Effect of electrolyte compositions on the corrosion behavior of oxide films onAZ91D magnesium alloy prepared by micro-arc oxidation

摘要

Oxide coatings on AZ91D magnesium alloy were prepared in an aluminate-based electrolyte with the addition of potassium fluoride, potassium hydroxide or sodium hydroxide, respectively by micro-arc oxidation (MAO), and their corrosion properties were investigated by the potentiodynamic tests in 3.5 wt % NaCl solution. All oxide coatings were mainly composed of MgAl_2O_4 phases. MAO films formed in electrolyte containing potassium fluoride showed a homogeneous macro-porous surface morphology without cracks, and oxide film was composed of two parts, porous inner layer and dense outer layer. On the other hand, MAO film formed in KOH- or NaOH-containing electrolyte exhibited inhomogeneous surface with cracks and defects, and the coatings showed only porous layer. The MAO film obtained in KF-containing electrolyte had lowest current density and highest polarization resistance.