The Manufacture and Characterisation of Aluminium Foams Made by Investment Casting Using Dissolvable Spherical Sodium Chloride Bead Preforms

Open cell Al foams have been made by infiltrating molten Al into preforms made from porous salt spheres. Infiltration has been effected using simple pressure-assisted vacuum investment casting where the maximum infiltration pressure difference was less than 36 psi. The preform and resulting foam density decreased with increasing compaction pressure and the foam density increased with increasing infiltration pressure. For low pressure infiltration, and high density preforms, salt dissolution was rapid due to the porous nature of the salt spheres. Infiltration of molten Al occurred into the beads and, for high density preforms and higher infiltration pressures, the volume of metal in the beads exceeded that in the cell walls, drastically decreasing the NaCl dissolution rate. A simple approach is shown whereby the data from mercury porosimetry can be used to predict the resulting foam density, thereby aiding the design of preform and beads structures.