Effect of electromagnetic stirring on growth and morphology of primary silicon crystals of hypereutectic Al-Si alloys

The effect of electromagnetic stirring on the growth and the morphology of primary silicon crystals in hypereutectic Al-Si alloys during solidification has been studied systematically in this paper. The experimental results show that when the silicon content is equal to or lower than 30%, the primary silicon crystals can be refined significantly and their nodular shape can be obtained by electromagnetic stirring. When the silicon content is more than 30%, however, the refinement of primary silicon crystals is limited and there are still some large lamellar primary silicon crystals in the microstructure. When the cooling rate of the melt during electromagnetic stirring is increased, the grain size of the primary silicon crystals can be reduced. The grain size of the primary silicon crystals can be further decreased by the electromagnetic stirring with positive running and reverse running. In case of electromagnetic stirring, the main reasons for the refining and nodulizing of primary silicon crystals are: the homogenization of temperature field and solute field, the mechanical breakage of silicon crystals and the mutual friction among the crystals which restrains the anisotropic growth of primary silicon crystals.