Microstructure And Fatigue Properties Of T2 Copper Planar Microspring Cold Extrusion Forming

MEMS is a micro-component system produced by micro-processing.As the key structure of mechanical movement and energy storage in MEMS,the running state of planar microspring is directly related to the stability and reliability of MEMS.At present,the preparation methods of planar micro spring include UV-LIGA preparation technology of silicon material,micro electroforming technology and micro cold extrusion technology of metal material.Its fatigue performance has been improved with the change of preparation technology,but it still can not meet the growing long-term use demand.In this paper,T2 copper was used to extrude and prepare planar micro spring,and the influence of various process parameters on the microstructure evolution and the relationship between process parameters and fatigue properties of micro spring were studied.The conclusion is as follows:The extrusion process of micro spring is divided into three stages.When the equiaxed billet is used for extrusion,the microstructure in the upsetting and filling stage is mainly equiaxed,with small deformation degree;the grains in the initial extrusion stage are sheared at the die angle,and the sharp deformation forms a area of arc streamline;the grains in the edge area of the stable extrusion stage have large deformation,forming a black slip line parallel to the extrusion direction.When the 70% rolling reduction is used to extrude the blank,the density of the fiber structure increases under the shear action of the rolling deformation structure in the edge area of the rough filling stage of the pier;the rolling deformation structure in the initial extrusion stage is sheared at the die angle,forming the arc streamline zone;the structure in the stable extrusion stage flows along the extrusion direction on the basis of the rolling deformation,forming dense and continuous fibrous tissue.The results show that the linewidth of micro spring decreases,the difficulty of metal flow increases,the strain gradient effect is more obvious,the plastic deformation is more concentrated on the outer surface,and the uniformity of microstructure decreases;With the increase of preheating temperature,the grain size increases,and the plastic deformation is more concentrated on the outer surface,and the uniformity of microstructure decreases.When the rolling reduction rate is increased from 0 to 35%,the grains of the billets will be refined,and the homogeneity of the structure will be improved during extrusion;when the rolling reduction rate is increased to 70%,the microstructure of the billets will be fibrous,and the micro springs with dense and continuous fibrous structure can be prepared by micro extrusion.With the increase of extrusion speed and the optimization of lubrication conditions,the grain size of the micro spring column will be refined and the microstructure uniformity will be improved.The failure cycles of the micro spring prepared in this paper are in the range of 599 ?42558.When the initial angle of the fiber structure is increased,the continuity of the fiber structure in the working plane of the microspring is improved,which can inhibit the initiation and propagation of microcracks in the stress concentration area,the number of failure cycles of the micro spring increases from 1074 to 3346.The microstructure of the working plane of the micro spring with the initial angle of 90° has the best continuity and the best fatigue performance.The smaller the grain size of the microspring is,the better the structure uniformity is,and the better the fatigue properties is;reducing the thickness of micro spring and increasing the strain amplitude will reduce the failure cycle times of micro spring.