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 Zn 5 Cl 2 (OH) 8 · H 2 O 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 Fe 3 O 4 (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.

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