Study On Microstructure And Property Of Mg-0.4Zr-xZn-yMn Biodegradable Magnesium Alloy For Cardiovascular Stent Application

As an essential trace element,magnesium has a good biological compatibility,and can be degraded in vivo without the need for secondary surgery,so magnesium and magnesium alloy are regarded as promising biological implant material.In recent years,due to the introduction of new alloy and new technology,mechanical properties and corrosion resistance of magnesium alloy have been further improved,so it makes the application of magnesium alloy possible in the biological implant material.The purpose of the study is to develop a bio-magnesium alloy material for cardiovascular stent,which has excellent mechanical properties and corrosion resistance.In this study,with good biocompatibility,fine grain refinement and improved mechanical properties and corrosion resistance,Zn 、 Zr and Mn elements were selected as alloying elements.Then Mg-Zr-Zn-Mn bio-magnesium alloy was designed and prepared for cardiovascular stent.The effects of Mn and Zn contents on the microstructure,mechanical properties and corrosion resistance of Mg-Zr-Zn-Mn alloys were investigated respectively,hence,the optimum Mn and Zn contents were found,which had excellent comprehensive performance.Finally,the alloy with excellent performance was extruded at different extrusion temperatures.The effects of hot extruded on the microstructure,mechanical properties and corrosion resistance of the magnesium alloy were studied,and the optimum extruded temperature was determined.The results of the study are as follows:The microstructure,mechanical properties and corrosion resistance of the magnesium alloy are significantly improved by adding Mn and Zn elements respectively and hot extruded treatment.(1)Effect of Mn element on microstructure and mechanical properties of magnesium alloy show that the addition of Mn element can refine the grain and improve the mechanical properties of the magnesium alloy.Because of Mn intermetallic compounds are not found,the as-cast alloys are composed of the matrix α-Mg,Mg0.97Zn0.03 and Mn particle phase.With the increase of Mn content,a part of spherical Mg0.97Zn0.03 phases are transformed into the strip-like phases,and the strip-like phases are distributed along the grain boundaries.Mn particle phases are evenly dispersed in the matrix.When the content of Mn element is 1.5wt%,the mechanical properties of the as-cast alloy are obviously improved and possessed the superior mechanics performance(YS 122 MPa,UTS 240 MPa,Elongation 11.94%).(2)Effect of Zn element on microstructure and mechanical properties of magnesium alloy show that the addition of Zn element can eliminate Mn segregation to make the Mn particles more evenly distribute,which is contribute to refine the grain of magnesium alloy.With the increasing of Zn content,the grain is further refined and the number of Mg0.97Zn0.03 are also gradually increasing.When Zn content is 2wt%,the alloy has the best elongation of 14.42%.And with the increasing of Zn content from 2 to 4wt%,the yield strength and tensile strength of the alloy improve,which is attributed to grain refinement due to the number of second phase increasing.When Zn content is 4wt%,the yield strength and tensile strength reach maximum.But when the content of Zn element exceeds 4wt%,the number of the strip-like phase are obviously increasing,which is bad for mechanical properties of the alloy.(3)Hot extruded can significantly refine the grain size of the magnesium alloy,which greatly improves the mechanical properties.The grain size of hot extruded alloy is obviously reduced from about 163.9μm to 7μm.In addition,the second phase of hot extruded alloy is fine and disperse,which is favorable for the further improvement of the mechanical properties.The extruded temperature has a great influence on the mechanical properties.When the extruded temperature reaches to 300℃,the extruded alloy has the best mechanical properties,exhibiting a yield strength of 220 MPa,a tensile strength of 300 MPa and an elongation of 18.71%.With the increase of extruded temperature,the mechanical properties are gradually reduced.The gross dendrites and second phase dissolve in the matrix by homogenization heat treatment before extrusion,which can improve the extrudability of the alloy.(4)The corrosion testing show that adding the appropriate Mn content can increase the corrosion resistance of the magnesium alloy.However,the corrosion resistance is reduced when Mn content exceeds 1.5wt%.The corrosion resistance of the magnesium alloy is remarkably improved with Zn addition and the best corrosion resistance is obtained at 2wt%.But the corrosion resistance decreases when the content of Zn element is over 2wt%.Hot extruded can significantly increase the corrosion resistance of Mg-0.4Zr-4Zn-1.5Mn alloy.In addition,when the extruded temperature reaches 300℃,the extruded alloy has the best the corrosion resistance.