Distribution and Morphology of α-Al, Si and Fe-Rich Phases in Al-Si-Fe Alloys under an Electromagnetic Field

Natural convection is present in all liquid alloys whereas forced convection may be applied as the method to improve material properties. To understand the effect of forced convection, the solidification in simple cylindrical samples was studied using a rotating magnetic field with a low cooling rate and low temperature gradient. The composition of Al-Si-Fe alloys was chosen to enable independent growth or joint growth of occurring α-Al, β-Al₅FeSi, δ-AlFeSi_T4 phases and Si crystals and analysis of structure modifications. Stirring produced rosettes instead of equiaxed dendrites, which altered the secondary dendrite arm spacing and the specific surface of α-Al and also modified β-Al₅FeSi. The melt flow caused a modification of iron rich δ-AlFeSi_T4 phases and gathered them inside the sample of the β/Si alloy, where δ together with Si were the first precipitating phases. The separation of δ and β phases and Si crystals was found by their joint growth along the monovariant line. A reduction in the amount of Si crystals and the formation of a thin Si-rich layer outside the sample was observed in the hypereutectic alloy. The separation and reduction in iron-rich phases may play a role in the removal of Fe from Al-Si alloys, and the control of Si may be applied in materials for the solar photovoltaic industry.