Effect of Multi-Scale Thermoelectric Magnetic Convection on Solidification Microstructure in Directionally Solidified Al-Si Alloys Under a Transverse Magnetic Field

Abstract

The influence of a transverse magnetic field (B < 1 T) on the solidification structure in directionally solidified Al-Si alloys was investigated. Experimental results indicate that the magnetic field caused macrosegregation, dendrite refinement, and a decrease in the length of the mushy zone in both Al-7 wt pct Si alloy and Al-7 wt pct Si-1 wt pct Fe alloys. Moreover, the application of the magnetic field is capable of separating the Fe-rich intermetallic phases from Al-7 wt pct Si-1 wt pct Fe alloy. Thermoelectric magnetic convection (TEMC) was numerically simulated during the directional solidification of Al-Si alloys. The results reveal that the TEMC increases to a maximum ($u_{\rm{max} }$) when the magnetic field reaches a critical magnetic field strength ($B_{\rm{max} }$), and then decreases as the magnetic field strength increases further. The TEMC exhibits the multi-scales effects: the $u_{\rm{max} }$ and $B_{\rm{max} }$ values are different at various scales, with $u_{\rm{max} }$ decreasing and $B_{\rm{max} }$ increasing as the scale decreases. The modification of the solidification structure under the magnetic field should be attributed to the TEMC on the sample and dendrite scales.