试样尺寸对Al-4.5%Cu合金定向凝固组织和界面稳定性的影响

Effects of Specimen Dimensions on Directional Solidification Microstructure and Interface Stability of Al-4.5%Cu Alloy

在传统Bridgeman方法下,利用Al-4.5%Cu合金内外同心嵌套试样,研究了自然对流对凝固过程及组织的影响。试验结果显示,温度梯度和抽拉速率均相同的定向凝固试样,尺寸较大试样的组织呈规则胞状或树枝状时,对应尺寸较小试样组织胞晶尖端发生分叉或杂乱树枝状,表明尺寸较小的试样液-固界面稳定性较差。较小试样尺寸限制了液相中自然对流致使溶质原子液-固界面处大量富集是凝固组织不规则与液-固界面不稳定的主要原因。

The paper investigated the effects of natural convection on directional solidification and microstructure of AI-4.5%Cu alloy by using assembly of concentric tubes with different diameter. Results revealed that during the directional solidification with the same temperature gradient and growth rate, the larger specimens appeared regular cellular or dendritic microstructures, while the smaller specimens were cellular crystals with branches at the cell tips or dendritic crystals with developed secondary dendrites. This suggests that during the directional solidification, interface stability of the smaller specimens is worse than that of the larger samples. The reason is the greater solute enrichment ahead of the interface in the smaller specimens due to the weaker convection caused by crucible wall.