| With the development of society,human cardiovascular diseases are also increasing,and degradable stents are one of the important ways to treat cardiovascular diseases.Magnesium alloy has the advantages of good biocompatibility,degradability,high specific strength and specific rigidity,and the degradable magnesium alloy stent has also been a research hotspot.However,magnesium alloys still have shortcomings such as too fast corrosion rate,not easy to deform,low strength,and low elongation,which greatly limits the development of magnesium alloys in vascular stents.Therefore,this article has done a systematic study on how to improve the mechanical properties of magnesium alloys.In this experiment,based on the research results of previous fellows in the research group,Mg-3Zn-Y-0.4Zr was selected as the basic alloy system,and a new type of dilute magnesium alloy cardiovascular stent material was developed: Mg-3Zn-Y-x Nd-0.4Zr.Then through optical microscope(OM),plasma photoelectric direct reading spectrometer(ICP),scanning electron microscope(SEM&EDS),X-ray diffraction(XRD),transmission electron microscopy(TEM),differential thermal analysis(DSC),etc.Means,room temperature tensile,Vickers hardness test,to observe the microstructure of the as-cast,heat-treated,and extruded alloys,and analyze the mechanical properties.The main experimental results are as follows:(1)In the as-cast Mg-3Zn-Y-x Nd-0.4Zr alloy,with the increase of Nd content,the crystal grains transform from petal-like dendrites to equiaxed crystals,and the grain boundaries transform from discontinuous second phases It is a continuous second phase,and the crystal grains are also significantly refined.The microstructure of the alloy Mg-3Zn-Y-1.5Nd-0.4Zr is composed of uniform equiaxed crystals,a continuous network second phase at the grain boundaries and a lamellar eutectic structure at the triangular grain boundaries,and shows the most Excellent mechanical properties,the ultimate tensile strength of Mg-3Zn-Y-1.5Nd-0.4Zr alloy is 218 MPa,the yield strength is 112 MPa,and the elongation is 12%.With the Mg-3ZnY-0.4Zr alloy,it has increased by 25.3%,10.9% and 41%,respectively.(2)The Mg-3Zn-1Y-1.5Nd-0.4Zr alloy was subjected to solution treatment at a temperature of 490℃ for different times.As the solution time increases,the lamellar eutectic structure at the triangular grain boundary disappears,The networked second phase at the grain boundary transforms into a spherical-like second phase distributed between the extended grain boundary phases.When the solution time is 26 h,the alloy exhibits the best mechanical properties,with a yield strength of 145 MPa and ultimate tensile strength It is 252 MPa and the elongation is 26%.Compared with the as-cast alloy,it is increased by 22.9%,40.7% and 116.7%in turn.(3)Adjust the three extrusion parameters of pre-extrusion heat treatment,extrusion speed and extrusion temperature of the extruded Mg-3Zn-1Y-1.5Nd-0.4Zr alloy.The results show that the heat treatment temperature before extrusion is higher and the time is longer,the structure after extrusion is more uniform,and the degree of recrystallization is higher;with the acceleration of the extrusion speed,the higher the degree of dynamic recrystallization,the larger the crystal grains;With the increase of extrusion temperature,the degree of dynamic recrystallization first increases and then decreases,and the crystal grains continue to grow.Among them,the alloy after heat treatment at 490℃&26 h obtains the best mechanical properties after being extruded at 350℃&50mm/min.Its yield strength is 235 MPa,ultimate tensile strength is 263 MPa,and elongation is 27.1%. |
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