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 SiO 2 layer. The results from an X-ray diffraction and scanning electron microscope clearly show that a layer of sol-gel-derived SiO 2 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/cm 2 and the larger polarization resistance of 5.35 × 10 4 Ω cm 2 were found for sol-gel/PEO-coated AA7075 alloy as compared with 3.68 × 10 −6 A/cm 2 and 9.81 × 10 3 Ω cm 2 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.