共晶合金作为重要的金属材料，其性能主要由凝固组织决定。强磁场对金属凝固过程的潜在调控效果逐渐得到证实，开展强磁场下的金属凝固理论研究具有重要意义。本工作在有无强磁场和不同凝固速率条件下进行了Al-12.7%Si (质量分数)共晶合金的定向凝固和淬火实验，考察了磁场和凝固速率对合金定向凝固组织及溶质迁移行为的影响。结果表明，Al-12.7%Si共晶合金随着凝固速率的增加，发生了从粗大共晶向细小共晶，再向亚共晶组织的转变。而在相同凝固速率下，施加强磁场同样可以诱发从粗大共晶向细小共晶，再向亚共晶组织的转变。合金固/液界面淬火组织和溶质分布结果表明，上述强磁场诱发的组织演变是由于Lorentz力抑制液相中的对流，显著影响固/液界面前沿溶质迁移行为导致。相比于凝固速率，强磁场可以作为调控共晶合金凝固组织的另一个工艺参数。

As an important metal material, the properties of eutectic alloy are mainly determined by solidification microstructures. The potential control effect of high magnetic field on metal solidification process has been gradually confirmed, making it highly significant to carry out the research on the theory of metal solidification under high magnetic field. In this study, the experiments of directional solidification and quenching of Al-12.7%Si (mass fraction) eutectic alloys without and with a 6 T high magnetic field at various growth velocities were carried out. The effects of the magnetic field and growth velocity on the solidified structures of the alloys and the solute migration behavior were investigated. It is found that with increasing growth velocity the alloy underwent a transformation of a coarsened eutectic to a refined eutectic, and then a hypoeutectic microstructure. While with the same growth velocity, applying a 6 T high magnetic field during the directional solidification process of the alloy could also induce the transformation from a coarsened eutectic to a refined eutectic, and then a hypoeutectic microstructure. The analyses of the quenched solid-liquid interface microstructure and solute distribution suggested that the high magnetic field induced microstructure transformation can be linked to the modification of the solute migration caused by the suppression of the convection by the Lorentz force. The above results indicate that similar with growth velocity, high magnetic field can be another parameter for controlling the solidification microstructures of eutectic alloys.