Wrought Al-Cu-Mg aluminum alloy (D16) was treated by bipolar plasma electrolytic oxidation to create a base plasma electrolytic oxidation (PEO)-coating with corrosion protection and mechanical properties superior to bare alloy’s natural oxide layer. Additional protection was provided by the application of polymer, thus creating a composite coating. Electrochemical and scratch tests, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction studies were performed. Degradation of coatings in the marine atmosphere and seawater was evaluated. The composite polymer-containing coating provided better corrosion protection of aluminum alloy compared to the PEO-coating, although seawater affected both. During the atmospheric exposure, the PEO-coating provided reasonably good protection, and the composite coating showed excellent performance.

Changes in impedance spectra of hot-water sealed and unsealed coatings at the aluminum alloy from the Al–Cu–Li–Zn-system during their corrosion testing in NaCl solution and salt spray chamber are studied. During the testing in NaCl solution, the coatings’ barrier properties are severely degraded after the appearance of corrosion damage spots, which manifests itself in the lowering of the impedance modulus in low-frequency region. The NaCl solution induced rapid growth of corrosion area, the more so, for the unsealed coating. Compared to the NaCl solution testing, the growth of corrosion spots is by order of magnitude slower for the salt-spray testing, at which the isolated corrosion damage spots are prevailing.

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This paper reviews research on the application of equivalent electrical circuits (EEC) for extracting electrochemical parameters of the aluminum alloys oxi