WE43Magnesium Alloy Stents Tube Forming Process And Organization Performance

Among medically-applied metal vascular stents are stainless steel, nickel titaniumalloys and cobalt alloys, which are prone to stimulate the surrounding tissue so thatinflammatory response, vascular intimal hyperplasia and restenosis occur when implanted aspermanent foreign body. Fortunately, Magnesium alloys with non-toxic and biodegradableproperties have been grown to vascular stent candidate.The objective of the thesis is the preparation of biodegradable WE43magnesium alloytube stent. In this thesis, excellent performance of extruding blank was prepared throughexperiments of alloy smelting and homogenization treatment, etc; a tube extrusion die wasdesigned and extrusion process was modeled; the effect of deformation conditions and heattreatment on microstructure and properties of tube was investigated; capillary vascular stentwith the size of4×0.2mm was successfully prepared.This paper has conclusions as follow:(1)Cast WE43alloy was mainly composed of α-Mg, β and Mg24Y5. Afterhomogenization treatment, the dendritic segregation and Non-equilibrium phase dissolved.The optimal homogenizing annealing system was450℃by18h.(2)A set of magnesium alloy pipe extrusion die was designed. Extrusion cup wasdesigned with model angle of60o, working with a length of5mm, the entrance radius was3mm. To avoid bending, squeeze needle diameter was slope design.(3)The numerical simulations of tube extrusion show that during extrusion process, theconcave cavity flow fast near the inside of the hollow billet. After extrusion billet, the flowrate, equivalent strain, equivalent strain rate, temperature, equivalent stress of the die’sworking band distribute for concentration with the larger value, including that in these areassevere deformation occurred;(4)At the extrusion temperature of450, extrusion speed of2mm/s, extrusion ratio of69.6, the tube with the size of10×1.5mm could be smooth out.(5)Reducing extrusion temperature, increasing extrusion speed and enhancing extrusionratio could make pipe recrystallization grain size smaller.After480℃×8h+200℃×20hsolution treatment and aging treatment, pipes were provided with excellent comprehensivemechanical properties, the tensile strength and yield strength reached to289.5MPa and 190.3MPa, the elongation reached to16.6%.