| MA Lin-meng,ZOU Zhong-li,LIU Kun.Effect of Samarium Salt Content on Corrosion Resistance of Ferricyanide Conversion Coating on AZ31B Magnesium Alloy[J],51(12):188-196, 207 |
| Effect of Samarium Salt Content on Corrosion Resistance of Ferricyanide Conversion Coating on AZ31B Magnesium Alloy |
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| DOI：10.16490/j.cnki.issn.1001-3660.2022.12.019 |
| KeyWord:samarium salt content potassium ferricyanide composite film electrochemical AC impedance corrosion resistance |
| Author | Institution |
| MA Lin-meng |
School of Materials Science and Engineering, North Minzu University, Yinchuan , China |
| ZOU Zhong-li |
School of Materials Science and Engineering, North Minzu University, Yinchuan , China |
| LIU Kun |
School of Materials Science and Engineering, North Minzu University, Yinchuan , China |
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| Abstract: |
| A single potassium ferricyanide conversion coating on the surface of magnesium alloys can improve the corrosion resistance. On the contrary, there are still defects such as poor bonding between the coating and the substrate. The film layer on the surface was easy to peel off after soaking for a period of time in a corrosive environment, and its corrosion resistance needs to be further improved. In order to solve this problem, the author's research team used samarium salt to treat the potassium ferricyanide film on the surface of magnesium alloy, and optimized its process, focusing on the effect of samarium salt content on the composite film. In this paper, a two-step method was used to form the film. First, a layer of potassium ferricyanide conversion film was prepared on the surface of the pretreated sample with a size of 20 mm × 20 mm × 1 mm by chemical dipping method, and then the sample was placed on the same method. In the samarium nitrate solution, the secondary film formation treatment was performed to obtain the final composite film layer, which was finally dried by hot air and then placed in a blast drying oven for heat preservation and drying, and then taken out for testing. In this paper, the scanning electron microscopy (SEM), X-ray diffractometer (XRD), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were used to analyze and characterize the surface morphology and composition of the composite film; The polarization curve (Tafel) and electrochemical impedance (EIS) were used to explore the corrosion behavior of the composite film at different stages in 3.5wt.% NaCl solution; the coating thickness gauge was applied to measure the thickness of the film formed under different samarium salt content treatment; used 3% copper sulfate solution for spot drop test, observed that the solution changes from blue to colorless and produces small black spots on the sample time; the metallographic microscope and scanner was used to observe the surface morphology of different samples for long-term soaking experiments, and then to explore the film adhesion and stability of the composite film. The results showed that a new film layer was formed on the surface of the magnesium alloy potassium ferricyanide conversion film treated with samarium salt, and the main components of the composite film layer were SmFe(CN)6 and Sm(OH)3. It had better corrosion resistance than a single film layer, and the bonding force between the film layer and the substrate was also improved. The composite film layer was more stable and could play a better protective effect on the substrate. In addition, when the content of samarium salt was 5 g/L, the film was the most compact and smooth, the self-corrosion current density was the lowest, which was 2.129×10‒9 A/cm2, and the charge transfer resistance and film resistance were the largest, which were 8.164×104 Ω.cm2 and 1.293×107 Ω.cm2, the corrosion resistance of the film was the best. All in all, the use of samarium salt to modify the potassium ferricyanide film layer on the surface of magnesium alloy can not only further improve the adhesion between the film layer and the substrate, and improved the corrosion resistance of magnesium alloy, but also the surface of the formed composite film layer was more uniform, dense and stable. Its optimum samarium salt content was 5 g/L. |
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