(57) A composite material comprising a refractory, inorganic filler material (e.g. SiC or Al₂O₃) in a matrix of aluminium or an aluminium-containing alloy is made by incorporating the filler material into the aluminium or aluminium-containing alloy at a temperature above its liquidus, e.g. by vacuum stirring, followed by cooling to solidify the composite. In order to improve the wettability of the filler by the molten metal, the filler has a bismuth additive, for example in the form of a bismuth compound such as bismuth oxide, dispersed therein. This may be done by intimately mixing elemental bismuth with particulate filler followed by oxidation of the bismuth to bismuth oxide. e.g. by heating in air.