Improving corrosion behavior and in vitro bioactivity of plasma electrolytic oxidized AZ91 magnesium alloy using calcium fluoride containing electrolyte

Modified oxide layer was successfully prepared on AZ91 magnesium alloy by plasma electrolytic oxidation (PEO) using phosphate electrolyte containing calcium fluoride (CaF₂). Evaluating the corrosion behavior of the oxidized AZ91 magnesium alloy by potentiodynamic polarization in simulated body fluid (SBF) solution indicated that addition of CaF₂ to electrolyte leads to considerable decrease in corrosion rate caused by surface porosity, oxide layer thickness, and formation of MgF₂ phase. Electrochemical impedance spectroscopy (EIS) revealed that the resistance of the outer porous and the inner barrier parts of the oxide layer increased by 3 and 41 times, respectively. Presence of biological calcium ion along with fluorine and phosphorous ions in the oxide layer composition created a higher driving force for nucleation and growth of bioactive layer by decreasing the contact angle with SBF solution.