| The bio-degradable metal materials caused wide public concern due to their excellent mechanical properties and good processing performance. Recently, more researches have been focused on the Mg-based and iron-based alloys. However, the degradation rate of Mg alloys is unacceptable high, while the Fe alloys is too slow, which makes both of them hardly to be applied as implanted device. It is noted that the standard electrochemical potential of zinc is between that of Mg and Fe, which means Zn and Zn-based alloys may be a new kind of bio-degradable materials. But the reports on the bio-degradable Zn-based alloys is very few. The as-cast Zn-1.5wt.%Mg based alloys have been only studied, and their mechanical properties cannot meet the requirements. Therefore, in this study, the Zn-Mg(-Ag) alloys have been prepared by the indirect hot extrusion process. Firstly the Mg content was optimized by investigating the microstructure, mechanical properties and corrosion resistance of as-extruded Zn-Mg binary alloys. And the silver (Ag) was added to prepare the anti-bacterial Zn-Mg-Ag alloys. Their microstructure, mechanical properties, biocompatibility and corrosion resistance in simulated body fluid have been finally investigated, so that it would provide a valuable foundation data for the design and preparation of new bio-degradable Zn alloys.Zn-(0～1.0wt.%)Mg binary alloys were prepared by indirect hot extrusion at200℃. The microstructures indicate that the dynamic recrystallization undergones completely during the extrusion process. With the additions of Mg, the average grain size of the alloys decreases, and reaches a minimum20μm or less. Meanwhile, the quantity of second phase Mg2Zn11increases. Moreover, the yield strength and tensile strength increases from66MPa and110MPa for pure Zn to260MPa and320MPa for Zn-1Mg alloy, respectively, while the elongation of the alloy firstly increases and then decreases. The Zn-0.05Mg alloy has good strength, ductility and symmetry in tension and compression.After adding a small amount of Ag to the Zn-0.05Mg alloys, the second phase is still primarily Mg2Zn11. The grain size increases slightly. The strength increases slightly but the elongation reduces. Pure Zn and Zn-Mg(-Ag) alloys show non-pyrogenic, non-acute toxicity, and anti-hemolytic performance, which means these alloys mentioned above possess good biocompatibility.The corrosion resistance of pure Zn, Zn-0.05Mg, Zn-0.05Mg-0.5Ag and Zn-0.05Mg-lAg alloys have been measured by means of polarization curves and weight loss by immersion in simulated body fluid (SBF). After addition of Mg and Ag, pitting corrosion tendency occurrs during anodic polarization process. The corrosion potential (Ecorr) reduces about0.1V. The corrosion current density (jcor) reduces in varying degrees, compared with pure Zn, and the Zn-0.05Mg reaches22μA/cm2. The corrosion rates of the Zn-Mg(-Ag) alloys are smaller than pure Zn at the beginning of the immersion. With the extension of the immersion time, all the alloys reach a stable corrosion rate of about3g/m2/d, which is an order of magnitude smaller than the steady corrosion rate of the as-extruded and solid-solution Mg alloy (approximately18g/m2/d). The corrosion products are mainly Zn and/or Mg carbonates and phosphates. It means zinc and zinc alloys may become the new bio-degradable metal materials with proper degradation rate. |
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