Research On Composition Design,Microstructure And Properties Of High Strength And High Conductivity Cu-Cr-Mg-Si Alloy

As a typical aging precipitation-strengthened copper alloy,Cu-Cr alloys were widely used in aerospace,rail transit catenary wire,large-scale integrated circuit and other modern industrial fields due to high strength and high conductivity simultaneously.The essence of the good comprehensive properties of Cu-Cr alloys lies in the sufficient precipitation of nano-scale Cr particles during the aging process.Cu-0.26Cr-0.14 Mg,Cu-0.26Cr-0.14Mg-0.02 Si,Cu-0.26Cr-0.14Mg-0.05 Si,Cu-0.26Cr-0.14Mg-0.08 Si alloys were prepared by melting in argon environment in medium frequency induction furnace.The evolution of the microstructure and properties of the designed alloys in the process of cold deformation and heat treatment was systematically studied by using the processes of solid solution treatment-cold deformation-aging and secondary cold deformation + aging combined with metallographic structure,SEM,TEM,ESBD results.Using strength calculation,kinetic calculation,the effect of Si element on the microstructure and properties of the Cu-Cr-Mg alloy in the aging process was explored.The following conclusions are drawn:(1)The metallographic structure of the Cu-Cr-Mg-(Si)alloy is uniform with obvious equiaxed crystals and no obvious precipitates after solid solution treated at 950 ℃ for 2 h.After 80% cold rolling + aging,the mechanical properties of the alloys increase with the increase of Si content,and the electrical conductivity changed nonlinearly with Si content.The Cu-0.6Cr-0.14Mg-0.02 Si alloy with Si content of 0.02%(wt.%)has the best comprehensive properties.(2)The Cu-0.26Cr-0.14Mg-0.02 Si alloy has higher tensile strength and conductivity than Cu-0.26Cr-0.14 Mg alloy after aged at 500 ℃,and the softening temperature was equivalent to that of Cu-0.26Cr-0.14 Mg alloy,both exceeding 570 ℃.After cold rolling for 80%-500 ℃ for 20 min,the peak aging hardness of Cu-0.26Cr-0.14Mg-0.02 Si alloy was 163 HV,the electrical conductivity was 82.0% IACS,the tensile strength was523 MPa and the elongation was 15.6%.Combined thermomechanical treatment can greatly improve the properties of Cu-0.26Cr-0.14Mg-0.02 Si alloy.After solid solution treated at 950 ℃ for 2 h-cold rolling for 80%-450 ℃ aging for 4 h-secondary cold rolling for 80%-400 ℃ aging for2.5 min,the hardness of the alloy was 178 HV,the electrical conductivity was 80.4 %IACS,the tensile strength was 575 MPa and the elongation was13.8%.(3)The CR80% Cu-0.26Cr-0.14Mg-0.02 Si alloy had a similar precipitation sequence to the Cu-0.26Cr-0.14 Mg alloy during aging at500 ℃: G.P.zones(Completely coherent with the Cu matrix)→ fcc-Cr phase(coherent or semi-coherent with the Cu matrix)→ bcc-Cr phase(K-S orientation relationship with the Cu matrix).Texture evolution during combined deformation heat-treatment was: Rotational cubic → Copper →Gauss / Brass,and S texture existed in the whole cold deformation stage.(4)The addition of a small amount of Si was beneficial to promote the precipitation of Cr element.The main strengthening methods of Cu-Cr-Mg-0.02 Si alloy were precipitation strengthening,dislocation strengthening and grain strengthening,which accounted for 40.8%,30.7%and 13.8% of the total strengthening mechanism,respectively.