Micro-defect characterization and growth mechanism of plasma electrolytic oxidation coating on 6082-T6 alloy.

This work reports micro-defects and growth mechanism of the plasma electrolytic oxidation (PEO) coating formed on the surface of 6082-T6 aluminum alloy. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray computed tomography techniques were used to characterize the morphology, phase, microstructure, and porosity of the PEO coating, respectively. The results confirmed a porous outer layer and a dense inner layer in the coating. The PEO coating was composed of γ- and α-Al 2 O 3 phases, and amorphous phases. A layer with only amorphous structures was found near the coating/substrate (C/S) interface, which could be ascribed to the high concentration of P element in the electrolyte. Micro-defects with different sizes and shapes inside the coating were successfully characterized by the high-resolution X-ray computed tomography technique, and the volume reconstruction result revealed a porosity fraction of 5.43% for the coating. A growth model was complemented to explain the growth mechanism and interconnected micro-defects of the PEO coating. • Micro-defects in the plasma electrolytic oxidation (PEO) coating formed on 6082-T6 alloy were firstly characterized by high-resolution X-ray computed tomography technique. • Formation of the amorphous structure at the coating/substrate (C/S) interface was highly dependent on P element in the electrolyte. • Growth mechanism of the coating was clarified based on the microstructural observation and micro-defect characterization. [ABSTRACT FROM AUTHOR]