Morphological instabilities and alignment of lamellar eutectics during directional solidification under a strong magnetic field

The effects of a strong magnetic field on Al-Al2Cu and Pb-Sn lamellar eutectics during directional solidification have been investigated experimentally. The results show that the application of a strong magnetic field caused "tilting and oscillatory" morphological instabilities and deformation of the eutectic lamellae. Moreover, it was found that the Al-Al2Cu eutectic grain became aligned under a strong magnetic field and that with an increase in the magnetic field intensity this alignment was gradually enhanced. Further, the stresses caused by the magnetization force and the thermoelectric magnetic force during directional solidification under a strong magnetic field were analyzed and it was found that they are likely responsible for the "tilting and oscillatory" morphological instabilities and deformation. This is experimental evidence that the stresses imposed on a solid are capable of inducing the morphological instabilities of lamellar eutectics. The magnetic crystalline anisotropy of the Al2Cu phases and the growth relationship between the primary Al2Cu phase and the eutectic phases was investigated and it was found that the Al2Cu phase had a remarkable magnetic crystalline anisotropy which determined the growth of the Al-Al2Cu eutectic grain. Thus, alignment of the Al-Al2Cu eutectic grain under a strong magnetic field may be attributed to the magnetic crystalline anisotropy of the Al2Cu phase. Based on the growth behaviour of Al-Al2Cu and Pb-Sn lamellar eutectics under a strong magnetic field, an alignment model of lamellar eutectics during directional solidification under a strong magnetic field is proposed. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.