Filtration Efficiency of Functionalized Ceramic Foam Filters for Aluminum Melt Filtration
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high-quality aluminum production.[1] The main cleanliness criteria are dissolved hydrogen (potentially resulting in porosity) and non-metallic inclusions. For cast parts, non-metallic inclusions may impair the castability, the mechanical properties, and the machinability of the components.[2] In thin rolled products (e.g., aluminum cans and foil), inclusions can create pinholes, while in thick rolled products (used e.g., in transportation), inclusions may restrict fatigue life. These effects of inclusions illustrate the fact that the continuous improvement of melt cleanliness is essential to meet the ever-increasing quality requirements of today’s final products. Inclusions also have different origins, e.g., from scrap melting, oxidation of the melt surface, and erosion of the refractory material. In aluminum castings, CLAUDIA VOIGT and CHRISTOS G. ANEZIRIS are with the Institute of Ceramic, Glass and Construction Materials, Technical University Bergakademie Freiberg, Agricolastr. 17, 09599, Freiberg, Germany. Contact e-mail: [email protected] EVA JA¨CKEL and GOTTHARD WOLF are with the Institute of Foundry Technology, Technische Universita¨t Bergakademie Freiberg, Bernhard-von-Cotta-Straße 4, 09599, Freiberg, Germany. Contact e-mail: [email protected] FABIO TAINA and PIERRE LE BRUN are with the Constellium C-Tec, 725 rue Aristide Berge`s, 38341 Voreppe Ce´dex, France. TILO ZIENERT and ANTON SALOMON are with the Institute of Material Science, Technische Universita¨t Bergakademie Freiberg, Gustav-Zeuner-Straße 5,09599, Freiberg, Germany. Claudia Voigt and Eva Ja¨ckel have equally contributed. Manuscript submitted May 22, 2015. Article published online December 2, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
oxides (Al2O3, MgO, MgAl2O4, 3Al2O3Æ2SiO2, SiO2), carbides, and nitrides are the most common types of inclusion.[3] A simple, relatively cheap, and efficient way to meet the increasing requirements of aluminum castings relies on ceramic filters during the casting process. The ceramic foam filter (CFF) is the most common filter type for aluminum. A significant amount of work has been done to assess the efficiency of filters.[4,5] The filter is selected based on processing, thermo-mechanical, and economic criteria. It is known that inclusion capture in a CFF mainly occurs by hydrodynamic effects, which leads to instability risks during operation.[5] Creating a chemical interaction between the inclusion and a filter surface would be of interest with this respect. Furthermore, an active filter surface may lead to a selective capture of inclusions. There is only limited information, however, on the influence of the filter surface material on the filtration efficiency of liquid aluminum. According to Go¨rner et al., for example, an active filter surface made of AlF3 removes Na and Mg by forming NaF and MgF2.[6] According to Zhou et al., for example, an active coating made of enamel can capture non-metallic inclusions and dissolve Al2O3 during the casting of aluminum. They find an increase in the elongation at t
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