Preparation Of Zinc-plating Layer On Medical Magnesium Alloy And The Study Of Their Corrosion Behavior And Biological Performance

Biomedical magnesium alloys are promising in the fields of cardiovascular disease therapy,bone injury repair and reconstruction due to their biodegradability.However,there are some problems in the process of in vivo service post-implantation,such as high degradation rate,poor wear resistance and bacterial infection,which may eventually cause implantation failure.Surface modification technologies,allowing for the generation of new structure,component and performance on the material surface,have been extensively applied to improve the mechanical properties,corrosion resistance,antibacterial abilities and cytocompatibility of magnesium alloys.In this project,AZ31B magnesium alloy was selected as the matrix material,zinc was selected as permeation element,and the zinc-alloyed layer was formed on the surface by solid thermal diffusion technique.The phase composition,mechanical properties,corrosion performance,in vitro antibacterial property and cytotoxicity of the layer were evaluated.The specific research content and results are as follows:（1）The morphology,phase structure and chemical composition of the samples prepared at 380℃with holding time of 4,6 and 8 hours were analyzed by SEM,XRD,EDS and XPS.The results show that the surface of Mg-Zn layer is uniform.The layer is mainly composed of MgZn and Mg₂Zn₁₁binary phases.（2）The hardness of the layer and the bond strength between the layer and the substrate were analyzed by microhardness and scratch tests.The tribological properties of the layer were analyzed by wear experiments.The results show that the layer treated for 8 hours is firmly bonded to the substrate,and the microhardness and tribological properties are significantly improved compared to the substrate.（3）The electrochemical corrosion and degradation performance of the layers were analyzed by electrochemical corrosion experiments and in vitro immersion test.The results show that the Mg-Zn layer increases the polarization resistance of the magnesium alloy in phosphate buffered saline（PBS）and reduces the corrosion current density.The amount of hydrogen evolution of the magnesium alloy substrate is much larger than that of the treated sample.The pH value of the solution after immersion was lower than that of the AZ31B magnesium alloy matrix,indicating that the Mg-Zn layer can effectively slow the degradation rate of AZ31B magnesium alloy in PBS.（4）The antibacterial properties of the surface of the layer were analyzed by antibacterial experiments.The results show that the Mg-Zn layer has good antibacterial property,and the antibacterial rates of the samples treated for 6and 8 hours approach 100%.（5）The cytotoxicity of the surface modified samples and sample extracts was analyzed by cell live/death and cell proliferation experiments.The results showed that the cytotoxicity of the treated samples was lower than that of the magnesium alloy substrate,and the extracts of the samples before and after the treatment have no obvious cytotoxicity.