Biodegradation behavior of micro-arc oxidized AZ31 magnesium alloys formed in two different electrolytes

Degradation behavior of coated magnesium alloys is among most prominent factors for their biomedical applications. In this study, bio-corrosion behavior of micro-arc oxidized magnesium AZ31 alloys formed in silicate and phosphate baths was investigated in r-SBF medium. For this purpose polarization behavior and open circuit profile of the coated samples were achieved by electrochemical and immersion tests, respectively. Moreover, the morphology and composition of the coatings were evaluated before and after immersion test using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The results showed that the phosphate film had better corrosion resistance and greater thickness than silicate film and, in turn, the lesser degradability in SBF solution, so that Ca2+ and PO43− containing compounds were more abundant on silicate film than phosphate film. Moreover phosphate film had greater surface roughness and lesser hydrophilic nature.

► Phosphate coating has lesser degradation rate than silicate coating in r-SBF solution. ► Farringtonite phase is chemically more stable than forsterite phase in SBF solution. ► Apatite forming ability of forsterite containing coating is better than farringtonite containing film. ► The hydrophilisity nature of silicate film on magnesium alloy with respect to its roughness, is greater than phosphate film.