Electrochemical noise analysis of the corrosion of high-purity Mg-Al alloys

Corrosion of high-purity Mg-Al alloys containing 3, 6 and 9 wt.% Al was investigated using electrochemical noise (EN) analysis. Changes in the EN signals were correlated with macroscopically observable events on the sample surfaces, which were recorded using time-lapse photography. Steady-state corrosion in all alloys was highly localised. For the Mg3%Al alloy, localised corrosion was preceeded by a period of general corrosion. The corrosion rate of the as-cast Mg9%Al alloy was less than those of the other materials but increased with solution annealing time. The results are consistent with strong galvanic coupling between Al-depleted and -enriched zones of the a-phase.