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通过电磁悬浮(EML)熔炼设备对Al-70%Si合金进行深过冷处理,利用高速摄影仪(HSC)和SEM分别对凝固过程和凝固后的组织进行了观测,研究了不同过冷度下初生Si的生长规律.结果表明,过冷度对初生Si的生长有很大影响.当过冷度较小时,初生Si为粗大的长条状,有特殊的边和面,且具有明显的孪晶痕迹,表现出小平面生长的特征;当过冷度较大时,初生Si为细小的枝晶和球状晶,表面光滑,表现出非小平面生长的特征;当过冷度居于中间时,初生Si为粗大的块状和规则排列的枝晶状,块状有特殊的边和面,枝晶表面光滑,表现出小平面和非小平面混合生长的特征.随着过冷度的增加,初生Si的生长方式由小平面生长转变为中间方式生长,再由中间方式生长转变为非小平面生长,生长方式间发生转变的临界过冷度分别为122和230 K.
Al-70% Si alloy was deeply undercooled by electromagnetic levitation (EML) smelting equipment. The solidification process and the microstructure after solidification were observed by HSC and SEM respectively. The effects of primary cooling Si.The results show that undercooling has a great influence on the growth of primary Si.When the degree of undercooling is small, primary Si is coarse and long strip with special edges and faces, and has obvious twin Trace, showing the characteristics of facet growth; when the undercooling is large, primary Si is fine dendrites and spherulites, the surface is smooth, showing non-faceted growth characteristics; when the degree of subcooling in the middle, the primary Si is coarse and regularly arranged dendrites, with special edges and faces, dendrites with smooth surface, showing the characteristics of mixed growth between facets and non-facets.As the degree of undercooling increases, Si The growth mode of Si is changed from facet growth to intermediate growth, then from intermediate growth to non-facet growth, and the critical undercooling transitions between growth modes are 122 and 230 K, respectively.