Deformation Behavior And Microstructure Evolution Of T-Shaper Micro-Upsetting In Ultrafine-Grained Pure Copper

With the rapid development of micro system technology and micro electro mechanical system,the current industry is developing towards miniaturi zation and miniaturization.Using traditional industrial materials to produce miniature parts,as the grain size is similar to one dimension of micro parts,appears obviously size effect and affects the dimensional accuracy of final production,improves the costs,and reduces the efficiency in the actual production.The research shows that the above defects can be improved obviously when ultrafine grained materials are used to produce micro parts,which greatly improves the production efficiency and product quality,and paves the way for the development of micro forming technology.Compared with the traditional compression,T-shape micro-upsetting experiment has the advantages of simple die structure and convenient operation and so on.Extrusion deformation and compression deformation occur at the same time in the metal,materials deform severely,and different sizes samples can use the same mold.In this paper,we use ECAP to produce ultra-fine grained copper material first.In order to analysis the deformation behavior of T-shape micro-upsetting,we use Deform-3D finite element analysis software to simulate,and experiment the T-shape micro-upsetting test on ultra-fine grained pure copper at room temperature and high temperature.Finely we analysis the microstructure of ultrafine grained materials in T-shape micro-upsetting.The T-shape micro-upsetting test can be divided into two stages according to the flow law of metal materials.In the first stage,the speed of extruding into the mold cavity is larger than the speed of expanding above the die,and the main deformation is extrusion in the sample.While in the second stage,the speed of later is larger than the former,and the main deformation is compression deformation.Both the finite element analysis and experimental results show that the dimension of the mold cavity have a significant effect on deformation force,extrusion rib height and high aspect ratio in the T-shape micro-upsetting.The die surface roughness has little effect on the deformation force in the first stage,while in th e second stage,the deformation force increases with the increase of the surface roughness.The die radius and the opening angle has a significant impact on the force in whole deformation,the force becomes lager with the increase of die radius and angle.The extrusion height and high aspect ratio decrease linearly with the increase of die surface roughness,fillet radius and the opening angle.Increasing the deformation temperature can decrease the force significantly due to dynamic recovery and dynamic recrystallization in the ultrafine grained copper;the dynamic recovery occurs when the deformation temperature is lower than 200?,while the deformation force and high aspect ratio decreased slowly,but extrusion bar height increases slowly,and the grain grows not obviously;when the deformation temperature is above 250?,the deformation force decreases rapidly,extrusion bar height and the height to width ratio increase rapidly,and the grain growth significantly;when the deformation temperature reaches 400?,the average grain size grows from 0.44?m to 3.4?m.