Modification Of Extruded Pure Magnesium By NaMgF₃ And Its Effect On Hydroxyapatite Film

Magnesium and its alloys have great potential in biomedicine,while poor corrosion resistance is one of the most important reasons which restricts their wide clinical application.In This paper,the effect of hot extrusion on corrosion resistance of pure magnesium in SBF solution is researched.Results shows that extruded pure magnesium has better corrosion resistance and machinability than as cast pure magnesium.But the influence of extrusion ratio on microstructure,corrosion resistance and mechanical properties of extruded pure magnesium is not obvious.The NaMgF₃ film was prepared on the surface of extruded pure magnesium by chemical transformation,the effect of processing time and the concentrationof glacial acetic acid on the quality of the coating was explored.The results show that the quality of NaMgF₃ coating is best when the magnesium is processed in 4 wt.%NaF and 5 vol.%glacial acetic acid solution for 8h.The thickness of the coating is about 500 nm,which is made up of cubic particles with a length of about 300 nm.After modification,the corrosion resistance of the sample is improved obviously.The corrosion potential in SBF solution is increased by 740 mV,and the corrosion current density is reduced by 2orders of magnitude.Then,the HA film is prepared on the surface of fluorinated pure magnesium by hydrothermal method.The process of film formation and the effect of pH value on film formation is studied.The results show that this coating has better corrosion resistance than the HA film prepared directly.When the pH value of the solution is 8.6,the thickness of the F-HA film is about 2?m.The film is uniform,dense and smooth,and is well bonded with the substrate.