| The micro-arc oxidation and electrophoresis (MAO-EPD) complex coatingcontaining hydroxyapatite (HA) was prepared on the AZ31Mg alloy by micro arcoxidation (MAO) and electrophoresis deposition (EPD) technologies. First, a MAOceramic layer was formed on the AZ31magnesium alloy by MAO in the electrolytecontaining aluminate, phosphate, and ethylenediaminetetraacetic acid calcium disodiumsalt. The influence of adding glycerol into the electrolyte on the forming of MAOceramic layer and its properties was studied. The thickness, composition and surfaceof composite coatings were characterized by coating thickness gauge, X-raydiffraction (XRD), scanning electron microscope (SEM), X-ray fluorescence (XRF),and the X-ray energy spectrometer (EDS). The corrosion resistance of samples wasmeasured by potentiodynamic polarization curve in simulated body fluid (Hank’ssolution). In addition, wear resistance of the sample was represented by friction andwear test. The results showed that the concentration of glycerol on the performance ofmicro arc oxidation ceramic layer had a great impact. With the increase ofconcentration of glycerol, the thickness of ceramic layer decreased, the porosity wasreduced, and the corrosion wear resistance increased gradually. When theconcentration of glycerol was3mL/L, the MAO ceramic layers had the best corrosionand wear resistance.Then, the composite layer rich in HA was gained by EPD in electrophoresisliquid containing HA on the basis of micro-arc oxidation. The influence direct currentelectrophoresis deposition (DC-EPD) and pulse current electrophoresis deposition(PC-EPD) on the composition, structure and performance of composite layes wascomparatively studied. Process parameter of EPD was determined by the experiment,process parameters for DC-EPD: electrophoresis voltage80V, electrophoresis time300s; process parameters of PC-EPD were as follows: electrophoresis voltage160V,electrophoresis time of300s, positive duty cycle45%, negative duty cycle25%.The surface of obtained composite coatings containing HA was smooth and had no pore and consisted of MgO, MgAl2O4, Ca3(PO4)2and HA. The value of Ca/Pincreased with the increase of voltage and time. Compared with MAO coating, thepotentiodynamic polarization curves of composite layer moved to the direction ofhigher voltage and lower corrosion current density, indicating the composite layer hada higher corrosion resistance than MAO coating. This corrosion resistance wasstrengthened and then weakened with the increase of electrophoresis voltage and theextension of electrophoresis time. The composite layer also exhibited betterbiocompatibility than MAO coating in the test soaking in simulated body fluid.Besides, the coating prepared by PC-EPD had higher corrosion and wear resistance,and better biocompatibility than DC-EPD. |
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