Metal-matrix composites (MMC) comprising powder aluminium alloys reinforced by particulate ceramic are being developed for widespread aerospace structural applications ranging from fuselage and missile components to undercarriage parts. Most interest is centred on MMCs with an Al-Cu-Mg (2 1 2 4) matrix alloy. These MMCs possess high levels of specific stiffness with high specific strengths but can exhibit lower ductility and toughness than conventional unreinforced aluminium alloys. To overcome these problems the effects of alloy com position on the ageing behaviour and notched tensile properties of Al-Cu-Mg and Al-Cu based alloys reinforced with 20 wt% silicon carbide particulate have been investigated. Al-Cu-Mg MMCs gave higher strengths and moduli than unreinforced sheet. Lowering the copper and magnesium content resulted in reduced strength but did not affect the rate of age hardening. The Al-Cu MMCs gave the lowest strengths but the absence of natural ageing may prove advantageous, enabling sheet to be formed and subsequently heat-treated to the peak strength condition.