Study On Mechanical And Corrosion Properties Of Megnesium-zinc Based Alloys For Biomaterial

Biodegradable materials have become the forefront and hotspot of international research of current biological materials field, because they can be degraded by the body after being implanted, and the degradation products can be absorbed in vivo or exhausted in vitro by the organism. At present, biodegradable materials of orthopedic are mainly polymer materials such as polylactic acid (PLA) and polyglycolic acid (PGA), but the strength is generally hard to bear large loads, and the degradation product is acid, which is apt to cause inflammation. Magnesium and its alloys not only have good mechanical properties, but also are non-toxic to human body and can be degraded gradually via corrosion in the body. Therefore, Mg and its alloys have great potential application for biodegradable implantation materials. However, their application as biomaterials is restricted due to the low corrosion resistance and loss of carrying capacity before bone healing. So it is important for the development of Mg alloys used in the medical implants to fabricate alloys with the acceptable mechanical and corrosion properties.Mg-2Zn-0.22Mn, Mg-2.1Zn-0.22Ca and Mg-1.99Zn-0.17Ca-0.51Si alloys were fabricated for the study, and the alloys were detected from microstructure, mechanical and corrosion properties analysis. From microstrure properties analysis, the microstructure of alloys wereα-Mg+α-Mn,α-Mg+Ca₂Mg₆Zn₃andα-Mg+Mg₂Si respectively, and from the difference, it could be concoluded that, Mg-2.lZn-0.22Ca had a better properties among the three alloys, and its grain size was about 85um, the tensile strength about 180MPa, strain at break about 11%, E_corr in SBF -1.71V, the rate of mass loss in SBF 0.9g/(cm²Â·year).The microstructure, mechanical and corrosion properties of Mg-2Zn-xCa (x=0.024, 0.22, 0.29, 0.46) were detected, and the results show that the second phase Ca₂Mg₆Zn₃ become more with the increase of Ca content, distributed in grain boundary, and when Ca content reached to 0.46wt.%, the net of second phase Ca₂Mg₆Zn₃ in grain boundary became wide. Compared with the four alloys mechanical and corrosion properties, Mg-2.1Zn-0.22Ca alloy had better properties.In order to improve the strength of Mg-2.lZn-0.22Ca as-cast alloy, heat treatment was carried out. And the microstructure, mechanical and corrosion properties of Mg-2.1Zn-0.22Ca alloy under different heat treatment condition were detected. Compared with the alloys, the alloys with better properties under a certain heat treatment was obtained, and the mechanism of heat treatment infecting alloy properties was analyzed. The results showed that the second phase Ca₂Mg₆Zn₃ would decrease with extension of holding time under the same temperature, and the second phase Ca₂Mg₆Zn₃ would also decrease with increase of temperature under the same staying time; The properties of the alloy under the heat treatment (360℃+4h holding time+ water quenching) were better, and the tensile strength was 210MPa, strain at break about 21%, and increase were 24% and 90%, campared with as-cast Mg-2.1Zn-0.22Ca alloy.Electrochemical corrosion, mass loss and the value of pH were detected for corrosion properties evolution. The results showed that, the potentials of heat treatment alloys were close, compared with each other, between -1.83V and -1.75V. The corrosion properties totally became worse with increase of heat treatment temperature. Under the same temperature, the corrosion properties totally became worse with the holding time. From the data of mass loss and the value of pH, the curve of mass loss and the value of pH were similar, so the corrosion properties changed little after heat treatment.In this study, the Mg-2.1Zn-0.22Ca alloy with better mechanical and corrosion properties was obtained by a certain heat treatment, for application of degradable biomaterials. And it will be helpful to further study of biocompatibility and implantation.