Abstract
Alumina/aluminium composites with an interpenetrating microstructure were made by infiltrating an alumina preform which had the structure of a reticulated ceramic foam. Low density preforms (6% relative density)with porous struts were prepared from a polyurethane suspension of alumina powder which was pyrolysed and partially sintered after foaming. Higher density preforms consisted of ceramic foams with open cells and dense struts. All these preforms were infiltrated with 6061 aluminium alloy using a modified squeeze caster fitted with a vacuum system and fine control of speed and pressure. Such MMCs had a microstructure in which two 3D networks were interpenetrating. One was either a ceramic reinforced alloy (50 vol.-%reinforcement) or a dense ceramic phase while the other was the unreinforced alloy. The microstructure of the preform fitted an established relationship between the ratio of window diameter to cell diameter k and void volume fraction V p. In addition, a short fibre foam was made to compare with the traditional fibre preforms.
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