In Situ Observation of Dendritic Growth during Directional Solidification under Magnetic Field

Controlling dendritic solidification is crucial for determining mechanical properties in roll casting. This study employs a transparent succinonitrile (SCN)–Fe3O4 model alloy for in situ observation of directional solidification under magnetic fields (50–70 mT). Here, it was found that the magnetic field can progressively thin the dendritic layer, enhancing fragmentation, and widening the kiss point to ∼7 mm at 70 mT. Meanwhile, the field can also promote a transition from coarse dendritic to refined equiaxed structures. A force-flow-interface mechanism is proposed, where magnetic forces generate convection that disrupts transport processes and destabilizes the solid–liquid interface according to the Mullins–Sekerka criterion. Verification with 6061 aluminum alloy confirms that magnetic fields reduce defects, refine grains, and improve tensile properties, providing insights for electromagnetic materials processing.