Study On Technology And Theory Preparing High Strength And High Conductivity Cu-Cr-Zr Alloys

The smelting process, microstructure evolution, hot deformation behavior and plate texture of Cu-Cr-Zr alloys were mainly investigated in this paper so to resolve the anti-vaccum melting and process technology of the alloys. The melting process experiments were studied by self-designed non-vacuum melting furnace and casting equipment. The melting, deformation and heat treatment process parameters were optimized by condition experiments. Specific contents and new conclusion are as follows:The Gibbs free energy changes of reactions of copper, chromium and zirconium with some compnents such as O₂, N₂, crucible and furnace lining materials, were calculated at the melting temperature. The possibilities of the relevant reactions were analyzed by the Gibbs free energy changes. The dynamic studies of diffusion and chemical reaction process show that chromium and zirconium can react with O₂ and N₂ under protective atmosphere; the zirconia and magnesia have a good stability for Cr and Zr, therefore, they can be used as crucible and furnace lining materials for Cu-Cr-Zr alloy melting. The favorable factor of the smelting process such as smelting atmopshere, refractory material, deoxidizing agent and so on were put forwarded and relevant equipment were deisgned. The smelting experiment results indicated that the melting loss rate of Cr and Zr elements are 9.69 wt.% and 9.7%, respectively. The casted microstructure of the alloy is clean.Phase equilibrium thermodynamics calculation for low solute Cu-Cr-Zr system is practiced. Precipitated phase and its mass fraction in the process of casting, hot-rolling, and aging are predicted by means of CALPHAD technology. The calculation results can give guide to the optimization of alloy chemical constitution and it is demonstrated that the main phase occurred in the process of thermomechanical treatment are (Cu), Cr and Cu₅Zr phase. The Cr phase is the main precipitated phase while the value of Cr/Zr≥3.5, and Cu₅Zr is the main precipitated phase while the value of Cr/Zr≤3.5.The microstructure evolution of Cu-Cr-Zr alloys in the process of casting, solution and aging treatment was studied by optical microscope (OM) and high resolution transmission electron microscope(HRTEM), It is found that when the content of Cr is higher, a large number of Cr phase congregated together in the grain boundary during the course of iron mould casting. The increase of cooling speed can inhibit the precipitation and gathering of Cr phase. The precipitated Cr phase cannot completely resolute into matrix after solution treatment. Furthermore, some precipitated Cr phases congregate and grow up. The precipitation temperature decreases with the increase of Cr content and Cr/Zr value while the precipitation speed is on the contrary in the course of aging. Cr phase exists in the matrix mainly with the shape of acerose, claviform, globosity and hexagon. Zr phase occurs with irregular shape, The CrCu₂(Zr,Mg) phase maybe decompose into chromium-rich phase and zirconium-rich phase at aging temperature above 425°C.The deformation behavior of Cu-Cr-Zr alloy was investigated by compression tests with Gleeble-1500D thermal simulator system. The tests temperatures are 700℃, 750℃, 800℃and 820℃, respectively. The strain rates are 0.01s^-1, 0.1s^-1,1s^-1 and 10s^-1. The results show that the flow behavior could be described by the hyperbolic sine constitutive equation, and an active energy of 597.53 kJ/mol was calculated. The processing maps were calculated and analyzed according to the dynamic materials model. And the processing parameters of hot deformation in the range of this experiment were attained by the maps. The optimal hot deformation temperature was 800-820℃and the strain rate was 0.01-0.1s^-1.The instability zones of flow behavior can also be recognized by the maps.Texture evolution of Cu-Cr-Zr alloy at different processing stage was investigated by mean of orientation distribution functions(ODF), the volume fraction of the typical orientations also were calculated. Electrical conductivity, tensile strength and micro-hardness also were investigated at different process. The results show that the cold deformation texture, consisted of copper orientation(mainly {113}<332>), Brass orientation, S orientation and Goss orientation, was very strong, especially the Copper orientation and the Brass orientation. In addition, Copper orientation transformed to Brass orientation with the increase of cold deformation rate. Brass orientation dominates in the aged alloy, and the S orientation and Copper orientation was relatively lower, and no {113}<332> orientation was observed. The volume friction of the {113}<332> orientation was more than 60% in cold rolling samples after aging. When Copper texture was mainly orientation, the tensile strength and elongation of the strip increased at the orientation from 0 degree to 90 degree, the electrical conductivity decreased. When volume fraction of Copper orientation equal to that of Brass orientation, the tensile strength, elongation and electrical conductivity have little different on the orientation from 0 degree to 90 degree.Base on the abve investigation, the preparation processing parameters are optimized by conditions experiments, and a suit of optimal processing parameters with respect to different working procedure of melting, casting, hot-rolling, solution treatment, cold-rolling and aging are obtained. These results provide instructive attemps for the semis-inductrial production of 200kg.