Study On Microstructure And Mechanical Properties Of Zn-0.1Mg-1Mn Alloys During Drawing

Pure Zn and its alloys have good biocompatibility and appropriate degradation rate.Although the mechanical properties of Zn-based alloys have been improved to varying degrees through alloying and deformation processing,most of them still do not satisfy the mechanical requirements of the biodegradable materials.Current studies have found that it's an effective method to prepare high strength and high plastic biodegradable Zn-based alloys through alloying Mg and Mn element and deformation treatment.Moreover,implant devices such as bone nails,sutures and cardiovascular stents need to be extruded and drawn.In present,there are few studies on the drawing process of Zn-based alloys,and the evolution of microstructure and mechanical properties during drawing need to be further studied.Therefore,in present work,the Zn-0.1Mg-1Mn alloy bars and wires were prepared by hot indirect extrusion and drawing at room temperature.The relationship between the extrusion process,drawing process,microstructure and mechanical properties was studied.The main results are as follows:With the increase of extrusion temperature,the average grain size gradually increases from 1.27 ?m to 4.28 ?m,the texture exhibits transformation from non-basal texture with {0001} basal planes titled away from ED about 15° to ED?{0001} basal texture,both YS and UTS decrease from 401 and 440 MPa to 336 and 386 MPa.At different extrusion speeds,the bars all show non-basal texture with {0001} basal planes,and the average grain size of the bar prepared at 1 mm/s can reach to 1.27 ?m,the average grain size of the bar prepared at 0.2 mm/s increases to 1.41 ?m,both YS and UTS decrease to 340 and 402 MPa,the average grain size of the bar prepared at 4 mm/s significantly increases to 2.86 ?m,both YS and UTS decrease to 324 and 362 MPa.Overall,the bar extruded at 100? and 1 mm/s has excellent mechanical properties,its YS and UTS reach up to 401 and 440 MPa,and the elongation is 25%.The good mechanical properties are closely related to the fine-grained structure with an average grain size of 1.27 ?m,the finely dispersed MnZn13 phase and the non-basal texture.In the drawing process with a speed of 30 mm/s,the phenomenon of "work softening" appears.Both YS and UTS gradually decrease from 401 and 440 MPa for the as-extruded alloy to 293 MPa and 373 MPa for the as-drawn alloy with cumulative area reduction of 51%,and the elongation increases from 25%to 42%.The average grain size gradually decreases from 1.27 ?m to 0.53 ?m,the number of LAGB and MnZn13 phase increases,the texture changes from non-basal texture with basal planes titled away from DD about 15° to deformation texture DD?<0001>due to dislocation slip and {1012} twinning.In the drawing process,intermediate annealing is required.The phenomenon of"annealing hardening" appears after annealing at 200? for 20 min.The YS increases from 293 MPa to 320 MPa,and the elongation to the failure decreases from 42%to 19%,Recrystallization occurs after annealing,the average grain size increases from 0.53 ?m to 1.36 ?m,and the finely dispersed MnZn13 phase is also dissolved into the Zn matrix during the annealing process.After annealing,the phenomenon of "work softening" also appears in the drawing process with a speed of 30 mm/s.The YS and UTS of the final as-drawn wire with a diameter of 1.85 mm reach to 288 and 354 MPa,and the elongation is 55%.The YS and UTS decrease form 320 and 377 MPa for as-annealed bar to 259 and 320 MPa for as-drawn bar with cumulative area reduction of 30%,and the strength slightly increases during subsequent drawing.The elongation shows the opposite changing trend,the elongation increases from 19%for the bar after annealing to 57%for the bar with cumulative area reduction of 30%,and then the elongation is 55?58%for else bars with cumulative area reduction of 50?80%.In the drawing process,the average grain size gradually decreases,the number of dislocations and LAGB gradually increases.Dynamic recrystallization occurs when cumulative area reduction reaches to 50%,the higher the deformation.the higher the recrystallization.The content of finely dispersed MnZn13 phase increases again.The texture changes from annealing texture to non-basal texture with basal planes titled away from DD about 15° due to dislocation slip and dynamic recrystallization.In the drawing process with a speed of 70 mm/s.the phenomenon of "work softening" and "annealing hardening" also occurs.The evolution of microstructure and mechanical properties is basically the same as that during the drawing process with a speed of 30 mm/s.However,in the drawing process before annealing,grain grow abnormally due to the rise in temperature,the average grain size can reach to 1.93 ?m,the YS and UTS decrease to 212 and 260 MPa,and the elongation decreases to 18%.The YS and UTS of the final as-drawn wire reach to 250 and 315 MPa,and the elongation is 55%.