| As a typical aging strengthening alloy,Cu-Ni-Si alloy has the advantages of high tensile.strength,excellent conductivity and thermal stability.It is widely used in electronic connectors,lead frame materials and electronic packaging materials.There are some problems in the production of Cu-Ni-Si alloy by traditional hot rolling process,such as coarse solidification structure,serious dendrite segregation,low solid solubility of solute elements and complicated process.Relevant researches at home and abroad have shown that improving the cooling rate during solidification can not only refine the solidification structure of alloy,but also improve the solid solubility of solute elements in the matrix,inhibit the segregation of elements,and play the role of fine grain strengthening and solid solution strengthening.Based on this,the thin strip continuous casting process with the characteristic of sub-rapid solidification is introduced into the preparation of Cu-Ni-Si alloy.The solidification structure and element segregation behavior of Cu-3.2Ni-0.75Si alloy under the condition of thin strip continuous casting process are systematically studied by means of Confocal Scanning Laser Microscope,Scanning Electron Microscope and Electron Probe Microanalysis.According to the evolution of microstructure,properties and precipitation behavior of the alloy in different processes,the optimal solution and aging process of Cu-3.2Ni-0.75Si alloy was determined,and the effect of Ce on the microstructure and properties of Cu-3.2Ni-0.75Si alloy was analyzed.The main research results of this paper are as follows:(1)The nucleation process of Cu-3.2Ni-0.75Si alloy at different cooling rates was observed in situ by CSLM with a cooling rate gradient of 0.1?100?/s.It was found that when the cooling rate increased from 0.1 ?/s to 100?/s,the crystallization temperature of the alloy decreased from 1096? to 890?,and the secondary dendrite spacing decreased from 78 ?m to 24?m.(2)The solidification structure and segregation behavior of Cu-3.2Ni-0.75Si alloy ingot and casting strip were compared and analyzed.It was found that the thin strip continuous casting process with sub-rapid solidification characteristics can refine the solidification structure of the alloy and inhibit the segregation of solute elements.The average grain size of the solidification structure of the alloy decreased from 2 mm below ingot casting to 200 ?m below casting strip.(3)The microstructure and segregation behavior of Cu-3.2Ni-0.75Si alloy under different solution processes were studied.It was found that with the increase of temperature,the microstructure of the casting strip gradually experienced recovery,recrystallization and recrystallization grain growth.After solution at 900? for 1 h,the best solution effect was achieved.At this time,the apparent microhardness and conductivity of the alloy were 67.2 HV and 16.1%IACS,respectively.(4)The evolution of microstructure and properties of cold-rolled Cu-3.2Ni-0.75Si alloy under different aging processes was studied.It was found that with the extension of aging time and the increase of aging temperature,the change rule of tensile strength of the alloy first increased to the peak value,and then decreased;the change rule of electrical conductivity of the alloy first increased to the peak value,and then increased slowly.Combined with the evolution of microstructure,the optimum aging process is determined as 450?×4 h,at which the tensile strength and conductivity are 711 MPa and 43.2%IACS,respectively.(5)The effect of Ce on the microstructure and properties of Cu-3.2Ni-0.75Si alloy was studied.It was found that Ce can refine the solidification structure,increase the recrystallization temperature of the solution structure,refine the solution recrystallization grains and accelerate the aging precipitation process of the alloy.After aging at 450 ? for 1 h,the alloy has the best performance.At this time,the tensile strength and conductivity are 747 MPa and 44.9%IACS,respectively. |
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