Study On Microstructure And Properties Of Cu-Ni-Si-Mg Alloy Used For Lead Frame

As a typical aging strengthen alloy, Cu-Ni-Si alloy was an ideal material of leadframe of large integrated circuits because of its excellent strength and electricalconductivity and has a wide application prospects. Scholars from various countrieshave been research its organization, performance and improve its treating process.In this paper, the structure and properties changes in the aging process of differentstates of Cu-2.8Ni-0.7Si-0.15Mg alloys were researched by the test methods of thehardness measurement, conductivity measurement, tensile test and metallographicanalysis and high-resolution transmission electron microscopy analysis, and optimizethe alloy production process. The effect of addition trace element Mg on hardness,tensile strength, electrical conductivity and precipitation activation energy of Cu-2.8Ni-0.7Si-0.15Mg alloy were studied, and the recrystallization behavior of the alloyswere in-depth discussions.The aging behavior of Cu-2.8Ni-0.7Si-0.15Mg alloy under hot-rolled state andsolid solution state were researched. The results showed that: cold deformation prior toaging accelerate the second phase precipitate in the aging process, increase thehardness and conductivity. Such as, the alloy without deformation after hot rollingaging at450°C for0.5h, the hardness and conductivity reach214HV and31%IACSrespectively. But the alloy by80%deformation in the same process, the hardness andconductivity were245HV and34.6%IACS. The alloy aging after solid solution, theprecipitates are δ-Ni2Si and β-Ni3Si. The alloy through hot-rolled+40%cold rolled+aging at500°Cfor30min can make the microhardness and electrical conductivity asthe optimum combination and the electrical conductivity and microhardness were36%IACS and242HV.On the basis of analysising the changes of aging properties of Cu-2.8Ni-0.7Si andCu-2.8Ni-0.7Si-0.15Mg alloy in the solid solution state, the influence of traceelements Mg to the precipitation hardening of the alloy were studied. With the Mg addition, the values of the microhardness and tensile strength could increased16%and7.9%, after aging at400°C for8h, and the value of electrical conductivity decreased4.2%, and the precipitation activation energy of the alloy dropped from54.04KJ/molto25.89KJ/mol, which make the alloy has a better performance in early aging stage.The avrami phase transformation kinetics equation and the electrical conductivity werederived by analysising the changes of electrical conductivity of the two alloys.Increasing the annealing temperature and the deformation can accelerated therecrystallization process of Cu-2.8Ni-0.7Si-0.15Mg alloy. The deformation reduces thesoftening temperature and recrystallization temperature, for example, therecrystallization temperature of the alloy with40%deformation is550°C, while that ofthe alloy with80%deformation is between450°C to500°C.