Effect of Electrolyte Compositions on the Corrosion Behavior of Oxide Films on AZ91D Magnesium Alloy Prepared by Micro-Arc Oxidation

In order to increase corrosion resistance, a protective ceramic films were prepared by micro-arc oxdiation (MAO) of AZ91D magnesium alloys (AZ91D)in an aluminate electrolyte containing potasium hydroxide, potassium fluoride, or sodium hydroxide, and the influence of theses electrolyte additives on corrosion behavior was elucidate.A porous films were formed, mainly consisting of MgAl2O4. The MAO films formed in KF-containing electrolyte consisted of porous outer layer and dense inner layer, but in KOH- or NaOH- electrolyte, no dense inner layer was extinctly observed. The corrosion resistance of MAO films was performed by EG&G potentiostat/galvanostat model 273 in 3.5 wt% NaCl solution, and the corrosion resistance of MAO films were found to be strongly dependent on electrolyte components. All MAO samples have thigher corrosion potential, lower corrosion density and higher polarization resistance than uncoated sample. Particullary, MAO films formed in KF-containing eletctrolyte exhibited a wide passivation region and the best corrosion resistance.