The effects of the synergistic addition of Er and Sc on the aging and interfacial segregation behaviors of alloys were systematically studied using transmission electron microscopy (TEM) and high-angle annular dark field (HAADF) imaging. The TEM results show that Al₃(Sc,Zr) with a core-shell structure can act as nucleation particles for θ′ to promote uniform and fine precipitation. The STEM results show that Er solute atoms were preferentially enriched inside the θ′ precipitate during thermal exposure at 225 °C for 150 h. However, Sc and Mn solute atoms segregated at the θ′/α-Al matrix interface were observed at 300 °C. Due to the early enrichment of Er in the θ′ precipitate, the slowly diffusing Sc and Mn were segregated to the interface of the θ′ precipitate before the severe coarsening of the θ′ precipitate, thus further stabilizing the θ′ precipitate at higher temperatures.