| Cu-Cr alloys are widely used in rail transit,electrical and electronic industries because of their high strength,excellent electrical and thermal conductivity,and good processability.This dissertation uses high-purity cathode copper(99.95 wt.%),Cu-10 Cr master alloy and 99.99% Ag as raw materials.?3 mm Cu-Cr-Ag alloy rods of high performance are prepared through "melting-iron mold casting-extrusion-drawing-solid solution-aging-drawing" and "leading continuous casting-drawing-solid solution-Drawing-aging - drawing.The evolution of the mechanical and electrical properties of the alloy in the preparation process was studied,and the softening resistance of the material was evaluated.The metallographic microstructure and the second phase of the alloy were characterized by metallographic and scanning electron microscopy.The dislocations and the characteristics of the precipitating phase of the alloy were investigated by transmission electron microscopy.The effects of deformation and aging treatments on the microstructure and properties of Cu-Cr-Ag alloys were discussed in detail,and the relationship between the preparation process of Cu-Cr-Ag alloys and the microstructure-mechanical properties was revealed.The main results are as follows:(1)The average size of as-cast Cu-0.3Cr-0.1Ag alloy grains is approximately 500 ?m.The Cr-rich secondary phases are distributed on the wafrix.The strength(158 MPa)and electrical conductivity(52.3 %IACS)of the alloy are lower.After hot extrusion(?80 mm-?13 mm)deformation,the alloy grains are broken,the average size is about 80 ?m,and dynamic recrystallization occurs.The stick phase appears in the organization.Relative to the as-cast alloy,the strength is increased by 48 MPa and the conductivity is slightly reduced.After multi-pass drawing with the amount of deformation of 88%,the alloy grains are greatly elongated in the drawing direction and the morphology of the second phase particles is not significantly changed.The strength of the alloy is increased to 378.3 MPa,and the electrical conductivity is slightly reduced(by a decrease of 5 %IACS).(2)The effect of solid solution aging on the microstructure and properties of cold-drawn Cu-0.3Cr-0.1Ag alloy is obvious.After solution treatment,the alloy recrystallizes completely and the grains become larger(about 200 ?m).Most of the second-phase particles have dissolved in the copper matrix,but there is still a small amount of retention.In addition,the alloy dislocations were reduced and the work hardening was eliminated.The strength of the alloy was reduced to 256.3 MPa,and the electrical conductivity reached 62.6 %IACS.During the aging process,nano-sized Cr phase particles are precipitated from the matrix,and the comprehensive properties of the alloy are enhanced by precipitation strengthening.The best aging temperature of the alloy is aging at 500? for 120 min.At this time,the tensile strength,electrical conductivity and elongation of the alloy are 381 MPa,92 %IACS and 19% respectively.After this state alloy was redrawn(deformation amount 55%),the tensile strength and electrical conductivity reached 495.5 MPa and 83 %IACS,respectively,and the softening temperature of the alloy exceeded 550?.(3)The grain of the upper continuous casting Cu-0.3Cr-0.1Ag alloy is in the form of a long strip,the length direction is consistent with the upward direction casting direction,and the maximum aspect ratio is 33.The second phase distributed between the elongated grains is spherical and the size is between 2-3 ?m.The characteristics of continuous strip casting such as elongated grain structure and second-phase directional distribution make it have good strength(230 MPa)and plasticity matching.After drawing 71% of the deformation,the alloy grains are fibrous and the dislocations increase and they accumulate along grain boundaries.The tensile strength of the alloy is increased to 388 MPa,the elongation is 6.7%,and the conductivity is slightly decreased.(4)The effect of deformation heat treatment on the microstructure and properties of up-lead continuous casting Cu-Cr-Ag alloy is obvious.After the high-temperature solution quenching treatment,some grains still have a typical long strip morphology.There is still undissolved residual second phase in the alloy.The strength of the alloy decreases,and the elongation and conductivity increase.After the second drawing(58% deformation),the elongation of the alloy grain is elongated.Dislocations increase and entangle with each other to form a high dislocation density cellular substructure.The strength,elongation,and conductivity of the alloy are 333 MPa,2.4%,and 55 %IACS,respectively.After the aging treatment,the alloy structure still maintains the deformed structure,and the Cr-rich second phase is distributed at the grain boundaries of the long-grained grains.A large number of nanoscale fcc-structured Cr phases appear in the alloy matrix.In addition,the aging treatment reduces the dislocation density of the alloy,and the Ag element is always distributed in the matrix in the form of solute atoms.The best aging process for the alloy is 450? for 120 min.The tensile strength,electrical conductivity and elongation of the alloy are 441 MPa,88 %IACS and 12% respectively.After 55% deformation drawing,the strength of the alloy increased to 541 MPa,and the corresponding hardness,electrical conductivity and elongation were 188 HV,84 %IACS,2%.The softening temperature of the alloy is close to 550 ?... |
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