Preparation and Corrosion Resistance of Anodic Oxidation Coatings on 2198 and 5A90 Al-Li Alloys

2198 and 5A90 Al-Li alloys were anodized with a constant DC potential in 18%H2SO4 solution (Solu.A) and the mixture solution of 18%H2SO4+5%C2H2O4 (Solu.B) at room temperature. 12 and 11 V was optimized as the applied oxidation potential for 2198 and 5A90 alloys, respectively. Cross-sectional morphology, surface morphology and elements distribution of anodic oxidation coatings were observed by scanning electron microscope equipped with energy dispersive X-ray analysis (SEM/EDX). Corrosion resistance was tested by potentiodynamic polarization plot in 3.5%NaCl solution. The results showed that the thicknesses of coatings obtained at the selected potential in Solu.A and Solu.B were about 50 μm/110 μm for 2198 alloy and 80 μm/110 μm for 5A90 alloy. In both solutions, anodic oxidation coatings of 2198 alloy were primarily composed of Al oxides; those of 5A90 alloy were mainly consisted of Al oxides and a small amount of Mg oxides. The results of potentiodynamic polarization showed that anodic oxidation coatings of 2198 and 5A90 Al-Li alloys had better corrosion resistances than that of untreated alloys.