Abstract:

In order to restrain the excess growth of the coatings induced by reactive steel containing silicon during the hot-dipped galvanizing process, Ti was added in a Zn bath with a mass fraction of less 0. 1% , and the microstructures of the coatings on the steel containing 0. 09% of Si were investigated. Then, the corrosion resistances of Zn and Zn-Ti coatings were studied by means of the neutral salt spray test, the electrochemical polarization and the X-ray photoelectron spectrum. The results show that, with the increase of the Ti content in Zn bath, the growth of ζ phase in the coating is obviously restrained, the excess growth of the coating is thus effectively restrained, and the thickness of ζ ＋ δ phase gradually decreases. It is also indicated that there arise Г2 particles when the Ti content in Zn bath is more than 0.05%, that the Zn-Ti coating in 5% NaCl solution is of lower corrosion current, larger polarization resistance, less spontaneous corrosion tendency and better corrosion resistance than pure Zn coating, and that the oxidized film of Zn-Ti coating is composed of ZnO and TiO₂. As a result, the excellent corrosion resistance of Zn-Ti coating is due to the presence of steadier TiO₂ film on the coating surface.

Key words: hot-dipped galvanizing, Zn-Ti coating, microstructure, corrosion resistance