Evolution processes of the corrosion behavior and structural characteristics of plasma electrolytic oxidation coatings on AZ31 magnesium alloy

Highlights: • The corrosion protectiveness of PEO coatings on AZ31 Mg alloy, treated in the simple silicate electrolyte, decreases with the PEO time. • A compact thin inner layer and discharge channels can be observed on the fractured cross-sections of the detached coatings. • Compared to polished cross-section morphology, fractured one is more actual and coincident with the electrochemical analysis results. • XRD analysis of Mg alloy-based detached PEO coatings is performed for the first time. Evolution processes of the corrosion behavior and structural characteristics of the plasma electrolytic oxidation (PEO) coated AZ31 magnesium alloy were investigated by using scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), potentio-dynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Detached coating samples were fabricated by an electrochemical method and more details of the internal micro-structure of coatings were clearly observed on the fractured cross-section morphologies of the samples compared to general polished cross-section morphologies. Evolution mechanisms of the coating corrosion behavior in relation to the evolution of micro-structural characteristics were discussed in detail.