Effect Of Micro-Mg/Mn And Extrusion Process On Microstructure And Mechanical Properties Of Zn Based Alloys

Cardiovascular disease is one of the major fatal diseases that human beings are facing,and cardiovascular stenosis accounts for a large proportion of cardiovascular diseases.Stent implantation is the most effective and economical therapy for the cardiovascular stenosis.But the sent has a strict biological and mechanical properties requirement for the materal.Stent materials experienced permanent materials to biodegradable materials with the development of time.Biodegradable materials mainly include polymer material,magnesium alloy,iron alloy and zinc alloy.The latest zinc alloy is becoming a research hotspot due to its proper degradation rate and good biocompatibility.At present,the main disadvantage of Zn alloy as a scaffold material is that its poor mechanical properties cannot meet the requirements.The routine to improve the mechanical properties of the materials include alloying and deformation treatment.With the increase of the alloying elements’ content,the second phase paticales’s size will get large which will directly affect the performance of the stent,for the sent usually get a thickness no more than 0.15 mm.Deformation treatment can effectively change the microstructure of the alloy and improve the mechanical properties.In this paper,we fouced on the effect of the Mg(<0.1 wt.%)and Mn(<1 wt.%)alloying elements’ content and extrusion velocity on the properties and microstructure of the microalloyed Zn-MgMn alloy.The main conclusions are as bellow:(1)Based on the influence of Mg and Mn elements’ content and the extrusion vilocity,aimed at minimizing the second phase,Zn-0.05Mg-0.5Mn alloy extrude at 1 mm/s can meet the mechanical properties and structure requirements of the vascular scaffolds,with the yield strength,tensile strength and elongation are 333±1 MPa,361±2MPa and 25±1%,respectively.The second particles also distributed evenly.(2)Zn-xMg-1Mn(x=0.05,0.08,0.1)alloy was extruded at 1.5mm/s and 100℃.When the Mg element content decreased from 0.1 wt.%to 0.05 wt.%,the yield strength and tensile strength of the alloy increased slightly from 392±2 MPa,432±1 MPa to 418±3 MPa and 447±3 MPa,respectively,the elongation decreased from 17±1%to 12±1%.The combination of the second phase strengthening and dispersion strengthening increases the strength slightly.The decrease of elongation is mainly due to the decrease of Mg content and the increase of grain size.(3)When the Zn-0.07Mg-1Mn alloy was extruded at different speeds(1.5 mm/s,1 mm/s and 0.5 mm/s)at 100℃,the yield strength and tensile strength of the alloy gradually decreased from 418±15 MPa and 467±1 MPa at 1.5 mm/s to 344±2 MPa and 437±2 MPa at 0.5 mm/s.The elongation increased from 21±4%of 1.5 mm/s to 31±1%of 0.5 mm/s,The main reason for the increase of plasticity is the decrease of average grain size with the decrease of extrusion velocity,while the decrease of strength is the result of the second phase’s emergence.(4)When Zn-0.05Mg-xMn(x=0.7,0.5,0.2)alloy was extruded at 0.5 mm/s and 100℃.With the decrease of Mn content,the yield strength,tensile strength and elongation decreased from 326±4 MPa,412±1 MPa and 21±3%of Zn-0.05Mg-0.7Mn to 314±4 MPa,378±3 MPa and 18±1%of Zn-0.05Mg-0.2Mn,respectively.The main reason is that the second phase decreases with the content of Mn decreases,and the average grain size of the alloy does not change much.(5)When the Zn-0.05Mg-0.5Mn alloy was extruded at different speeds(1.5 mm/s,1 mm/s and 0.5 mm/s)at 100℃ The yield strength and tensile strength of the alloy increased from 325±1 MPa and 332±1 MPa at 1.5 mm/s to 331±6 MPa and 399±3 MPa at 0.5 mm/s.The elongation increased first and then decreased,which was 20±1%at 1.5 mm/s,25±1%at 1 mm/s,and 21±1%at 0.5 mm/s.In addition to the average grain size,the elongation is also affected by the distribution of the second phase,which requires specific analysis.The increase of strength is due to the decrease of the grain size.(6)After the Zn-0.1Mg-1Mn alloy was kept at 300℃ for 10 min,20 min and 30 min,the strength of the alloy increased and the plasticity decreased.The reason for this abnormal change needs to be analyzed from the solid solution and precipitation of the second phase,which is our next research topic.