Characterisation of sealed anodic films on 7050 T74 and 2214 T6 aluminium alloys

Anodic films grown on 7050 T74 and 2214 T6 aluminium alloys by sulfuric acid anodising, and sealed in a Ni and Co acetate solution have been observed by scanning (SEM) and transmission (TEM) electron microscopy, and have been chemically analysed by X-ray photoelectron, secondary ion mass and glow-discharge optical emission spectroscopy. Corrosion behaviour has been investigated in a 0.1 M sodium chloride solution at the corrosion potential, using electrochemical impedance spectroscopy (EIS). The morphology of the oxide layer was dependent on the aluminium substrate. For the 7050 alloy, the surface presented a homogeneous structure, whereas for the 2214 alloy, the layer appeared porous and disorganised. For both alloys, surface enrichment of the oxide films in sealing bath elements has been observed. This enrichment was greater for the 2214 alloy. The protective efficiency of the sealed anodic film remained high for the 7050 alloy and decreased with immersion time for the 2214 alloy, in keeping with the disorganised structure of the oxide film on the latter.