INFLUENCE OF THE FOAMING PRECURSOR'S COMPOSITION AND DENSITY ON THE FOAMING EFFICIENCY, MICROSTRUCTURE DEVELOPMENT AND MECHANICAL PROPERTIES OF ALUMINIUM FOAMS

摘要

In this work, the influence of the composition, density and porosity of foaming precursors on the foaming efficiency, microstmcture development and mechanical properties of aluminium foams are presented and discussed. The foams were prepared, starting from precursors made either by powder metallurgy (PM) or by the melt route. Following the PM route, precursors were made by mixing Al powder and 3-10 % of volume fractions of dolomite or calcium carbonate particles of particle size from 20 ìm to 120 ìm and cold isostatically pressing the mixture at 700 MPa. In the case of the melting route, precursors were made by introducing dolomite or calcium carbonate particles directly into the molten aluminium at 700 °C. After melt stirring, the precursors were prepared by casting the semi-solid slurry into a cylindrical, water-cooled mould. Finally, aluminium foams were made in all cases by inserting precursors into a cylindrical stainless-steel mould and heating the arrangement at 750 °C for 10 min. After that, the mould was removed from the furnace and the foaming process was stopped by cooling in air to room temperature. The microstructure of the obtained foams was investigated by optical and scanning electron microscopy (SEM-EDS), while XRD was applied for a detailed identification of phases. The quality of the precursors was evaluated by determining their mechanical properties (uniaxial room-temperature compression stress-strain curve, compressive strength and energy absorption after a 30 % strain) and the foaming efficiency (the relative density of the foam obtained). The concentration of the foaming agent and the density of precursors were found to have a detrimental influence on the foaming efficiency as well as on the foam's microstructure and mechanical properties. The foaming of precursors with open porosity were inefficient.