Influence of thermoelectric effects on the morphology of Al-Si eutectic during directional solidification under an axial strong magnetic field

摘要

Because of thermoelectric (TE) effects, a local electric current density appears at an interphase interface during directional solidification of a binary metallic eutectic alloy. Thus, when a magnetic field is applied, a Lorentz force is created. As a result, a thermoelectric magnetic convection (TEMC) in the liquid near the liquid/solid interface will develop. At the same time, a thermoelectric magnetic force (TEMF) will produce on eutectic phases. In this work, first of all, the TEMC and the TEMF during directional solidification of Al-Si eutectic are numerically simulated. The results show that when an applied magnetic field is below 10T, the values of the TEMC and the TEMF increase as the magnetic field increases. Under a 10T magnetic field, the values of the TEMC and the TEMF are of the order of 10~(-6)m/s and 10~6N/m~3, respectively. Then, Al-Si alloys are solidified directionally under an axial strong magnetic field and the effect of the magnetic field on the morphology of Al-Si alloys is investigated. The experimental results reveal that the application of the magnetic field has changed the morphology of Al-Si alloys significantly. Indeed, the magnetic field has destroyed the coupled growth of Al-Si eutectic and induced the CET of the primary Si dendrite. This is attributed to the TEMC in the liquid and the TEMF acting on eutectic phases. Above experimental results imply that thermoelectric effects play an important role to affect the growth of Al-Si eutectic during directional solidification under the strong magnetic field. Present work may initiate a new method to modify the microstructure of Al-Si alloys via an application of the magnetic field during directional solidification.