Atmospheric corrosion of bare and anodised aluminium in a wide range of environmental conditions. Part II: Electrochemical responses

This study compares the behaviour of aluminium in the bare condition and when protected with anodic films of approximately 7, 17 and 28 μm thickness for up to 42 months of exposure in 11 atmospheres of very different aggressivities, with salinity values ranging between 2.1 and 684 mg Cl− m−2 d−1. The results of a previous study based on visual inspection and traditional gravimetric techniques are complemented by the application, essentially, of electrochemical impedance spectroscopy (EIS). The specimens were characterised by EIS when recently obtained and after 12, 24 and 42 months of exposure in the different testing stations. Exposure leads to an improvement in all the quality indices of anodic films, irrespective of their thickness or the degree of environmental pollution. Anodising and sealing prevents localised corrosion — which is characteristic of aluminium in marine or industrial atmospheres — even in the most unfavourable situations, except in the case of 7 μm films, the lowest thickness tested.