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 similar to 441.3 MPa through precipitation strengthening after aging at 12 h in AlCuMgSiErSc alloy. Meanwhile, the AlCuMgSiErSc alloy shows approximately similar to 6.9 % and similar to 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 sigma-Al5Cu6Mg2 precipitates are rarely observed in AlCuMgSiErSc alloy indicating that the formation of sigma-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 0' precipitate, which inhibits the diffusion of solute atoms and stabilizes the coarsening of precipitates. This work may provide a strategy for designing Al-Cu series alloys with thermally stable microstructures.