Effect Of Impurity Phase Migration On Al-30wt.%Si Solvent Refining With Zr Additions During Directional Solidification

The effect of migration behavior of the impurity phases on the Al-30wt.%Si solvent refining during the electromagnetic directional solidification process was investigated. The simulation shows that there is a strong convection inside the melt, and it weakens with the pull-down process of the samples. Because the nucleation and growth temperature of the ZrB2 phase is higher than that of the primary Si, the strong convection in the melt results in a distribution of the ZrB2 phase at the top and the bottom of the sample. With the excessive Zr addition, the ZrSi2 phase, whose growth temperature range is between the liquidus and the eutectic point, mainly appears in the Si-rich area. The distribution position of the two Zr-rich phases in the sample is affected by different factors (flow field and temperature gradient), which has a great influence on the impurity contents in the primary Si. Separate tests on different areas of the Si-rich part in the samples show that the B content in the different areas presents a gradient distribution, and the B content of the upper part is obviously lower than that of the bottom part. This study provides a new idea for improving the control of the impurity phase distribution during the directional solidification of Al-Si solvent refining.