| By means of analysis method of metallographic analysis, X-Ray diffraction, scanning electron microscope and energy spectrum. The influence of Si addition on the microstructure and properties in Cu-7.5Ni-5.0Sn alloy was studied. Meanwhile, effect of the Heat treatment process and Machining process on the Cu-7.5Ni-5.0Sn alloy microstructure and properties was studied. The results were as followed:(1) There existed serious dendritic segregation in the as-cast structure of Cu-7.5Ni-5.0Sn alloy. The as-cast microstructure is composed of three parts:gray dendrite (α phase, Cu-Ni solid solution), interdendritic clip white matter or bony tissue (γ-(Cux, Ni1-x)3Sn), dark gray tissue, transitional (α phase and γ phase). The as-cast microstructure is still composed of three parts after the trace element Si was added. With the increase of Si content, the dendrite refinement effect is obvious. But the content of Si is more than0.58%, refinement effect tends to be stable. The addition of Si element in the alloy mainly formed Ni2Si, Ni3Si and Ni31Si12phase. The main formation of the addition Si are Ni2Si phase and Ni3Si phase when the content of Si is low. Otherwise, it was mainly formed Ni3Si and Ni31Si12phase. It can be Ni3Si phase refine the dendrite.(2) Effect of homogenization temperature is superior to time. The addition of Si element can delay the homogenization process of the alloy. With the increasing of the Si addition, the delayed effect is more obvious. The Si phase is stable from the beginning to end of the Homogenization treatment. After added Si alloy, its homogenization kinetics homogenization kinetics equation is1/T=R/OIn(4π2Dot/4.6L2). Although Homogenization treatment can eliminate alloys dendrite segregation, but still can not meet the requirements of cold rolled cogging.(3) The cold rolling rate of the alloy without addition Si element is content to therequirements of cold rolled cogging after780℃for24uniform cooling in water. Its cold rolling rate up to30%. Effect of solution temperature is greater than time. After800℃for1h solution treatment, the γ phase can be dissolved. Ni17Sn3phase and a little γ phases may affect the subsequent cold rolling process of the alloy. The alloy was aged treatment at400℃for4h after cold rolling50%rate. Its hardness value and conductivity can up to280HB and17%IACS respectively.(4) During solution treatment, the addition Si mainly form Ni3Si and Ni31Si12phase in thealloy grain boundary. Ni3Si and Ni31Si12phase block the mobile of grain boundary edge and contribute to the inhibition of grain growth.With the increase of solution temperature, the solubility of Ni3Si and Ni31Si12phase was increased. When the solution temperature is higher than850℃. Ni3Si is dissolved, partial dissolution of Ni31Si12phase.(5) Alloy containing Si is treated by36h at800℃water cooling, the cold rolling rate can reach50%. Then,800℃for1h solid solution treatment and80%cold rolled and aging treatment. With the increase of Si content, hardness and electrical conductivity of the alloy showed similar rule:first increased and then decreased. The content of Si element is lower than0.5%, it can suppress the discontinuous precipitation of Cu-7.5Ni-5.0Sn alloy. However, Si content is more than0.5%, it is a promoting effect on the discontinuous precipitation. Cu-7.5Ni-5.0Sn-0.58Si alloy was aged treatment at400℃for6h. Its hardness, conductivity and tensile strength up to270HB,22%IACS and975Mpa respectively, which is close to the performance of beryllium bronze. The Si addition result in the tensile strength of the alloy decreasing slightly. The cold deformation before aging treatment promotes the increase of hardness and electrical conductivity of the alloy. |
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