The Use of Steady Electromagnetic Fields to Control the Columnar Solidification of Binary-Metal Alloys
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DURING the nondirectional solidification of a binary-metal alloy, the thermosolutal convection is responsible for the final macrosegregation pattern. Because of the high electrical conductivity of liquid metals, the application of electromagnetic fields is widely used to reduce segregations and to improve the microstructure of solidified materials.[1] In particular, it has been shown that the application of a strong external magnetic field can significantly damp the melt flow and minimize the solute- segregation pattern.[2–5] Prescott and Incropera[2] conducted a numerical study of the effects of a uniform axial magnetic field with the magnetic induction, Bz, of 0.1 and 0.5 T on the fluid flow and macrosegregation during the solidification of a Pb-19 wt pct Sn alloy. They used an expression of the radial Lorentz force, which was proportional only to ur B2z . It was shown that a sufficiently steady axial magnetic field favors the development of the channels in the mushy zone and increases the macrosegregation in the outer regions of the ingot. Recently, Samanta and Zabaras[5] performed a detailed numerical study of the effect of magnetic fields on the solidification of metallic alloys with significant mushy zones. A volume-averaged electric-potential equation was used to model the Lorentz force. It was shown that a high magnetic
induction of approximately 5 T is required to eliminate macrosegregation significantly. Recently, Nikrityuk et al.[6] explored the impact of a low-voltage electricalcurrent application on the unidirectional solidification of a hypereutectic metal alloy in a cylindrical cavity. It was demonstrated that the interaction between the steady electric current passing through the melt and its own magnetic field leads to the appearance of an electrovortex flow, which forms an axial jet in the direction of decreasing electric-current density. This induced flow causes a positive segregation on the axis of the cavity. However, to the best of our knowledge, there are no published investigations regarding the effect of rotation of the liquid phase induced by interplay between an external magnetic field and an additional DC current on the macrosegregation during alloy solidification. This article is organized as follows. In Section II, the problem under investigation and input parameters for three different cases are described. In Section III, the mathematical model used for the calculation is introduced. Section IV is devoted to a description of the results of the simulations and to the discussion of open questions. The results are summarized in Section V.
II. P.A. NIKRITYUK, formerly Postdoctoral Fellow, Institute for Aerospace Engineering, is Chair of Magnetofluiddynamics, Institute of Fluid Dynamics, Technische Universita¨t Dresden. Contact e-mail: [email protected] K. ECKERT, formerly Group Leader, Institute for Aerospace Engineering, is Chair of Magnetofluiddynamics, Institute of Fluid Dynamics, Technische Universita¨t Dresden. R. GRUNDMANN, Professor, is with the Institute for Aerospace Engineering, Technische Univers
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