Study On The Extrusion And Finite Element Simulation Of Medical Magnesium Alloy Tube With Fine Diameter

Magnesium has good biocompatibility and biodegradability,and can be used for the preparation of medical implant products such as bone repair implants and cardio-cerebral vascular stents.However,it has low strength,poor formability and high degradation rate in the human body.Through alloying of magnesium and large plastic deformation,grain microstructure can be refined to improve its mechanical properties and reduce corrosion rate,which has become the key research direction of medical magnesium alloys.This article relies on Shaanxi Province industrial Science and Technology research project and Xi'an Weiyang District Science and Technology Plan project,through the experiments of magnesium alloy smelting,thermal compression,extrusion and electrochemical etching,combined with the finite element simulation technology to make a systematic study of the plastic deformation Meanwhile,optimum extrusion process parameters of the magnesium alloy fine-diameter tube has been obtained.Then the micro-organization,mechanical properties and corrosion behavior of magnesium alloy tube have been analyzed comprehensively.The main conclusions are as follows:The Mg-3Zn alloy and Mg-3Zn-1Zr alloy were prepared by alloying of pure magnesium,and it was found that,with the addition of Zn and Zr elements,grain refinement was obvious,its grain size was reduced from a few millimeters to 135?m and 40?m respectively,and the strength was 1.5 times and twice times higher than pure magnesium(66 MPa)successively.,the ductility also increases.The corrosion behavior of the Mg-3Zn-1Zr alloy shows that the rate of corrosion remains high although the grain refinement is significant.It still produces pitting erosion,which is related to the uneven microstructure and nonuniform composition of the cast state.In this paper,the peak stress model and dynamic recrystallization model of MG-3Zn-1Zr alloy are established,and a study on the hot extrusion process of Mg alloy by using deform finite element analysis software shows that,when the extrusion ratio increases from 44 to 124,the grain size of the tube is refined,and ratio of grain which less than 10 ?m has increased from 4.4%to 21.4%.With the increase of extrusion speed,the grain distribution of the tubes becomes even,and when the extrusion speed is 10mm/s,most of the grains have a size between 11-16?m.When the temperature rises from 320? to 400?,the grains grew up in one times,reaching to 19.6?m.Finally,the optimum extrusion process parameters are determined by the simulation results.Then fine-diameter tubes of pure magnesium,Mg-3Zn alloy and MG-3Zn-1Zr alloy with good inner and outer surface quality are extruded,the maximum deviation of the outer diameter is 1.7%,and the maximum deviation of the wall thickness is 4%.The study on the mechanical properties of the extruded tubes showed that the strength of pure magnesium,Mg-3Zn alloy and Mg-3Zn-1Zr alloy tubes were improved by 150%,20%and 30%,and the microstructure was also refined obviously,in which the grains of MG-3Zn-1Zr alloy tubes were reduced to 9.5?m.and the processing state of the tube has shown good plasticity.Through the extrusion process of large deformation,the inhomogeneity of the microstructure and composition of the cast-state is obviously improved,and the corrosion resistance is improved greatly Among them,the corrosion resistance of Mg-3Zn-1Zr alloy is best,and the etching rate is 0.11 mm/y according to the ASTM-G31-72 standard.