| Cu-Cr-Zr alloy is a typical aging-precipitation strengthening copper alloy.It is the only high-strength and high-conductivity copper alloy developed to meet the requirements of VLSI lead frame materials,which required tensile strength more than 600MPa and electrical conductivity more than 80%IACS.In recent years,it has become a representative of third generation high-performance copper alloy materials.The traditional hot-rolling process for producing Cu-Cr-Zr alloy mainly has the problems of serious segregation,low solid solubility,and complicated process,resulting low production efficiency and high cost.Studies at home and abroad have shown that increasing the solidification rate of the alloy can effectively increase the solid solubility of Cr and Zr in copper matrix,and the larger undercooling and heterogeneous nucleation can effectively inhibit element segregation and grain growth,enhanced solid-solution strengthening and fine-grained strengthening.In view of the background,the two-roll strip casting process was introduced into the preparation of Cu-Cr-Zr alloy with high strength and high conductivity in this subject.Fristly,the solidification microstructure,segregation behavior of elements and the solid solution effect of Cu-Cr-Zr alloy under sub-rapid solidification were systematically studied.Meanwhile,according to the evolution of microstructure and properties in the whole process,the strengthening mechanism and conducting mechanism of alloy in different process were analyzed.Finally,we obtained the technological process,microstructure and precipitation characteristics of the best properties,which provided a theoretical basis for the efficient preparation of alloys.Through the experiment,the following main conclusions are drawn.(1)Subrapid solidification of strip casting can effectively refine the grain,inhibit the segregation of Cr element,and greatly increase the solid solubility of Cr and Zr in the copper matrix,creating favourable conditions for subsequent aging processes.The experimental results show that there are a large number of crystal defects such as dislocations and substructures in the microstructure of cast strip.By DSC analysis,we can discover a tiny peak of heat flow in the 975?,so the microstructure of the cast strip is equivalent to that of the traditional process hot rolling&partial solid solution effect.Therefore,the complicated homogenization and hot rolling process can be eliminated in this process,and solid solution is required for a certain time at 975?.(2)When the cast strip was solution treatment at 975?,with the prolongation of solution time,the different type grains in the cast strip begin to grow,gradually fuse and interweave.Under the action of the elastic strain field and interfacial energy caused by the alloy elements dissolved in the matrix,they are gradually tending to equiaxed crystals.In this process,the segregation of Cr element is restrained with the migration of grain boundary.When the solution time reached 2h,the optimal solution effect was achieved,which the hardness was 68.7HV,and the electrical conductivity was 34.6%IACS.(3)During primary aging,with the increase of aging temperature and time,the tensile strength and hardness of the alloy both show a tendency of rising first and then decreasing.Meanwhile,the conductivity increases rapidly before reaching the peak value,then slowly rise again.After 95%cold rolling deformation and 450?×2h aging,Cu-0.8Cr-0.1Zr alloy reached the best comprehensive performance of primary aging.The tensile strength,hardness and electrical conductivity were 563MPa,227.1HV and 85.6%IACS.(4)The primary cold rolling deformation has the greatest effect on the properties of secondary aging.The larger the primary deformation,the smaller the elastic strain caused by precipitated particles in secondary cold rolling,and the uniform deformation of the alloy leads to more dislocations,so the precipitation kinetics of secondary aging is greatly enhanced.The primary cold-rolled 90%+450?×3h aging+secondary cold-rolled 80%alloy,has been achieved the final best properties after secondary aging at 300?×0.5h.The tensile strength,hardness and electrical conductivity were 669MPa,238.2HV and 84.3%IACS.At this time,the strengthening mechanism of the alloy is mainly coherent strengthening,in which the dislocation cut enhanced particles improving the surface energy and strengthening the matrix.At the same time,the bulk centered cubic structure Cr phase and the face centered cubic structure Cu matrix maintain a significant N-W phase relation.The increase of matrix dilution is the main reason for maintaining high electrical conductivity. |
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