Research On BP-ECAP Block Forming Process Of Ultra-Fine-Grained Pure Copper Chips

Ultra-fine-grained materials have small crystal size,high crystal defects,good strength,hardness,plasticity and excellent wear resistance.They are widely used in aerospace,national defense,chemical industry,metallurgy,electronics,bioengineering and core technology.Therefore,it is widely valued by researchers.Large-strain cutting can produce large shear strains in the chips in a single deformation stage to prepare high-strength metals and alloys with ultra-fine crystal/nano-structures,and at the same time overcome the limitations of traditional hyperplastic deformation methods.However,the ultra-fine crystal/nano chips produced by high-strain cutting are small in size and various in shape,and cannot be directly used to manufacture structural devices.Therefore,under the premise of ensuring the ultra-fine crystal structure of the chips,the research on the block forming of the chips has important research value and development prospects.Equal channel angular pressing with back pressure(BP-ECAP)can deform and refine crystal grains at a lower temperature,increase density and avoid cracks.In this paper,the BP-ECAP process is used to study the forming process of ultra-fine-grained pure copper swarf block.While ensuring the compactness of the formed block,the ultra-fine-grained microstructure and good mechanical properties are controlled.In this paper,the macro finite element model and the microstructure cellular automata CA model of pure copper are established through Deform-3D,and the BP-ECAP numerical simulation of the pure copper material with a porosity of 0.7 is carried out to explore the influence of back pressure,temperature and pass times on extrusion The law of influence of the effect was finally verified by experimental research.(1)Based on the pure copper material data in the Deform-3D software database,establish a microstructure cellular automata CA model,including the establishment of a flow strain model,a dislocation density model,a recovery model,a dynamic recrystallization nucleation model,and a dynamic recrystallization Growth model and dynamic recrystallization volume fraction and recrystallization grain size equations.(2)Based on the results of the previous research ECAP,a set of optimal basic mold process parameters were selected,which mainly included the corners of the mold inside and outside,the extrusion speed,the extrusion path and the coefficient of friction.On this basis,the effects of different back pressure values and temperatures on the load,equivalent strain,equivalent strain uniformity,microstructure and other properties of BP-ECAP extrusion deformation are explored,and the best BP-ECAP process parameters are obtained,and The multi-pass BP-ECAP under the best BP-ECAP process parameters is further explored,which provides guidance for subsequent experiments.(3)A BP-ECAP mold capable of realizing the back pressure function was designed,and the pure copper tube was subjected to high-strain cutting,pre-extrusion,compression extrusion and BP-ECAP four-pass extrusion test,and the compactness was obtained.Pure copper rod block with high performance.With the help of EBSD technology and micro Vickers hardness tester,the mechanical properties of the microstructure of the copper rod obtained by BP-ECAP were tested.The results show that the average grain size of the sample obtained by four passes of BP-ECAP is 0.32,and the grains are obviously refined.Within the four passes,the average hardness values of the samples were 125,138,147,and 154 HV,respectively,and the hardness increased with the increase of the extrusion passes.Compared with as-cast pure copper,the hardness of the sample is better.