Surface treatments are always needed to enhance corrosion-resistant performance of aluminum (Al) alloys when they are used in seawater environments. The paper aimed to prepare the composite oxide ceramic coating on Al alloy 7075 by combining micro-arc oxidation (MAO) and magnetron sputtering technology. The Al substrate was precoated with titanium (Ti) layer by using the magnetron sputtering technology and then treated by MAO in the alkaline aluminate electrolyte, resulting in a composite MAO coating, which is composed of Al 2 O 3 and TiO 2 along with the complex oxide (Al 2 TiO 5 ). The potentiodynamic polarization and electrochemical impedance spectroscopy were carried out to evaluate the corrosion performance of the MAO coatings in 3.5 wt% NaCl solution. Better corrosion resistance was observed for composite oxide coating than the reference MAO coating on the bare Al, as evidenced by the higher corrosion potential of −0.664 V versus Ag/AgCl and the lower corrosion current density of 4.41 × 10 -6 A/cm 2 .

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.