Research to achieve dark shade on aluminum surface is a challenge but worthwhile. In this research work, plasma electrolytic oxidation treatment was carried out on the surface of the AA7075 substrate in different combinations of K2TiF6, (NH4)6Mo7O24 and Na2WO4 containing electrolytes so as to fabricate high-absorption black corrosion-resistant ceramic oxide coatings for spacecraft applications. The effect of three different kinds of electrolytes on thickness, morphology, chemical composition, phase composition, thermal control property and corrosion resistance was investigated. The results showed that sample KTW, PEO treated with K2TiF6 and Na2WO4, showed the higher thickness of 29.7 μm. Scanning electron microscopy surface morphology study revealed that micropores were less for coating KTW than the other PEO-treated samples. Energy-dispersive spectroscopy elemental composition analysis indicated that molybdenum, titanium and tungsten species were incorporated into the coating structure. Dark black colored KTM sample, PEO treated with K2TiF6 and (NH4)6Mo7O24, showed lower absorption value in absorption spectra obtained by UV–Vis spectrophotometer. Potentiodynamic polarization study confirmed that higher thickness, less porous and W element containing PEO-treated sample KTW showed excellent corrosion resistance than the sample treated with K2TiF6 (KT) and the sample treated with K2TiF6 and (NH4)6Mo7O24 (KTM).
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The author (Dr. NRB) is thankful to the DRDO, New Delhi, for sponsoring the ER & IPR project (No: ERIP/ER/DG-NS & M/991015704/M/01/1684) for carrying out this research investigation. The authors are also thankful to the Director, National Institute of Technology, Tiruchirappalli (NITT), for providing the Sophisticated Instrumentation Facility at NITT for carrying out this research investigation.