| With the excellent integrated mechanical properties, the copper alloy with high strength and electrical conductivity is widely used in the conductive structure, lead frame, and etc. Among these copper alloy, the application of Cu-(Ni, Co)-Be is used a lot and be the hot spot of copper alloy today because of its good aging strengthening effect. However, the element of Be joined in this cooper alloy is harmful to people’s health and seriously pollutes the environment during the process of heat treatment. Thus, this paper designs a type cooper alloy that adds the main element of Co and the selected elements of Zr, Si, Ti and other rare earth elements which realize the green environmental protection. The nominal composition of this alloy is Cu-1.96Co-0.45Si-0.07 Zr. After the heat treatments, this copper alloy can achieve the effect of multivariate composite strengthening and meet the properties requirements of the lead frame materials.Different solid solution, cold deformation and aging treatments were carried out on Cu-1.96Co-0.45Si-0.07 Zr alloy. In order to study the effects of different treatments on the microstructure and mechanical properties of this alloy, the hardness tester, eddy conductivity apparatus and tensile testing machine were used to test the hardness, electrical conductivity and strength, and the optical microscope(OM) was used to observe the microstructure of the alloy. Then we can determine parameters of the alloy under heat treatment process. The rule of aging precipitation under different aging processes was known by X-ray diffraction(XRD), transmission electron microscopy(TEM), high-resolution transmission electron microscopy(HRTEM), and other means, then we could determine the aging precipitated phase by PDF cards and the software of Digital Micrograph. In the end the strengthening mechanisms would be revealed of the alloy in this paper. The main contributions are as follows:The solution and aging process carried on Cu-Co-Si-Zr alloy is 980℃×2h, cooling in water and 510℃×3h, cooling in air, at this process, the hardness is 198.2HB, the conductivity is 47.9%IACS(27.8 MS/M), the tensile strength is 658.5MPa, the yield strength is 560.1MPa, and the elongation is 12.9%. To the Cu-Co-Si-Zr alloy after the solid solution process, different treatments of cold deformation(cold pressing or cold drawing) were going on, it was found that with the increasing of cold deformation, the hardness and strength rised continuously. In conclusion, the reinforcement process is 980℃×2h, cooling n water, 60%cold deformation and 480℃×2h, cooling in air, at this process, the hardness is 225.5HB, the conductivity is 45.2%IACS(26.6MS/M), the tensile strength is 738.2MPa, the yield strength is 699.7MPa, and the elongation is 11.6%. The fracture is ductile fracture as the shape of dimple. Also because of the existence of cold drawing, in the alloy there were large sums of staggered twin belts in the grain emerged in the type of slim stripe.By microstructure analyzing to the Cu-Co-Si-Zr alloy after the process of solid solution at 980℃ for 2h, cooling in water and aging at 510℃ for different time of 8min and 3h, colling in air. The bright field images observed by TEM were shown as corrugate strain field contrast after the aging time for 8min, and the diffraction patterns presented in condition of satellite spots. In combination with the side effects presented by X-ray diffraction diagrams of the different aging treatments for 8 min, 3h and 8h, we concluded that in the early part of the aging there was spinodal decomposition in Cu-1.96Co-0.45Si-0.07 Zr alloy.It was found that with the aging processes Cu-Co-Si-Zr alloy as a typical aging strengthened alloy would went through three stages: spinodal decomposition formed G.P area gradually in the early stage of aging process. And then, with the increasing of aging time or temperature, G.P area began to grow up and turned into the middle transition phase which formed coherent valvate stress field and kept coherent relationship with the matrix little by little. Finally, when the alloy entered into the stage of overaging, the intermediate phase transitted into a specific crystal structure of precipitated phase Co2 Si, and the coherent relationship between precipitated phase and matrix was broken that would lead the decline of the hardness. According the precipitated phase in the microstructure after the treatment of aging at 510℃ for 3h, we could get the conclusion that in this stage there were ordered phase, coherent precipitated phase and precipitated phase Co2 Si exsiting in the Cu matrix at the same time, and we could determine that the precipitated process of the alloy was continuous. |
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