Influence of content of oxygen on corrosion behavior of automotive hot-dip galvanized steel under alkaline mud adhesion

In environments of different oxygen contents, the corrosion behaviors of hot-dip galvanized (HDG) steel sheet used in automobile under mud adhesion were investigated by scanning electronic microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The results show that the zinc coating is eroded mostly, and some red rust and black rust appear on the substrate in the environment of oxygen supplied intermittently. The corrosion products on the galvanized steel sheet are needle-like objects. While in the environment of nitrogen supplied intermittently, a little area of the zinc coating is erode, and no red rust appears on the substrate. Corrosion products form on the blocks. With time prolongs, the corrosion rates of mass loss increase firstly whereas then decrease, and the corrosion rate of mass loss with oxygen supply is about two times greater than that with nitrogen supply under the mud adhesion up to 200 h. The corrosion processes of the galvanized steel sheet under alkaline mud adhesion are controlled by oxygen depolarization reactions.