Vacuum Foaming of Aluminum Scrap
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Vacuum Foaming of Aluminum Scrap J. A. Garabito1*, H. Granados 1, V. H. López1, A. R. Kennedy2, J. E. Bedolla1 1
Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio “U” Ciudad Universitaria, Morelia, Mich., México. 2 Faculty of Engineering, University of Nottingham, University Park, NG72RD, UK. E-mail: [email protected]
ABSTRACT In this study, scrap from the automotive industry was used to produce aluminium foams under vacuum. Chips of an aluminium alloy LM26 were melted and 1wt. % of Mg was added for creating a viscous casting with uniform distribution of oxides. An ingot was obtained of this alloy after casting and solidification. Trials for foaming this alloy were performed by re-melting pieces under vacuum at different temperatures. A window in the vacuum chamber allowed observation of the foaming and collapse of the porous structures was observed during cooling. Characterization of the aluminum foams revealed different levels of expansion, porous structures and degrees of drainage. The best foams were obtained at 680 °C with a density of 0.78 g/cm3. This technique appears to be a feasible low cost route for producing Al foams based on scrap material. Keywords: Al, Casting, Foam, Oxide, Porosity. INTRODUCTION The potential applications of aluminum foams, in virtue of their unique combination of physical and mechanical properties, have been envisaged in the area of the automotive industry, light weight construction materials, silencers, flame arresters, heaters and heat exchangers, catalysts, electrochemical applications, military armour vehicles and aircraft [1]. However, an inherent drawback of this kind of materials is given by their high cost, which is basically due to the production process use to produce cellular metals. Fabricating aluminium foams entirely from scrap is attractive owing to the cost savings offered by a lowcost matrix and the potential for eliminating expensive and embrittling foam-stabilising additives. For example, maintaining the Fe content in the lower levels and avoiding long periods of cooling are key aspects for preventing the formation of β-type Al-Fe-Si precipitates in a recycled Al-Si-Mg alloy [2]. Re-melted Al scrap in the form of used beverage cans, has been used [3], in conjunction with TiH2 blowing agent, to produce Al foams. It is reported that the scrap, via the oxides introduced from their surfaces, acts as a viscosity thickener, aiding foaming [3]. Highly distorted cell structures were, however, observed and attributed to the inhomogeneous distributions of the introduced oxides. It was concluded that the agglomerated oxide particles introduced could not act as a foam stabiliser. More recently, Alcoa reported the development of a commercial Al foam derived from scrap material made by a liquid route using CaCO3 as a foaming agent [4]. In order to obtain aluminum foams with close porosity, the present work is based in the selection of an economical production process along with the use of low price raw materials (recy
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