Abstract Microstructure and fracture behavior in a high-pressure die-casting Al-10 wt%Si alloy have been investigated using optical microscope (OM), scanning electron microscope (SEM) and a high-resolution laboratory computed tomography (CT). The results showed that a typical heterogeneous microstructure of the alloy comprised α-Al rich region, eutectic silicon band region and porosity. The microstructure patterns highly dependent on fluid convection and rapid solidification. Under high filling speed, externally solidified crystals (ESCs) and the growing dendrites migrated in center and formed α-Al rich region. Si particles was discharged and enriched in the final solidified liquid, forming eutectic silicon band. Hard Si particles and brittle Fe-rich phases served as obstacles prevented dislocation migration, causing local stress concentration. Due to large movable slip systems in α-Al rich region, the propagation path of the crack was greatly extended. Net-shrinkage that induced by dense impinging dendrites led to the microcracks along the boundary of dendrites which promoted intergranular fracture.

中文翻译：

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高压压铸Al-10wt%Si合金的显微组织和断口表征

摘要 使用光学显微镜 (OM)、扫描电子显微镜 (SEM) 和高分辨率实验室计算机断层扫描 (CT) 研究了高压压铸 Al-10 wt% Si 合金的显微组织和断裂行为。结果表明，该合金典型的异质组织包括富α-Al区、共晶硅带区和孔隙。微观结构模式高度依赖于流体对流和快速凝固。在高填充速度下，外部凝固晶体（ESCs）和生长的枝晶向中心迁移并形成富含α-Al的区域。硅颗粒被排出并富集在最终凝固的液体中，形成共晶硅带。硬硅颗粒和脆性富铁相作为阻碍位错迁移的障碍物，导致局部应力集中。由于富α-Al区域存在较大的可动滑移系统，裂纹的传播路径大大延长。密集撞击枝晶引起的净收缩导致沿枝晶边界的微裂纹，促进晶间断裂。