Aerogel Filled Metals: a Syntactic Cellular Material

Abstract

We report in this paper on a new method to produce lightweight aluminium alloys introducing nanostructured materials like silica-aerogels into an Al-alloy melt. Since these filler materials in the range of a few 100 micron to a few millimetres have vanishing density (100g/L) they need not to be removed from the final cast product. Their shape, size and volume fraction determines the materials properties. Different methods were used to prepare metal-aerogel syntactic foam composites. Filling of aerogel particles into a mould and using centrifugal casting to backfill the void space between the silica-aerogel particles is one way to produce such a material. This process was employed to prepare samples using Silica aerogels and an A357 alloy. Vermiculites and Hyperlite as a filler materials. The materials have densities around 1000g/L, compressive yields stress of around 10-20 MPa with maximum compressibility of around 60%. Another method is an inverse squeeze casting process. The aerogel granulate bed is preheated and slowly pressed into a superheated AlSi11 melt. The composite material typically has a density of around 900 g/L, compressive yields stress of around 8 MPa and the energy absorption at a deformation of 40% is around 8kJ/kg. In a third processing routine we employed a kind of suction casting (or inverse low pressure die casting). A tube filled with millimetre sized Silica-aerogel particles is evacuated, preheated and submerged partially into an AlSi11 melt. The melt penetrates into the void space and composite materials up to 500 mm length can be produced. The paper describes the materials preparation methods, the microstructures as observed with light microscopy and X-ray tomography, the deformation behaviour and discusses the different techniques and their advantages and limitations.