Effects of Electromagnetic Force on Segregation Phenomena of Primary Crystals and Changes in Solidification Structure of Al-10Fe and Al-25Si Alloys

In this study, solidification structure changes under electromagnetic force (EMF) were examined for Al-10Fe and Al-25Si alloys. One directional EMF was induced by applying DC currents of 100A and 130A with static magnetic fields. Solidification structure was examined using an optical microscope, X-ray computed tomography, and X-ray fluorescence mapping. When EMF was imposed from above the liquidus temperature, primary crystals were not segregated into one side of the ingots and instead were found to be segregated all along the ingot periphery for both Al-10Fe and Al-25Si. A fine hypo-eutectic structure containing Al dendrites was observed in areas devoid of primary crystals in the central parts of the Al-25Si ingots. These segregation phenomena of primary crystals did not occur when EMF was imposed from the point below the liquidus temperature, suggesting that EMF does not exert an effect on free crystals existing in the liquid metal. It also suggests that segregated primary crystals were not moved towards the periphery by EMF. It may prevent nucleating primary crystals from separating from the wall surface, hence enhancing nucleation on the wall and dense growth of crystals from the wall surface, resulting in a highly segregated solidification structure.