This work deals with the effect of 0.67 wt% Gd addition on the microstructure and tensile properties of Mg–4Al–5RE (where RE represents La–Ce mischmetal) alloy produced by sand casting (SC), permanent mold casting (PMC), and high-pressure die casting (HPDC). The results show that Gd addition could refine the grains, but its efficiency decreases by increasing the cooling rate due to the shifting from SC to PMC and finally to the HPDC method. Meanwhile, the acicular Al₁₁RE₃ phase is modified into the short-rod or granular-like shape under the three casting conditions. Such refined and modified microstructures are due to the Al₂(Gd, RE) phases, which act as the nucleation sites in both the α-Mg matrix and Al₁₁RE₃ phase. Also, the weakening grain refinement effect in the increased cooling rates can be attributed to the narrow constitutional undercooling zone. After Gd addition, the 0.2% proof strength of the SC and PMC alloys increases by about 16.9% and 12.7%, respectively, while in the HPDC alloy, it decreases by about 5.9%. The main factor in the strength increment of the SC and PMC alloys is the grain boundary strengthening due to grain refinement which is proved by modeling the related mechanisms, whereas weak secondary phases and grain boundary strengthening mechanisms in the HPDC alloy lead to strength reduction. After Gd addition, the elongation to failure of the SC, PMC, and HPDC alloys is significantly enhanced by about 34.8%, 20.2%, and 12.3%, respectively, due to the crack resistance nature of the modified short-rod/granular Al₁₁(RE, Gd)₃ phase compared to the acicular one.

本工作研究了 0.67 wt% Gd 添加对砂型铸造 (SC)、永久型铸造 (PMC) 和 Mg-4Al-5RE（其中 RE 代表 La-Ce 混合金属）合金的微观结构和拉伸性能的影响。高压压铸 (HPDC)。结果表明，添加 Gd 可以细化晶粒，但由于从 SC 到 PMC 并最终到 HPDC 方法的转变，其效率会随着冷却速度的增加而降低。同时，针状Al ₁₁ RE ₃相在三种铸造条件下均变质为短棒状或粒状。这种细化和改性的微观结构是由于 Al ₂ (Gd, RE) 相，它们在 α-Mg 基体和 Al ₁₁ RE _{3 中}充当成核位点阶段。此外，冷却速度增加时晶粒细化作用减弱可归因于狭窄的构成过冷区。添加Gd后，SC和PMC合金的0.2%屈服强度分别提高了约16.9%和12.7%，而HPDC合金则降低了约5.9%。SC 和 PMC 合金强度增加的主要因素是晶粒细化导致的晶界强化，这通过相关机制建模得到证明，而 HPDC 合金中弱第二相和晶界强化机制导致强度降低。添加 Gd 后，SC、PMC 和 HPDC 合金的断裂伸长率分别显着提高了约 34.8%、20.2% 和 12.3%，这是由于改性短棒/粒状铝的抗裂性₁₁ (RE, Gd) ₃相与针状相相比。