Preparation, Microstructure And Properties Of Biomedical Degradable Zn-Sn And Zn-Mg-Sn Alloys

Biomedical degradable metal materials have been favored by researchers because of their good mechanical properties,bio-compatibility,and non-toxic degradable products.Bio-degradable metal materials have been extensively studied,such as magnesium and magnesium-based alloys and iron and iron-based alloys metal materials,but the problems of these types of alloys are limited in clinical applications:the degradable rate of magnesium and magnesium-based alloys is too fast,the pH value of the implants is too high with the appearance of hydrogen balloon;the degradable rate of iron and iron-based alloys is too slow,and the elastic modulus is so high,that it is causing the"stress shielding"effect.The standard electrode potential of zinc is between the magnesium and iron.The degradable rate is matched with the clinical application requirements,but the mechanical properties of pure zinc are so poor,which limit its development.In this article,the alloying method was used to improve the mechanical properties of zinc alloys.Zn-Sn and Zn-Mg-Sn alloys with different contents of Sn were prepared by adding tin and magnesium alloy elements to pure zinc,and then using the graphite mold casting.The article characterized and analyzed the optical metallographic microstructure,mechanical properties,degradable performance and blood compatibility of the alloys,and the corrosion degradation mechanism.Research indicated:?1?The optical metallographic microstructures of the Zn-Sn alloys had been improved and refined the grain size.Sn and the Zn-based alloys do not form a solid solution or a mesophase.And Sn is uniformly distributed in the grain boundary of the Zn-based alloys,which hinders the growth of the grains and increases the number of nucleation locations.The mechanical properties are improved.The yield strength and elongation increases,the hardness and tensile strength increases at first and then decreases,and the fracture mode is mixed fracture.The mechanical properties of Zn-2Sn are the best,and the tensile strength,yield strength,elongation and hardness are 129.1 MPa,91.2 MPa,5.10%and 49.3 HV respectively.The corrosion rate of Zn-Sn alloys decreases first and then increases with the increase of Sn,but the corrosion rate is ideal.The pH value changed greatly in the initial stage of immersion,and the fluctuation in the late immersion was small.The corroded surfaces of Zn-2Sn are the best,and the corrosion of the whole material is uniform,there is no serious appearance of cracking or corrosion deep pit.?2?The optical metallographic microstructures of the Zn-Mg-Sn alloys had been improved,the grain size is refined,and the Mg₄Zn₇ phase and the Mg₂Sn phase are precipitated at the grain boundary of the grain,which hinders the growth of crystal grains during solidification and increases nucleation location.The mechanical properties of the alloys increased obviously.With the content of Sn increased,the elongation of the alloys increased,and the yield strength,hardness and tensile strength first increased and then decreased,and the fracture mode was mixed fracture dominated by ductile fracture.The mechanical properties of Zn-Mg-2Sn are the best.The tensile strength,yield strength,elongation and hardness are 173.2 MPa,120.7 MPa,5.64%and 76.9 HV respectively.The corrosion rate of Zn-Mg-Sn alloys is consistent with pure zinc.The pH value changes relatively in the initial stage of immersion,and the fluctuation in the late immersion is small.The corroded surfaces show that the immersion morphology of Zn-Mg-1Sn is the best and the process of corrosion is uniform and stable.?3?The hemolysis rate of the alloys is less than the safety threshold required for clinical application,they have good hemolysis rate.The hemolysis rate of Zn-2Sn is only 0.40%,Zn-2Sn and Zn-Mg-1Sn have the optimal platelet adhesion properties.Considering the properties of the all alloys,Zn-Mg-1Sn has the best properties,the tensile strength reached 167.9 MPa,the elongation was 4.23%,and the degradation rate in SBF solution for 60 days was 0.164 mm/year,the highest pH value is 8.63,and the hemolysis rate is only 0.81%,which meets the requirements of clinical application of orthopedic degradable implant materials.