Corrosion protection of AZ91D magnesium alloy by a duplex coating

A duplex coating was formed under potentiostatic conditions on magnesium alloy AZ91D in order to improve its corrosion resistance in a simulated physiological environment. The first layer was formed by anodization at low potentials in molybdate solution. The outer layer was a PPy film electrosynthesized in sodium salicylate solution. The conditions of the formation were determined to obtain a layer with globular morphology. The bilayer was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion protection properties of the coatings were examined in Ringer solution by monitoring the open circuit potential (OCP), polarization techniques, and electrochemical impedance spectroscopy (EIS). The obtained results showed that the bilayer improves the corrosion resistance of the substrate. Moreover, the duplex coating presented better anticorrosive properties than a single PPy film. Afterwards, the bilayer was modified by cementation of silver ions from a solution containing AgNO3. The modified electrode exhibited good antibacterial properties.