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The aim of this study is the investigation of a technological synthesis of MgAlON, which is a prospective coating material on ceramic foam filters for the filtration of magnesium, aluminum, and other metal melts. Thermodynamic calculations are performed, and the synthesis is carried out at 1500 °C in nitrogen atmosphere using samples consisting of different fractions of Al2O3, MgO, and AlN as starting materials. The effect of the quantity of these components on the conversion degree of the educts is evaluated. Furthermore, the effect of the holding time at the synthesis temperature, as well as the composition points or regions showing the highest conversion degree, are determined. XRD analysis is performed to evaluate the phase fractions and lattice parameters of the spinel after the respective reaction, and the nitrogen content of selected samples is evaluated. Sessile drop tests using AlSi7Mg are performed at 950 °C on selected sintered samples, determining their wettability, and therefore, applicability of the material in light metal melt filtration.

Due to its low density, high specific strength, and resource availability, magnesium and its alloys, such as AZ91, have a high potential for various lightweight applications. [1][2][3] A major hindrance for its widespread processing and use is its high reactivity, contributing to high dross-and sludge formation in the melt, which results in the metal being prone to corrosion and containing high quantities of nonmetallic inclusions, if the handling of the melt has not been accurate. The inclusions can be divided into oxide films, lumps, and clusters, as well as intermetallic particles; gas-and shrinkage pores, may also be present. [1][2][3][4][5] While measures are taken to protect and cleanse magnesium melts on industrial scale, such as gas purging treatments by Ar, N 2 , or Cl 2 , the usage of a variety of possible cover gases or fluxes and the optimization of the casting system toward a high grade of enclosure, [1,6] the application of ceramic foam filters is seen as a promising method for cleansing the melt and improving the mechanical properties of the casting. [7][8][9] Ideally, an auxiliary addition of fluxes would be avoided, while delivering the same quality of melt cleanliness. [10][11][12] Wu et al. emphasized the effectiveness of ceramic foam filters made from MgO or Al 2 O 3 in AZ91, improving the elongation-to-failure of cast samples up to relative 58%. [13] In contrast to oxidic, sintered filters, carbon-bonded ceramic foam filters show higher resistance toward thermal shock and creep deformation, as well as lower energy consumption during their manufacture, due to their lower manufacturing temperature. [14] After carbon-bonded alumina filters showed promising results in the filtration of steel melts, [15] short-term immersion tests in AZ91 have been carried out to evaluate their applicability in a magnesium alloy melt. Interface reactions between the AZ91 melt and variously coated ceramic Al 2 O 3 -C filters have been investigated after immersion times of 10-120 s. [16] The investigated filter coatings consisted of Al 2 O 3 , MgO-C, MgAl 2 O 4 , or carbon nanotubes/ alumina nanosheets. The formation of MgO in situ layers was shown on filter surfaces containing Al 2 O 3 or MgAl 2 O 4 . [16] Therefore, the next step toward assessing the applicability of oxidic as well as carbon-bonded ceramic foam filters in the field of magnesium melt filtration is the evaluation of their long-term resistance toward the magnesium melt, with a special regard toward melt contamination and inclusion content.In this study, additional ceramic foam filter materials, namely ZrO 2 [13] and MgAlON, [17] were added to the selected materials

Carbon‐bonded alumina foams, prepared by means of the replica technique, are typically used as metal melt filters for the filtration of steel due to their low wettability and their good resistance towards thermal shock and corrosion. According to literature, there are different process routes for the preparation of carbon‐bonded alumina foams, for example, dipping/rolling, spray‐ and dip/centrifugation coating. The influence of such process variations on macro‐ and microstructure and mechanical properties of carbon‐bonded ceramic foams has not been analyzed fully yet. Herein, carbon‐bonded alumina foams are manufactured by applying varying process routes regarding slurry preparation and coating steps. The macrostructure of the foams is analyzed by computer tomography, and for evaluating the microstructure, mercury intrusion porosimetry, optical microscopy, and scanning electron microscopy are applied. The determination of the cold‐crushing strength of the carbon‐bonded alumina foams allows the correlation of the structure and mechanical properties.