强磁场条件下金属凝固过程中第二相的迁移行为

Effect of high magnetic fields on the migration of second phases during the solidification of metals

理论分析表明,第二相的迁移行为可以通过迁移速度进行表征.影响迁移速度的因素包括第二相和熔体的物理性质、磁场强度和梯度大小、第二相的形状和体积等因素.强磁场下洛伦兹力的效果为促进第二相在基体中的均匀分布,其效率在磁场强度大于某一定值时逐渐降低.在梯度强磁场条件下,第二相迁移行为和分布状态的主要控制参数是梯度磁场下的磁化力.在磁场梯度较小时,因洛伦兹力的制约磁化力控制第二相迁移的效果不明显,随着磁场梯度的增加,磁化力的作用效果逐渐增强.通过研究强磁场下Al-Si合金、Al-Ni合金中原位自生第二相的迁移行为实验验证了理论分析结果.

Theoretical analysis shows that the migration behavior of a second phase during solidification processes in a high magnetic field （HMF） can be described by the migration velocity,which is a function of properties of melt matrix and the second phase,magnetic intensity and its gradient,as well as the geometry and size of the second phase. Lorentz force tends to make the second phase distribute homogenously,although its efficiency decreases with the increase of magnetic intensity beyond a certain value. When a gradient HMF is imposed,magnetization force becomes the dominant factor for the migration behavior of second phase. The effect of magnetization force increases with magnetic gradient,while it is difficult to control the migration of a second phase due to the constraint of Lorentz force when magnetic gradient is small. The theory has been experimentally verified by controlling the migration of in situ prepared particles in Al-Si and Al-Ni alloys under HMF conditions.