Al-Si合金熔析结晶过程中界面稳定性与硅晶体生长的控制

Control of the Stability of Solid-Liquid Interface and Growth of Si Crystal during Solvent Refining Process of Al-Si Alloy

利用交变磁场与温度场耦合作用,通过控制Al-Si合金熔析结晶时硅晶体生长过程中固液界面的稳定性,解决硅熔析精炼过程中硅晶体与合金熔剂分离难的问题,分析了耦合物理场在结晶过程中的作用机理.结果表明,硅铝合金熔体中硅含量越高,越难发生成分过冷现象,固液界面越稳定,有助于生成致密的块状硅晶体;坩埚内径由3 cm降至1 cm,熔体内温度场分布发生变化,固液界面曲率由16.7变为125,形成的硅晶体更致密,硅晶体与合金熔剂的分离效果增强,硅晶体区域所占比例由0.57减小至0.42;下拉速度越慢,固液界面越稳定,硅晶体与合金熔剂的原位分离效果越好,当其为0.05 mm/min时,样品底部硅晶体比例为99.9%,而样品顶部基本没有硅晶体.电磁场的电磁搅拌作用可增大熔体流动,强化熔体传质,增大固液界面前沿硅含量,提高固液界面稳定性.

To solve the problem of separation of Si crystal with melting agent, the stability of solid-liquid interface was controlled during Si crystal growth in A1-Si melt by combining electromagnetic and thermal fields, and the functional mechanism of physic fields during the crystallization analyzed. The result showed that with increasing of Si content in A1-Si melt, the occurrence of compositional supercooling phenomenon was more difficult, and the solid-liquid interface was more stable, which was beneficial to the densification of Si crystals. When the inner diameter of crucible was reduced from 3 to 1 cm, the temperature distribution in the alloy melt changed, and the curvature of solid-liquid interface varied from 16.7 to 125, which resulted in denser Si crystals, enhanced separation efficiency of Si crystals with melting agent, and reduced existing portion of Si crystals from 0.57 to 0.42. The slower the lowering rate, the stabler the solid-liquid interface, and the better the in situ separation effect of Si crystals with melting agent. When the lowering rate was 0.05 mm/min, the content of Si crystals reached 99.9% at the bottom of sample, while the Si crystals could hardly be found on the top. Electromagnetic stirring could strengthen the flow and mass transfer in the melt, so the Si content in the frontier of solid-liquid interface was increased and the interfacial stability enhanced.