MECHANISM OF FILM GROWTH DURING ANODIZING OF AL-ALLOY-8090/SIC METAL MATRIX COMPOSITE IN SULPHURIC ACID ELECTROLYTE

摘要

Metal matrix composites (MMCs) consisting of Al-alloy 8090 reinforced with SiC particulate have previously proved to be susceptible to corrosion in chloride-containing environments. A study was carried out to investigate the possibility of anodizing the MMC for protection against corrosion. Sulphuric acid was found to be a preferred anodizing electrolyte for the composite, as it allowed a relatively thick anodic film to be formed on the surface. The investigation regarding the mechanism of film formation, performed on a scanning electron microscope, revealed that the thickness of the anodic film was non-uniform; however, the film-solution interface was relatively uniform compared with film-composite interface. Observation in the transmission electron microscope indicated that the pores in the anodic film which was formed, appeared round when they grew perpendicular to the surface and revealed elongated like ''finger prints'' when they developed at an angle on a rough surface, due to presence of SiC particles. The corrosion rate of the MMC, which was about 21 times the corrosion rate of ultra-pure aluminium in a chloride-containing environment, became negligible after anodizing. [References: 14]