Enhanced multiple precipitation and long-term stability in AlCuMgSi(Sc) alloys with Er additions

The precipitate evolution and microstructure stability of AlCuMgSiSc alloys with Er additions were intentionally investigated. It reveals that the Cu-containing metastable precipitates (rod-liked Q′ and lath-liked L precipitates) are promoted and achieved highest tensile strength of ∼441.3 MPa through precipitation strengthening after aging at 12 h in AlCuMgSiErSc alloy. Meanwhile, the AlCuMgSiErSc alloy shows approximately ∼6.9 % and ∼ 10.8 % higher UTS (27.7 MPa) and YS (34.1 MPa) than AlCuMgSiSc alloy after severe over aging for 150 h, respectively. Surprisingly, the σ-Al₅Cu₆Mg₂ precipitates are rarely observed in AlCuMgSiErSc alloy indicating that the formation of σ-Al₅Cu₆Mg₂ is inhibited. The excellent thermal stability can be explained by the high density of Q′ precipitates with hybrid structures and L precipitates. Moreover, Er solute atoms preferentially segregate at the interface of the Q′ precipitates and enrich the θ' precipitate, which inhibits the diffusion of solute atoms and stabilizes the coarsening of precipitates. This work may provide a strategy for designing AlCu series alloys with thermally stable microstructures.