Abstract Preforms with a volume fraction of 60% were prepared by the compression molding method. SiC/Al composites were prepared by the pressureless infiltration process. Analytical characterization of SiC preforms and SiC/Al composites was obtained using metallurgical microscopy, X-ray diffractometry (XRD), scanning electron microscopy (SEM), etc. The effects of magnesium additives and infiltration atmospheres on the infiltration behavior of aluminum alloy melts and the infiltration characteris