| Currently magnesium alloys as vascular scaffolds attract most attention in thebiodegradable materials field all over the world. Commercial magnesium alloysbecause of their mechanical properties and corrosion resistance of the materials donot meet the requirements of stent. By plastic deformation can improve themechanical properties and corrosion resistance of magnesium alloys. However, due tothe type of crystal of magnesium alloy restrictions on it deformation. Therefore,developing a new type of deformation, with mechanical properties and excellentcorrosion resistance of stent materials becomes an urgent problem.In this paper, for processing requirements and performance requirements ofmagnesium alloy stent, according to the influence of alloying elements on solutionstrength, performance and biocompatibility of magnesium alloy. Developed a newtype of Mg-Zn-Y-Nd(-Zr) alloys for stent. Through adjusting the Y, Nd content ofalloying elements in the alloy composition to obtain optimal organization, and thenadding the element Zr to refine grain. While using the extrusion process for alloy torefine grain deeply and improve the mechanical properties and corrosion resistance.The microstructure、corrosion property and mechanical property of as-cast andextrution Mg-Zn-Y-Nd(-Zr) alloys were studied by OM, SEM&EDS, HRTEM, XRD,electrochemical test, microhardness test and tensile test.The results showed that: along with the increasing of Y and Nd, the secondphase increased, there are many dendritic crystals appeared. With the addition of Zr,the organization of the alloy tends to be equiaxed. After extrusion, the alloymicrostructure is significantly refined. The Mg-Zn-Y-1.0Nd(-Zr) alloys with thehomogeneity of structure. The XRD analysis shows that a new phase of MgZn2emerge with the increase of Nd. Addition of Zr and extrusion processing do not affectthe composition of the second phase. According to Comprehensive organizationalanalysis， the most optimized alloy composition is Mg-Zn-Y-xNd(-Zr) alloys(x=0.5,1.0%).The mechanical properties tests show that: Nd has little contribution to themechanical properties of the alloy. After extrusion, Mg-Zn-Y-0.5Nd alloy andMg-Zn-Y-1.0Nd alloy yield strength of231MPa and249MPa, respectively, improved79.2%and121.3%. The Tensile strength of the extruded Mg-Zn-Y-0.5Nd-Zr alloyand Mg-Zn-Y-1.0Nd-Zr alloy345MPa and280MPa, respectively, improved60.46%and36.59%. The yield strength of280MPa and265MPa, which were increased201.08%and170.41%. Elongation rate was28.5%and29.8%, respectively,decreased25.97%and21.33%. The yield strength of the extruded WE43alloy is235MPa, tensile strength is294MPa, elongation is25.4%. Research shows that themechanical properties of Mg-Zn-Y-xNd (-Zr) alloy (x=0.5,1.0%) are better thanWE43alloy, which meets the requirement of material for stent requirements.The results of corrosion resistance of alloys show that: When Mg-Zn-Y-0.5Ndalloy and Mg-Zn-Y-1.0Nd alloy were immersed120h, the corrosion rate were0.534mg/(cm2·h) and0.921mg/(cm2·h). After adding the Zr, the corrosion rate werereduced to0.501mg/(cm2·h) and0.217mg/(cm2·h), which were decreased by6.2%and76.4%. After extrusion, Mg-Zn-Y-0.5Nd alloy, Mg-Zn-Y-1.0Nd alloy, Mg-Zn-Y-0.5Nd-Zralloy, Mg-Zn-Y-1.0Nd-Zr alloy, were immersed120h, the corrosion rate were0.235mg/(cm2·h),0.064mg/(cm2·h),0.176mg/(cm2·h),0.077mg/(cm2·h), which Werereduced compared solidified by56.0%,93.1%,64.9%and64.5%. Analysis of thecorrosion products shows that as the Nd content increases, it makes the corrosionproducts contain Nd, Zn element, and increases the density of the etching layer, andreduces the corrosion rate of the alloy. The corrosion property of alloys can jointlyvalidated by electrochemical test, hydrogen evolution experiments and weightlessnessexperiments. Studies show that after the extrusion, the corrosion resistance ofMg-Zn-Y-xNd(-Zr) alloys (x=0.5,1.0%) have increased by nearly70%compared withthe corrosion rate of extruded WE43alloy was0.266mg/(cm2·h). |
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