Corrosion Behavior of Micro-Arc Oxidized Magnesium with Calcium Phosphate Coating in Flowing Simulated Body Fluids

A micro-arc oxide (MAO) layer and calcium phosphate (Ca-P) coating were prepared on magnesium using a micro-oxidation technique and chemical deposition. The corrosion behavior of the MAO magnesium with and without a Ca-P coating in static and flowing simulated body fluids (SBF) was studied by electrochemical polarization and impedance spectroscopy. The microstructure of the coating was examined by scanning electron microscopy, X-ray diffraction and infrared spectroscopy. The results indicated that the micro-arc oxide layer was easily broken by the SBF, which breached the oxide layer and corroded the underlying magnesium. Solution flow promoted the failure of the oxide layer and the process of MAO magnesium corrosion. The prepared Ca-P coating consisted of hydroxyapatite (HA) and dicalcium phosphate dihydrate (DCPD). Although the Ca-P coating itself exhibited low resistance to corrosion, it effectively protected the oxide layer against failure, which then inhibited the corrosion of the Ca-P coated MAO in SBF. The presence of the Ca-P coating weakened the effect of flow on the corrosion of the coated MAO. Moreover, the Ca-P coating transformed into a thick apatite layer even in flowing SBF, which further improved the protection of the MAO magnesium. (C) 2015 The Electrochemical Society. All rights reserved.