ECAP Simulation And Experimental Study Of Nanocrystalline Chip

Nanomaterials perform better than conventional materials.As an emerging severe plastic deformation process,large strain cutting has the advantage of being able to efficiently prepare ultrafine crystal chips,and it is difficult to be widely used in industrial fields because the prepared chips are too small and small.Therefore,it is particularly important to study the preparation method of nano-chip bulk molding.The severe plastic deformation method(SPD)is effective for bulk molding.Equal-channel angular extrusion(ECAP)is the most widely used and most used in all SPD methods.For the foreground method,this paper uses the ECAP process to study the formation of nano-chips.In this paper,the ECAP Deform-3D numerical simulation is carried out on pure copper material with a porosity of 0.75.The influence of process parameters such as mold structure and temperature on the extrusion effect is explored.Through experiment,the ECAP process is optimized by back pressure.The contents are as follows:(1)Exploring the ECAP process factors,and obtaining a set of optimal friction coefficient,extrusion speed and temperature value.Under this circumstance,explore the external arc angle and internal rotation angle of different molds to the equivalent strain during ECAP extrusion deformation.Equivalent strain uniformity,temperature and other performance effects,and then get the best ECAP process parameters,providing some guiding significance for subsequent experiments.(2)Perform large strain cutting on pure copper bar,carry out ECAP extrusion test on pre-extrusion and compression extrusion of nanochips prepared by different tool rake angles,and explore the tool front angle and extrusion pass pairs.The influence of the ECAP block forming effect indicates that the obtained sample is generally poor in compactness.During the experiment,some samples were squeezed into elbows to produce a certain back pressure,which resulted in better compactness than other samples.(3)EBSD and hardness analysis were performed on the above elbow samples by means of EBSD observation and hardness measurement.Investigate the influence of back pressure on the microstructure and hardness of ultrafine crystal pure copper chips obtained from three different tool rake angles,and compare the results with the corresponding chips.The results show that the average grain size of ultrafine grained pure copper blocks prepared by different tool rake angles is 4.73 um,3.54 um and 4.43 um,respectively.The grain size increases and the hardness decreases.This is because the experiment is at 400?,this temperature is higher than the recrystallization temperature of pure copper,and pure copper recrystallizes,resulting in grain growth.(4)Using BP-ECAP extrusion of pure copper material with porosity of 0.75 at room temperature by Deform-3D,the equivalent strain,equivalent strain uniformity,equivalent stress and temperature change of the sample under different back pressures were investigated.The situation is compared with the results when no back pressure is applied,and the optimal back pressure is 50 MPa.Then,under the condition of constant back pressure(50 MPa),the effect of different temperature of ECAP on the extrusion results is studied,and the optimum temperature is 400?.