Coupled Numerical Simulation On Fluid Flow, Heat And Solute Distribution In Directional Solidification With Electromagnetic Field

Theory of electromagnetic field applied to directional solidification technology is a promising way to manufacture new material, intensity of electromagnetic field can be adjusted according to practical need to form what we want. Because of difficulties in experimentally investigating the transportation phenomenon, using numerical simulation method to analyze fluid flow, heat and solute distribution in directional solidification with electromagnetic field is significant both in theory and practice.The mathematical model, based on the continuum formulation and the study of electromagnetic characteristic and conventional directional solidification, is built to evaluate momentum, heat and mass transfers during directional solidification with electromagnetic field. A set of expressions coupling liquidus and solid fraction with multicomponent concentrations was determined based on the pseudobinary approach. Then the corresponding simulation program was developed to analyze Ni-5.8%A1-15.2Ta alloy solidification transportation mechanism and the influencing factors with the change of electromagnetic parameters and technical parameters.Firstly, calculation result of Maxwell-3D and ePhysics software indicate that, with the current frequency increased in the sample, the intensity of magnetic induction, eddy current and electromagnetic volume force reduced, but they are not proportional;While with the current intensity enhanced in the sample, the magnetic flux density and eddy current increased, basically the trend of their changes is proportional, and electromagnetic force also increased significantly;At the same time if the calculation conditions remain unchanged, surface temperature of graphite stove will keep constant after stabilization.Secondly, channel segregation was mainly induced by the density inversion due to the thermo-solutal diffuse in front of the solid/liquid interface during conventional directional solidification. The solute-rich liquid in the channels flows from mush into liquid, in order to maintain the mass equilibrium in the channels;the fresh liquid may penetrate via the mushy zone from pure liquid region. The plumes appeared in the strand center was unstable, but the stable channel was formed on both sides of thesample.Finally, in the course of directional solidification forced by electromagnetic field, the reducing of current frequency lead to fluid flow increase, and eventually macrosegregation decrease appreciably;Intensity of current impact the temperature field significantly during solidification, the larger current intensity, resulting in greater heat affected zones, meanwhile both interface temperature gradient and fluid flow, on the other hand macroscopical structure of sample refined;In the domain of the calculated pulling velocity, with the pulling velocity reduced, temperature gradient of the front of the solid-liquid interface will get some certain increasing, width of mushy zone reduced but macrosegregation multiplied. Compared with conventional directional solidification, electromagnetic field marked lessens macrosegregation and isothermal distribution obvious differences.