| In recent years, the improvement of people’s living condition and the change of people’s lifestyle have caused the high incidence of cardiovascular disease. Cardiovascular disease has become a threat to human health and ranked at the first place. Stent implantation technique is one of the most effective means of treating cardiovascular disease. So it has a significant meaning to study the cardiovascular stent. In all biological materials, magnesium alloy because of it’s good biological compatibility, non-toxic, degraded in the human body, and many other excellent properties, is regarded as a promising biological magnesium alloy. The purpose of this study is to develop a new, bio magnes ium alloy material for cardiovascular stent, and study the material corrosion resistance, mechanical properties, strengthening mechanisms to determine it’s feasibility as a vascular stent. In this study, the Ca and Y alloy which can improve the corrosion and mechanical properties of the alloy were selected as alloying elements to design the Mg-Zn-Ca and Mg-Zn-Ca-Y based biomagnesium alloys.This article use the method of metal mold casting to melting Mg-Zn-Ca and Mg-Zn-Ca-Y alloy, then by the means of OM, XRD, SEM, EDS, immersion test, electrochemical experiments and tensile testing we study the alloy microstructure, corrosion resistance and mechanical properties. The result of the study is shown below:(1) Adding different concentration of Ca(0.2 wt %, 0.5 wt % and 0.7 wt %, 1.0 wt %,) to Mg-4Zn-xCa alloy, along with the increas ing of the content of Ca the grain size refined constantly. Mg-4Zn-0.2Ca alloy is mainly composed of α-Mg and MgZn phases. With the content of Ca up to 0.5wt. % there formed Ca2Mg6Zn3 phase in the alloy, and when the content of Ca is more than 0.5wt.% there formed Mg2 Ca phase and Ca2Mg6Zn3 phase in the alloy.(2) The addition of a small amount of Ca elements can improve the resistance of the alloys, it is because the addition of Ca can refine the grain, and formed Ca2Mg6Zn3 phases, which can refine and reduce Mg Zn phase to improve corrosion resistance of the alloy. But after the Ca content is more than 0.5wt.%, the corrosion resistance of the alloy begin to decrease. This is due to the Mg2 Ca phases with the Mg matrix around can form micro-galvanic, result in an increase in current density and a decrease in corrosion resistance.(3) Ca alloy can refine grain of Mg-4Zn-xCa alloys, so that the mechanical properties of the alloy increase. The Mg-4Zn-0.5Ca alloy has a maximum tens ile strength of 190 MPa, but an excess of Ca in the alloy form a large number of brittle Mg2 Ca phases, which fragmented the alloy result in decline in mechanical properties. So the key is to control the content of Ca to improve the mechanical properties of the alloy.(4) Adding Y in the Mg-4Zn-0.5Ca alloy,the microstructure has changed a lot. The structure of the Y free alloy is network like, when add some Y to the alloy the structure became dendritic like. And the grain of the alloy has been refined, the higher content of Y the refiner of the grain.(5) A part of Y soluted in the Mg-4Zn-0.5Ca-y Y alloy forming solid solution phases, the other part of the Y combine with Zn and Mg precipitated at the grain boundary forming new phases. When the Y content is between 0.5wt.%-1.0 wt.%, the new Y containing phase is I pahse(Mg3YZn6), and when the content of Y is 1.5w.%, the new Y containing phase are I and W(Mg3Y2Zn3) phases.(6) The addition of Y can improve the corrosion resistance of the Mg-4Zn-0.5Ca alloy. This is because the Y elements can refine the grain, optimize the structure to improve the corrosion resistance of the alloy. When the adding 1wt.% Y there formed a large amount of second phases along the grain boundaries. The new phases in the grain boundaries can form micro-galvanic with the surrounding matrix. The corrosion resistance of the alloy can be decreased with the increase of the second phases.(7) Y elements in the Mg-4Zn-0.5Ca-y Y alloy can cause solid solution strengthening, precipitation strengthening and fine grain strengthening, so the addition of Y can improve the mechanical properties of the alloy. A small amount of Y precipitation at the grain boundary formed phase I witch have a good combination with the Mg matrix can impede the movement of dislocations. But the excess of Y elements can form W phases in the alloy, became the source of crack, causing the deterioration of the mechanical properties. In contrast to all of the alloys, the mechanical properties and corrosion resistance of Mg-4Zn-0.5Ca-1.0Y alloy is the best. Its corrosion resistance has reached 0.165mm/a, tensile strength is 216 MPa, and elongation reaches 12.36%. |
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