Preparation of PEO/silane composite coating on AZ31 magnesium alloy and investigation of its properties

Abstract A composite Plasma Electrolytic Oxidation together with silane (PEO/silane) was deposited on AZ31 magnesium alloy, and the coating properties were compared to PEO and silane single-layer coatings individually. SEM, AFM, XRD, FT-IR (transmission and ATR), and pull off tests were utilized to characterize the coatings and evaluate them as pretreatment for an epoxy coating. The results showed that the PEO/silane coating improved the adhesion strength of the epoxy coating. EIS, EDS, and SEM were used to investigate the corrosion resistance of the coatings and their degradation mechanism. The results revealed that the PEO/silane coating had superior corrosion resistance in comparison with both the PEO and silane single-layer coatings. The corrosion resistance of the PEO and silane coatings decreased and they degraded during 168 h of immersion in 3.5% NaCl, however; the PEO/silane coating maintained its corrosion resistance and did not undergo any degradation.