Effect of Current Density on Morphology and Corrosion Resistance of Anodized Coating on SiCp/2024 Al Composite
The effects of current densities on the morphology and corrosion resistance of anodized coating formed on a SiCp/2024 Al metal matrix composite (MMC) in sulfuric acid solution were investigated by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and polarization curve. The results showed that the surface of the coating was not flat, and cracks existed when the current density increased to 20mA/cm2. The SiC particles could be oxidized during anodizing of the MMC. And the SiC particle anodized at a significantly reduced rate compared with the adjacent Al matrix. This gave rise to alumina film encroachment beneath the particle and occlusion of the partly anodized particle in the coating. As a consequence, the oxide/substrate interface became locally scalloped, and the anodized coating was non-uniform in thickness. Further, oxidation of SiC appeared to be associated with gas-filled cavities in the coating material. The size of cavities above the SiC particles increased obviously and the surface cracks developed when the current density increased. This shows that the anodized coating formed at higher current density has a structural feature with lower corrosion resistance. The polarization results indicated that the corrosion resistance of the coating decreases when the current density increases.
Yafang Han et al.
C. L. He and Q. K. Cai, "Effect of Current Density on Morphology and Corrosion Resistance of Anodized Coating on SiCp/2024 Al Composite", Materials Science Forum, Vols. 546-549, pp. 661-666, 2007