Simulation on DC casting of magnesium alloy under out-of-phase pulsed magnetic field with different coil connection strategies

Abstract

Four annular coils arranged vertically that have been loaded with two pulsed currents with different initial phases were used to create out-of-phase pulsed magnetic field (PMF) during direct-chill (DC) casting of magnesium alloy. A 2D axisymmetric mathematical model that couples electromagnetic field with fluid field and thermal field was established based on the finite element method by using COMSOL Multiphysics software. A two-step approach was adopted to handle the coupling problems, which the varying Lorentz force and Joule heat were treated as the averaged values during the steady calculation of DC casting process. Effects of coil connection strategies on the resulting Lorentz force, melt flow and solidification characteristics during DC casting of magnesium alloy under out-of-phase PMF were investigated and discussed. Results show that the application of magnetic field greatly strengthens the melt convection when compared to no magnetic field. Using out-of-phase PMF could control the range and intensity of melt convection by changing coil connection strategies, achieving lower overheating in the central part and higher temperature uniformity from the center to the edge or reducing the sump depth than a single PMF in which four coils are connected in series and loaded with the same pulsed current.