Plasma Electrolytic Oxidation Treatment of AZ31 Magnesium Alloy for Biomedical Applications: The Influence of Applied Current on Corrosion Resistance and Surface Characteristics

Abstract

Magnesium alloys are an exciting challenge for the biomaterials field given their well-established biodegradability and biocompatibility. However, when exposed to biological fluids, their rapid degradation and hydrogen release are the main drawbacks for clinical applications. This work aimed to investigate the influence of the current density applied during the plasma electrolytic oxidation (PEO) treatment on the durability of an AZ31 magnesium alloy. In particular, specific interest was directed to the degradation rate undergone by the PEO coating, obtained under two different current density conditions, when exposed to Hank’s solution at 37 °C to simulate the physiological environment, employing the techniques of potentiodynamic polarization and electrochemical impedance spectroscopy. Experimental results highlighted that the plasma electrolytic oxidation technique resulted in an improvement in the corrosion resistance of the magnesium alloy in the test solution. The current density affected the morphology of the coating. In particular, the anodic oxide coating obtained by applying the highest current density showed a higher thickness and fewer but larger pores, while the lowest current density generated a thinner PEO coating characterized by several but smaller pores. Surprisingly, the best corrosion resistance has been exhibited by the anodic oxide coating grown at the highest current density.