Structural Characterisation of Malallic Foam Produced by P/M Method

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Cellular metals are of interest both from the viewpoint of stiff lightweight structures and theire functional efficiencies in sound absorption, impact energy absorption, electromagnetic shielding and vibration damping. In the present project, a powder metallurgical technique for the production of foamed cellular aluminum has been studied. Obtained results are as follows :1) The foamed aluminum produced by free expansion usually shows excessive bulging which is accompanied with a rather large surface roughness and micro-cracks on its bulged surface. A use of a steel sleeve to restrict the bulging of the compacts during expansion is effective both to improve the surface quality and to achieve a higher porosity of the foamed products by preventing the evolved gas to leak.2) Optimum foaming conditions to produce aluminum foams with very low apparent densities are established : the foaming temperature and the addition of the foaming agent are of most important to controll both the porosity achieved and the cellular structure. Floatable aluminum foam can be produced by controlling its cell structure as closed one.3) It is determined from the image analizing study that the homogeneity of the cellular structures is much improved by the P/M process as compared with the conventional liquid process.4) The cellular structures obtained by the P/M process bear a striking resemblance to the Voronoi's cell.5) Foamable beads and/or wires are abvailable for expanding forming of foamed melallic parts with complex shape.