| Magnesium(Mg)alloy has become a typical and new representative material of degradable implants,because of its comprehensive mechanical properties matched with natural bone and excellent biodegradation characteristics.Based on our group research of Mg-Zn series medical degradable magnesium alloys in recent ten years,the effects of alloying elements Ca,Zr,Sr and Ag on the structure,mechanical properties and corrosion resistance of Mg-3Zn alloy were studied by means of alloying in this paper.The synergistic mechanism between alloying elements was explored and the following results were obtained:(1)The mechanical properties of Mg-3Zn-0.2Ca(wt.%)(ZX30),Mg-3Zn-0.8Zr(wt.%)(ZK30),Mg-3Zn-0.8Zr-0.3Sr(wt.%)(ZKJ300),Mg-3Zn-0.8Zr-0.3Ca-0.3Ag(wt.%)(ZKXQ3000)were compared by tensile and compressive tests.It was found that the ultimate compressive strength(UCS)of four extruded alloys was about 360 MPa,but the ultimate tensile strength(UTS)had a significant difference.Compared with ZX30 and ZK30 alloys,the UTS of ZKJ300 and ZKXQ3000 alloys was increased by 20%,but the plasticity was reduced by 26%.The electrochemical corrosion properties of four alloys were studied by electrochemical polarization,impedance and noise tests.The results showed that the corrosion resistance of ZK30 and ZKXQ3000 alloys was better.The corrosion currents of ZK30 and ZKXQ3000 alloys were 53.9?m/cm~2 and 42.4?m/cm~2,which were much lower than those of ZX30 and ZKJ300 alloys.(2)Based on the mechanical properties and electrochemical corrosion behavior of four as-extruded alloys,Mg-3Zn-0.2Ca-xAg(x=0.1,0.3,0.5,0.7)alloys were melted in vacuum by selecting alloying elements with higher biological safety.And its optimal composition and heat treatment conditions were further studied.The results showed the comprehensive properties of Mg-3Zn-0.2Ca-0.3Ag were the best.The yield tensile strength(YTS),UTS,elongation,corrosion potential and current of Mg-3Zn-0.2Ca-0.3Ag were 277.67 MPa,305.33MPa and 16.47%,-1.386 V and 30.5?m/cm~2 respectively,which were much better than those of other alloys.The optimal solution condition of Mg-3Zn-0.2Ca-0.3Ag alloy was homogenization for 340°C×48 h+solution for 400°C×2 h and the best aging condition was 160°C×84 h by microstructure observation and hardness tests.(3)The corrosion rates of five alloys immersing for 15 days were calculated by weightlessness tests.It was found the corrosion rate of ZK30 alloy was the lowest,which was45%lower than that of ZX30 alloy.Corrosion products and mechanism of five alloys in different stages were investigateed by scanning electron microscopy(SEM)and X-ray energy spectrum(EDS).It showed that corrosion products of ZK30 alloy were dense calcium and phosphorus particles during the whole immersion process,while corrosion products with relatively poor compactness,such as rods and spheres,appeared in other alloys at different immersion stages.The main reason for corrosion behavior alienation of five alloys during immersion was the difference of the number,size,distribution of second phases and alloy average grain size. |
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