Preparation And Characterization Of Zn-Mg Based Alloy Microtubes For Vascular Stents

Coronary stent implantation is a kind of treatment for coronary atherosclerosis.Due to the excellent mechanical properties and suitable corrosion resistance of biodegradable metal materials,it has aroused the interest of many researchers.For a long time,researchers have studied more magnesium and its alloys and iron and its alloys,but magnesium and its alloys degraded too fast,the stents failed to meet the service tasks and lost mechanical integrity.Iron and its alloys have been degraded slowly,it will cause problems like inert metals.The standard electrode potential of zinc is between magnesium and iron.Theoretically,zinc has more suitable corrosion resistance,which has attracted the interest of researchers.However,the poor mechanical properties of pure zinc limit its development as a biomaterial.In addition,zinc is a densely arranged hexagonal structure with few slip systems and poor plastic deformation capacity.Therefore,it is an urgent problem to improve the mechanical properties of zinc and prepare uniformly distributed thin tubes that meet the clinical requirements.In addition,Zinc is HCP crystal structure,with few slip systems and poor plastic deformation capacity.Therefore,it is an urgent problem to improve the mechanical properties of zinc and prepare thin uniformly distributed thin tubes that meet the clinical requirements.In this paper,hot-extrusion + multi-pass long mandrel drawing is used to prepare zinc alloy micro-tubes for vascular stents.The alloy composition was selected from Zn-1.5Mg and Zn-1.5Mg-0.2Nd.The microstructure of the as-cast alloy and the tube was analyzed by metallographic microscope(OM)and scanning electron microscope(SEM)to study the microstructure changes during the processing of the tube.The mechanical properties of the tube were characterized by tensile test and hardness test.Electrochemical and weight loss tests characterize the corrosion resistance of pipes.The research indicates that the as-cast Zn-1.5Mg alloy consists of zinc solid solution and a small amount of Mg2Zn11 phase distributed at the grain boundary.The as-cast Zn-1.5Mg-0.2Nd alloy structure consists of zinc solid solution,Mg2Zn11 phase and NdZn11 phase,Mg2Zn11.The phase is distributed at the grain boundary,and a small amount of NdZn11 phase is at the matrix and grain boundaries.The as-cast Zn-1.5Mg alloy is heat treated at 330 ℃ for 3 days,the Mg2Zn11 phase at the grain boundary is solid-dissolved into the matrix,and the structure is equiaxed;Zn-1.5Mg-0.2Nd as-cast alloy is heat treated at 330 ℃ for 4 days,the alloy structure is a solid solution of zinc,a Mg2Zn11 phase and a NdZn11 phase,and the size of the second phase is reduced and the number is significantly reduced.The Zn-1.5Mg alloy undergoes complete dynamic recrystallization during hot extrusion.After hot extrusion,the grains are remarkably refined,and no obvious second phase is observed in the metallographic structure;the higher the extrusion temperature,the coarser the billet grains are.The grain size of the Zn-1.5Mg-0.2Nd alloy is significantly reduced after hot extrusion,and the Mg2Zn11 phase is broken during extrusion,distributed along the direction of extrusion flow,and the magnesium element is squeezed during the pressure process resulted in a significant increase in the number of Mg2Zn11 phases and an increase in size.The recrystallization temperature of Zn-1.5Mg alloy is higher than room temperature,and the Zn1.5Mg-0.2Nd alloy can recrystallize at room temperature.The metallographic structure of the drawn Zn-1.5Mg alloy tube is equiaxed crystal containing distorted structure.The metallographic structure of the Zn-1.5Mg-0.2Nd pipe is a solid solution of zinc,a Mg2Zn11 phase,and a NdZn11 phase.The mechanical properties of Zn-1.5Mg microtubes obtained under different processing parameters are different.The tensile strength of microtubes with the best mechanical properties can reach 217.03MPa and the elongation rate reaches 25.4%.The tensile strength ofφ2.44mmZn-1.5Mg-0.2Nd alloy microtubes reached 271.6MPa,and the elongation reached 10.1%.Through the electrochemical test of Zn-1.5Mg-0.2Nd pipe,the weight loss test can find that the zinc alloy pipe has good corrosion resistance.φ2.44mmZn-1.5Mg-0.2Nd pipe was immersed in SBF for 14d(day).The micro-tubes showed uniform corrosion during immersion,and there was no obvious pitting pit which could affect the mechanical properties of the pipe.