Preparation and corrosion resistance characterization of MAO coating on AZ31B magnesium alloy formed in the mixed silicate and phosphate electrolytes with pectin as an additive

AZ31B magnesium alloy as a medical implant material is hampered in its application due to its excessive corrosion rate in the human environment. This work used pectin as an electrolyte additive to prepare micro-arc oxidation (MAO) coatings on the surface of magnesium alloys. The surface and cross-section morphology, chemical composition of the coatings were examined using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometry. The effect of pectin concentrations on the corrosion resistance of the coatings under simulated body fluid media was evaluated by electrochemical tests. The results showed that the addition of pectin could fill the pores (resulting in a reduction in porosity by 2.3 %) and micro-cracks within the coatings, increasing the corrosion resistance with the increase in pectin concentration. Notably, the MAO-0.75 coating exhibited densest coating structure and then best corrosion resistance with the corrosion current density as low as 1.259 x 10-6 A/cm2, which was four order of magnitudes lower compared to the substrate. The experimental results showed that the use of pectin as an additive prolongs the service life of magnesium alloy MAO coatings in simulated body fluids, thus giving them great potential as medical implant materials.