The manufacture of spherical salt beads and their use as dissolvable templates for the production of cellular solids via a powder metallurgy route

A novel process has been demonstrated for the manufacture of spherical salt beads with sizes between 0.5 and 3.0 mm using a flour-based paste which is mechanically disintegrated in oil. The process has been shown to be repeatable. After thermal decomposition of the flour from the beads they contain a high fraction (16%) of interconnected porosity. Tapped beds of salt beads have been partially filled with an Al alloy powder using vibration. The fine Al powder penetrates the gaps between the salt beads, preserving the structure of the tapped bed, and is a highly attractive alternative to powder mixing methods. After compaction and sintering, and dissolution of the salt, a highly porous component is produced. The porous nature of the beads, which allows water to penetrate them, results in rapid dissolution of the salt from the component. Cellular aluminium parts can be produced with very small deviations in density due to the good control that is possible over the mass fractions of powders that are used and the compaction conditions. The reproducibility in the density results in reproducible mechanical properties.