| Up-to-date, the production and consumption of copper and its alloys in China is the largest allaround the world. There is a significant demand of high-performance copper alloys for thedevelopment of electronics, power industry and so on. Nowadays, the overproduction of low-gradecopper alloy products results in the abnormal competition in domestic markets. Compared withGermany, the United States, Japan and other developed countries, there is still a large disparity onthe scientific research and industrial production of high-performance copper alloys. Now all theabove situations have been a serious threat to the survival of the copper industry, as well as a seriousimpediment to the development of many other related industries. Therefore, research anddevelopment of high-performance copper alloys has become the primary task for the domesticcopper industry. In order to overcome this obstacle, this thesis focused on the research ofhigh-strength and high conductivity copper-chromium-zirconium alloys.In this thesis, orthogonal design method was adopted for the composition design of high-strengthand high-conductivity copper-chromium-zirconium alloys. The mechanical performance andelectrical conductivity of the high-strength and high-conductivity copper-chromium-zirconiumalloys were firstly systematically studied. Several preparation techniques were explored for thepreparation process of copper-chromium-zirconium alloys and master alloys. Relationships betweenmechanical properties, electrical properties and processing parameters were investigated. The phasetransition process was also characterized. Fast deformation treatment with ultra-low temperature wasdeveloped during the experiments, which proved to influence significantly on the mechanical andelectrical properties of the as-prepared copper alloys. Finite element simulation was finallyintroduced for the residual stress reduction and control technology during the production process andwelding process of copper-chromium-zirconium alloys. The main results are as follows.（1） With theoretical calculation, the composition range of copper-chromium-zirconium alloys wasdeveloped through orthogonal design method. And we selected9kinds of composition ratio for thefollowing experiments. Master alloys were introduced in our experiment and then melt together withthe copper matrix in the vacuum induction melting furnace. The final state performance of theas-designed9kinds of alloys were characterized and orthogonally analyzed. The best of the alloycomposition components should be Cu-1.4Cr-0.12Zr.（2） Solid solution treatment, deformation and aging process were carried out for the as-preparedcopper alloys. And the best parameters of solid solution, deformation and aging process wereobtained. The solution temperature had a serious influence on the conductivity of copper alloys. Butthe strengthening effect of solid solution on the tensile strength of the alloys was relatively small.The rolling deformation presented a slight influence on the conductive properties of the copperalloys. The increase of aging temperature and aging time was benefit for the alloy conductivity,which would simultaneously reduce the tensile strength of the alloys. The optimal treatment processwas done with solution treatment at920℃, rolling deformation percent80%and aging time onehour at450℃. After the best-choice treatment, the electrical conductivity87.05IACS%。 Thetensile strength and elongation ratio were559.86MPa and9.02%, separately.（3） The phase evolution process of high-strength an high-conductivity was characterized bymetallurgical microscopy, SEM, XRD and TEM. The microstructures and properties of alloys withdifferent state were also characterized for the investigation of phase transition during thedeformation and annealing process. The results indicated that the microstructure of Cu-Cr-Zr alloyswas dispersed distributed uniformly smelt at1180±30℃, which was beneficial to the following heat treatment and process. In addition, better properties of alloys were achieved after solid solutiontreatment at950℃and then quench in water for1h. When aging at450℃， recrystallizationappeared and the nuclei further expanded with long aging time or high aging temperature, which wasin accordance with the results in Chapter3. After successive diffusion annealing treatment,solidsolution treatment and aging treatment, phase evolution of precipitates was obtained in turn CuZr2Hx→CuZr2→Cu5Zr in the aforementioned treatment. And finally, dispersively and uniformlydistributed precipitate Cu5Zr was achieved, this provided more reinforced phase in the copper matrix,which was in favor of getting alloy with high strength.（4） Low temperature and fast deformation processing was employed to investigate treatment andproperties of Cu-Cr-Zr alloys. Relationship between microstructure and properties of alloys wasstudied and the microstructure change after low temperature and fast deformation was also discussed.The results presented that twin strengthening was an effective approach to enhance the strength ofalloys,meanwhile, it was not harmful to the conductivity of alloys. With the increase of deformationamount,phase difference of grain in the Cu-Cr-Zr alloy decreased dominated by small-angle grainboundaries. The textures transformed from {110}<112> to {110}<001> and {110}<011> after lowtemperature fast deformation. Metallurgical microscopy and TEM observation suggested that therewere a great amount of twins in the alloy matrix, although the conductivity of the alloy decreasedslightly, the strength of the alloy improved a lot.This was beneficial to get alloys with goodconductivity and strength.（5） We described the reduction of residual stress and control technology of the copper strips basedon the problems encountered in the production process in Tongling Nonferrous Metals JinweiCopper Co., Ltd. Through the strict control of the quality of the manufacturing process, includingequipment cleaning, liquid reagent concentration and process parameters of the trial, surface qualitycould be achieved with no scratches, oxidation, stains and other defects. The surface roughnessvalues were0.1μm-0.2μm, which could meet surface requirements of the high-precision frame stripalloys.（6） Finite element simulation was conducted for the welding process ofcopper-chromium-zirconium alloys. The thermal parameters of welding process were taken intoaccount as non-linear relationships. The three-dimensional dynamic temperature field and stress fieldof welding process were simulated using ANSYS software. The temperature field and melting poolshape were studied with different stress variation and residual stress distribution during the weldingprocess. The longitudinal stress along the center of the weld line was stressed during our experiment.The results showed that there was obvious temperature difference on the welding plate for thestarting5seconds. When the welding was completed, the plate temperature became the same onlyafter10seconds.80seconds later, the temperature variation was only1℃. The closer to roomtemperature, the slower cooling process was. During the welding process, there was longitudinalthermal pressure for the high-temperature region close to the weld side; and there was thermaltensile stress for the other side away from the weld line. After welding treatment with self cooling,there was always tensile stress near the weld zone and compressive stress a little far from the weldzone. |
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