Effects of Power Modes on Properties of Micro-Arc Oxidation Biological Coatings on Magnesium Alloy

Abstract

At present，there are few studies on the preparation of biological coatings by micro-arc oxidation under different power modes.In this work，micro-arc oxidation (MAO) process was carried out on the surface of ZK60 magnesium alloy to prepare the biological coatings by means of four different power modes (full stage constant voltage mode，full stage constant current mode，constant voltage-constant current mode，constant current-constant voltage mode).The changes of voltage/current with time in the reaction process under different power supply modes were real-time recorded and analyzed，and the phase，microstructure，element distribution，surface roughness and contact angle of the MAO biological coatings obtained under different power supply modes were investigated by means of scanning electron microscope (SEM)，energy dispersive spectrometer (EDS)，Diffractometer (XRD) and Confocal microscopy.Results indicated that the phase constituents of the coatings prepared under four power modes included Mg，MgO and calcium-phosphorus products such as Ca3(PO4)2.Under different power modes，the thickness and corrosion resistance of the coatings were correspondingly different.The thickness of coatings prepared under constant voltage mode was the smallest due to insufficient breakdown force in the later stage，which was much smaller than other coatings prepared under three different power modes.Therefore，the corresponding roughness was also the smallest.Under the constant current mode，part of the coatings fell off due to high energy in the later stage，which led to the poor quality of the corrosion resistance of the MAO coatings.In contrast，under constant voltage-constant current mode，the defects of single constant voltage and constant current modes could be avoided.Compared with other three ones，the coatings prepared under constant voltage-constant current mode had the characteristics of uniform and dense microstructure，with a large thickness of about 55 μm.The electrochemical test indicated that the MAO biological coating prepared under constant voltage-constant current mode had better corrosion resistance.At the same time，this mode had the lowest energy consumption，which met the requirements of energy saving and consumption reduction.In addition，the MAO coating prepared under the hybrid voltage-current mode had better bio-compatibility.

Keywords

• power modes|magnesium alloy|micro-arc oxidation|biological coatings|properties