Corrosion Resistance and Antibacterial Properties of Ag-Containing MAO Coatings on AZ31 Magnesium Alloy Formed by Microarc Oxidation

Silver-containing oxide coatings on AZ31 Mg alloys were fabricated by microarc oxidation (MAO) in AgNO 3 -containing sodium silicate (Na 2 SiO 3 )-based electrolyte, and their physical and chemical properties were investigated, particularly focusing on corrosion resistance and antibacterial activity. The porous oxide coatings consisting of Mg 2 SiO 4 and MgO formed in both AgNO 3 -containing and AgNO 3 -free electrolytes and the MAO coatings were composed of a porous outer layer and a dense inner layer. MAO in AgN0 3 -containing electrolyte resulted in a thicker oxide coating, especially a thicker fluorine (F)-rich inner layer. Fluorine (F) was rich in the dense inner layer, and Ag was preferentially located close to the coating surface. The potentiodynamic test indicated that Ag-containing MAO coating had a more positive corrosion potential (-1.42 V), lower corrosion current density (0.02 μA/cm 2 ), and thus higher corrosion resistance (1824 kΩ cm 2 ) compared to Ag-free MAO coatings (-1.53 V, 0.32 μA/cm 2 , and 131 kΩ cm 2 , respectively). The electrochemical impedance spectroscopy results revealed that the higher corrosion resistance of Ag-containing MAO coating was due to an order of magnitude higher resistance of the dense inner layer. Ag-containing MAO coating showed an excellent antibacterial activity over 99.9% against two strains of bacteria, Staphylococcus aureus and Escherichia coli.