| With high specific strength, high biological safety, biodegradable and excellent mechanical compatibility, Magnesium alloy has become a cardiovascular stents and bone fixation materials which is a very active field of reserch hot spots. magnesium aluminum(AZ) alloy and magnesium lithium alloy(LZ) is commonly used In the field of medical magnesium alloys. At present,there is two the mainly problems that is metal plastic deformation ability and corrosion resistance in the application of magnesium alloy cardiovascular stents. By simulating body fluid in vitro degradation experiment method medical magnesium alloy corrosion resistance could be observed,and Grain refinement is one of the most effective way to solve these two problems. Grain refinement methods of Magnesium alloy include rapid solidification, such as channel Angle extrusion, rolling stack and semi-solid forming. The method of rapid solidification is the most adopted in the field of medical magnesium alloys.This article selects magnesium aluminum(AZ) magnesium alloys and magnesium lithium(LZ) is commonly used in the cardiovascular stents areas. The best ingredients cardiovascular stents in magnesium alloy By analysising different result of experients,which cast different ingredients samples of magnesium alloy and the simulated body fluids degradation experiment,can be selected. the rapid solidification technology applied has laied the foundation in the field of cardiovascular stents, with different composition of magnesium alloy is melted by rapid solidification, exploring rapid solidification process. Main conclusions are as follows:(1)Casting magnesium alloy microstructure is composed of basic phaseα-Mg,and dendritic β phase. The main components of the β phase is Mg17Al12 phase. After adding rare earth elements Y, β smaller grain size, the addition of Y elements have played an important role in refining grain size. At the same time, the alloy will produce Mg24Y5 and Al2 Y phase, along with the increase of the content of rare earth element Mg24Y5 and Al2 Y relative content increase. Li content in casting magnesium lithium alloy was 9%, basic phase by α Mg alloy microstructure, long strips of β phase composition; Li content is 14%, the alloy microstructure for single β phase composition.(2)Rapid solidification experiments of LZ series magnesium alloy can not be done in air environment, because of properties of LZ series magnesium alloy is lively, but, AZ series magnesium alloys can be done double roller experiment in the external environment. Compared with the ingot casting organization, rapid solidification process does have played an important role in refining grain size. Experimental results show that double roller speed at 1200r/min, the optimal degree of alloy grain refinement, grain size in 3 to 5 microns.(3)It contribute to further refinement of rapid solidification Mg-Al alloy organization that add Rare earth element Y, and along with the increase of the content of Y small grains gradually. Al elements in alloy is reduced, β phase content in the group decreased, with the increase of the content of rare earth alloy tissue after rapid solidification becomes fine isometric distribution in grain.(4)The weightless rate is increasingly, and then with the increase of corrosion days slow decline or remain the same For different composition of(AZ) magnesium alloy. Corrosion After joining of rare earth elements alloy corrosion weightless rates decrease, but AZ is the corrosion resistance of magnesium alloys is not enhanced constantly with the adding of rare earth element Y. The weightlessness rate of those with lower Al content, the alloy will decline.(5)At first, different composition of alloy simulate fluid pH slowly rising, after reach the maximum, with the increase of number of days of corrosion, the pH of the solution basic remain unchanged. Al content does not cause to reduce the simulated body fluid pH is worth. The main form of corrosion process for pitting, corrosion in the process of Mg(OH) 2 new phase. |
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