| CHEN Cui,WANG Jin,CHEN Na-na,LIU Qian-qian,ZHANG Xin,XIAO Kui.Accelerated Indoor Corrosion Behavior and Mechanism of Galvanized Steel in Simulated Acid Rain Atmospheric Environment[J],52(6):327-336 |
| Accelerated Indoor Corrosion Behavior and Mechanism of Galvanized Steel in Simulated Acid Rain Atmospheric Environment |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.06.029 |
| KeyWord:hot-dip galvanized steel acid rain atmosphere indoor accelerated experiment corrosion mechanism |
| Author | Institution |
| CHEN Cui |
Center Iron and Steel Research Institute, Gansu Jiu Steel Group Hongxing Iron & Steel Co., Ltd., Gansu Jiayuguan , China |
| WANG Jin |
Center Iron and Steel Research Institute, Gansu Jiu Steel Group Hongxing Iron & Steel Co., Ltd., Gansu Jiayuguan , China |
| CHEN Na-na |
Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing , China |
| LIU Qian-qian |
Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing , China |
| ZHANG Xin |
Testing Center of USTB Co., Ltd., Beijing , China |
| XIAO Kui |
Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing , China |
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| Abstract: |
| To investigate the corrosion behavior and mechanism of hot-dip galvanized steel in the simulated acid rain atmosphere, the indoor cyclic accelerated test was adopted. Each cycle process was composed of acid salt spray conditions, dry conditions, and wet conditions for 8 h. The salt solution used in the acid salt spray condition was (1±0.1) g/L NaHSO3, and the pH value was about 2.5. When the test reached the four cycles of 24, 56, 104, and 120 d, the samples were taken out for further analysis. The corrosion kinetics of the samples was mainly studied by the weight loss method. Scanning electron microscope (SEM) was used to analyze the surface and cross-sectional micro-morphology of the corrosion samples, combined with an energy dispersive spectroscopy (EDS) to analyze the elemental composition and distribution. The components of corrosion products were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Then, the formation process of the corrosion products was obtained according to the product composition in different cycles. The surface morphology of samples after rust removal in different test cycles was observed by a 3D laser confocal microscope, and the pitting depth was measured. The protective properties of the coating on the sample surface were characterized by electrochemical impedance spectroscopy (EIS) measurements. Combined with these characterization methods, the corrosion mechanism of the galvanized steel in the simulated acid rain atmospheric environment was clarified. In this environment, the thickness loss was a power function of time. At the same time, with the extension of the test time, the corrosion rate of the hot-dip galvanized plate decreased continuously, and then showed an upward trend in the last cycle. However, during the whole corrosion process, the instantaneous corrosion rate of the zinc coating gradually decreased. After 120 days, the thickness reduction of the zinc coating was close to the original thickness of the coating, with serious red rust and intensive pitting corrosion observed on the sample surface, and the pitting was deep and narrow. In addition, it can be seen from the cross-sectional morphology that a double-layer corrosion product layer was formed. The main corrosion products were ZnO, Zn4SO4(OH)6 and the soluble products were ZnSO4.xH2O and Na2ZnSO4.4H2O. The insoluble corrosion product Zn4SO4(OH)6 had a certain protective effect on the coating. However, as the corrosion intensified, it would decompose into Na2ZnSO4.4H2O. In the simulated acid rain atmospheric environment, the corrosion resistance of the hot-dip galvanized layer itself quickly fails, and the corrosion rate is accelerated till the generated corrosion products form a relatively complete product film at the defects, which has a certain inhibitory effect on the corrosion of the coating. However, on the one hand, it can be known from the cross-sectional morphology that the corrosion product film in the acid rain environment is thin and easy to be damaged. And on the other hand, acid aerosols will promote the dissolution of the relatively stable corrosion products, resulting in the loss of protection of the coating and increase the electrochemical reaction rate at the interface, causing further corrosion of the steel. Therefore, the protective effect of the coating completely fails after 120 days of accelerated corrosion test. |
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