Corrosion behaviour of micro-arc oxidation coatings on Mg-2Sr prepared in poly(ethylene glycol)-incorporated electrolytes.

Microarc oxidized calcium phosphate (CaP) ceramic coatings were fabricated on Mg-2Sr alloy from silicate electrolytes with different concentration gradient poly(ethylene glycol) (PEG). The microstructure, phase and degradability of the ceramic coatings were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and simulation body fluid (SBF) immersion tests respectively. An electrochemical workstation was used to investigate the electrochemical corrosion properties of the coatings. It is found that microstructure, thickness, adhesive strength and degradation rate are influenced by PEG incorporation through adjusting the electrolyte activity and then altering the coating growth mechanism. Similar thicknesses (39.0-42.2 μm) are observed in PEG-containing coatings while their PEG-free counterparts possess the maximum value (51.5 μm). The weight gain in the first two days of SBF immersion suggests that a new layer containing CaP apatites is generated. Results show that ceramic coatings prepared in the electrolyte containing 8 g L PEG exhibits the highest corrosion resistance and lowest degradation rate.