Synergistic Effects of Er and Sc on the Aging Behavior and Θ' Precipitation Stability of Al-Cu Alloys

The synergistic effects of Er and Sc on the aging behavior and θ' precipitation stability of Al-Cu alloys were systematically investigated. The combination of Er and Sc plays an important role in promoting the formation of θ' precipitates and enhancing the stability of θ' precipitates. To this end, the effects of synergistic addition of Er and Sc on the aging and interfacial segregation behavior of the alloy were studied in detail by transmission electron microscopy (TEM) and high angle annular dark field (HAADF). The TEM results showed that the Al3(Sc, Zr) dispersoids with core-shell structure can act as the nucleation particles of θ' and promote the uniform and fine precipitation of θ' plate. The STEM results showed that Er solute atoms were preferentially enriched inside the θ' precipitate during thermal exposure at 225°C for 150 h, which inhibited the serious coarsening of the θ' precipitate. After thermal exposure at 300°C, Sc and Mn with slow diffusion rate segregated at the interface of the θ' precipitate. Due to the early enrichment of Er in the θ' precipitate, the slowly diffused Sc and Mn can be segregated to the interface of the θ' precipitate before the severe coarsening of the θ' precipitate, thus further stabilizing the θ' precipitate at a higher temperature.