| The bio-degradable metal materials have been increasingly attracted in the field of medical implant materials due to their excellent mechanical properties and good biodegradability.Up to now,Fe-based and Mg-based alloys have been focused by some scholars.the focus of the scholars to research these materials.But the degradation rate of Fe alloys in the body is too slow,and Mg alloys is too fast.Therefore,it is necessary to find a new type of metal material which is non-toxic and has suitable corrosion rate.Zinc is an essential trace element for human,and has good mechanical properties,Moreover,the standard electrochemical potential of zinc is between that of Fe and Mg,which expectedly makes Zn and Zn-based alloys develop into a new kind of bio-degradable materials.As the purpose of Zn-Mg alloys applied in surgical suture,?0.16mm filaments with cumulative deformation up to 90%are successfully produced by indirect extrusion and subsequent cold drawing.Then microstructures and mechanical properties of Zn-Mg alloys in the process of extrusion and drawing are studied by mean of optical microscopy,scanning electron microscopy,room temperature tensile tests and X-ray diffraction.The primary conclusions are as follows:The microstructures and properties of the as-extruded Zn-(O?1wt.%)Mg alloys are studied.As the Mg content increases in Zn-Mg based Zn alloys,second phases Mg2Zn11 appear and constantly increases,which has the fibrous distribution paralleling to the direction of extrusion.Meanwhile,the average grain size decreases,and reaches 10?m more or less for Zn-0.2Mg.In addition,with the additions of Mg,both hardness and strength of Zn-Mg based Zn alloys increase.The hardness,yield strength and tensile strength increases from 50HV,132MPa and 157MPa for Zn-0.005Mg alloys to 90HV,299MPa and 327MPa for Zn-1Mg alloys,respectively.While the elongation firstly increases from 23.1%for Zn-0.005Mg to 27%for Zn-0.02Mg,and then decreases to 4.1%for Zn-1Mg.On the basis of as-extruded alloys,Zn-0.005Mg,Zn-0.02Mg and Zn-0.2Mg alloys are prepared by cold drawing process with the single pass deformation in 13%?5%,and the speed of drawing in 37mm/s.Finally,?0.16mm wires with cumulative deformation up to 90%are produced.The microstructure evolution in process of cold drawing and intermediate annealing treatment indicates that the grains of three kind of Zn-Mg are constantly stretched and the typical fibrous tissue is finally presented with the increasing of cumulative deformation.The three alloys have completely recrystallization in annealing treatment of 150?/5min,whose grain size is minimum,4.7mm,3.3mm,2.9mm,respectively..Meanwhile,mechanical properties test results show that when cumulative deformation is the same,the more Mg content of Zn-Mg based Zn alloys is,the higher hardness is,and when alloy elements is the same,the larger cumulative deformation is,the higher hardness is.Finally,the hardness of ?0.16mm wires with more than 90%of the cumulative deformation is up to 100HV.Moreover,the yield strength and tensile strength of ?0.16mm drawn wires are significantly higher than that of extruded bars.The yield strength and tensile strength of Zn-0.02Mg increase more than twice from 136MPa,167MPa for ?05mm extruded bars to 352MPa,424MPa for ?0.16mm drawn wires.The texture types and texture evolution of the extruded,drawn and annealed Zn-Mg based Zn alloys are studied.The results show that the extruded bars have typical basal fiber texture,<10-10>parallel to the extrusion direction.And the texture type of drawn wires is the same as the annealed wires,which has the special texture feature with c-axis tilted at 36° from normal direction(ND)to the extrusion direction(ED)around the transverse direction(TD).And the intensity of the extruded texture decreases and this texture type disappears in the process of drawing.And then,the drawn texture appears and the intensity of drawn texture is strengthened with cold deformation.Finally,c-axis is tilted at 36° from normal direction(ND)to the extrusion direction(ED). |
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