The effect of Eu (Europium) element on eutectic Si in Al–7Si alloys was studied by scanning electron microscopy (SEM), thermal analysis, electron backscattering diffraction (EBSD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to elucidate modification mechanism of Eu on eutectic Si. The results indicate that the addition of Eu changes the morphology of eutectic Si from coarse plate-like to fine fibrous. With the increase in Eu content, the number of eutectic cells gradually decreased and the size of eutectic cells increased. Meanwhile, the eutectic nucleation temperature (T_N) and the minimum temperature (T_Min) decreased, which is caused by the poisoning of AlP particles by Eu. The segregation of phosphorus was found at the center of coarse Al₂Si₂Eu particle, and the "phosphorus layer" was found at the boundary between the Al₂Si₂Eu particle and matrix. The length direction of plate-like eutectic Si was <110>, and its outer surface was {111} plane. Few parallel twins were observed in unmodified plate-like eutectic Si. However, the growth of Eu-modified fibrous eutectic Si was isotropous. Multiply twins were often observed in fibrous eutectic Si after modification. The adsorption of Eu was observed along the <112>_Si growth direction of eutectic Si and at the intersection of two {111}_Si twins, verifying the existence of the poisoning of the TPRE mechanism and IIT mechanism.

通过扫描电子显微镜 (SEM)、热分析、电子背散射衍射 (EBSD)、高角度环形暗场扫描透射电子显微镜 (HAADF- STEM) 阐明 Eu 对共晶 Si 的改性机制。结果表明，Eu的加入使共晶Si的形态从粗大的板状变为细小的纤维状。随着Eu含量的增加，共晶胞数逐渐减少，共晶胞体积增大。同时，共晶成核温度 ( T _N ) 和最低温度 ( T _Min) 降低，这是由 Eu 对 AlP 粒子的中毒引起的。在粗大的Al ₂ Si ₂ Eu 颗粒的中心发现磷的偏析，在Al ₂ Si ₂ Eu 颗粒与基体的边界处发现了“磷层” 。片状共晶Si的长度方向为<110>，外表面为{111}面。在未改性的板状共晶硅中观察到很少的平行孪晶。然而，Eu 改性的纤维状共晶 Si 的生长是各向同性的。在改性后的纤维共晶Si中经常观察到多孪晶。沿共晶Si的<112> _Si生长方向以及两个{111} _Si的交点观察到Eu的吸附 twins，验证了TPRE机制和IIT机制中毒的存在。