Research On Deformation Behavior And Microstructural Evolution In Micro-extrusion Of Ultrafine-grained Pure Aluminum

Micro-system technology and micro-electromechanical systems have rapid development and gradually put into practical applications in the near future,micro-parts drive more attention in the application.Micro-heat exchangers,miniature reactors,micro-motors,optical sensors and other microelectromechanical systems important parts in the micro-electromechanical system of micro-structure manufacturing technology has become the focus of the majority of scientific research,ultra-precision machining,LIGA,engraved corrosion and other micro-device manufacturing technology in the types of materials can be processed,there are different levels of room for improvement of cost,processing efficiency.Plastic micro-extrusion has the characteristics of good repeatability,good mechanical properties of forming parts,low cost,high efficiency and simple process.Therefore,it is necessary to study the microextrusion technology.At first,we make the blank of micro-extrusion by equal-channel angular pressing.The microstructure and properties of the specimen were studied by means of micro-hardness measurement and electron backscatter diffraction microscopy.It was found that the grain refinement was mainly caused by the occurrence of the corner's material shear deformation.It make a small angle grain boundary and large angle grain boundary appear.Based on compression experiments on the blank,we find that UFG is more sensitive to the compression rate than other grain,while its forming accuracy is higher.In this paper,three-dimensional numerical simulation of the micro-extrusion process is carried out by using the finite element analysis software DEFORM-3D10.2.It is found that as the taper angle of the die becomes larger and bigger,the extrusion force becomes more and more,the plastic flow in the taper angle region becomes worse.And the stress process is analyzed in detail.The stress is concentrated in the cone angle region,and the strain is concentrated at the outer end of the deformed area.The top's velocity is faster than the bottom's velocity.The effect of the experimental mold and the experimental equipment on the geometrical dimensions of the blanks,the influence of the blank grain condition,the effect of different extrusion speed on the same size of the blanks are studied by the experiment of micro-extrusion.The squeezing force and displacement data are collected and processed.At beginning of extrusion,the diameter of blank decreases,the unit squeeze force decreases,when the blank's diameter reduces to 1mm,the unit squeeze force rises cause size effect.In the electron backscatter diffraction microstructure analysis of the microextrusion,it is found that the specimen can be divided into undeformed,deforming,deformed,extruded part's grain that is near the cone is elongated,It is found that the larger the ratio of grain size to mold size is,the worse the deformation coordination is.The thermal stability of the continuous extruded blank decreases at annealing's temperature of 300 ° C or higher.