2004Effect of inhibitor gas on mould-magnesium reactions in investment casting.pdfVIP

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2004Effect of inhibitor gas on mould-magnesium reactions in investment casting.pdf

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2004Effect of inhibitor gas on mould-magnesium reactions in investment casting

EFFECT OF INHIBITOR GAS ON MOULD-MAGNESIUM REACTIONS IN INVESTMENT CASTING Zhan Zhang1*, Guy Morin2 1Intermag-Modelex Inc., 820 Ch. Olivier St-Nicolas , (Quebec), G7A 2N1, Canada 2Centre Intégré de Fonderie et de Métallurgie, 3247, rue Foucher, Trois-Rivières, (Quebec), G8Z 1M6, Canada * Now with Alcan International Ltée, Arvida Research and Development Center, 1955 Mellon Blvd., Jonquière , G7S 4K8, Canada Keywords: mould-magnesium reactions, inhibitor gas, investment casting. Abstract In order to assess the behaviour of mould-magnesium reactions, the ceramic shell moulds with different binders and refractory particles were prepared for pouring AZ91 magnesium alloy. To restrict mould-magnesium reactions, inhibitor gas was guided into shell moulds for removal of oxygen in shell moulds and formation of barrage between mould and magnesium. The results of experiments show that a mixture of CO2 and proper concentration of SF6 used as inhibitor gas can effectively limit mould- magnesium reactions. A surface analysis with AES (auger electron spectroscopy) and ESCA (electron spectroscopy for chemical analysis) has been performed on the surface of magnesium parts cast under the inhibitor gas. It was discovered that a special layer appeared on the part surface, in which the elements such as magnesium, oxygen, fluorine, aluminum, sulphur, silicon, etc. were detected. The mechanisms of mould- magnesium reactions and their prevention are discussed in this paper. Introduction Ceramic shell moulds are made by applying ceramic coatings, which consist of ceramic slurry and coarse ceramic particles, to wax patterns. The main components of slurry are binder and filler, fine refractory particles. According to the thermodynamic data of refractory materials commonly used in shell moulds, magnesium would react with silica, zirconia, and alumina at the temperature from 20 to 1000°C [1]. The rank of the free energy of the materials is in the order with increasing in the following sequen