Raman and IR spectroscopy study of corrosion products on the surface of the hot-dip galvanized steel with alkaline mud adhesion

The corrosion products formed on hot-dip galvanized steel sheets for the automobile application with adhesion of alkaline mud containing different CI^- ion contents are investigated by means of Raman and infrared (IR) spectroscopy. Results show that the CI^- ion content in alkaline mud has great influence on the corrosion behavior of the galvanized steel. The CI^- ions are responsible for the formation of the Zn ₅CI₂(OH)₈· H₂O layer on the surface of the steel at the early stage of corrosion. The rest of the CI ^- ions then penetrate and interrupt corrosion product layer resulting in pitting corrosion. Subsequently, The red corrosion product of α-FeOOH (shaped as needle-like structure) is formed, which then transforms into black rust of Fe₃O₄ (having a shape of slim needle). It is interesting to find out that pitting depth is inversely proportional to the CI^- ion content. However, corrosion rate decreases with the increase of the CI^- ions in mud.