Study On Hot Deformation Behavior And Micro-tube Fabrication Of JDBM Magnesium Alloy For Biodegradable Vascular Stents

As the new generation biodegradable material,Mg and its alloy shows great potential on the vascular stents application due to their outstanding biocompatibility,mechanical compatibility and biodegradation.However,Mg alloys exhibit poor ambient temperature deformability because of the hexagonal close-packed(HCP)crystal structure,which gives rise to a big challenge to fabricate Mg alloys micro-tubes with high plasticity for biodegradable stents.In this study,we fabricated the as-extruded small tube blank of JDBM with outstanding mechanical properties based on the study of hot deformation behavior.After that,we succeeded in producing the high quality micro-tubes for vascular stents through the combined process of rolling and drawing.The main conclusions can be summarized as follows:1.The deformation activation energy is 176.5KJ/mol for JDBM magnesium alloy,and its flow stress behavior during hot compression deformation can be well described by the hyperbolic sine function.The constitutive equation is listed as below:(?) where(?) The relationship between the dynamic recrystallization grain size d and Z parameters can be described as:d=9.875×14Z-0.375652.As-extruded small tube blank with 3.5mm in outer diameter and 0.25mm in thickness can be fabricated at 380℃ by a speed of 1mm/s.The yield strength,ultimate tensile strength and elongation are 220MPa,267.5MPa and 48.8%,respectively.3.Micro-tubes with 3.25mm in outer diameter and 0.175mm in thickness can be fabricated by rolling based on the as-extruded small tube blank.After heat treatment at 390℃ for 40min,its yield strength,ultimate tensile strength and elongation are 159MPa,219MPa and 26.8%,respectively.Micro-tubes with 3.0mm in outer diameter,0.16mm in thickness and 2.4mm in outer diameter,0.16mm in thickness can be fabricated by drawing based on the as-rolled small tube blank.After heat treatment at 420℃ for 40min,their elongations are 23%and 27.5%,respectively,which can meet the requirement of the vascular stents.The corrosion rates in Hank’s solution are(0.29±0.01)mm/year and(0.26±0.06)mm/year,respectively.