| Magnesium alloy has become a research hotspot of medical implant materials in recent years because of its degradability and biocompatibility.However the problem of magnesium alloy application is that the corrosion rate too fast in the humoral environment and a large amount of hydrogen is released.At present the research focus is to delay and control the corrosion rate of magnesium alloy and extending the life of the magnesium alloy in the human body.Objective:Improve the long-term corrosion resistance of micro-arc oxidation coating on AZ31 magnesium alloy by ultrasonic cold forging treatment.Methods:AZ31 magnesium alloy was treated by ultrasonic cold forging?UCFT?and the Sr-Ca-P coating was prepared on the surface of AZ31 magnesium alloy by microarc oxidation.The Sr-Ca-P layer was checked by SEM,XRD,EDS,Evaluation of Surface Morphology and Phase composition of modified magnesium Alloy.Hydrogen evolution test and immersion test,potentiodynamic polarization curve were used to evaluate the corrosion resistance of the coating.The cytocompatibility of the coating was evaluated by MTT method.Results:After ultrasonic cold forging treatment?UCFT?on the surface of AZ31magnesium alloy,the surface grain size reached nanometer level.The metallographic microscopic observation of the modified magnesium alloy after etching revealed that the lattice of the magnesium alloy disappeared in the modified layer,and the thickness of the modified layer reached 400?m.The results of micro Vickers hardness indicate that the Vickers hardness of the surface of the modified layer is the highest within100um reached 85HV.After 100?m the Vickers hardness decreases with the increase of the depth of the modified layer.The Vickers hardness after 400um is the same as that of the AZ31 magnesium alloy substrate.Scanning electron microscopy?SEM?showed that the surface morphology of AZ31 micro-arc magnesium oxide alloy after ultrasonic cold forging treatment was microscopic porous structure.Compared with the surface morphology of micro-arc magnesium oxide alloy without ultrasonic cold forging treatment,the pore diameter decreased and the number of pores increases.EDS and XRD results show that UCFT pretreatment has no effect on the phase composition and elemental composition of the micro-arc magnesium oxide alloy containing Sr-Ca-P coating.The electrochemical results show that the corrosion potential of AZ31 magnesium alloy after UCFT treatment increases from-1.50V to-1.42V,indicating that UCFT pretreatment can improve the corrosion resistance of AZ31 magnesium alloy.In the micro-arc magnesium oxide alloy,the corrosion potential after UCFT treatment was-1.38V,and the corrosion current density was 9.78×10-9?A/cm2?.The corrosion potential is-1.42V,and the corrosion current density is 2.789×10-8?A/cm2?in the group without UCFT pretreatment,indicating that the UCFT treatment has improved corrosion resistance of magnesium alloys and magnesium alloys after micro-arc oxidation.The MTT results showed that the cell proliferation rate of micro-arc magnesium oxide alloy containing Sr-Ca-P was higher than that of the negative control group,indicating that the micro-arc magnesium oxide alloy containing Sr-Ca-P coating has good biocompatibility. |
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