Influence of Voltage on the Corrosion and Wear Resistance of Micro-Arc Oxidation Coating on Mg–8Li–2Ca Alloy

Abstract

Calcium phosphate (CaP) coatings were prepared on Mg–8Li–2Ca magnesium alloy by micro-arc oxidation (MAO) in an alkaline Na 3 PO 4 –Ca[C 3 H 7 O 6 P] base solution at the different applied voltages. Scanning electron microscope and X-ray diffraction were employed to characterize the microstructure and phase composition of the coatings, respectively. The corrosion resistance of the coatings was assessed by potential dynamic polarization curves, electrochemical impedance spectroscopy and hydrogen evolution experiment in simulated body fluids solution. The friction and wear properties were evaluated by friction and wear testing machine. The results demonstrate that the coating surface is porous and mainly composed of MgO, Ca 5 (PO 4 ) 3 (OH) and CaH 2 P 2 O 5 . With the increase in voltage, the corrosion resistance and wear resistance of the MAO coating are both enhanced. The corrosion current density of the MAO coating decreases about two orders of the magnitude compared to the substrate. Additionally, wear and corrosion mechanisms are discussed.