| LIU Yuanjing,LIU Dan,SHAN Dayong,HAN Enhou.Influence of Final Voltage on Formation Process of Black Micro-arc Oxidation Coating on Aluminum Alloy with Mo and V[J],53(9):34-42 |
| Influence of Final Voltage on Formation Process of Black Micro-arc Oxidation Coating on Aluminum Alloy with Mo and V |
| Received:February 29, 2024 Revised:April 11, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.09.004 |
| KeyWord:aluminum alloy black micro-arc oxidation corrosion resistance coloration mechanism absorbance electrochemistry |
| Author | Institution |
| LIU Yuanjing |
Institute of Corrosion Science and Technology, Guangzhou , China |
| LIU Dan |
Institute of Corrosion Science and Technology, Guangzhou , China |
| SHAN Dayong |
Institute of Corrosion Science and Technology, Guangzhou , China |
| HAN Enhou |
Institute of Corrosion Science and Technology, Guangzhou , China |
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| Abstract: |
| NH4VO3 and Na2MoO4 were chosen as colorants to investigate the influence of different final voltages on properties of black micro-arc oxidation coatings on aluminum alloys, and the formation process of the coatings. In the micro-arc oxidation system of sodium hexametaphosphate and sodium silicate, NH4VO3 and Na2MoO4 were added as colorants to obtain micro-arc oxidation films on the clean surface of 6063 aluminum alloy at different final voltages (350, 400, 450, 500, 550 V), with micro-arc oxidation electrical parameters set as constant current mode, with a current density of 10 A/dm2, frequency of 800 Hz, and a duty cycle of 10%. The morphology, structure, and composition of the coatings were analyzed by SEM, XRD, and XPS. The roughness and thickness of micro-arc oxidation coatings were conducted with a white light interferometer and a thickness gauge. The color characteristics and absorbance of the coatings were characterized with a colorimeter and a UV-visible spectrophotometer, and the electrochemical properties of the coatings were analyzed by polarization curves and electrochemical impedance spectroscopy. The crystallinity of the micro-arc oxidation coating was relatively low. The main components of the coating were O, Al, P, Si, Mo and V, with Mo and V existed as MoO3, MoO2, V2O5 and V2O3. The micro-arc oxidation coatings at different final voltage tightly bonded with the substrate, there were no obvious cracks between the coating and the substrate. As the final voltage increased from 350 V to 550 V, the micro-arc oxidation coating underwent remelting, the surface discharge channels on the coating transited from small and dense to large and sparse. And the average pore size increased from (0.82±0.64)μm to (2.58±1.8)μm. The color of the micro-arc oxidation coatings changed gradually from brown to black, the L value decreased from 65.01 to 22.63, the light absorption for visible light (wavelength 250-800 nm) increased from 69.4% to over 96.5%. The thickness and roughness of the coatings increased from 4.00 μm and 0.55 μm to 35.00 μm and 2.41 μm, respectively. With the increase of the final voltage of micro-arc oxidation, the corrosion resistance of the coating was significantly enhanced. The coating prepared at a final voltage of 550 V exhibited optimal corrosion resistance. The self-corrosion current density decreased to 1.48×10−6 A/cm2, the self-corrosion potential relative to the substrate increased from −0.84 V to −0.07 V, and the impedance increased to 2.48×105 Ω.cm2. NH4VO3 and Na2MoO4 were effective coloring agents for black micro-arc oxidation of aluminum alloys. In the process of micro-arc oxidation, the reaction of NH4VO3 and Na2MoO4 in the plating solution under the action of a strong electric field generated V2O5, V2O3, MoO3, and MoO2, which had their own color characteristics. Under the combined action of the generated substances, the micro-arc oxidation coating became black. The increase in final voltage promoted the accumulation of coloring components in the coating, thus enhancing the blackness of the membrane. With the increase of final voltage, both the light absorption performance and corrosion resistance of the coating were significantly enhanced. |
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