Melt injection – A novel method to produce metal foams

A novel method to produce foams from metallic melts was invented. It is referred here as melt injection method. An apparatus to produce foams by melt injection method was also developed. In this method, bubbles are created through air entrainment by injecting a jet of molten metal into a pool of molten metal. These bubbles rise to the surface of melt pool and create a foam there. This method works without the need of an additional processing step to produce or add stabilising particles in the melt. In this study, foam from pure Al melt was produced with 93% porosity. X-ray tomography was used to visualise the macrostructure of the foams. Microstructural and phase analysis were carried out using SEM and XRD, respectively. These studies revealed the formation of alumina layer and particles at the gas-solid interface of cell walls. Stabilisation of foams produced by melt injection method was attributed to the combined action of oxide layer and particles. The mechanism of bubble formation through air entrainment was studied by using a water model set up.