Effect of chloride ion level on the corrosion performance of MAO modified AZ31 alloy in NaCl solutions

Microarc oxidation coatings were fabricated on AZ31 magnesium alloy in the electrolyte of sodium phosphate. Potentiodynamic polarization and electrochemical impedance spectroscopy tests were employed to investigate the electrochemical corrosion behavior. The corroded surface was characterized by an optical microscope and X-ray diffraction. The influence of chloride ion concentration on the corrosion resistance of microarc oxidation coated AZ31 alloy is discussed. The corrosion current density enlarged ratio and the charge transfer resistance reduced ratio indicated that the extent of the corrosion damage of microarc oxidation coated AZ31 alloy is much higher when chloride ion concentration is greater than 5%. A corrosion mechanism related to the effect of chloride ion concentrations on the corrosion behavior is proposed.

► Cl− level considerably influences corrosion resistance of MAO coated AZ31 alloys.
► The extent of corrosion damage is much higher when Cl− level is greater than 5%.
► Corrosion mechanism related to the influence of Cl− level is proposed.