New foam stabilising additive for alumnium

Abstract

Liquid metals are mostly made foamable by Ca additions followed by a thickening period. There is a need for an additive that can be easily admixed to an aluminium alloy melt and makes this melt foamable. We have selected aluminium-based grain refiner composites to test their foamability. TiB₂, TiC or TiAl₃ particles were produced in the melt by flux-assisted melting using fluoride salts. The particle size was kept below 1 im for TiB₂ and TiC and around 10µm for TiAl₃. The composites were heated to above their melting point (700°C) and were then foamed by either the addition of TiH₂ or by injecting gases into the melt directly. Foams were successfully produced using TiB₂ and TiC particles, while TiAl₃ did not lead to any foam. Foam stability increased from TiB₂ to TiC. Ex-situ characterisation of the foams by SEM showed that the particles segregate to the surfaces of the cell walls and lead to almost dense coverages there. Even after dilution of the initial composite a significant amount of foam can be still produced, indicating that these composites are suitable foam stabilizing additive for aluminium alloys and that foams based on small volume fractions of nonmetallic additives can be produced.