| LI Min,DONG Ni-ni,PAN Ming,WANG Bao-yong,WANG Chang-cheng,SHAO Rong,LIU Wu-hua,LIU Yong-zhuang.Corrosion Resistance of Typical Galvanized Plate for Automobile[J],52(4):295-303, 318 |
| Corrosion Resistance of Typical Galvanized Plate for Automobile |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.04.026 |
| KeyWord:galvanized sheet cyclic corrosion adhesion atmospheric corrosion |
| Author | Institution |
| LI Min |
Research Institute of Technology of Shougang Group Co., Ltd., Beijing , China |
| DONG Ni-ni |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| PAN Ming |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| WANG Bao-yong |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| WANG Chang-cheng |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| SHAO Rong |
Research Institute of Technology of Shougang Group Co., Ltd., Beijing , China |
| LIU Wu-hua |
Shougang Jingtang United Iron and Steel Co., Ltd., Hebei Tangshan , China |
| LIU Yong-zhuang |
Research Institute of Technology of Shougang Group Co., Ltd., Beijing , China |
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| Abstract: |
| The corrosion resistance of the electrophoretic paint film of galvanized sheet for automobile after being damaged is the key to the anticorrosion of the whole automobile. The coating structures of three typical galvanized sheets GA, GI and ZM were studied by SEM, GDS, XPS and electrochemical workstation. The corrosion resistance of three galvanized sheets before electrophoresis was studied by cyclic salt spray test and atmospheric exposure test, and the corrosion resistance of three galvanized sheets after electrophoresis was studied by cyclic salt spray test. The surfaces of GI plate and ZM plate are smooth and flat, only part of the polished pits can be seen, and there are more Al oxides on the surface, more Mg oxides on the surface of ZM plate, and about 10% Fe in the coating of GA plate. Because of the ζ phase and δ phase, there are many small holes on the surface, and the hardness of ZM coating is higher than that of GI coating. The corrosion resistance of ZM before coating is better than that of GI and GA materials. The atmospheric corrosion results show that at 24 months, the corrosion weight loss of GI is greater than that of GA, and that of GA is greater than ZM, and the weight loss of GI is about 3 times that of ZM, which corresponds to the results of cyclic salt spray. This is because the ZM coating contains binary eutectic phase MgZn2 with negative potential. During the corrosion process, MgZn2 preferentially corrodes, because a large amount of OH‒ generated by cathodic oxygen reduction will lead to an increase in the pH value of the coating surface. The preferentially dissolved Mg ions can inhibit the alkalization of the thin liquid film on the coating surface, while the lower pH value can promote the formation of the protective coating Zn5(OH)8Cl2.H2O, and the reduction rate of oxygen on the surface is low, which has certain protection for the coating. The corrosion resistance of GA ZM and GA ZM materials after coating is better than that of GI materials, and there is a certain difference between the two mechanisms. The grains on the surface of GA plate are generally granular or long columnar or both, and the structural fluctuation of GA plate is obviously more than that of GI plate. Before curing, the electrophoretic solution can fill the small holes or gaps between columnar grains on the surface of the coating. After curing, a mechanical force similar to "tenon and mortise structure" is generated between the electrophoretic paint film and the coating, and the electrophoretic film has strong adhesion. Therefore, the corrosion resistance of coated GA board is better than that of GI. However, ZM coating has a good electrochemical protection effect on matrix Fe, and the reduction rate of cathode oxygen is relatively slow, so its corrosion resistance under the coating is better than that of GI. ZM plate has excellent corrosion resistance after coating, and it has a wide application prospect in the parts with high requirements for anti-corrosion grade of automobile body. |
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