Metal matrix composites have been produced by pressureless infiltration of pure Al into Mg doped SiC preforms after 1 h at 900°C. Aluminium has been found to infiltrate preforms containing between 2 and 14 wt-%Mg, however Al did not infiltrate a preform containing 1 wt-%Mg. Preforms doped with 1 wt-%Mg and Si did result in infiltration. Increasing the Mg content or increasing the Si content in the preform resulted in more extensive infiltration. The effect of Mg and Mg mixed with Si on pressureless infiltration of pure Al, microstructure of MMC as well as mechanical properties are discussed. Although the dopant was uniformly distributed throughout the preform microstructural analysis and hardness measurements indicate that the resultant composite may not be uniform due to infiltration inwards from the edge to the centre of preform.