Electrochemical Behavior of Magnesium Alloy AZ31 in 0.5 M KOH Solution

The open-circuit potential of the AZ31 alloy in 0.5 M KOH solution (pH 13.5) shifts toward less negative values, showing several falls with steady-state value in the range from -0.6 to -0.55 V (saturated calomel electrode), 1.2 V more positive than the initial potential. The formed film exhibits a superior corrosion resistance. X-ray photoelectron spectroscopy reveals that the film consists of MgO and Mg(OH) 2 with Al enrichment. Scanning electron microscopy shows the formation of a plateletlike layer which probably grows by a dissolution/precipitation mechanism. The dissolution process most likely starts by rupture of the outer layer of the film as a result of the low Pilling-Bedworth ratio of MgO/Mg compared with that of Mg(OH) 2 /Mg.