Effects of Silanes on the Structure and Properties of Chromium-Free Passivation

Steel is one of the most widely used metal materials, and corrosion of steel surfaces is a serious problem. Traditional chromate passivation produces hexavalent chromium with high toxicity and carcinogenicity. To solve toxicity and pollution problems, a chromium-free passivation method was adopted to replace the traditional process. Based on the reaction mechanisms of some silane coupling agents, a new method of chromium-free passivation and anti-white rust production is presented in this paper. The chromium-free passivation process of an inorganic material-silane-resin composite was used in the study. The microstructure and corrosion resistance of a hot-dip galvanized sheet and silane passivation film were compared by using a neutral salt spray test, scanning electron microscopy, infrared spectroscopy and X-ray photoelectron spectroscopy. The mechanism of film formation was studied. The results show that the surface of the passivation film is dense and smooth without sharp protrusions and has a stable skeleton structure inside. The structure of the passive film is C=O, Si–O, C–Si, C–H, Si–O–Zn, Si–O–Si, etc. A chromium-free passivation film prepared with a disilane can effectively prevent penetration between the corrosive medium and matrix. After a 96 h corrosion test, the corrosion area is less than 5%, which meets the requirements of some industrial production processes.