Study On The Microstructures And Properties Of Zn-Mg Based Alloys With High Strength And Toughness

Recently,Zn and Zn based alloys have attracted more and more attention due to their proper degradation rate and good biocompatibility,and it became a new type of biodegradable material after Mg based alloys and Fe based alloys.In view of the poor mechanical properties of pure Zn,the alloying used by Mg,Ca,Sr or the deformation treatment of binary and ternary Zn based alloys have been studied.The results show that the mechanical properties of the pure Zn were significantly improved,but the mechanical properties of the implants could not be satisfied.And,the relationship between mechanical properties and microstructure of Zn based alloys is not clear.Therefore,in this paper,Zn-xMg(x=0.5,1.0 wt.%)-yMn(y=0.1,0.3,0.5,1.0,1.5 wt.%)ternary alloys have been prepared by indirect hot extrusion process.The influence of alloying element Mn on microstructure,mechanical properties and corrosion behavior of Zn-Mg alloys was studied by means of EBSD,SEM,mechanical test,so that the valuable basic data are to be provided for the design and development of Zn based alloys with high strength and toughness.The results of the experiment are as follows:Two kinds of secondary phase such as Mg2Zn11 and MnZn13 are formed after adding of Mn element in the Zn-Mg alloys.After indirect hot extrusion at 200℃,the secondary phase is broken and elongated along the extrusion direction,which suppressed the growth of the dynamic recrystallization grain.The matrix grain size of Zn-Mg-Mn ternary alloys was significantly refined compared to Zn-Mg binary alloys.The grain size of Zn-0.5Mg-1Mn alloy is 2.1 μm,which is the smallest of them.At the same time,all samples formed {0002} strong basal texture after hot extrusion.Compare with the Zn-Mg binary alloys,the texture intensity is decreased after adding Mn element.The tensile yield and ultimate strength of Zn-0.5Mg-xMn alloys both increase with the increasing of Mn contents,from 221 MPa and 279 MPa for Zn-0.5Mg binary alloy to 333 MPa and 422 MPa for Zn-0.5Mg-1.5Mn ternary alloy,respectively.The elongation of Zn-0.5Mg-xMn alloys firstly increases and then decreases.The maximum elongation is 22.5%for Zn-0.5Mg-0.5Mn alloy.The compressive yield strength increases with the increasing of Mn contents from 233 MPa for Zn-0.5Mg binary alloy to 405 MPa for Zn-0.5Mg-1.5Mn ternary alloy.Compared with the pure Zn prepared under the same conditions,the tension compression asymmetry of Zn-Mg-Mn alloys obviously decreased.Creep tests at room temperature show that Mn can significantly improve the creep resistance of Zn-Mg alloy,and the steady-state creep rate of Zn-Mg-Mn ternary alloys is lower than that of Zn-Mg binary alloy.In conclusion,the strength and plasticity of Zn-Mg-Mn alloys were simultaneously improved by grain refinement,texture weakening and the second phase strengthening.Zn-Mg-Mn alloys with Mn content between 0.5 wt.%-1.0 wt.%have the best strength and toughness.The tensile yield and ultimate strength of Zn-1Mg-xMn alloys also increase gradually with the increasing of Mn contents,from 263 MPa and 332 MPa for Zn-1Mg binary alloy to 317 MPa and 403 MPa for Zn-1Mg-1Mn ternary alloy,respectively.The elongation of Zn-1Mg-xMn alloys gradually decreases,from 6.8%for Zn-1Mg binary alloy to 1.7%for Zn-1Mg-1Mn alloy.The compressive yield strength increases with the increasing of Mn contents,from 298 MPa for Zn-1Mg binary alloy to 447 MPa for Zn-1Mg-1.5Mn alloy.Compared with the pure Zn prepared under the same conditions,the tension compression asymmetry of Zn-Mg-Mn alloys was obviously decreased.Although the strength has been improved,the plasticity sharply reduced,mainly because the hard brittle second phase content is too high.The results of simulated body fluid soaking at 37℃ show that the corrosion rate of Zn-0.5Mg-xMn alloys decreased after adding different content of Mn element to the Zn-0.5Mg alloy.The corrosion rate of Zn-0.5Mg-xMn alloys are similar,remaining about 0.05 mm/year after 14 days immersion.The electrochemical experiment showed that the corrosion rate has a similar regularity with the simulated body fluid immersion test.It is further proved that the addition of Mn can improve the corrosion resistance of Zn-0.5Mg binary alloy.