THE CORROSION BEHAVIOUR OF AA356/SiC MMC

The corrosion behaviour of some aluminium-based Metal Matrix Composites (MMCs) has been studied in aerated NaCl solutions (chiefly 0.6M) to elucidate the influence of the reinforcement particulate (silicon carbide, SiC) content in the composite and the copper presence in the metallic matrices (Al-Si-Mg alloys). Weight loss measurements after alternate immersions, cathodic and anodic potentiodynamic polarization curve recordings have been performed. The corrosive attack has been documented by SEM and optical microscope observations. This attack takes place around SiC particles and, with Cu-rich matrices, around Cu-rich intermetallic precipitates. The reinforcement decreases the corrosion resistance of the tested MMCs by favouring the cathodic oxygen reduction, but it exerts a negligible effect on the anodic oxidation and on the pitting process. Also copper in the matrix stimulates the cathodic reaction and consequently the corrosion process