Growth and characterization of plasma electrolytic oxidation coating on 60%SiCp/2009 aluminum matrix composite

A ceramic coating on 60vol.%SiCP/2009 aluminum matrix composite was prepared by plasma electrolytic oxidation (PEO) in silicate solution. The microstructure, composition and wettability of the PEO coating and its corrosion resistance were investigated. The generation mechanism of spark discharge on the SiC particles surface was also discussed. It is found that the insoluble compound (SiO2) from silicate solution is vital for the ignition of spark discharge on the SiC particles surface. The defects in the Al−Si−O compounds provide a priority path for the conduction of discharge current on the SiC particles surface. A uniform coating of 5.5 μm was fabricated after 1200 s. Moreover, with the increase of time, the surface free energy of PEO coating reached the maximum of 37.10 mJ/cm2 at 40 s, and then decreased to 25.95 mJ/cm2 at 1200 s. Furthermore, the corrosion resistance of the composite was greatly improved by PEO treatment.