【摘要】 以Sn-Bi合金为研究对象,分析了旋转磁场对凝固组织的影响.发现旋转磁场能够消除宏观偏析、碎断枝晶和细化凝固组织,加快了熔体流动和固-液界面溶质的扩散速度,使共晶组织的层片间距变小及形成区域差别.同时,随着磁场旋转频率的增大,合金的生长形态经历了从枝晶→等轴晶→球状晶→枝晶的转变.枝晶碎断、生长形态的改变以及共晶组织层片间距变化的主要原因在于,旋转磁场加快了熔体流动,造成熔体中溶质场和温度场在分布上趋于均匀化.同时,电导率的不同造成了初生相与液体的相对运动.宏观偏析的消除是由于初生相同时受到重力、浮力和Lorentz力的合力作用的结果.分析了旋转磁场对凝固组织改变的物理机制.更多还原

【Abstract】 Through analyzing the solidified structure of Sn-Bi alloys in rotating magnetic field (RMF),it is found that the RMF can eliminate macrosegregation,cause the fracture of dendrites and refinement of solidification structure,accelerate the velocity of melt flow and the diffuse of solute near the solid-liquid interface,decrease eutectic spacing,and cause the regional difference of eutectic microstructure.At the same time,there is a transition of dendrite→equiaxed→globular→dendrite with increasing the rotating frequency.The basic reasons of dendrite fracture and transition of growth form and the eutectic spacing change are the enhancement of the melt flow velocity,the homogenizations of temperature and solute fields,and the relative motion between the primary phase and the melt caused by the electric conductivities difference.The reason of macrosegregation elimination is that the primary phase is subjected to resultant force of gravity,buoyancy and Lorentz force.Furthermore,the physical mechanism on the transition of solidification microstructure is discussed.更多还原