Detection and identification of defects and reinforcement phases in reaction-sintered hypereutectic Al-13.5Si-2.5 Mg alloy composites was studied using X-ray radiation. Both the coconut shell char-reinforced and zircon sand-reinforced alloy composites revealed cavities due to thermal defects, gas pores, and voids. The low-density char particles were not detected, but the high-density zircon particulates appeared as dark inclusions on the exographs and this offers a good visual measure of particle dispersion in the liquid-phase sintered parts. At the same conditions of irradiation, the low-density AI-SI alloy composites containing high-density zircon particles did not reveal any clear images. Clusters of alumina-silica short fibres as well as line defects appeared bright but their nature was not discernible, making it difficult to identify the defects in the radiographs.