A Research On Application,Microstructures And Properties Of Zinc Alloy Wires For Medical Use

With the development of modern biomedicine and the rise of new medical treatment ideas,medical degradable implant materials especially degradable metals are gradually becoming research focuses in the field of medical implant materials and biomedicine.Following magnesium-based and iron-based alloys,zinc-based alloys are expected to develop as potential medical degradable metals for its moderate degradation rate and favorable biocompatibility.However,the poor strength of pure zinc limits its application.Employing appropriate alloying elements which can increase the strength of zinc alloys without significantly sacrificing(or even improve)its plasticity and processing performance to enable medical micro-shape molds like metal wires to be processed easily needs to be solved urgently.In this paper,Cu and Mg are employed as alloying elements to prepare three ZnxCu(x=0.2,0.5,1wt.%)binary alloy ingots and three ZnxCu0.1wt.%Mg(x=0.2,0.5,1wt.%)ternary alloy ingots.Hot extrusion combined with multi-pass cold drawing is employed to prepare alloy wires with the diameter of 0.3mm.Microstructures,mechanical and degradation properties of alloy wires in Hank's solution are systematically studied to provide basic data for composition design and optimization.The prepared wires can also expand the application of zinc alloys in biomedical field.Studies have shown that alloying element Cu can refine the microstructures of as-cast zinc alloys and the more Cu added in alloys the finer microstructures will be fetched.Zn0.2Cu alloy is composed of?-Zn solid solution.While Zn0.5Cu and Zn1Cu alloys are both composed of?-Zn and a little?(Cu Zn₅)precipitation.Besides,arborescent structure is formed in both alloys.The strength,hardness,and elongation of as-cast ZnxCu alloys are improved gradually with the increase of Cu.Among three alloys,Zn1Cu alloy has the highest tensile strength and hardness reaching 86 MPa and 81 HV respectively.Pure Zn and ZnxCu alloys all have dynamic recrystallization during hot extrusion.As a result,microstructures transform into fine equiaxed grains.Compared with pure Zn,alloying element Cu refines the microstructures of extruded alloys obviously.The average grain size of extrude Zn1Cu alloy is 1.5?m.At the same time,?(Cu Zn₅)precipitates can be observed in extruded Zn0.5Cu and Zn1Cu alloys.Hot extrusion improves the strength and elongation of pure Zn and Zinc alloys by a large bargain.Zn1Cu alloy has the highest strength reaching218MPa while Zn0.5Cu alloy has the highest elongation reaching 25%.After cold drawing,microstructures of pure Zn and three alloy wires transform into finer recrystallized equiaxed grains,while?(Cu Zn₅)precipitation increases.The average grain sizes of Zn0.5Cu and Zn1Cu alloy wires are 0.9?m and 0.7?m respectively,which belong to ultrafine grain(100nm?1?m).Because of grain boundary sliding caused by ultrafine grains and Cu atoms which gather at the grain boundaries,alloy wires exhibit superplastic-like characteristics during tensile test.As a result,the elongations of the alloy wires are over 90%but strengths decrease by varying degrees.Zn0.2Cu alloy wire has the highest elongation reaching 170%.Mg can refine the grain significantly.Addition of 0.1wt.%Mg can remarkably refine the microstructures of as-cast ZnxCu alloys,and improve the strength and hardness of significantly.However,the formation of Mg₂Zn₁₁ induces a poor elongation.Mg further refines the grains of extruded zinc alloys and greatly improves the strength at sacrifice of elongation.The extruded Zn1Cu0.1Mg alloy has a novel tensile strength reaching 436MPa.Mg atoms strengthen the grain boundaries which reduces the mobility of the grain boundary.Therefore,the strengths of alloy wires don't decrease significantly and elongations don't have novel express.Ultimately the tensile strength and elongation of Zn0.2Cu0.1Mg alloy wire reach 306MPa and 52%respectively.While Zn0.5Cu0.1Mg alloy wire has tensile strength reaching 345MPa and elongation reaching 19%.The corrosion resistance of zinc alloy wires in Hank's solution decreases with the induce of alloy element.The degradation rate increases with the increase of Cu content in alloys,while Mg wakens the corrosion resistance further.Reaching stable degradation state,pure Zn wire has the lowest degradation rate that 0.0168mm/year.Degradation rate gradually increases to0.0219mm/year for Zn1Cu alloy wire.The addition of Mg further increased the stable degradation rates of alloy wires by 0.03?0.05mm/year.Ca-P coating is formed on the surface of alloy wires immersed for 16 days which makes the degradation rate slow down and tend to be stable.