The research on new DRA(discontinuous reinforced alloy) and CRA(continous reinforced alloy) composites has been carried out to improve the properties of ceramic fiber and particle reinforced metal matrix composites(MMCs). Effects of alloying elements and aging conditions on the microstructures and aging behavior of Al-Si-Cu-Mg-(Ni)-SiCp composite have been examined. The specimens used in this study were manufactured by duplex process. The first squeeze casting is the process to make precomposite and the second squeeze casting is the process to make final composite. The hardening behavior was accelerated with decreasing the size of SiCp particle in the composites. It is considered that the dislocation density increased with increasing SiCp size, due to the different thermal deformation between Al matrix and SiCp during quenching after the solution treatment. Peak aging time to obtain the maximum hardness in 3 ${mu}m$ SiCp reinforced Al composite was reduced than that in large size(5, 10 ${mu}m$) of SiCp because of difference in dislocation density. Aging hardening responce(${Delta}H$ = $H_{Max}.-H_{S.T}$) of composites was greater than that of unreinforced Al alloy because of higher density of second phases in matrix.