恒定磁场作用下Al-Pb合金快速定向凝固

RAPID DIRECTIONAL SOLIDIFICATION OF Al-Pb ALLOY UNDER A STATIC MAGNETIC FIELD

在恒定磁场作用下对Al-Pb合金进行了快速定向凝固实验,考察了磁场强度对凝固组织的影响,分析了磁场的作用机理.结果表明,恒定磁场能显著减弱熔体对流,提高凝固界面前沿液-液相变过程的空间均匀性,减缓液滴的碰撞凝并速度,使凝固试样中的弥散相粒子最大和平均尺寸减小,粒子尺寸分布范围变窄,有助于获得弥散型偏晶合金凝固组织.

The effect of a static magnetic field on the solidification of monotectic alloy has attracted great attentions. But up to date little is known about the details of the magnetic field influences on the microstructure development during the solidification of a monotectic alloy. In this paper, rapid directional solidification experiments are carried out with Al-Pb alloys under a static magnetic field. The dependence of the solidification microstructure on the intensity of the magnetic field is investigated. The mechanism through which the magnetic field affects the microstructure formation is analyzed. It is indicated that the static magnetic field causes only a small decrease in the Marangoni migration velocity and the Stokes settlement velocity of the minority phase droplets during the liquid liquid decomposition. Such a small change in the moving velocity of the droplets has only a negligible effect on the microstructure formation. The static magnetic field can suppress the convection efficiently. It enhances the spatial homogeneity of the liquid liquid phase transformation along the radial direction of the sample, reduces the collision and coagulation frequency between the minority phase droplets and, therefore, causes a decrease in the largest and average sizes of the Pbrich particles in the solidified sample as well as in the width of the particles size distribution. A static magnetic field is favorable for obtaining a monotectic alloy with well dispersed microstructure.