Effect Of Mn And Ca Additions On The Microstructures And Properties Of Biodegradable Zn-Mg Based Zn Alloys

As biodegradable materials,zinc alloys are more suitable in the corrosion rate,compared with magnesium alloys and ferrous alloy,at the same time,zinc and magnesium as trace elements in the human body have an irreplaceable role.So development of it is very important to develop the new type of zinc alloys.At present,researches on the biodegradable zinc alloy are few,mostly focused on the as-cast alloys.Although the as-cast Zn-Mg binary alloy has the suitable degradation rate,the mechanical properties are poor,and can’t meet the requirement as the implant material.therefore,in this paper,manganese and calcium were chosen as alloying elements,and the Zn-0.05Mg-xMn(x = 0.1,0.2,0.3 wt.%),Zn-0.2Mg-xMn(x = 0.1,0.3,0.5,0.8,wt.%)and Zn-0.2Mg-xCa(x = 0.06,0.15,0.3,wt.%)ternary alloys were indirectly extruded at 200 ℃ with the ratio of 16.Microstructures,mechanical properties and corrosion rate in the simulated body fluid(SBF)have been investigated by optical microscopy,X-ray diffraction,tensile and hardness test,so that it provides valuable basic data for the development of degradable Zn alloy implants..The conclusions are obtained as followed:The yield and tensile strength of the as-extruded Zn-0.05Mg-xMn(x = 0.1,0.2,0.3)and Zn-0.2Mg-xMn(x = 0.1,0.3,0.5,0.8)ternary alloys increase gradually with increasing Mn content.For the Zn-0.05Mg-xMn alloys,the tensile yield strength increases from 157MPa to 270MPa when the Mn additions are 0.3 wt.%,and the tensile strength increase from 227MPa to 282MPa While the elongation declined,compared with Zn-0.05Mg.For Zn-0.2Mg-xMn(x = 0.1,0.3,0.5,0.8)ternary alloys,the yield strength improves from 182MPa for Zn-0.2Mg to the 326MPa for Zn-0.2Mg-0.8Mn,and the tensile strength increases from 240MPa to 403MPa.While the elongation increases with the Mn additions from 18.5%for Zn-0.2Mg to 29%for Zn-0.2Mg-0.5Mn,but then decreases to 18%for Zn-0.2Mg-0.8Mn which is similar to Zn-0.2Mg.It is indicated through the microstructure observation and XRD analysis that the Zn matrix of as-extruded Zn-Mg-Mn ternary alloys possess equiaxial grains due to the complete dynamic recrystallization during the hot extrusion.The average grain size decreases greatly with the increasing of Mn content.And there are mainly two kinds of secondary phases,namely Mg2Zn11 and MnZn 13 with the size between 0.5 μm～5 μm,which inhibit recrystallization grain growth.The second phase particles tend to distribute along the extrusion direction.The amount of MnZn13 particles increases with the increasing of Mn content.So it indicates that the addition of Mn alloy elements can form a large number of second phases in the alloy,and the grain size of the matrix is significantly refined.For as-extruded Zn-0.2Mg-xCa(x = 0.06,0.15,0.3)alloys,,both the yield strength and tensile strength increase slightly with the addition of Ca,and reached the maximum in the Zn-0.2Mg-0.3Ca alloy,i.e.,,200MPa and 260MPa respectively,while the elongation significantly reduced to between 5%and 10%.The Zn matrix of the as-extruded Zn-Mg-Ca ternary alloys also possess equiaxial grains,but the average grain size does not change with the Ca additions.It is show according to the results of immersion test in SBF that after the addition of alloying elements Mn and Ca,the corrosion rates of these ternary alloys are lower than that of pure Zn and Zn-Mg alloys.And the corrosion rates tend to be stable after 8 days immersion,maintaining at about 0.5-2g/m2/d.It indicates that Mn and Ca addition can improve the corrosion resistance of Zn and Zn-0.2Mg alloy.