(1. 清华大学 新材料国际研发中心，北京100084；
2. 清华大学 机械工程系，北京100084；
3. 清华大学 航天航空学院，北京100084)
摘 要: 对A356合金熔体进行电磁搅拌并浇注至高温铸型中直接制备半固态浆料。利用光学显微镜和扫描电子显微镜研究了过热电磁搅拌对A356合金半固态浆料组织的影响。用Image-Pro Plus图像分析软件对α(Al)初晶的尺寸、圆整度以及Al-Si共晶间距进行分析测算。通过和直接浇注获得的浆料组织进行对比，研究了电磁场对合金熔体结构及其后续凝固行为的影响。结果表明：随着搅拌温度的降低至液相线附近时，电磁场对熔体凝固行为的影响逐渐显著；α(Al)初晶中树枝晶不断减少并逐渐转变蔷薇状晶和非枝晶；水淬后Al-Si共晶组织也由粗大的片层状转变为细小的纤维状和鳞片状结构。这些现象主要归因于电磁场作用下低温熔体中Al、Si的微观偏聚加剧，促进了α(Al)和共晶Si的形核。
关键字: 铝硅合金；电磁搅拌；熔体结构；凝固行为；半固态
（1. Advanced Materials International R&D Center, Tsinghua University, Beijing 100084, China;
2. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China;
3. School of Aerospace, Tsinghua University, Beijing 100084, China）
Abstract:The A356 melt was stirred by an electromagnetic field and then was poured in a high temperature mold. Thus the semi-solid slurry of A356 alloy was prepared directly. The influence of electromagnetic stirring (EMS) above alloy liquidus on microstructure of A356 alloy slurry was investigated by optical microscope and scanning electron microscope. The diameter and roundness of α(Al) and the space of Al-Si eutectic were measured by Image-Pro Plus. Compared with the microstructure of A356 alloy slurry without EMS, the influences of electromagnetic stirring on the structure of A356 melt and its solidification behavior were studied. The results show that the influence of electromagnetic stirring on the following solidification behavior is more outstanding when the stirring temperature is near the liquidus; the number of α(Al) dendrites is declined and the morphology is transformed into rosiness and non-dendritic grains; the Al-Si eutectic’s transition from lamellar structure to fibrous structure occurs in the eutectic reaction too. This phenomenon is probably attributed to the increase of nucleation rate, which is caused by segregation of Al and Si at the micro-scale levels after EMS.
Key words: aluminum silicon alloy; electromagnetic stirring; melt structure; solidification behavior; semi-solid
