Abstract
Spontaneous electrode potential, polarization behavior, and corrosion rate of superplastic Zn-22% Al alloy in a 3% NaCl solution were examined and compared with those of Zn and Al. The values of the spontaneous electrode potential of the alloy markedly shifted with a period of 20-30minutes in the directions of the noble and the base potentials alternately. In the anodic polarization process, Zn in the alloy dissolved preferentially, while the increase in polarizing current was retarded by the oxide films formed on the surface of Al matrix. In the cathodic polarization process, a tendency of passivation appeared. The corrosion rate was estimated from the intersection of the local anodic and local cathodic polarization curves. These were obtained by the measurments of the external electric current passed, and of the quantity of metals electrolytically dissolved during the potentiostatic polarization. The estimated values of corrosion rate of Al, Zn, and Zn-22%Al alloy were about 2, 17, and 10μA/cm2, respectively.
