Effect of Modulated Helical Magnetic Field on Solidifying Segregation of Sn–3.5 Wt Pct Pb Alloy in a Directional Solidification

In this paper, a modulated permanent helical magnetic field is imposed to improve segregation during directional solidification in a binary Sn–3.5 wt pct Pb alloy. The magnetic force created by this magnetic field significantly interferes with heat, mass and momentum transfer of molten metal during solidification. Our experimental results show that this magnetic field, with an appropriate modulation frequency, can not only promote columnar-to-equiaxed transition (CET) but also significantly reduce solute segregation otherwise caused by conventional helical magnetic fields. Our analysis demonstrates the advantages of this approach over natural convection and conventional electromagnetically forced convection.