<p>In order to improve the mechanical properties and corrosion resistance of cast AlCu5NiCoSbZr (RR350) alloy, different amounts of the rare earth element (Er) was added during casting and the effects of alloy were analyzed. At the same time, the adsorption behavior of Er elements on the crystal surface of the alloy were expounded combination with the first-principles density functional theory (DFT). The experiment results show that the 0.5% Er can led to best mechanical properties for RR350 alloy (The tensile strength can improve 24.79% compared to the alloy without addition, yield strength can increase 19.11%, elongation can improve 11.38% and hardness could up to 79.3HV). Also, adding 1.5% Er element can get the best corrosion resistance. The DFT simulation results show that Er can achieve stable adsorption in the Al₂Cu (001) crystal surface through charge transfer and orbital hybridization, which can promote the improvement of material strength. The synergistic effect of Er₂O₃-Al₂O₃ composite film protection and electrochemical corrosion inhibition by anodic sacrifice of Er-based phase would enhance the corrosion resistance of the alloy. But more Er element (Er&#xa0;&gt;&#xa0;1.5%) adding would promote the phase aggregation, which would lead to a decline in material performance. The strengthening and corrosion resistance mechanism of Er element in casting RR350 alloy is clarified, and the theoretical calculation results are consistent with the experimental conclusions, which can provide theoretical support for the design of high-performance Al-Cu alloys.</p>