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

摘要

The effects of a strong magnetic field on Al-Al_2Cu and Pb-Sn lamellar eutectics during directional solidification have been investi-gated 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-Al_2Cu 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 stres-ses 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 defor-mation. 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 Al_2Cu phases and the growth relationship between the primary Al_2Cu phase and the eutectic phases was investigated and it was found that the Al_2Cu phase had a remarkable magnetic crystalline anisotropy which determined the growth of the Al-Al_2Cu eutectic grain. Thus, alignment of the Al-Al_2Cu eutectic grain under a strong magnetic field may be attributed to the magnetic crystalline anisotropy of the Al_2Cu phase. Based on the growth behaviour of Al-Al_2Cu 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.