Performance Optimization Of Degradable Mg-Zn-Ca-Mn Alloy And Simulation Of Mechanical Properties Of The Cancellous Bone Screw

Magnesium and its alloys have shown great biocompatibility and similar mechanical properties to human bones,and can be degraded and absorbed in the body without the need for secondary surgery,which has caused widespread concern in the materials science and medical communities.Based on the research team's exploration of medical biodegradable magnesium alloys in the past ten years.In order to improve the comprehensive properties of magnesium alloys,in this paper,the Mg-3Zn-0.2Ca alloys with different Mn contents were obtained by using vacuum melting.The microstructures,mechanical properties and corrosion resistance of these alloys were investigated by using XRD and SEM-EDS,universal electronic tensile testing machine and electrochemical workstation,respectively.Furthermore,the effect of heat treatment process on the microstructure and properties of magnesium alloys was explored,and the mechanism of effect was analyzed.Finally,the mechanical properties of magnesium alloy bone screws with optimized performance were simulated by finite element analysis.The main results obtained are as follows:1.Comparative analysis of the microstructures for as-cast Mg-3Zn-0.2Ca,Mg-3Zn-0.2Ca-0.3Mn,Mg-3Zn-0.2Ca-0.5Mn,Mg-3Zn-0.2Ca-0.7Mn and Mg-3Zn-0.2Ca-0.9Mn(wt.%;ZX30,ZXM0.3,ZXM0.5,ZXM0.7 and ZXM0.9,respectively)alloys,the results shown that the addition of Mn element change the distribution of solute elements,and affected the average grain size of the alloys.Compared with ZX30 alloy,the average grain size of ZXM0.5 alloy was reduced by 40.1%.2.Comparative analysis of the mechanical properties of five as-extruded alloys after homogenization.The results show that the ZXM0.5 alloy has relatively optimal mechanical properties.Its yield strength and tensile strength are 302.3 MPa and 327.6MPa(compared to ZX30 alloy,increased by 25.1%and 3.1%),the elongation is13.92%(not significantly lower than ZX30 alloy).Electrochemical performance results of the ZXM0.5 alloy shows that the corrosion potential,corrosion current density and polarization resistance are 1.509 V,32.25?A/cm~2,and 0.97 k?·cm~2,respectively.ZXM0.5 alloy has best comprehensive properties.3.Comparative analysis of the microstructure of ZXM0.3,ZXM0.5,ZXM0.7and ZXM0.9 alloys after solution treatment.The ZXM0.5 alloy was selected to do aging treatment,the best aging treatment conditions was 180?temperature for 48 h.4.Comparing mechanical properties of as-extruded ZXM0.5 alloy before and after aging treatment,the results show that the yield strength and tensile strength of the ZXM0.5 alloy after aging treatment are 338.5 MPa and 345.6 MPa(compared to ZX30 alloy,Increased by 11.9%and 5.5%)respectively,and the elongation has not significant reduction.In addition,the electrochemical performance of as-extruded ZXM0.5 alloy before and after aging treatment were approximately the same.5.The finite element analysis software of Workbench was used to simulate the three-point bending and axial extraction process of magnesium alloy bone screws.The results show that the deformation degree of the bone screw cap is relatively largest,and the stress concentration part is mainly the thread root.The screw thread structure reduces stress concentration and deformation.