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采用彩色金相与能谱对半连续浇铸的AZ61镁合金进行了组织和成分上的观察,发现冷却速率较快的铸锭边部的二次枝晶间距比冷却速率较慢的铸锭心部的二次枝晶间距大,与普通模铸的显微组织呈现的规律不同,并对这一现象进行了理论上的分析讨论。分析认为边部二次枝晶间距的异常增大与二次枝晶臂表面溶质的微观偏析密切相关,粗枝晶臂表面溶质浓度与细枝晶臂表面溶质浓度差值越大,粗枝晶臂的粗化驱动能越大,枝晶的二次枝晶间距就越大。
The microstructure and composition of semi-continuous cast AZ61 magnesium alloy were observed by color metallography and energy dispersive spectroscopy. It was found that the secondary dendrite spacing at the edge of the ingot with higher cooling rate was higher than that of the ingot core with slower cooling rate The secondary dendrite spacing is large, which is different from the regularity of the microstructure of ordinary die-castings. Theoretical analysis and discussion of this phenomenon are also made. The analysis shows that the abnormal increase of the secondary dendrite spacing is closely related to the microsegregation of solutes on the secondary dendrite arm. The difference between the solute concentration on the surface of the dendrite arm and the solute concentration on the surface of the dendritic arm is larger. The larger the roughening drive energy of the arm, the larger the dendrite secondary dendrite spacing.