以Al-Y中间合金的形式,向7055铝合金基体中添加稀土元素钇,主要讨论了钇在7055铝合金熔炼过程中的热力学机制以及在凝固过程中的作用机制.结果表明:钇与熔体中氧、氢、氮、硫、铁等杂质元素有较强的结合作用,起到了熔体净化效果.加入钇后,基体晶粒的尺寸从60-70 μm下降到40-50 μm.原因是钇在铝中固溶度小,偏聚在固液边界层,阻碍了Zn、Mg、Cu等溶质原子的扩散,造成凝固前沿的成分过冷,促进了胞状枝晶生长.界面处共晶体数量增加,且尺寸较不加钇时减小.
The rare earth element yttrium was added into 7055 aluminum alloys in the form of Al-Y intermediate alloy. The thermodynamic mechanism during melting and effect mechanism during solidification of yttrium were analyzed based on the classical theories of physical chemistry and crystal growth. Results show that there are strong binding between yttrium and impurity elements, such as oxygen, hydrogen, nitrogen, sulfur, iron and so on, which can purify the aluminum melt. The grain size of as-cast alloys is decreased from 60-70 μm to 40-50 μm after yttrium addition. It is due to the small solubility of yttrium element in molten aluminum. Most of yttrium segregates at the solid-liquid boundary, and prevent the Zn, Mg and Cu atoms from diffusing resulting in the constitutional supercooling at the frontier of solidification, which accelerate the growth of cellular dendrite. Furthermore, the amount of eutectic increases, the size of which is smaller than that without yttrium.
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