In the present work, a SiCp/Al composite was fabricated by pressureless infiltration of aluminum alloy into loose-packed SiC particles preform, and its microstructure and hardness performance were investigated. The results showed that the composite was fully infiltrated and the particles were distributed uniformly in the composite. Interfacial reactions were found in the as-cast composite and the reaction product was identified as MgAl2O4 by TEM observation and XRD analysis. The interfacial reactions enhanced the wettability and promote the spontaneous infiltration process. The thermal exposure process increased the Brinell hardness of the composite. After the thermal exposure process, the block-like interfacial reaction products were distributed discretely, but the amount of the reaction products was increased.