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Please cite this article as: M.Curioni, F.Scenini, T.Monetta, F.Bellucci, Correlation between electrochemical impedance measurements and corrosion rate of magnesium investigated by real-time hydrogen measurement and optical imaging, Electrochimica Acta http://dx. AbstractThe corrosion behaviour of magnesium in chloride-containing aqueous environment was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) performed simultaneously with real-time hydrogen evolution measurements and optical imaging of the corroding surface. The potentiodynamic investigation revealed substantial deviations from linearity in close proximity of the corrosion potential. In particular, differences in the slope of the current/potential curves were observed for small polarizations above or below the corrosion potential. These observations, suggest that the usual method based on the use of the Stern-Geary equation to convert a value of resistance into a value of corrosion current is inadequate.Nonetheless, a very good correlation between values of resistances estimated by EIS and corrosion currents obtained from real-time hydrogen measurement was found. Real-time hydrogen measurement also enabled, for the first time, direct measurement of an 'apparent' Stern-Geary coefficient for magnesium. In order to rationalize the complex behaviours experimentally observed, an electrical model for the corroding magnesium surface is presented.

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The anodic film generated in acid electrolytes on high-purity aluminum shows a porous morphology, formed by the packing of approximately hexagonal cells of alumina, containing a centrally located cylindrical pore. Conversely, during anodizing of an AA2024 T3 alloy, the presence of alloying elements, both in solid solution and as second-phase material, influences the filming behavior, with a less regular film morphology developed above the aluminum alloy matrix, and characteristic morphologies generated above and in the zone of influence of second-phase particles. Further, the anodizing behavior of the alloying elements is determined by the applied potential. In this work, the anodizing behavior of AA2024 T3 commercial alloy in sulfuric acid electrolyte has been characterized. Specifically, phenomena related to the oxidation of the second-phase particles have been separated from those associated with the oxidation of the copper-containing aluminum matrix. This has used electrochemical data obtained under potentiostatic and potentiodynamic conditions for the AA2024 T3 alloy, high-purity aluminum, and model Al-Cu alloys, which have been correlated with detailed examination of plan and sectional views of the anodized substrates.

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