Characterisation of ceramic coatings produced by plasma electrolytic oxidation of aluminum alloy

Ceramic coatings were prepared on aluminum alloy by plasma electrolytic oxidation method in an environmental-friendly solution. Evolvement of surface morphology, composition and thickness of ceramic coatings on aluminum alloy were studied during plasma electrolytic processes by scanning electron microscopy and X-ray diffractometer. Analysis show that the two-layer structure ceramic coatings consist of different states of Al2O3 such as α-Al2O3, γ-Al2O3 and θ-Al2O3. For short treatment times, the formation processes of ceramic coatings follows a linear kinetics, while for longer times the kinetics departs from the linear behavior. During PEO processes, the average size of the discharge channels increase gradually as the treatment time increased, while the density of the discharge channel decreases with increasing coating time. The results also show that tremendous energy input results in breaking off of the surface coatings.