Preparation,Microstructure And Properties Of Zinc Based Alloys For Medical Use

With the development of modern biomedicine,medical biomaterials have become one of the most active branches in the current medical and materials science frontiers.In recent years,following the studies of degradable magnesium alloys and iron-based alloys,attention is now being focused on biodegradable zinc based alloys.Zinc is one of the essential trace elements of the human body.Zinc is expected to develop into a new generation of biodegradable implant material,with a moderate standard electrode potential.However,as-cast pure zinc has poor mechanical properties,slow degradation rate and can not be directly used as implants in clinical applications.Alloying technology and the optimized plastic processing technology must be used to improve its comprehensive performance to meet clinical application requirements.In this paper,pure zinc and five zinc-magnesium binary alloys were chosen as the research object.Zn-Mg alloy wire with the diameter of 0.3 mm was prepared by extrusion and multi-pass cold drawing.The microstructure,mechanical properties and degradation behavior of the alloyed wire in Hank's solution(simulated body fluid)was systematically studied to provide useful basic data for the application of zinc alloy in the biomedical field.Studies have shown that the structure of as-cast alloys can be significantly refined by adding a small amount of Mg.The microstructure of the Zn-Mg binary alloy with addition of trace Mg is a single-phase a-Zn solid solution.With the increase of the amount of Mg,the ?+Mg2Zn11 eutectic appeared in the microstructure which was distributed in the matrix phase a-Zn grains.With the increase of Mg content in the alloy,the volume fraction of ?+ Mg2Zn11 eutectic in the microstructure increases,dendritic structure was formed,which leaded to the increase of the strength and hardness and the decrease of the plasticity.In this paper,the tensile strength and hardness of Zn-2Mg alloy which had the highest Mg content was 125MPa and 135HV respectively.Degradation experiments showed that the corrosion resistance of the alloy was decreased by the addition of Mg and a corrosion model was established.Dynamic recrystallization occurred in the four different compositions of Zn-Mg alloy after hot extrusion deformation.Compared with the as-cast alloy,the microstructure of the alloy after extrusion was remarkably refincd and the strength was significantly increased.After multi-pass drawing deformation,the strength of the four alloys had been further enhanced.The tensile strength of the pure Zn,Zn-0.02Mg,Zn-0.05Mg and Zn-0.2Mg alloy reached 132,245,255 and 265 MPa,respectively.Small subgrains were found in the structure of pure Zn after the process of drawing deformation due to the occurrence of dynamic response,so the pure Zn wire after drawing obtained good strength and plasticity.Other Zn-Mg binary alloy wire undergone significant hardening in the drawing process,which means the strength is significantly increased and the plasticity is significantly decreased.Recrystallization occurred in the microstructure of the as-drawn Zn-Mg alloy wire after annealing at a certain temperature.The recrystallization temperature of the alloy wire increased with the increase of Mg content.The recrystallization temperature of Zn-0.02Mg alloy wire was 200 ?,and the recrystallization temperature of Zn-0.05Mg and Zn-0.2Mg alloy wire was 250 ? respectively.The strength and hardness of Zn-Mg alloy wire were decreased with the increase of annealing temperature and annealing time.Different from the law of strength variation,the plasticity of the alloy wire was increased and then decreased with the annealing temperature.The best mechanical properties was achieved when Zn-0.02Mg alloy wire was annealed at 200 ?,Zn-0.05Mg and Zn-0.2Mg alloy wire was annealed at 250 ? for 10 min.The corrosion rates of pure Zn and Zn-Mg alloys in Hank's solution after being deformed were all less than those of the as-cast specimens.The plastic deformation can significantly refine the microstructure and a relatively dense passivation film was generated at the surface of the alloy,which to some extent,improving the corrosion resistance.In the samples which had different compositions,after being soaked for 28 days,pure Zn wire had the smallest corrosion rate which was 0.011 mm/year measured by the weight loss method.The corrosion rate of the Zn-0.02Mg,Zn-0.05Mg and Zn-0.2Mg alloy wires were 0.021,0.029 and 0.095 mm/year respectively,when soaked to the 28th day.