Removal of Inclusions from Molten Aluminum by Supergravity Filtration
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num generally contains a large number of contaminants, such as nonmetallic inclusions (especially oxides, nitrides, and carbides), intermetallic compounds (such as iron-rich phase), and dissolved gasses (especially hydrogen), during the processes of smelting and refining.[1] The presence of these contaminants, such as nonmetallic inclusions, is considered to have detrimental effects on the castability,[2] machinability,[3] and mechanical properties[4] of alloys. The increasing desire for high-quality aluminum alloys to be used in the automobile manufacturing and aerospace industry, as well as for construction and electrical components,[5] has strongly motivated manufacturers to produce cleaner aluminum alloys. Therefore, further reducing the level of inclusions from aluminum melt is necessary with respect to the metal yield and quality. Removal of inclusions from liquid aluminum alloys is an essential melt treatment step in the refining process. Many different conventional methods have been applied for removing inclusions from aluminum melt, such as sedimentation,[6] filtration,[5,7] bubble floatation,[8] and flux refining.[9] However, these methods can hardly meet the cleanliness level requirement in many applications because of their low removal efficiency in the case of GAOYANG SONG, YUHOU YANG, and JING ZHANG, Ph.D. Candidates, BO SONG, Professor, and ZHANBING YANG, Associate Professor, are with the School of Metallurgical and Ecological Engineering and the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China. Contact email: [email protected] Manuscript submitted April 25, 2016. Article published online September 20, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
very fine size and small difference in density between inclusion and metal.[6,10] Therefore, innovative or improved methods for removing inclusion deserve to be explored. In recent years, the supergravity method has attracted much attention due to its efficiency in removing the inclusions and its higher yield.[11] Supergravity technology has been studied to remove the impurity elements (such as Fe and Si) from aluminum alloys[12,13] and to purify metallurgical grade silicon,[14] as well as to enrich the valuable elements (such as Ti, V, and RE) from various metallurgical slags,[15–17] and has been proven to be a potential high-efficiency separation method. However, the study on separating nonmetallic inclusions from the aluminum melt with supergravity is seldom reported as a whole. Separation behavior of nonmetallic inclusions (MgAl2O4 spinel) in aluminum melt with supergravity has been investigated in our earlier study,[18] which indicated that supergravity separating technology for purifying metal melt is an effective method. However, it is noteworthy that inclusions were just gathered to the bottom area of samples and not separated from aluminum matrix thoroughly. Also, further treatment is required to separate these inclusions using mechanical and chemical methods. Therefore, it is essential to de
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