对Al-Pb偏晶合金开展了快速定向凝固实验,试样组织观察表明,在试样表面形成了一贫Pb层；建立了偏晶合金定向凝固过程中液-液相变的理论模型,模型中考虑了液滴的形核、扩散长大、液滴的空间迁移以及熔体的对流运动的影响.根据实际凝固条件进行了相关模拟计算,结果表明在凝固界面前沿存在一过冷区,在过冷度的峰值点附近弥散相液滴形核；贫Pb层的形成是形成相与坩埚的润湿性、液滴的径向迁移和熔体的对流运动共同作用的结果.%Directional solidification experiments were carried out with Al-Pb monotectic alloy. A Pb-depleted layer appears on the surface of the sample. A model is developed to analyze the microstructure evolution in a continuously solidified monotectic alloy. The model takes into account the common actions of the nucleation and diffusional growth/shrinkage of the minority phase droplets, spatial phase segregation of phases and convections of the melt. The microstructure formation in a continuously solidified monotectic alloy is calculated according to the experimental situations. The numerical results agree with the experimental ones well. They demonstrate that an undercooling region appears in the front of the solidification interface. The nucleation of the minority phase droplets occurs in a region around the peak of the undercooling. The formation of the Pb-depleted layer on the surface of the sample is from the results of the common actions of wetting behavior between the minority phase droplet and the crucible, the radial migration of the minority phase droplets and the convections of the melt.
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