Study On Surface Modification Of The Biodegradable Mg-Zn-Zr Alloys

Deposition of calcium and phosphorus, as one of the most common surfacetreatments, will reduce the degradation rate, and induce better bone-implantinterfaces with no side effects. However, the binding force between directlydeposited Ca-P coating and Mg alloy is not good. The deposition of slow titrationand the deposition after anodization are mentioned to improve it.Firstly, the deposition with slow titration is compared with direct deposition;and controlling variable method is adopted based on solution concentration,immersion time. Then, the improvement of anodization on the pre-phosphatizationchemical deposition is researched and the optimum pretreatment technique is got.Lastly, orthogonal optimization of pre-phosphatization chemical deposition wasdesigned based on pre-phosphatization time、Ca/P、immersion time, and find theoptimum pretreatment technique. The results are listed as follows:[1] The complete coating of CaHPO4has been grown by the deposition withslow titration, instead of direct deposition. The optimum pre-calcification chemicaldeposition coating could be got in the solution concentration which Ca/P=1.5 andKH2PO4is 0.15mol/L. After deposition in this solution for 4 days, the loading forceis 9.0N, and the ecorr is -1.505V.[2] As the current density increases, anodizing films tend to have larger poresand lower binding force with Mg alloy. Anodization as the pretreatment can makethe Ca-P coating denser; remarkably increase the binding force with Mg alloy, at thesame time shift the corrosion potential to a higher range. The best pretreatment isthe two-step anodizing method (current density 8 mA/cm2for 10 min + currentdensity 16 mA/cm2for 10 min).[3] The microstructure and adhering force of pre-phosphatization chemicaldeposition coating is determined by immersion time，and the adhering force is alsoinfluenced by prephosphating time. The optimum deposition technique ispre-phosphatization 5h and immersion 24h in the solution of Ca/P=1.67, and theloading force is 10.7N, the ecorr is -1.260V.