Abstract: | The corrosion products formed on hot‐dip galvanized steel sheets for the automobile application with adhesion of alkaline mud containing different Cl− ion contents are investigated by means of Raman and infrared (IR) spectroscopy. Results show that the Cl− ion content in alkaline mud has great influence on the corrosion behavior of the galvanized steel. The Cl− ions are responsible for the formation of the Zn5Cl2(OH)8· H2O layer on the surface of the steel at the early stage of corrosion. The rest of the Cl− 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 Cl− ion content. However, corrosion rate decreases with the increase of the Cl− ions in mud. Copyright © 2009 John Wiley & Sons, Ltd. |