The influence of age hardening on the corrosion behavior of Al-Si-Mg-based metal matrix composites (MMCs) has been investigated in aerated and deaerated 3.5 wt% aqueous NaCl solutions. Silicon carbide particle (SiCp) reinforced composites consisting of 10 and 20 vol% SiC(p)s are produced by the compocasting technique. After the extrusion process, the composites are artificially aged (T6). The corrosion resistances of the aged composites are analyzed by measuring the cyclic potentiodynamic polarization. The surface morphology of the composites before and after the corrosion tests are determined by using metallographic methods and scanning electron microscopy (SEM). In addition, the X-ray diffraction technique (XRD) has been used to determine the phases that occur at the matrix-reinforcement interface. The results demonstrate that the E-pit values of unreinforced matrix alloy and composites increase negatively with increasing aging time. It is also observed that corrosion preferentially starts at the interface of Al-Mg2Si and Al-SiCp.