Formation of Anticorrosive Film for Suppressing Pitting Corrosion on Al-Mg-Si Alloy by Steam Coating

Al alloys offer excellent physical and mechanical properties, such as a low density, high specific strength, and good ductility. However, their low corrosion resistance has restricted their application in corrosive environments. There is a need, therefore, for a novel coating technology that is capable of improving the corrosion resistance of Al alloys. In the present study, we examined a steam-based method of forming a corrosion-resistant film on Al alloys. Al-Mg-Si alloy was used as the substrate. The cleaned substrates were set in an autoclave with ultrapure water as the steam source and processed using different temperatures and holding times, resulting in the formation of anticorrosive films on the alloy. FE-SEM images of the film surfaces showed that plate-like nanocrystals were densely formed over the entire surface. XRD patterns indicated that the film was composed mainly of AlOOH crystals. The potentiodynamic polarization curves revealed that the corrosion current density of the film-coated substrates significantly decreased, and that the pitting corrosion was completely suppressed, indicating that the corrosion resistance of the Al-Mg-Si alloy was improved by the film formed by means of steam coating.