Characteristics and corrosion resistance of plasma electrolytic oxidation coatings on AZ31B Mg alloy formed in phosphate – Silicate mixture electrolytes

•PEO coatings formed on AZ31B in various P:Si ratio electrolytes were studied.•The effect of P:Si ratio on the corrosion resistance was investigated.•Si-coating showed superior corrosion resistance to P-coating.•The highest corrosion resistance was achieved with a ratio of P:Si = 20:80.

AZ31B magnesium alloy was treated by plasma electrolytic oxidation (PEO) in phosphate–silicate mixture electrolytes. The concentration ratio of phosphate to silicate was varied from 100:0 to 0:100 in order to investigate the influence of the electrolyte composition on the morphology, compositions and corrosion resistance of PEO coatings by using SEM, EDS, XRD, XPS analyses, immersion test, salt spray test and potentiodynamic polarization. When a mixture electrolyte with an optimum concentration ratio of phosphate to silicate (i.e. P:Si = 20:80) is used, the corrosion resistance of PEO coatings is the highest.