Corrosion Behavior of Cast Aluminum Matrix Composites (A3xx. x∕SiCp) in Chloride Media

The influence of silicon carbide particles (SiCp) proportion and matrix composition of four aluminum metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) on their corrosion behavior in 1, 2, and NaCl solutions has been studied. The matrix of composites is virtually free of Cu whereas the A380/SiC/xxp matrix contains Ni and Cu. The kinetics of the corrosion process was studied on the basis of gravimetric tests and the corrosion process was evaluated by electrochemical impedance spectroscopy during immersion in NaCl solutions. The nature of the corrosion products was analyzed, before and after accelerated testing, by scanning electron microscopy and low angle X-ray diffraction, to determine the influence of microstructural changes on corrosion behavior during exposure to the corrosive environment. The extent of the corrosion damage of composites depends on the SiCp proportion, chloride ion concentration, and matrix composition. The preferential nucleation sites are located at the matrix/particle and matrix/intermetallic compound interfaces. The corrosion process is influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement. The corrosion product is a compact and stable layer that protects materials against corrosion.