| Cu-Ni-Si alloy is a kind of precipitation strengthening type alloy. It has high strength, excellent elasticity, good conductive properties and good anti-stress relaxation properties. Meanwhile, it can be widely used in the manufacture of various elastic components in the electrical appliance and instrument. In a word, it is a new copper matrix elastic material which is expected to replace beryllium bronze. And Cu-Ni-Co-Si alloy is Olin company on the basis of the research and development Cu-Ni-Si alloy, which has a higher strength, conductivity and anti-stress relaxation.Based on the National High-rech R&D Project—key technology study of the high-speed rail transportation of copper alloy wire and Beijing science and technology project—a new generation of high-performance copper alloy materials and the preparation and processing technology research funding, a series of new alloys of Cu-Ni-Co-Si with high strength, conductivity, and elasticity were designed and prepared in this study. By means of materials research measurements, such as thermodynamic calculation, hardness and electrical conductivity measurements, room temperature tensile tests, X-ray diffraction (XRD), optical microscopy (OM), scanning and transmission electron microscopy analysis (SEM, TEM, HREM), and stress relaxation testing, the relation of the structure and properties of the alloys with the ratio Ni/Co was studies, mechanical properties, microstructure and it’s evolution of the alloys were investigated. Meanwhile, the influence of Co content on the microstructure and properties in the studies alloys was also investigated. And then strengthening mechanism and the form and effect of the Co element in the alloys were presented. Several important conclusions can be summarized as follows:(1) The type and fraction of the precipitates was analyzed through the CALPHAD and Pandat thermodynamic calculation software. The theoretically analysed results showed that with increasing the content of Co, its Ni2Si phase reduced, and Co2Si phase increased. When the Co content achieved1.2Wt.%, the two phase have intersection points.(2) On aging at the temperature at500℃in Cu-Ni-Si alloy, there were three different tans formation products:a modulated structure resulting form spinodal decomposition, DO22ordering structure nucleation form the modulated structure, and Ni2Si phase with disc-like structure appearing in (Ni. Si)-rich regions. Replace part of Ni with Co, Co suppressed spinodal decomposition to form the desired vacancies move and promotion of (Ni. Co.):Si phase precipitation, the aging products directly precipitates (Ni. Co):Si phase.(3) Replace part of Ni with Co. Cu-Ni-Co-Si alloy precipitation aging organization and Cu-Ni-Si alloy during aging precipitation-Ni2Si phase with the same structure and morphology. And the relationship between the matrix and precipitates is that:[001]cu//[1101p,(010)(U//(001)p;[112]Cu//[324]P,(110)Cu//(211)P.(4) By means of transmission electron microscope (TKM). high-resolution transmission electron microscope (HRHM) the aing precipitates in the Cu-1.6Co-1.2Ni-0.6Si alloy aged at45O-55O℃was studied. It wans first to apply DigitalMicrograph software to analysis the coherent, semi-coherent and the coherency loss between precipitates and Cu matrix. The coexistin raduium of (Ni, Co)2Si coherent/semi-coherent precipitates was about12-25nm, the calculated value of critical transition radius for the coherency loss was given as10.3nm.(5) By transmission electron microscopy, image analysis and statistical analysis, the growth and coarsening and the regulatities of distribution of aging precipitates in Cu-1.6Co-1.2Ni-0.6Si was investigated. The results showed that the growth behavior of disc-like (Ni, Co)2Si was in good agreement with LSW theoretical model when Cu-1.6Co-1.2Ni-0.6Si aged at500℃. The mean radius of (Ni. Co2Si precipitates with t1/3is linear relation, which suggested that the growth and coarsening of (Ni. Co)2Si precipitates were dominated by diffusion. The size distribution of (Ni, Co)2Si precipitates was proximity normal distribution curve, which was also in good agreement with LSW theoretical.(6) Upon aging after solid solution for the Cu-Ni-Co-Si alloy, there could be linearity between electrical conductivity and volume fraction of precipitates. Based on the linear relationship, Avrami phase transformation kinetics equation and electrical conductivity equation at different aging temperatures are described for the Cu-Ni-Co-Si alloy.(7) Before aging of the solid solution alloy cold deformation can accelerate aging early second-phase precipitates, the conductivity was the quick reply. After cold rolling- aging along the dislocation distribution with many small precipitates, dislocation movement difficult in the aging process, so that the rapid increase in hardness in the aging process. The precipitation of the precipites severely blocks the recrystallization of the deformed structure in the alloys.(8) The Cu-Ni-Co-Si alloys relaxation could be divided into two stages, stress relaxed fast in the first stage while slowly in the second stage and tended to a certain limit value after a long time. During the first stage, there are many the movable dislocations, dislocation resistance to movement comparisonsmall, the driving force of the dislocation movement is relatively large, so the larger the stress relaxation rate in the first stage of the stress relaxation. In the second stage, due to dislocations with the impurity atom and the second phase particle interactions, could lead to dislocation multiplication, and the emergence of cross-slip. In the area of micro-plastic deformation caused dislocation pile-up and tangling, resulting in stress concentration, the stress distribution is very uneven, slip caused by the movement of dislocations under high stress relaxation.(9) The stress relaxation values of the Cu-Ni-Co-Si alloy are smaller than the Cu-Ni-Si alloy, these could be explained by two aspect. The first is replace part of Ni with Co, Co suppressed spinodal decomposition to form the desired vacancies move and promotion of (Ni, Co.)2Si phase precipitation, resulting suppressed the dislocation slip move. On the other hand, the precipitates were promoted in the Cu-Ni-Co-Si alloy. The precipitate phase uniformly distributed in the grain boundaries and the matrix, during the relaxed condition, the dislocations moving was blocked by the precipitates. And then formation of stable Conttroll air mass, the movable dislocations gathered into a post-deposition dislocation group, which caused the dislocation moving difficult.(10) The device of semi-continuous casting technique and on-line technique was designed and optimized, thus it is possible to manufacture the solution high strength and excellent elasticity Cu-Ni-Si alloy strip. |
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