Influence of second phase particles on initial electrochemical properties of AA7010-T76

The initial behavior of the open-circuit potential of differently prepared AA7010 samples was investigated using conventional immersion experiments and microcapillary experiments. For macroscopic samples a strong increase of the open-circuit potential can be observed, which is due to selective magnesium dissolution from the Mg2Si phase leaving a remnant silicon oxide particle. This silicon oxide particle is smaller than the initial Mg2Si phase and thus a micro-crevice is formed, being the initiation site of localized corrosion of the surrounding matrix. Optical micrographs, SEM and EDX confirm this interpretation of the open-circuit potential behavior.