Separating Behavior of Nonmetallic Inclusions in Molten Aluminum Under Super-Gravity Field
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the rapid growth of automobile manufacturing and aerospace industry, high-quality aluminum alloys are increasingly needed. However, the presence of inclusions within aluminum alloys is considered to have a serious effect on the castability,[1] machinability,[2] and mechanical properties[3,4] of alloys. What is worse, it is almost impossible to avoid the formation of nonmetallic inclusions during the smelting and refining processes of alloys. Therefore, further reducing the level of nonmetallic inclusions in aluminum melt is essential. Various conventional methods have been proposed for removing inclusions from aluminum melt, such as sedimentation,[5] filtration,[6] bubble floatation,[7] and flux refining.[2] However, due to kinetics and operational limitations,[8] these methods are hardly effective for inclusions removal especially in the case of very fine size and small difference in density between inclusion and metal. For example, the regular gravity sedimentation method is only effective for inclusion larger than 100 lm.[9] Ceramic foam filter is generally effective to remove inclusions larger than 40 lm, but the removal efficiency of inclusions less than 10 lm is only 30 pct.[10] GAOYANG SONG, WENBIN XIN, and YUHOU YANG, Ph.D. Candidates, BO SONG, Professor, and ZHANBING YANG, Associate Professor, are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Xueyuan Road 30, Haidian District, Beijing 100083, P.R. China and also with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing. Contact e-mail: songbo@metall. ustb.edu.cn Manuscript submitted January 22, 2015. Article published online July 9, 2015. 2190—VOLUME 46B, OCTOBER 2015
Therefore, as the demand for cleaner metals becomes strict, more efficient methods for inclusion removal are strongly desired. Higee technology based on super gravity was originally proposed as a process intensification technology in 1979.[11] At present, it has attracted considerable interests from metallurgists because of its advantages of higher efficiency and free-pollution.[12] For example, according to the difference of density between impurities and melt, super gravity can effectively enrich and remove the impurity elements from aluminum alloys, which have been proved to be a potential method for the large-scale purification of metals.[13–15] In addition, enriching the valuable elements from different slags, such as rare-earth-rich slag, by super gravity was investigated, and the recovery ratios of valuable elements were prominent.[16–18] Nevertheless, the study on super-gravity separation of nonmetallic inclusions in the molten metal is seldom reported. In our previous study, the effect of gravity coefficient on inclusion removal in aluminum melt has been investigated by experiments.[19] The results show that inclusions can be effectively separated by super gravity and the separating efficiency increases with increasing of gravity coefficient. However, the moving velocity of inclusions under super-gravity field was
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