(1. 清華大學 新材料國際研發(fā)中心，北京100084；
2. 清華大學 機械工程系，北京100084；
3. 清華大學 航天航空學院，北京100084)
摘 要: 對A356合金熔體進行電磁攪拌并澆注至高溫鑄型中直接制備半固態(tài)漿料。利用光學顯微鏡和掃描電子顯微鏡研究了過熱電磁攪拌對A356合金半固態(tài)漿料組織的影響。用Image-Pro Plus圖像分析軟件對α(Al)初晶的尺寸、圓整度以及Al-Si共晶間距進行分析測算。通過和直接澆注獲得的漿料組織進行對比，研究了電磁場對合金熔體結構及其后續(xù)凝固行為的影響。結果表明：隨著攪拌溫度的降低至液相線附近時，電磁場對熔體凝固行為的影響逐漸顯著；α(Al)初晶中樹枝晶不斷減少并逐漸轉變薔薇狀晶和非枝晶；水淬后Al-Si共晶組織也由粗大的片層狀轉變?yōu)榧毿〉睦w維狀和鱗片狀結構。這些現(xiàn)象主要歸因于電磁場作用下低溫熔體中Al、Si的微觀偏聚加劇，促進了α(Al)和共晶Si的形核。
關鍵字: 鋁硅合金；電磁攪拌；熔體結構；凝固行為；半固態(tài)
（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
