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

Abstract

Silver-containing oxide coatings on AZ31 Mg alloys were fabricated by microarc oxidation (MAO) in AgNO3 -containing sodium silicate (Na2SiO3) -based electrolyte, and their physical and chemical properties were investigated, particularly focusing on corrosion resistance and antibacterial activity. The porous oxide coatings consisting of Mg2SiO4 and MgO formed in both AgNO3 -containing and AgNO3 -free electrolytes and the MAO coatings were composed of a porous outer layer and a dense inner layer. MAO in AgNO3 -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 (0.02μA/cm2) , and thus higher corrosion resistance (1824kΩcm2) compared to Ag-free MAO coatings (−1.53 V, 0.32μA/cm2 , and 131kΩcm2 , 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.

Corrosion and corrosion fatigue performances of micro‐arc oxidation coating on AZ31B cast magnesium alloy

“…The main components of the MAO coatings are MgO, Mg 2 SiO 4 , and MgF 2 ; in addition to some complex silicate compounds, Mg 3 Al 2 (SiO 4 ) 3 and Mg x F y (SiO 4 ) z . These results are in good agreement with previous reports describing MAO coatings as mixtures of MgO (periclase), Mg 2 SiO 4 (forsterite), and MgF 2 (magnesium fluoride) compounds . The variation of the processing current density did not result in any significant change in the phase species of the MAO coating within the current density range studied in this work.…”

The effect of current mode and discharge type on the corrosion resistance of plasma electrolytic oxidation (PEO) coated magnesium alloy AJ62

“…However as the porosity level in the unipolar sample coating (S1) was quite high, it exhibited a lower corrosion potential compared to samples S2-S4 prepared using a bipolar current mode. Therefore, for better localized corrosion resistance the coating needs to be not only thicker, but also should be free from defects such as porosity [33,38]. The properties of the plasma discharges themselves in the bipolar current mode differ from those of the unipolar one.…”

Surface modification of valve metals using plasma electrolytic oxidation for antibacterial applications: A review

“…Ag bearing PEO layer on magnesium alloy AZ31 has also been deposited by the addition of Ag nitrate in Na 2 SiO 3 ‐based electrolyte. Ag incorporated coatings did not only show excellent antibacterial resistance against Gram positive and Gram‐negative bacteria but also improved the corrosion resistance significantly . Similarly, antibacterial layer on Ti by high current anodization has also been reported in Ag nitrate containing electrolyte .…”

“…Ag incorporation in PEO coatings has also been reported through the addition of Ag bearing compound such as Ag acetate or Ag nitrate in the electrolyte. Muhaffel et al prepared antibacterial coatings through the addition of 0.1 and 0.4 g/L Ag acetate in the electrolyte, resulting in enhanced bioactivity and antibacterial properties of HA layer.…”