor Sc addition. The 3DAP tomography indicates that the Al3(Sc,Zr) precipitates have a core-shell structure with Zr atoms mainly close to the shell and Sc atoms enriched in the core. It is believed that such precipitate is only probably composed of Al and Sc at the initial stage, and then Zr enters into them at the later stage, which hinders the diffusion of Sc in the matrix through the boundary into the interior of the particle and thus makes the coarsening rate of Al3Sc decrease. (c) 2022 Elsevier B.V. All rights reserved.