Experimental Heat Transfer, Vol.9, No.2, 105-131, 1996
Influence of electromagnetic stirring on the solidification of a binary metal alloy
Electromagnetic induction if considered as a means of altering convection during the solidification of a Pb-19wt% Sn alloy in a vertical annular mold. While thermal buoyancy forces are opposed by solutal buoyancy forces during solidification, they can be either augmented or opposed by Lorentz forces induced with an axisymmetric linear motor. Experiments were performed to investigate the effects of direction and strength of a traveling magnetic field on convection and macrosegregation during solidification. Conditions for which Lorentz and buoyancy forces are of the same order of magnitude me considered, and results are compared to those obtained from experiments without stirring. Temperature measurements reveal that electromagnetic stirring significantly enhances mixing in the melt, thereby reducing temperature gradients and the time period associated with recalescence. Stirring direction is found to affect the vertical temperature distribution and the location of initial solidification, as well as the degree of macrosegregation in the solidified ingot. With Lorentz forces acting upward, opposing thermal buoyancy forces, solidification begins at the top of the cooled mold wall due to inverted thermal stratification. Furthermore, since solutal buoyancy forces are augmented during solidification, macrosegregation is enhanced. When Lorentz forces net downward and augment and oppose thermal and solutal buoyancy forces, respectively, solidification begins at the bottom of the cooled mold wall, which is similar to conditions without electromagnetic stirring. However, miring is enhanced, and when downward-acting Lorentz forces are increased turbulent mixing is enhanced and macrosegregation is reduced.