Fabrication of aluminum foams using vapor explosion

This work investigated the feasibility of using vapor explosion as a means of generating highly porous aluminum foams via a precursor method with little foaming agent. This technique employed a precursor fabricated by extruding an inexpensive A1050 aluminum alloy sheet combined with titanium hydride powder as the foaming agent. This precursor was heated at 700°C in an electric furnace to generate internal bubbles and subsequently immersed in water. The molten metal was found to expand rapidly and to a significant extent when placed in water as microscopic vapor explosions occurred in the bubbles. The maximum mean porosity of specimens fabricated in this manner was as high as 60%, compared with 20% for air-cooled specimens. These results demonstrate that a vapor explosion technique can be used to foam alloy precursors. Vapor explosion foaming was attempted modeling as plastic deformation of a spherical shell. The calculated pore diameter and porosity were larger than the experimental values. This is thought to be due to the fact that the outflow of water vapor during foaming was neglected. In addition, the diameter of the pore obtained by the vapor explosion might be underestimated because the pore connections with neighboring pores were neglected.