Numerical Investigation of Axial Magnetic Field Effects on Melt Flow and Macrosegregation in TC17 Alloy Vacuum Arc Remelting

Abstract

The TC17 alloy ingot is produced through vacuum arc remelting (VAR). However, the self-induced electromagnetic force enhances forced convection, which can lead to potential macrosegregation, particularly as the ingot diameter increases. To address this issue, an engineering solution involves applying an axial magnetic field (AMF) to modify the flow in the molten pool. In this study, the solidification process of the VAR ingots was simulated using a built-in solidification model in ANSYS Fluent. The solver is based on the finite volume method. A 2D-axisymmetric simulation considering the swirl flow was performed, incorporating the multi-physics coupling of heat transfer, solute transfer, melt flow, and electromagnetic effects. The reasonable agreement between the simulation and experiment regarding the molten pool contour and segregation profile demonstrates the robustness and applicability of the model. On this base, a numerical parameter study was performed to study the effect of the AMF, with particular emphasis on the alternative AMF direction change and the resulting melt flow. The results show that the applied AMF generates an electromagnetic force in the tangential direction, creating a rotational swirl flow and a centrifugal force directed radially outward. Consequently, a secondary flow along the side walls towards the bottom centre within the molten pool is induced. This modified flow pattern in the molten pool helps reduce macrosegregation in VAR ingots, hence improving the service life and mechanical properties of aviation titanium alloys. Qualitative simulation-experiment agreement regarding the shape of the molten pool profile and segregation distribution is achieved. However, future model improvement, e.g. considering the solidification crystal morphology, multiphase flow, and potential formation of freckles, is necessary.