Electrochemical investigation of corrosion of anodised 1050 aluminium alloy in marine environments

The corrosion susceptibility of untreated and anodised aluminium alloy 1050, with and without the presence of corrosion products, has been investigated in 3·5%NaCl solution and simu.lated sea water. Corrosion rates in the presence of corrosion products were calculated from weight loss measurements under an applied anodic current. This procedure ensured the development and accumulation of corrosion products in the solution and on the alloy surface. Experiments in the absence of corrosion products were carried out under potentiodynamic polarisation at a high scan rate and corrosion rates were calculated from polarisation curves. Anodised coatings up to 20 μm in thickness were found to protect the alloy in 3·5%NaCl solution under both sets of experimental conditions. In sea water these coatings protected the alloy only in the absence of corrosion products. In the presence of corrosion products, higher corrosion rates were observed in sea water than in 3·5%NaCl. Higher corrosion rates and anodic currents were also observed in sea water in the absence of corrosion products, but the corrosion and pitting potentials moved to more positive values. An explanation is given of the results, based on the protective properties of anodic coatings, the influence of sea water composition, and the influence of corrosion products.