Abstract The high performance of as-cast Mg-RE alloys is always related to their high RE additions. However, RE elements can be readily segregated in Mg alloys and the segregation becomes more significant with the increasing RE content. In this research, the effect of cooling rate on the macro- and micro-segregation in the as-cast Mg–8Gd alloy was studied. The Gd content at the bottom of the fabricated ingot with the cooling rate of 4.6–6.9 °C/s was ~1.7 times of that at the top and coarse eutectics as well as some non-equilibrium phases of α-Gd, MgGd, Mg2Gd were distributed along the grain boundaries. The formation mechanisms of the specific gravity segregation and grain boundary segregation were also proposed. Upon the application of the water-cooled copper mold with the cooling rate of 27–200 °C/s, only fine Mg5Gd and some nanoscale metastable β1 and β′ phases were found to disperse uniformly in the grain interior, thus the homogeneity of the composition, microstructure, and performance within the whole ingot was considerably improved. It is expected that these results will facilitate the processing design for the fabrication of the highly-homogenized Mg-RE alloy castings.

中文翻译：

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凝固过程中的快速冷却对铸态 Mg-Gd 合金宏观和微观偏析的影响

摘要 铸态Mg-RE合金的高性能始终与其高RE添加量有关。然而，稀土元素在镁合金中很容易偏析，随着稀土含量的增加，偏析变得更加明显。在这项研究中，研究了冷却速度对铸态 Mg-8Gd 合金宏观和微观偏析的影响。冷却速度为 4.6-6.9 °C/s 时制成的铸锭底部的 Gd 含量是顶部和粗共晶以及一些非平衡相的 α-Gd、MgGd、Mg2Gd 的 ~1.7 倍沿晶界分布。还提出了比重偏析和晶界偏析的形成机制。应用冷却速度为 27-200°C/s 的水冷铜模时，仅发现细小的 Mg5Gd 和一些纳米级亚稳 β1 和 β' 相均匀分散在晶粒内部，因此整个铸锭内的成分、微观结构和性能的均匀性得到显着改善。预计这些结果将有助于制造高度均质的 Mg-RE 合金铸件的工艺设计。