Use of AC magnetic fields for flow control in solidifying metallic alloys

AC magnetic fields unlock an enormous potential to realize a variety of flow structures in molten metals, which makes the electromagnetic stirring attractive for controlling the melt flow during solidification. We present an experimental study concerning the solidification of AlSi alloys exposed to a pulsed rotating magnetic field. Isothermal flow measurements were carried out in order to understand the flow structures resulting from the application of time-modulated magnetic fields. These investigations revealed transient flow regimes showing distinct inertial oscillations and coherent vortex structures. An intense melt flow with periodic reversals of the flow direction at the solidification front can be created by a suitable choice of the magnetic field parameters. Such resonant states of the flow pattern have been proven to provide beneficial conditions for solidification processes. Optimized flow conditions realized in a solidifying melt result in a significant grain refinement without provoking the formation of harmful segregation freckles.