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Flow control during solidification of SnPb-Alloys using time-modulated AC magnetic fields

Räbiger, D.; Leonhardt, M.; Eckert, S.; Gerbeth, G.

Electromagnetic stirring during solidification has been proved to be a striking method for achieving a purposeful alteration of the microstructure of casting ingots, such as grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic groth (CET). However, the imposition of a rotating (RMF) or a travelling magnetic field (TMF) also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface. A permanent radial inward (RMF and downward TMF) or outward (upward TMF) flow along the solidification front is responsible for the transport of solute to the axis or the wall of the ingot resulting in typical freckle segregation pattern filled with alloy of eutectic composition. It was shown, that modulated AC magnetic fields are appropriate to overcome these problems.
This present study examines the directional solidification of SnPb alloys from a water cooled copper chill. Time-modulated combinations of rotating and travelling magnetic field are used to agitate the melt. Our results reveal the potential of modulated magnetic fields to realize an effective flow control for achieving grain refinement without the formation of segregation freckles.

Keywords: solidification; melt flow; electromagnetic stirring; grain refinement; segregation

Permalink: https://www.hzdr.de/publications/Publ-15368
Publ.-Id: 15368