Influence of an axial high magnetic field on the liquid-solid transformation in Al-Cu hypoeutectic alloys and on the microstructure of the solid

The influence of an axial high magnetic field (up to 10 T) on the liquid-solid interface morphology and microstructure of the solid has been investigated experimentally during Bridgman growth of Al-Cu hypoeutectic alloys. It is found that the field causes the interface to become destabilized and irregular, and promotes planar-cellular and cellular-dendritic transformation. The field has a great influence on the cellular and dendrite array morphology. Indeed, the field causes severe distortion in the cellular array and enhances cell branching. The field makes the morphology of the dendrite array more complex and, with the increase of the magnetic field intensities and decrease of the growth velocities, the dendrites become broken and orientate with the (III)-direction along the solidification direction instead of the (I 00 -direction. Furthermore, the field also enlarges the primary dendrite spacing and promotes the branching of the dendrites to form higher-order arms. The above phenomena may be attributed to the change of the equilibrium partition coefficient k and the liquidus slope m(L) caused by the field, the magnetic anisotropy of the alpha-Al crystal and the flow created by the thermoelectromagnetic convection. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.