Improvement Of Mechanical Properties Of Zinc-aluminum Alloy And Process Simulation And Optimization Of Tube Drawing

Zinc-aluminum based alloys(referred to as Zn-Al alloys)have the characteristics of environmental protection,low hardness,superplasticity at room temperature,low flow stress,and good wear resistance.Through heat treatment and plastic deformation processing,The ultrafine grain structure and excellent mechanical properties can be obtained.It is expected to replace the currently widely used poisonous heavy metal lead-antimony(Pb-Sb)alloy used in the manufacture of detonator delay bodies,as well as to replace the easily degradedmild steel damper which are made as architectural shock absorbers.In this thesis,based on available literatures as well as previous researches in our laboratory,the effect of rare earth(RE)content on the microstructure and mechanical properties of as-cast zinc-aluminum alloys were studied systematically.Then using heat treatment and super:plastic deformation process,the modified microstructures and mechanical properties were studied further.Meanwhile the stress-strain curve of alloy tube during drawing and diameter reducing processes were simulated using the Deform-3D numerical simulation software package,and the influence of friction coefficient,drawing speed,tube wall thickness dimension on thedrawing force were studied systematically;Through the drawing test of unfilled hollow tube,the variation of inner diameter,wall thickness and outer diameter under different drawing passes were studied;Finally,the tubulins filled with delayed powders were subjected to multi-path drawing process to reduce drawing the tube diameter.The Zn-Al alloy delay body was fabricated experimentally,and the delay body were assembled to detonators and then explosion tests were further carried out.The delay time(milliseconds,ms)of the delaying detonators were tested and compared with the traditional delaying detonators with Pb-Sb alloy delay body.The delaying effect of the delay body,as well as the substitution possibility of lead and antimony delay body were evaluated.The main research results are shown in the following:Rare earths addition is modifying and strengthening addition of the matrix in zinc-aluminum alloy.Adding additional rare earth,the primary thick dendrite phase tends to become smaller,and the alloy exhibits fine equated grains.The microstructure of the alloy is optimally fine when the content of rare earth is 0.4wt%.The hardness of as-cast alloys without heat treated process was in the range of 65.18 to 77.17 HV,while the hardness of the alloy after solid solution heat treatment was decreased below 40 HV,so the hardness decreased significantly.With the increase of rare earth content,the tensile strength elongation tends to change in the same tendency and they both increase initially,and then decrease.Compared with the alloy without rare earth,the tensile strength increases from 132MPa to 154MPa,elongation from 34%to 65%;It was found that for the alloys with the same rare earth content,the microhardness increases with increasing aging temperature,but when the rare earth content is over(>0.4wt%),it will have an adverse effect on the alloy,and the strength and hardness of the alloy will decrease.The alloy is treated by solution treatment+hot rolling(by 76%)+AC,the tensile strength reaches a maximum of 284MPa and the elongation reaches 165%.The drawing process of the empty tube at room temperature were simulated.The influence of process parameters on the drawing results was studied systematically.The results show that the drawing resistance force increase with the increase of friction coefficient and drawing speed.With the increase of the drawing cone angle,the contact area between the tube and the mold is less,thus the friction force decreases,and the drawing resistance force also decreases.Adjusting the width of the sizing zone,the drawing resistance is the smallest when the width of the sizing zone is 5 mm.The results show that the larger the deformation,the larger the drawing resistance force and the larger the wall thickness.The single-pass drawing simulation on the tubes with different initial wall thickness shows that the critical thickness-to-diameter ratio of aluminum alloy hollow tube is 13.13%,and if the critical thickness exceeds the critical value,the wall thickness will increase.Below the critical value,the wall thickness will reduce.A equation y=0.9526x+0.7679 was obtained by regression analysis,where x represent thickness diameter ratio,and y is thickness diameter ratio.The zinc-aluminum alloy delay body was prepared successfully,and the delay detonator were assembled and ignited experiments in factory,the delay time(millisecond,ms)were obtained and professionally evaluation was completed.The accuracy of delay time is qualified according to the specification authoritized by Industrial explosive industry,and the lead-free replacement of delay body using the new zinc-aluminum alloy component has basically reached the practical level.