Abstract
The coatings with high emissivity and corrosion resistance are prepared successfully on 7075 aluminum alloy by plasma electrolytic oxidation (PEO). The effect of frequencies of 100 Hz, 200 Hz, 400 Hz, and 600 Hz on the microstructure, chemical composition, emissivity and corrosion resistance of the coatings are investigated. The results show that the main chemical composition of PEO coatings includes Al, O, Si, P, and V elements, and the content of different vanadium oxides determines the emissivity of the coatings, that is, the black V2O3 instead of brown V2O5 can greatly enhance the emissivity. Under the action of bipolar pulse, frequency exhibits an opposite effect on the emissivity and corrosion resistance of the PEO coatings. With increasing frequencies, the emissivity of the PEO coatings declines due to the decrease of V2O3 content, while the corrosion resistance is improved due to the decrease of spark discharge intensity to avoid pores and cracks in the coatings. The PEO coating prepared under the frequency of 400 Hz presents the highest infrared emissivity larger than 0.85 and good corrosion resistance.
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