Effect of Electromagnetic Vibration on the Agglomeration Behavior of Primary Silicon in Hypereutectic Al-Si Alloy
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well known that aluminum alloys have been used widely in automotive, aviation, construction, and other industries. However, inclusions in aluminum alloys deteriorate mechanical properties and increase porosity while decreasing corrosion resistance. Four purification methods are conventionally used: gravity sedimentation, flotation, filtering, and electromagnetic separation.[1] But they all have limited ability to remove fine inclusions. For example, the gravity sedimentation method acts only on inclusions larger than 100 lm,[1] and the ceramic foam filter method only has an efficiency in removing 30 pct inclusions smaller than 10 lm.[2] As a promising method, electromagnetic separation is easily implemented[2–5] in the production of ultraclean metals. But it is also difficult to remove fine inclusions efficiently as the forces acting on them are small. One feasible way to remove the fine inclusions from the alloy melts is agglomerating the fine inclusions into large clusters or particles that can be separated easily. Miki et al.[6] found that many agglomeration pairs in the steel ingot were treated with a rotating electromagnetic field, and this inclusion agglomeration effect improved the deoxidation capability of the electromagnetic stirring YECONG HAN and YANJIE HE, Masters, are with the Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, P.R. China. QIULIN LI, Professor, is with the Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University. WEI LIU, Professor, is with the Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University. Contact e-mail: [email protected] Manuscript submitted October 1, 2011. Article published online March 9, 2012 1400—VOLUME 43A, MAY 2012
system substantially. He et al.[7] found that the silicon particles subjected to traveling magnetic field (TMF) tend to congregate and form large silicon clusters in the aluminum melt. This fact improved the separating efficiency of the combined magnetic field, which consists of rotating magnetic field and TMF.[7] Electromagnetic vibration may be another good method to agglomerate the inclusions in melts. It causes an intense oscillating flow and turbulence, and thus, it highly increases the probability of collision between the inclusions.[8] And the inclusions may be inclined to agglomerate to reduce the interfacial energy after collision. Radjai et al.[9] have pointed out that the silicon particles in the aluminum melt locally agglomerated during the solidification process under electromagnetic vibration. Numerous studies focused on the application of different types of electromagnetic fields and different separation apparatus for the removal of inclusions.[3,10,11] However, little work has been done on the agglomeration effect of electromagnetic vibration on the inclusions in melts. In this article, the primary silicon particles in a hypereutectic Al-Si alloy melt are regarded as nonmetallic inclusions. Electromagnetic vibration is induced by the simultaneous
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