This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd (RE represents La-Ce mischmetal; = 0, 0.2, 0.7 wt.%) alloys cast by high-pressure die casting (HPDC), permanent mold casting (PMC), and sand casting (SC) techniques. The results indicated that with increasing Gd content, the grain sizes of the HPDC alloy had a slight change, but the grains of the PMC and SC alloys were significantly refined. Besides, the acicular AlRE phase was modified into the short-rod shape under the three casting conditions. The impact toughness of the studied alloy was mainly dominated by the absorbed energy during the crack initiation. With increasing Gd content, the impact toughness of the studied alloy monotonically increased due to the lower tendency of the modified second phase toward crack initiation. The impact stress was higher than the tensile stress, exhibiting a strain rate sensitivity for the mechanical response; however, the HPDC alloy had an inconsistent strain rate sensitivity during the impact event due to the transformation of the deformation mechanism from twinning to slip with increasing strain. Abundant dimples covered the fracture surface of the fine-grained HPDC alloys, indicating a typical ductile fracture. Nevertheless, due to the deficient {102} twinning activity and the suppressed grain boundary sliding during the impact event, the HPDC alloys showed insufficient plastic deformation capacity.

中文翻译：

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Mg-4Al-5RE-xGd铸造镁合金的显微组织和冲击行为


这项工作研究了通过高压压铸 (HPDC)、金属模铸造 ( PMC）和砂型铸造（SC）技术。结果表明，随着Gd含量的增加，HPDC合金的晶粒尺寸略有变化，而PMC和SC合金的晶粒明显细化。此外，在三种铸造条件下，针状AlRE相均被改性为短棒状。研究合金的冲击韧性主要由裂纹萌生过程中吸收的能量决定。随着 Gd 含量的增加，由于改性第二相裂纹萌生的趋势较低，所研究合金的冲击韧性单调增加。冲击应力高于拉伸应力，表现出对机械响应的应变率敏感性；然而，由于随着应变的增加，变形机制从孪生转变为滑移，HPDC 合金在冲击事件期间具有不一致的应变率敏感性。细晶HPDC合金的断口表面覆盖着丰富的韧窝，表明是典型的韧性断裂。然而，由于{102}孪晶活性不足以及冲击事件期间晶界滑动受到抑制，HPDC合金表现出不足的塑性变形能力。