| Biodegradable orthopedic implant materials have become the international research front and hot spot in the field of biological materials in recent times, because they can degarde continuously after implanting into the living body without remove surgery. Magnesium alloy not only has good mechanical compatibility, biocompatibility, and also can gradually degrade in vivo, thus, which has become favored as a promising biodegradable bone implant material. At present, the most commonly used biomedical magnesium alloys like AZ31, WE43contain aluminum and rare earth elements, which have been considered to have toxic effects on the human body. Therefore, there is a high practical value to develope a brand new series of magnesium alloy, which have both good mechanical properties, corrosion resistance, and also is not toxic and maybe play a therapeutic effect to human body.Zinc, calcium and Strontium element which were considered as biocompatible elements were introduced as microalloying elements in the brand new series of Mg-Zn-Ca-Sr alloys. The influence of element Ca and Sr to the microstructure, mechanical properties and corrosion resistance of the Mg-Zn-Ca-Sr alloy was researched systematically. Heat treatment was used improving alloy’s properties, and the best set criteria of solution treatment was found with variation of the performance of the alloy by changing the conditions of heat treatment. The results showed that Ca and Sr elements can all refine the grain of alloys highly. The cast microstructure of alloy mainly contained a-Mg and Ca, Sr-containing second phase, and the second phase was mostly located at the boundaries of grain. With the increase of Sr element content in the alloy, the grain size of alloy decreased, but the second phase and grain boundaries had a refinement trend firstly and then coarsened. When the content of Sr element increased, a large number of second phase gathered at the grain bounderies and formed a coarse mesh structure. The impact of Ca and Sr element to the second phase were different, because the second phase of alloy coarsed with the increase of Ca element content.Mechanical properties like tensile strength, flexural strength, compressive strength of alloy increased firstly and then decreased with the increase of Ca and Sr content. With the increase of the second phase, the corrosion resistance of alloy declined, but the influence of a spot of Sr and Ca content was small on the corrosion resistance of alloys. It could be concoluded that Mg-2Zn-0.25Ca-0.3Sr had a better properties among the other alloys. Through scanning on the corrosion products of alloys, Sr element can be found in the product layer, which already had been researched to play a protective role when the alloy was corroded in vivo and increase the corrosion resistance. The detected Sr in the corrosion product also can help living organism forming new bone.In order to further improve the performance of the alloy, solution treatment was carried out. The microstructure, mechanical and corrosion properties of alloy under different heat treatment condition were detected. The results showed that in the same solution temperature conditions, with the increase of the holding time, the content of the second phase decreased. Within the same time of solution, as the solution temperature increased, the solid solution of elements into the matrix was increasing. The tensile properties of the alloys presented the increased firstly and then decreased trend with the increase of the solution temperture, and the corrosion potential of the alloys was rising continuously, which improved the corrosion resistance of the alloys. The alloy will occur the overheat and over-burning phenomenon in too long solution time and high temperature condition, which will make the grain coarsening and the grain bounderies weakening signficantly, then the mechanical properties of the alloy will decrease.360℃and4hours were the most appropriate solution temperature and time.In this study, the Mg-2Zn-0.25Ca-0.3Sr alloy with a better mechanical and corrosion was obtained by a certain heat treatment for application of degradable biomaterials. And it will be helpful to further study of biocompatibility and implantation. |
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