Growth Behavior and Wear Resistance of PEO Coatings in Bipolar Mode

Plasma electrolytic oxidation (PEO) coatings were prepared using a pulsed bipolar power supply to investigate the effects of different cathodic currents on the growth mechanism of PEO coatings on 6061 aluminum alloy. The phase composition, microstructure, element distribution and content of the coatings were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). It was found that the coating growth rate enhanced obviously and the discrete pores reduced significantly when the cathodic current increased. In particular, when the cathodic current density was 7.5 A/dm(2), there was a soft plasma discharge phenomenon, and more alpha-Al2O3 crystals were generated. The distribution of Si elements reveals that the soft plasma discharge is a form of internal discharge and the coating exhibits higher hardness and compactness. It was tested using the friction tester, and the coating showed excellent wear resistance.