Enhanced corrosion‐resistant performance of the PEO coatings on AA7075 alloy by a sol–gel‐derived silica layer

Abstract

The paper aimed to increase the corrosion-resistant performance of AA7075 alloy by the incorporation of sol–gel with plasma electrolytic oxidation (PEO) technologies. The AA7075 alloy substrate was first coated by an oxide ceramic layer with the help of the PEO process and then covered by a sol–gel-derived SiO2 layer. The results from an X-ray diffraction and scanning electron microscope clearly show that a layer of sol–gel-derived SiO2 uniformly covered and sealed the surface microporous structure of PEO coatings on AA7075 alloy, effectively enhancing the corrosion-resistant performance of PEO-coated AA7075 alloy in an aqueous solution containing 3.5-wt.% NaCl. The lower current density of 2.09 × 10−7 A/cm2 and the larger polarization resistance of 5.35 × 104 Ω cm2 were found for sol–gel/PEO-coated AA7075 alloy as compared with 3.68 × 10−6 A/cm2 and 9.81 × 103 Ω cm2 for individual PEO-coated AA7075 alloy. Thus, it is an effective strategy to improve the corrosion-resistant performance of the AA7075 alloy by combining the PEO and sol–gel techniques.