| To meet the property requirements for large-scale integrated circuits of the lead frame materials,three kinds of new high-strength and medium-conductivity Cu-Ni-Si alloys were successfully developed by use of trace alloy principle for copper alloy such as Cu-2.0Ni-0.5Si,Cu-2.0Ni-0.5Si-0.15Ag and Cu-2.0Ni-0.5Si-0.03P alloys. The aging properties, precipitates structures, high-temperature plastic deformation and dynamic recrystallization behavior were comparatively studied.The aging behavior and strengthen mechanism were comparatively studied for the three alloys.The effect of addition trace elements Ag and P on the precipitation strengthening properties were studied.While the solid solution Cu-2.0Ni-0.5Si alloy aging at 400～500℃,the micro-hardness greatly increased at the early stage of aging.The higher the aging temperature,the higher the micro-hardness.The electrical conductivity rapidly increased at the same time and the higher the aging temperature,the higher the electrical conductivity.The cold rolling deformation before aging accelerated aging precipitation.The electrical conductivity was effectively increased by addition trace element Ag. The microhardness and tensile strength were effectively increased by addition trace element P. With the 0.15% Ag addition, the values of the microhardness, electrical conductivity and the tensile strength could increase 2.1%,15.3%,8.7% after aging at 450℃for 2h,respectively. With the 0.03% P addition, the values of the microhardness, electrical conductivity and the tensile strength could increase 18.6%,2.3%,29.8% after aging at 450℃for 2h,respectively.The Ni2Si was the precipitated phase to strengthen the Cu-2.0Ni-0.5Si and Cu-2.0Ni-0.5Si-0.15Ag alloys,the Ni2Si and Ni3P were the precipitated phases to strengthen Cu-2.0Ni-0.5Si-0.03P alloy on aging process by means of transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) analysis. On the basis of analysising the changes of electrical conductivity for Cu-2.0Ni-0.5Si alloy,the Avrami phase transformation kinetics equation and electrical conductivity equation were derived by use of the linearity between electrical conductivity and volume fraction of precipitates under the aging process.The crystal structure,combining energy and power,electronic structure of 8-Ni2Si were studied by using the plane wave pseudo-potential method(PWP) with GGA and DFT of the first principle method for the first time.The result show thatδ-Ni2Si was a stable precipitate phase. The results deepened on the understanding of precipitation mechanism of Cu-Ni-Si alloy. The results also show that the DFT-GGA-PWP method can be used to analysis and forecast the structure of precipitating strengthen copper-alloy.The flow stress behaviors of Cu-2.0Ni-0.5Si,Cu-2.0Ni-0.5Si-0.15Ag and Cu-2.0Ni-0.5Si-0.03P alloys during hot compression deformation was studied by isothermal compression test with Gleeble-1500D thermal-mechanical simulator when the temperature from 600℃to 800℃and strain rate from 0.01s-1 to 5s-1 under maxium strain of 60%. The relationship between the flow stress,strain rates and deformation temperatures were studied.The microstructure of the experimental alloys were studied in the hot-compression procedure. Stress index n,stress scale parameter a, hot deformation activation energy Q,and constitutive equation were derived from the correlativity of flow stress,strain rate and temperature. The condition of dynamic recrystallizaiton (DRX) for the Cu-2.0Ni-0.5Si-0.15Ag and Cu-2.0Ni-0.5Si-0.03P alloys is T≥700℃by using plot of work-hardening rate versus strain (θ-ε) curves.The relationship between the critical condition of dynamic recrystallizaiton (DRX) and deformation condition was obtained.The DRX kinetic equation is submitted and the calculated fraction of DRX by using the model has good agreement with that of experiments. The relationship between the dynamic recrystallizaiton (DRX) grain size and the parameter Z was obtained.A dynamic recrystallizaiton (DRX) grain size model was obtained.Thg aging processes for Cu-Ni-Si lead frame alloy were developed based on the optimization of the process parameters.The multi-aging production process for Cu-Ni-Si alloy was as follow:solid solution at 900℃for 1h→40% cold rolling→aging at 450℃for 2h→40% cold rolling→aging at 420℃and 460℃.The electrical conductivity and strength have optimum combination after the alloy aged at 420℃for 0.5h.The combinations of electrical conductivity,tensile strength and soft temperatures were as follow: 54.2%IACS,754.8MPa and 475℃for Cu-2.0Ni-0.5Si-0.15Ag alloy respectively; 48.6%IACS,803.9MPa and 475℃for Cu-2.0Ni-0.5Si-0.03P alloy respectively. These properties can meet the requirements of high strength and high electrical conductivity copper alloy for lead frame.
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