The Technology And Performance Of Non-chromium Passivation On Hot Dip Galvanized Plate

Steel is the most consumed metal in daily life, but steel corrosion brings huge loss. In the world. Galvanization is the common method to prevent steel rust, but zinc coating is easily corroded and turns into some white and gray thing, so zinc coating surface needs tobe passivated to improve its corrosion resistance. In the past, the most useful passivation method is chromate passivation, but chromate is poisonous, so some new environmentally friendly non-chromium passivation treatment need to be researched to replace chromate passivation.In this paper, single silane/inorganic composite non-chromium passivating treatment and double silane/inorganic composite non-chromium passivating treatment were developed on the hot dip galvanized plate, and tested their corrosion resistance with neuter salt spray test and electrochemistry test. Then it is confirmed that double silane/inorganic composite non-chromium passivating treatment is the main object to be studied in this paper.The orthogonal experimental method and single factor experimantal method were used to determinate the content of passivation liquid and the passivation process parameters. The corrosion resistance, heat resistance, fingerprint resistance, water resistance and film adhesion of the double silane/inorganic composite non-chromium passivating treatment after improvement were also tested.The surface and section morphology of the double silane/inorganic composite film was observed with Scanning Electron Microscope (SEM) and Laser scanning confocal microscope (LSCM), The surface of hot dip galvanized plate was changed after passivation, the thickness was at submicron level.The structure of the film was analyzed by Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS). The test results showed that there were C-C, C-Si, C-O, C-N,-CH3,-CH2, C=O, O-H, N-H, Si-O,etc. in the film.Through analyze the results of SEM, LSCM, electrochemical test, XPS, ATR-FTIR, it can be know that the film and zinc coating combined with chemical bond, the chemical bond was Si-O-Zn. Si-OHs shrank into Si-O-Sis, then the close passivation film was formed.