| HU Chang-Gang,CHEN Jin-Ju,WANG Yan,LIU Ling.Effects of Colorants on Properties of Black Micro-arc Oxidation Coating on 6061 Aluminum Alloy[J],51(12):285-294 |
| Effects of Colorants on Properties of Black Micro-arc Oxidation Coating on 6061 Aluminum Alloy |
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| DOI：10.16490/j.cnki.issn.1001-3660.2022.12.029 |
| KeyWord:aluminum alloy black micro-arc oxidation colorant impact |
| Author | Institution |
| HU Chang-Gang |
School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu , China |
| CHEN Jin-Ju |
School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu , China |
| WANG Yan |
School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu , China |
| LIU Ling |
School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu , China |
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| Abstract: |
| The work aims to investigate the effects of NH4VO3 and K2Cr2O7 on the black microarc oxide coating. By setting up three sets of control tests, the black coatings and the base coating were prepared by adding ammonium metavanadate and potassium dichromate to the base electrolyte composed of sodium silicate and sodium hexametaphosphate, respectively. The black coatings prepared by the two colorants (NH4VO3 and K2Cr2O7) showed an absorbance of more than 98% in the UV to visible light range. The hardness, wear resistance and impact resistance of the coating were evaluated by Vickers hardness tester, ball-disc friction and wear test and drop hammer impact test respectively. The surface and microscopic morphology of the coatings were observed by SEM. The absorptivity of the coating was measured by UV-visible spectrophotometer and the phase composition was analyzed by X-ray diffraction. The surface of the V-containing coating was mainly pancake type and crater type, and the crater type accounted for less of the surface morphology, while the Cr-containing coating was mainly crater type morphology. According to the cross-sectional SEM images of the three coatings, there were more pores in the V-containing coating near the substrate side and less pores near the resin side, leading to the internal and external delamination. The Cr-containing coating had a more uniform distribution of pores, and the base coating had fewer pores in its cross-section. When the discharge intensity was higher, the crater type morphology and the number of internal pores were more, which indicated that potassium dichromate can improve the discharge intensity of the microarc oxidation reaction and the pore distribution was all uniform. According to the EDS analysis of the line sweep of the coating cross-section, the content of the coloring element Cr was uniformly distributed from inside to outside along the film cross-section, while the content of the chromogenic element V increased linearly from inside to outside. According to the XRD analysis, the crystallinity of the V-containing coating was low and only a small amount of γ-Al2O3 diffraction peaks existed, while the Cr-containing coating was dominated by α-Al2O3 phase with high crystallinity, indicating that potassium dichromate can promote the generation of α-Al2O3 phase. Therefore, the hardness of the Cr-containing coating was higher, and the hardness value was mainly above 1 500HV, while the hardness value of the V-containing coating was mainly below 1 500HV. The friction test was performed for 20 min under a load of 4 N. The V-containing coating was worn through at 16 min, while the Cr-containing coating remained stable at a coefficient of friction near 0.35 throughout the friction process, which was due to the difference in the physical phases of the layers. The impact of 1 kg steel ball on the film layer was tested by free fall at 20 cm, 30 cm and 40 cm, respectively, and the impact of the steel ball on the coating caused the deformation of the coating, especially at the edge of the impact crater, where the deformation was the most fragile. When the impact height was 20 cm, a small area was peeled off at the upper left corner of the impact crater of the V-containing coating, and the area peeled off became larger and larger when the height increased to 30 cm and 40 cm. The Cr-containing coating was still firmly bonded to the substrate when the impact height was 20 cm and 30 cm, while the coating peeled off when the height was 40 cm. According to the XRD analysis, K2Cr2O7 can promote the generation of α-Al2O3 phase in the coating. The phase can greatly improve the properties of the coating, including hardness and wear resistance. |
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