Aluminum foams - processing, properties, and applications

FOAMS AND OTHER HIGHLY POROUSMATERIALS with cellular structure find widespread use in everyday life for cushioning, insulating, damping, constructing, and filtering purposes and in many other applications. Such materials are known to have interesting property combinations, for example, high stiffness in conjunction with a very low specific weight (Ref 1). Cellular or foam structures can be placed into two broader categories (Ref 2): foams in which all of the pores are connected to each other and with the environment(open-pore foams), and foams in which every single pore is completely enclosed by the matrix (closed-pore foams). Strictly open- or closed-pore foams are rare, but most technical foams can approximately be assigned to one of those groups. However, there also exist foam types that combine considerable fractions of open and closed porosity, for example, sintered hollow-sphere structures (Ref 3) and advanced pore morphology aluminum foams (Ref 4).Porous structures can be found in nature in manifold forms and are produced in considerable quantities from polymer and nonmetallic inorganic materials. Porosity is also found in metallic components, in some cases as undesirable results of process conditions (gas and shrinkage porosity in castings, residual porosity in sintered parts) and in some cases purpose fully adjusted for special applications(filters, bearings). Nevertheless, the production and application of highly porous metal parts-the subject of this article-is relatively new, and such parts are still not in widespread use. For the present discussion, highly porous metals will be understood, somewhat arbitrarily, as those with at least 50% porosity.