深过冷Si-Al合金的凝固过程和组织特征研究

Study on the Solidification and Structure Behaviors of Highly Undercooled Silicon-aluminum Alloy

用高速摄影和扫描电镜研究了电磁悬浮熔炼条件下,Si-20%Al合金的凝固过程及其组织特征。结果发现,将Si-20%Al合金在氩气中进行电磁悬浮熔炼可使其获得375K的过冷度。过冷合金先结晶相的形貌和尺寸与其形核过冷度有关。在小过冷度下,合金的初生硅为粗大的长片多面体;过冷度增大到126 K后,初生硅变为均匀细小的等轴多面体。在过冷度小于328 K以前,初生硅的表面有明显棱角,表现出小平面生长的特征;过冷度大于328 K后,初生硅变为细小均匀表面有圆滑钟乳石状凸起、没有明显棱角的不规则多面体,表现出了非小平面生长的特征。

Using an electromagnetic levitation facility, droplets of Si-20at pct AI alloy were undercooled to a degree as high as 375 K by levitating it in pure argon. The crystal morphologies on the surface of the droplets during solidification process and after solidification were recorded by using a high speed camera and observed by scanning electron microscopy. The crystal morphology and size were found to vary with the nucleation undercooling. The morphology of the primary silicon is large elongate polyhedron in low undercooling region, and transforms to small isometric polyhedron when the undercooling is increased beyond 126 K. The surface of the polyhedral primary silicon has pronounced edges when the undercooling is lower than 328 K, which shows the behavior of lateral growth. As the undercooling is increased over 328K, the morphology of the primary silicon transforms to irregular polyhedron with one or several stalactitic bulges on its surface, which shows the behavior of continuous growth.