Effect Of Cold Rolling And Annealing On Microstructure And Properties Of M2 Cu Processed By ECAP-C And Its Physical Mechanism Of Action

With the rapid development of electronic information,transportation and other fields,the demand for high strength and high conductivity copper and its alloys is increasing in industry.However,at present there are many problems in processing and production of high strength and high conductivity copper product in China,including large quantities of copper can’t meet the requirements of high strength and high conductivity,which is directly related to the development of basic industries in our country.In order to produce large quantities of high strength and high conductivity copper,this work takes industrial pure copper(M2 Cu,Russian bronze medal number)processed by ECAP-Conform(ECAP-C)as the research object.The microstructure of copper was controlled by plastic deformation technique(room temperature rolling(RTR)and cryogenic rolling(CR))and annealing treatment to improve the strength of the material without damaging its electrical conductivity,so as to meet the requirements of the material for high-speed train contact wire.Meanwhile,OM,SEM,EBSD,TEM and XRD were used to study the influence of different rolling deformation,different rolling temperature and different annealing temperature on the microstructure of copper.In addition,the mechanical and electrical properties of copper under different conditions were measured by microhardness tester,conductance tester and tensile tester.The results are shown as follow:(1)The M2 Cu processed by ECAP-C in different routes was rolled at room temperature with different deformations.It was found that with the increase of deformations,the grains were gradually elongated and broken along the rolling direction(RD),forming lamellar grains and fuzzy discontinuous grain boundaries.Meanwhile,the grain size decreases and the dislocation density increases with the increase of deformation.At the action of rolling,the microstructure has obvious preferred orientation along(220)plane,and the larger the deformation is,the more obvious the preferred orientation is.The Brass texture {110}<112> is strongest in M2 Cu processed by ECAP-C routes A and rolled at room temperature with 90%deformation.In addition,the strength and hardness of M2 Cu increase gradually with the increase of deformation,and the elongation and conductivity decrease gradually,but to a small extent.Dislocation is the main factor affecting the strength and hardness,followed by grain boundary,while the resistivity induced by the two factors is extremely low,resulting in little adverse effect on the electrical conductivity.(2)The M2 Cu processed by ECAP-C in different routes and RTR was held at100～400 ℃ for 30 min.It was found that with the increase of annealing temperature,the grain morphology gradually developed to equiaxed grain,the grain size gradually increased,the grain boundary gradually changed from fuzzy discontinuous to clear continuous,and the large angle grain boundary gradually increased.Meanwhile,the deformation texture caused by rolling deformation gradually disappeares and the dislocation density gradually decreases.When the annealing temperature is T≤200 ℃,the recrystallization degree is low and the grain growth is not obvious.The microstructure of M2 Cu prossced by ECAP-C in routes A and RTR90% after annealing at 200 ℃ mainly contains Copper texture{112}<111> and S texture{123}<634> that are still a typical rolling texture,resulting in the less loss of hardness and strength.However,when the annealing temperature T≥300 ℃,the recrystallization degree is higher,the grain obviously grows up,the hardness and strength sharply decrease,and the elongation and electrical conductivity significantly increase.Among them,a large number of annealing twins appeares in the annealing process at 400 ℃.(3)The M2 Cu processed by ECAP-C in different routes was rolled at cryogenic rolling(liquid nitrogen temperature)with different deformations.It was found that the evolution trend of grain morphology,grain boundary type,texture and the various properties with the amount of deformation was similar to RTR,but the grain refinement effect of CR was better,and the accumulated dislocation density in the microstructure was higher,which resulted in a significant increase in strength and hardness,a slight increase in elongation,and a slight decrease in electrical conductivity.The microstructure of M2 Cu processed with ECAP-C by routes Bc and rolled at low temperature with the deformation of 90% mainly consists of Brass,Copper,S and Goss texture {011}<100>.Compared with RTR,the texture strength of Goss,Copper and S is higher,but Brass texture is weaker.Similarly,dislocation is the main factor affecting the strength,followed by grain boundary,and the resistivity induced by both factors is very low,resulting in little adverse effect on the conductivity.(4)The M2 Cu processed by different routes of ECAP-C + CR was held at100～400 ℃ for 30 min.It was found that the change of microstructure and properties of M2 Cu treated by different paths of ECAP-C + CR were basically the same as annealing at room temperature,but the recrystallization degree of low temperature rolling was higher at 300 ℃ annealing.Among them,the ECAP-C routes Bc +CR90% + 200 ℃ / 30 min annealing treatment of the M2 Cu has excellent mechanical properties and electrical conductivity.The hardness is 138.3 HV0.1,tensile strength is 506.38 MPa,the elongation is 9.8%,and conductivity is 91.9%IACS,which basically meet the performance requirements of high-speed train contact wire(tensile strength is greater than 450 MPa,conductivity is greater than80% IACS).