Study On Microstructures And Properties Of High Strength And High Conductivity Beryllium Bronze Alloy Wire During Drawing And Heat Treatment

Beryllium bronze has the advantages of high strength,excellent conductivity,nonmagnetic,high elastic limit and small elastic hysteresis,spark resistance,wear resistance,corrosion resistance,etc.It is widely used in aerospace,automotive,power electronics,computers and other high-tech fields.Presently,the related researches at home and abroad mainly concentrate on the casting process,heat treatment process and properties of high-strength beryllium bronze alloys with beryllium content of 1.6～2.0wt.%.It is not systematic to study the changes of microstructure and properties of high conductivity beryllium bronze with 0.2～0.6 wt.% beryllium content by cold drawing with large deformation and heat treatment after strong plastic deformation.Drawing forming is an important processing method to obtain high quality beryllium bronze wire products,which is of great significance for the development of high-strength and highconductivity beryllium bronze alloys with excellent comprehensive properties.In this work,three kinds of pure copper,Cu-0.2Be alloy and Cu-0.2Be-0.3Co-0.08 Mg alloy rod billets with continuous columnar-grained microstructure were prepared by the continuous unidirectional solidification method.Through the multipass cold drawing forming process with small deformation,pure copper and beryllium bronze wires with different diameters are obtained,and focus on the Cu-0.2Be alloy heat treatment under different temperature and time conditions,preliminary exploration of aging strengthening mechanism.The evolution of microstructure and texture,mechanical-electrical properties and deformation energy storage of alloys in the process of extreme plastic deformation and heat treatment at room temperature were studied,in order to explore the internal mechanism and influence,and develop high-strength and high-conductivity beryllium bronze wire.Provide experimental and theoretical basis for the development of high-strength and high-conductivity beryllium bronze wire.The main research results obtained in this work are as follows:With the increase of cold drawing deformation,the number of grains and the degree of distortion of the microstructure of pure copper and beryllium bronze alloys gradually increase.Cracking and fragmentation of grains and uneven deformation throughout the entire drawing process.The microhardness and tensile strength gradually increased,the plasticity decreased gradually,and the electrical conductivity decreased slightly.The hardness of Cu-0.2Be-0.3Co-0.08 Mg alloy with deformation0～99% increased from 69 HV to 182 HV,the tensile strength increased from 203 MPa to 574 MPa,and the elongation decreased from 43% to 1%,and the conductivity decreased from 40.3% IACS to 37.1% IACS.The continuous columnar-grained pure copper and beryllium bronze alloys both have the original preferred orientation of <001>,and with the increase of cold drawing deformation,the grains gradually shift away from the <001> direction and toward the<111> direction.Finally,a large number of <111> + a small amount of <001> fiber textures are formed,and the <111> deformation texture develops slowly,while the content of the <001> deformation texture is higher.The proportion of low-angle grain boundaries in pure copper and beryllium bronze alloys decreased from 94% to 40%,and the large-angle grain boundaries increased significantly,with a maximum proportion of 48%.When the deformation is 0%,the transverse section is composed of a large amount of Cube texture + a small amount of S texture,and the longitudinal section is mainly composed of a large amount of Cube texture + Goss texture.With the increase of cold drawing deformation,the transverse section Cube texture gradually decreases,while the S texture and Copper texture gradually increase,S texture and Copper texture gradually increase.The Cube texture and Goss in the longitudinal section gradually transform to Brass texture,Copper texture and S texture,and the five textures are scattered along the drawing direction.Pure copper and beryllium bronze have high KAM value near the grain boundary and deformation zone.With the increase of deformation,the KAM value gradually increases,and the stress is more concentrated.Under the same deformation,the transverse section has a higher stored energy than the longitudinal section,and the <001>texture component has a lower stored energy than the <111> orientation texture component.The stored energy of Cu-0.2Be-0.3Co-0.08 Mg alloy is greater than that of Cu-0.2Be alloy and that of pure copper.When solution at 950℃×1 h,the deformation structure of Cu-0.2Be alloy is completely replaced by recrystallized structure,and “transgranular” twins appear in some recrystallized grains.The low-angle boundaries orientation is almost completely transformed into the high-angle boundaries orientation of ～60°,and the drawn <001>+ <111> texture gradually transforms to the <111> fiber texture,and the texture strength decreases significantly.The solution Cu-0.2Be alloy can obtain greater hardness when aged at 460～480℃for 4 h,when aged at 480～500℃ for 4 h,which can obtain greater conductivity.when aged at 480℃×4 h,the hardness and conductivity are 77.8 HV and 73.5% IACS.