Modelling the fluid flow, solidification and segregation behavior in electromagnetic DC casting of magnesium alloy

Abstract

Making clear the metallurgical transport behaviors during direct chill (DC) casting is of great significance to control the solidified structure and reduce the casting defects, but it still remains difficult because the high temperature and the opaque of melt make them hard to observe and detect directly. Numerical modelling provides a way to reveal the physical fields involved during DC casting. The present research used a two-dimensional axisymmetric model which coupled the heat transfer, fluid flow, solidification and species transfer in order to study the effect of different magnetic fields (harmonic magnetic field (HMF), pulsed magnetic field (PMF) and out-of-phase pulsed magnetic field (OPMF)) on the flow pattern, solidification characteristic and solute distribution in the electromagnetic DC casting of magnesium alloy billet having the diameter of 500 mm. The results show that when the magnetic field is on, there are the desirable variations including the homogenous temperature profile and faster solidification rate, as well as the alleviated central negative segregation and the reduced whole segregation level on the cross section of the billet. For the different magnetic fields, OPMF shows the strongest stirring effect, leading to the highest solidification rate at the initial solidification stage. Furthermore, the central negative segregation and the segregation level along the cross section are alleviated most as compared to other magnetic fields.