Correlation between the corrosion resistance and the semiconducting properties of the oxide film formed on AZ91D alloy after solution treatment

The corrosion resistance and semiconducting properties of the oxide film formed on the AZ91D alloy were evaluated. The alloy was tested in the as-cast condition and after a solution annealing treatment. Electrochemical impedance spectroscopy measurements and potentiodynamic polarization curves were obtained in a H3BO3 (0.05 M) + Na2B4O7⋅10H2O (0.075 M) solution with pH = 9.2 at room temperature. The semiconducting properties of the oxide film were evaluated using Mott–Schottky plots. The corrosion resistance of the AZ91D was reduced after the solution treatment while the semiconducting properties of the passive films were little affected.

► The corrosion resistance of the AZ91D alloy was markedly affected by solution annealing.
► Solution annealing led to the formation of thinner and less corrosion resistant oxide layers.
► The corrosion resistance increased with time for both the as-cast and solution annealed alloy.
► The semiconducting character of the passive film changed from p-type to n-type with the immersion time.
► The charge carrier concentration in the passive film decreased with the immersion time.