Fluid flow and microstructure formation in a rotating magnetic field during the directional solidification process

The influence of the fluid flow driven by rotating magnetic field (RMF) on the solidification microstructures of Sn–Bi alloys was investigated. It is found that, for the Sn–50 wt.% Bi hypoeutectic alloy, the primary phase (Sn) shows a morphology transition from coarse dendrite to equiaxed dendrite, moreover, the grains are fractured and refined with the application of RMF. As for the Sn–65 wt.% Bi hypereutectic alloy, the volume fraction gradient of the primary phases (Bi) at different positions reduces with the increase of magnetic intensity, and the macrosegregation is eliminated effectively. The theoretical calculation indicates that the tangential rate of the fluid flow has a maximum value at 0.55r0, which is three magnitudes larger than the radial component. Furthermore, the microstructure formation mechanisms under the RMF condition were analyzed on basis of the calculation results and solidification theories.