Influences Of Organic Zinc-Containing Electrolytes On Property Of Micro-Arc Oxidation Coatings Developed On Medical Magnesium Alloy

Magnesium element is widely distributed in natural world,and is an essential micro element of human body.Magnesium alloy is the lightest structural metal material,and has the similar density and Young's modulus to human bone.Magnesium alloy can be used as a degradable implant material to avoid secondary surgery,and therefore it has been suggested as a revolutionary biodegradable metal for use as anorthopaedic material.However,the too fast degradation rate in vivo restricts its clinical applications.As an effective surface treatment technology,micro-arc oxidation(Micro-arc oxidation,MAO)can significantly improve the corrosion resistance of magnesium alloy under maintaining its excellent biological material property.In addition,by selecting electrolytes,some beneficial elements for human body can be introduced into ceramic coatings in order to achieve coating functionalization.In the neutral and alkaline solutions,several zinc-containing electrolytes were selected in the paper and zinc-containing MAO coatings were fabricated on WE43 magnesium alloy in order to improve the corrosion resistance of magnesium alloy and prepare functional coatings.The main work of the paper includes the following three aspects:1.In neutral solutions,the influences of EDTA-ZnNa₂,zinc gluconate(Zn(C₆H₁₁O₇)₂)and zinc acetate((CH₃COO)₂Zn×2H₂O)on surface morphology,chemical compositions and corrosion resistance of MAO coatings were compared.The results showed that three kinds of MAO coatings fabricated in solutions containing EDTA-ZnNa₂,Zn(C₆H₁₁O₇)₂ and(CH₃COO)₂Zn×2H₂O)could effectively improve the corrosion resistance of magnesium alloy.The MAO coatings developed in the solution with Zn(C₆H₁₁O₇)₂ and EDTA-ZnNa₂ separately achieved the best and the worst corrosion resistance.With the increase of Zn(C₆H₁₁O₇)₂ concentration,the zinc content in MAO coatings became higher.However,the coating corrosion resistance firstly improved with the increasing Zn(C₆H₁₁O₇)₂ concentration and achieved the best value at 0.0344 mol/L,but then decreased.2.Based on the results achieved by the first chapter,Zn(C₆H₁₁O₇)₂ was selected as the zinc-containing electrolyte,and the influences of Zn(C₆H₁₁O₇)₂ concentrations on coating morphology,chemical compositions and corrosion resistance were investigated by using alkaline solutions.The results demonstrate that MAO treatment can evidently improve the corrosion resistance of magnesium alloys.Both the corrosion resistance and the zinc content of MAO coatings firstly increased and achieved the best value at 8 g/L but then decreased.3.In the same base solution,the influences of zinc glycinate,zinc aspartate and zinc amino acid chelate with 5 g/L on coating performance were compared.The results showed that the MAO coating fabricated in the solution with zinc aspartate achieved the highest zinc content and the best corrosion resistance.By using an orthogonal experiment with four factors and three levels,the influence of sodium hydroxide(Na OH)concentration,sodium phytate concentration,sodium silicate and zinc aspartate concentration on coating corrosion resistance was investigated and the results demonstrated that the influencing sequence on corrosion resistance was sodium phytate>Na OH>sodium silicate>zinc aspartate.The influencing order on the coating zinc content was zinc aspartate>sodium phytate>Na OH>sodium silicate.In the solution consisted of 8 g/L Na OH,8 g/L sodium phytate,10 g/L sodium silicate and 3g/L zinc aspartate,the developed MAO coating achieved the best corrosion resistance.