2004 Volume 44 Issue 10 Pages 1727-1732
The corrosion of 55mass%Al-1.6mass%Si-Zn (GL) alloy has been tested under a wet-dry cyclic condition using an AC impedance technique to clarify its corrosion behavior. The results have been compared with that of a zinc sample exposed under identical condition. The sample was exposed to alternate conditions of immersion for 1 h in a 0.05 kmol/m3 NaCl solution and drying for 7 h at 298 K and 60% RH, and the corrosion rate was monitored for 10 d (30 cycles) using a two-electrode type probe. Simultaneously, the corrosion potential was continuously monitored using a special arrangement in combination with a Luggin probe tip. From the monitoring results of the corrosion rate and corrosion potential and the polarization curve, it was found that the corrosion rate of GL was decreased by inhibition of the cathodic reaction.
The impedance response was evaluated by using an equivalent circuit considering the charge and mass transfer consequences of the coupled corrosion processes. It was found from the time constant of the diffusion impedance that the corrosion product layer formed on GL alloy acted more effectively as a diffusion barrier against oxygen transport compared to zinc.