Investigation On Microstructure And Properties Of Zn-Mg-Zr/Cu And Zn-Cu-Ti Biomedical Zinc Alloys

At present,biomedical biodegradable metals mainly focus on iron-based alloys and magnesium-based alloys.However,their excessive or too slow corrosion rate hinders the clinical use process.In recent years,more and more researchers have paid attention to the fact that zinc alloys have a better corrosion rate than iron-based alloys and magnesium-based alloys.However,the mechanical properties of pure zinc is poor and can’t meet the required of clinical application.In order to improve the mechanical properties of pure zinc,as-cast Zn-0.8Mg-xZr,as-cast Zn-0.8Mg-xCu,as-cast Zn-2Cu-xTi and as-extruded Zn-0.8Mg-xCu alloys were prepared by melting-casting and hot extrusion and their solidification microstructure,mechanicalproperties and corrosion behavior were also investigated in the present work.The main contents and conclusions of the dissertation are as follows:The addition of Zr element to Zn-0.8Mg alloy generated Zn₂₂Zr phase exceptη-Zn phase and Mg₂Zn₁₁1 phase.With increasing the addition amount of Zr element,the grain size of primaryη-Zn phase increased gradually.After introducing Zr element,the tensile strength,compressive yield strength and elongation of the alloy decreased.Upon adding 0.2wt.%Zr element,the tensile strength and compressive yield strength of the alloy were only 91.6MPa,193.6MPa and 0.7%,which were decreased by29.3%,23.3%and 66.7%respectively compared with those of the unrefined alloy.Both electrochemical test and corrosion immersion test showed that the corrosion rate of the alloy increased with the addition of Zr element.With increasing the addition amount of Zr element,the corrosion rate of alloys increased gradually.The addition of Cu element to Zn-0.8Mg alloy did not generated new phase.but was still composed of theη-Zn phase and Mg₂Zn₁₁1 phase.With increasing the addition amount of Zr element,the grain size of primaryη-Zn phase decreased gradually and the area ratio of secondary phase further increased.With increasing the addition amount of Zr element,the tensile strength,yield strength,compressive yield strength and hardness of the alloys increased gradually.Upon adding 0.6wt.%Cu element,the tensile strength,yield strength and compressive yield strength of the alloys reached the maximum values of 156.9 MPa,139.7 MPa and 334.7 MPa respectively,which were increased by 19.9%,45.2%and 32.5%respectively compared with those of the unrefined alloy.Both electrochemical test and corrosion immersion test showed that the corrosion rate of the alloys increased with the addition of Cu element.With increasing the addition amount of Cu element,the corrosion rate of the alloys increased gradually.The addition of Ti element to the Zn-2Cu alloy,besidesη-Zn phase,CuZn₅ phase and TiZn₁₆6 phase,Cu₂TiZn₂₂2 phase was also formed when Ti content reached 0.2wt%.With increasing the addition amount of Ti element,the size of CuZn₅ phase decreased and the distribution was more diffuse.With increasing the addition amount of Ti element,the tensile strength,yield strength,elongation and compressive yield strength of the alloys increase first and then decrease.Upon adding 0.05wt.%Ti element,the tensile strength,yield strength,and elongation of the alloys reached the maximum values of 177.4MPa,132.3MPa,2.5%and 205.3MPa respectively,which were increased by 38.7%,24.3%,19.0%and 52.7%respectively compared with those of the unrefined alloy.Both electrochemical test and corrosion immersion test showed that the corrosion rate of the alloys increased with the addition of Ti element.With increasing the addition amount of Ti element,the corrosion rates increased gradually.After extrusion of Zn-0.8Mg-xCu alloy,η-Zn phase elongated along the extrusion direction,the second phase distributes flocculently along the extrusion direction,and the extrusion microstructure of the alloy had no obvious change with increasing the addition amount of Cu element.The tensile strength,yield strength,hardness and elongation of the alloys were greatly improved by extrusion treatment.When adding 0.6wt.%Cu element,the tensile strength,yield strength,hardness and elongation of the alloy reached the maximum,which were 354.3MPa,259.2MPa104HV and 8.6%respectively,which were increased by 125.8%,85.5%,26.8%and561.5%compared with the as-cast alloy with the same composition.Both electrochemical test and corrosion immersion test showed that extrusion treatment can improve the corrosion rate of the alloy,and the degradation rate of the alloys increased with increasing the addition amount of Cu element.