Investigation On The Preparation,Microstructure And Properties Of Lamellarr Structured CuCrZr Alloy

In recent years,China's high-speed rail vehicles have developed rapidly.Therefore,power transmission lines that require power supply have higher tensile strength(> 550 MPa)and electrical conductivity(> 80 % IACS).Copper alloy has become the best material due to its excellent electrical conductivity,strong plasticity,and relatively low cost.Heterogeneous lamellar structure,as a material design model that adjusts the comprehensive properties of materials,can be easily introduced during the deformation and subsequent heat treatment of metal materials.In this paper,two kinds of cold deformation technologies including rotary swaging(RS)and diffusion welding+rolling and subsequent heat treatment technologies are used to prepare the lamellar structure copper alloy materials from the micro and macro respectively.The optical microscopy,scanning electron microscopy,electron backscatter diffraction and transmission electron microscopy were used to characterize the microstructure evolution of copper alloys under different deformation states.The mechanical and electrical properties of copper alloys were measured by means of hardness,uniaxial tensile experiments and electrical performance testing taking the test.The main conclusions are as follows:(1)Study on preparation of lamellar structure CuCrZr alloy by rotary swaging and heat treatmentAfter solid solution at 920 °C for 2h,the materials were subjected to rotary swaging with true strain ? of 0.5,1.0,1.5,2.0,and 2.5,respectively,and then aging experiments at 450 °C(0-30 hours).The results showed that: With the increase of ?,the grains continue to refine and have a long lamellar structure,and the subsequent precipitation strengthening effect is more obvious.The grain size of the sample with ?= 0 is 68.5 ?m,and the sample with ? = 2.5 was 2.6 ?m.Before aging,the electrical conductivity of the material decreases as the amount of rotary swaging deformation increases,and after aging,the electrical conductivity of the material increases as the amount of rotary swaging deformation increases.Before ageing,the conductivity is35.8 %IACS at ?=0,and 32.3 %IACS for samples with ? = 2.5;after ageing,the conductivity is 72.3 %IACS at ?=0 and 80.3 %IACS at ? = 2.5.This is because before the aging,the defects inside the material reduce the conductivity to dominate,and after aging,the precipitated phase to increase the conductivity dominates.In addition,the lamellar fine crystals produced by the special deformation process of spin forging make the number of dislocations on the current propagation smaller than that of the equiaxed fine crystals,and further improve the conductivity.The hardness and tensile strength of the material increase continuously with the increase of the amount of deformation of the forging.Before aging,when ? = 0,the hardness value,yield strength,and tensile strength of the material were 63 HV,148 MPa,and 305 MPa,respectively.When ? = 2.5,the hardness value,yield strength,and tensile strength reached 141 HV,518 MPa,and 518 MPa.After aging,when ? = 0,the hardness value,yield strength and tensile strength of the material are 123 HV,298 MPa and 443 MPa,and the hardness value,yield strength and tensile strength at ? = 2.5 reaches 180 HV,627 MPa and 671 MPa,respectively.This is mainly due to the dispersion distribution of the enhancement phase,lamellar fine grain,and accumulation of dislocations.(2)Study on the preparation of lamellar structure Cu/CuCrZr composite sheet by diffusion welding + rolling heat treatmentDiffusion welding-cold rolling-annealing technology has been successfully used to make soft/hard Cu/CuCrZr composite plate interfaces with transition interface layers and has achieved excellent overall performance.This superior combined strength and ductility(final strength of approximately 312 MPa and a uniform elongation of 15 % and an elongation at break of 23 %)are due to the combination of a good transition interface,which can produce geometrically necessary dislocations(GNDs),which results in a larger strain gradient(15 ?m).This strain gradient enhances the strength and ductility of the material through the front/back stress strengthening mechanism.The microstructure and hardness ratio of soft/hard alloys have a huge impact on front/back stress strengthening.The high-density dislocations in the soft and hard layers annealed and annealed at 250 °C after rolling will hinder the generation and accumulation of GNDs and weaken the effect of front stress strengthening on ductility.Severe results in a relative decline in overall performance.Therefore,less misaligned Cu/CuCrZr composite sheets annealed at 350 °C have the best overall performance.In addition,the accumulation of the number of layers also enhances the front/back stress enhancement effect.