Effect of graphene oxide on properties of AZ91 magnesium alloys coating developed by micro-arc oxidation process

In this work micro-arc oxidation (MAO) process in the presence of an alkaline electrolyte with different amounts of graphene oxide (0, 10, 20 and 30 mg/L) has been applied on AZ91 magnesium alloys, successfully. Microstructure, phase evaluation, scratch test, corrosion behavior, bioactivity and antibacterial properties of fabricated ceramic coating were compared. The results reveal that in addition to the GO, composite coating contains MgO and Mg2SiO4 ceramics that were produced as a result of oxidation and electrolyte reaction with the Mg during MAO treatment. Addition of the GO into the electrolyte cause to reduction of the pores and cavities produced due to exhausting of the gas bubbles from the discharges channels in the MAO process. Coating with 20 mg/L of GO additive includes a uniform surface and the lowest pores in diameter in comparison with the other specimens that cause to clearly reduction of the corrosion current density to 0.24 A/m2. The damaged width of the scratch decreased from about 137 µm for non-added GO to 87 µm for sample 20GO due to strengthening of the ceramic coating by GO reinforcement. Hydroxyapatite phase has grown in a favorable composition over the coatings after soaking in the SBF solution, and the increasing of the GO addition cause to increasing of the antibacterial behavior of the ceramic coating against both of the S. aureus and E. coli bacteria.