| LI Min,SHAO Rong,WANG Changcheng,GUO Min,WANG Baoyong,ZHANG Chen,DONG Nini,LU Yangze,LIU Yongzhuang.Corrosion Resistance of Passivation Films on Four Typical Hot-dip Galvanized Plates[J],53(6):99-110 |
| Corrosion Resistance of Passivation Films on Four Typical Hot-dip Galvanized Plates |
| Received:March 21, 2023 Revised:October 11, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.06.009 |
| KeyWord:chromium-free passivation trivalent chromium passivation cross corrosion resistance |
| Author | Institution |
| LI Min |
Research Institute of Technology of Shougang Group Co., Ltd., Beijing , China |
| SHAO Rong |
Research Institute of Technology of Shougang Group Co., Ltd., Beijing , China |
| WANG Changcheng |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| GUO Min |
Marketing Center, Beijing Shougang Shares Co., Ltd., Beijing , China |
| WANG Baoyong |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| ZHANG Chen |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| DONG Nini |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| LU Yangze |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| LIU Yongzhuang |
Research Institute of Technology of Shougang Group Co., Ltd., Beijing , China |
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| Abstract: |
| The work aims to analyze the composition of four passivation films for hot-dip galvanized plates, and investigate the corrosion resistance and corrosion protection mechanism of different passivation films. The microstructure and chemical composition of four passivation films were analyzed by SEM, XPS, GDS, IR and wetting angle. The corrosion resistance of the passivation film of a galvanized plate was verified by electrochemical, neutral salt spray and cyclic salt spray tests. The fingerprint resistant film, self-lubricating film and total chromium-free passivation all contained Si and O, and the film thickness was about 1 μm. The fingerprint resistant film also contained Sn and P, while the self-lubricating film and total chromium-free passivation film contained more P and Sn. The trivalent chromium passivation film mainly contained Si, O, Cr, C and P, and the film thickness was only 0.05 μm. There was a strong correspondence between the composition distribution of the four passivation films and the smooth pit. The combination forms of Si in the four passivation films mainly existed in the form of Si—O—Si(102.4 eV) and Si—C(102.8 eV) and there was also Si—O—Zn(100.7 eV) in chromium-free, fingerprint-resistant and trivalent chromium. The Si—O—Si bond was the hydrolysis of silane coupling agent in passivation solution to form silanol. The hydrolysis-condensation rate was affected by silane concentration, pH value and solvent type, etc. The Si—O—Si bond in chromium-free passivation was obviously more than that in other passivation films, which might be due to the fact that the type and concentration of silane in chromium-free passivation solution were different from others, and it was hydrolyzed into more silanol in passivation solution. After curing into a film, its cross-linking density was higher and the film was denser. The Si—O—Zn bond proved that partially hydrolyzed silanol formed with zinc coating. The film thickness in the smooth pit was thick, and the apparent Zn element intensity appeared outside the smooth pit, which indicated that the passivation film here was thin, trivalent chromium had the best hydrophobicity, all chromium-free and fingerprint-resistant had better hydrophobicity, and the self-lubricating plate had poor hydrophobicity. The self-corrosion current density of trivalent chromium passivation was 0.97 µA/cm2, and all chromium-free, self-lubricating and fingerprint-resistant were 1.6, 2.3, 2.6 µA/cm2 in turn. All-chromium-free resin had higher cross-linking density, dense oxide film in trivalent chromium passivation, better hydrophobicity, stronger barrier ability to depolarizer, and greater resistance to charge transfer at interface, while fingerprint resistant plate and self-lubricating plate had some pores, so their plane corrosion resistance was slightly poor. In the cyclic corrosion process, due to the alternation of wet and dry, the sustained attack time of passivation film in high-salt environment was short, so the corrosion resistance of the four passivation films in the cyclic corrosion process was better than that in neutral salt spray environment, and the salt spray results were in good agreement with the electrochemical results. The corrosion resistance of different surface films is different. Trivalent chromium and total chromium-free film have better plane corrosion resistance and cross corrosion resistance. |
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