The present work examines the influence of heat treatment on the microstructure related to the interfacial reaction and corrosion behavior of SiC_p/Al-6%Mg composites prepared by using a pressureless infiltration technique. The experimental results show the occurrence of the precipitates of Si, MgA1₂O₄ and Mg₂Si as a result of the interfacial reaction between the SiC particle and matrix of the composites during heat treatment. The precipitates contents(f) of composites are correlated with T1, T4, T6 and annealing heat treatment, following the order of f_T1< f_T4< f_T6annealing. The precipitates located near SiC particles are responsible to pitting corrosion as a degradation mechanism of the composites. The heat treatments carried out on the composites present a significant influence on the corrosion rate (j_corr). The correlation between j_corr and heat treatment present the characteristics of j_corr-ann> j_corr-T6> j_corr-T4> j_corr-T1, which may be attributed to the the interfacial reaction precipitates of the composites during heat treatment.