The surface of the annealed steel and the exfoliated interface of the coating for the hot dip galvanized Si containing steel sheets was characterized by using SEM (Scanning Electron Microscope), AES (Auger Electron Spectroscopy) and TEM (Transmission Electron Microscopy). The adhesion of the coatings have depended on the Si content of the steel. It have been found that MnSiO3 particles are formed at the surface of the annealed steels having high Si content and that two types of grain having different distribution of the oxide exist in the steels. Large oxide particles have been formed in one type of grain and small particles are formed in the other type of grain. The different type of Fe-Zn alloy are formed on two types of grains. It have been observed that the oxide particles exist at the interface of exfoliated coatings after the adhesion test for the steels with high Si content. The distribution of the oxide particles observed at the bottom of the exfoliated coating is quite similar to that of the surface oxide of the annealed steel. From these results, the exfoliation of the coating has initiated at the oxide particles of the steel surface that has been not reduced during the hot dip galvanizing.
