Surface Modification of Mg-3Zn-0.8Ca Alloy Using Dual Micro-arc Oxidation (MAO) and Fluoridated Hydroxyapatite (FHA) Coatings

OME unsolved problems currently limit the use of Mg alloys for …. orthopedic application. Firstly, the coatings usually have poor adhesion if they are applied without an appropriate pre-treatment. Secondly, it is difficult to prepare a uniform, pore-free layer. The present article aims to overcome these obstacles and improve the corrosion resistance of the Mg alloy via combination between surface treatment and electrodeposition. The alloy surface was pretreated using micro-arc oxidation (MAO) to form an oxide layer upon which a top layer of fluoridated-hydroxyapatite (FHA) was electrodeposited. The corrosion behavior of both layers was evaluated in simulated body fluid (SBF) using potentiodynamic polarization and electrochemical impedance techniques. Surface characterization of the FHA, MAO, and MAO/FHA coatings was performed. Results show that MAO treatment decreases the corrosion current (icorr) of the Mg alloy from 7.5x10-5 A cm-2 to 1.19x10-6 A cm-2 and also increases the polarization resistance (Rp) about 6 times compared to the untreated alloy. FHA coat further enhances corrosion resistance of the alloy as shown by the increase of Rp by 14 times compared to the uncoated alloy. Pores blocking at MAO layer via FHA as top coat plays a key role in obvious corrosion resistance enhancement