| DU Baoshuai,YAN Zhicheng,ZHANG Zhongwen,ZHANG Duqing,SUO Shuai,LI Xinmei.Investigation on Structure and Corrosion Resistance of Ag-Bi Alloy Coating Fabricated by Brush Plating[J],53(4):110-116, 183 |
| Investigation on Structure and Corrosion Resistance of Ag-Bi Alloy Coating Fabricated by Brush Plating |
| Received:January 03, 2023 Revised:March 21, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.04.010 |
| KeyWord:brush plating Ag-Bi coating corrosion resistance microhardness |
| Author | Institution |
| DU Baoshuai |
State Grid Shandong Electric Power Research Institute, Jinan , China |
| YAN Zhicheng |
State Grid Shandong Electric Power Research Institute, Jinan , China |
| ZHANG Zhongwen |
State Grid Shandong Electric Power Research Institute, Jinan , China |
| ZHANG Duqing |
State Grid Shandong Electric Power Research Institute, Jinan , China |
| SUO Shuai |
State Grid Shandong Electric Power Research Institute, Jinan , China |
| LI Xinmei |
State Grid Shandong Electric Power Research Institute, Jinan , China |
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| Abstract: |
| Silver coating has been used extensively in the field of power electronics and aerospace industry. However, due to its inherent FCC crystal structure and sensitivity to corrosive factors such as Cl− and SiO2, it suffers from low wear and corrosion resistance. Non-cyanide silver alloy plating shows promise in improving the comprehensive properties of silver coating. The work aims to fabricate Ag-Bi alloy coating by brush plating technology and reveal its characteristic microstructure and corrosion resistance property. Based on acidic non-cyanide sodium thiosulfate plating bath, pure Ag and Ag-Bi alloy coatings were synthesized on copper by brush plating. Bi(NO)3 was used as the source of Bi element in the coating and varied in the plating bath to control the content of Bi in the alloy coating. T2 copper was used as the substrate, and it was ground with sand paper and subject to electro-cleaning and activation before the brush plating process. XRD and SEM were used to analyze the phase constituent and micro-morphology. Microhardness tester was employed to measure the hardness of the coatings. Corrosion resistance of the coatings was characterized by polarization curve and electrochemical impedance spectroscopy. Results showed that FCC supersaturated Ag(Bi) phase was presented for all the coatings, and hexagonal α-Bi phase was found in the Ag-15.64Bi alloy coating, which indicated the phase separation for this coating. The phenomenon of Ag(Bi) diffraction peak shifting to the left was found due to the solid solution effect of Bi element. The brush plated coatings possessed nano-sized grain structure which was in the range of 13.5-21 nm. Surface of the pure Ag coating showed the cauliflower-like morphology, while Ag-Bi coatings presented much refined granular structure. Compared with the pure Ag coating, brush plated Ag-Bi alloy coatings showed improved compactness and surface roughness. With the increase of Bi content in the alloy coating, the microhardness increased accordingly, reaching a maximum value of 220.7HV for the Ag-15.64Bi alloy coating. Electrochemical test showed that in general, the incorporation of Bi element in the Ag coating improved the corrosion resistance of the alloyed coating. Corrosion potential and charge transfer resistance increased firstly and then decreased with the increase of Bi content in the coating, while corrosion current density showed the opposite trend. Ag-4.52Bi showed the best corrosion resistance property, with corrosion potential of −0.189 V, corrosion current density of 1.76×10−2 mA.cm–2, and charge transfer resistance of 1 635 Ω.cm2. Electrochemical impedance spectroscopy of the tested coatings showed the feature of single time constant, corresponding to the interface of Ag coating and electrolyte solution. Conclusion can be made that by adding sodium thiosulfate in the acidic plating bath, Ag-Bi alloy coating can be fabricated by brush plating. Content of Bi has significant effect on the microhardness and corrosion resistance of the coating. With the increase of Bi content in the coating, the hardness of the coating is improved due to the solution strengthening and grain refinement strengthening. Corrosion medium is blocked because of the reduction of structure defects such as pores and crevices, and Bi element can promote the formation of passive film on the coating, resulting in the enhancement of corrosion resistance of the Ag-Bi alloyed coating. |
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