Effect Of Plastic Deformation On Microstructure And Properties Of Cu-Ni-Si Alloy

With the rapid development of Integrated Circuit(IC),lead frame materials with high strength and electrical conductivity are urgently required.Cu-Ni-Si alloys are considered as one of the most promising lead frame materials,and making balance between their strength and electrical conductivity is the key problem of the research works on Cu-Ni-Si alloys.In this paper,Cu-Ni-Si alloy with 90wt%Cu.content and weight ratio of Ni/Si 5:1 was prepared by the method of melting and casting,and then a serials of post-treatments,including homogenizing treatment,hot forging,aging treatments and rolling,were carried out.Microstructure observation was accomplished by scanning electron microscopy(SEM),optical microscopy(OM)and transmission electron microscopy(TEM),respectively,Phase composition was investigated by X-ray diffractormeter,energy dispersive spectrum(EDS)and TEM diffraction patterns.Electrical conductivity,hardness and tensile strength were also measured by Eddy current conductivity meter;Brinell hardness tester and Material universal testing machine.Based on the above experimental results,the effects of mechanical treatments and hot treatments on both microstructure and properties of Cu-Ni-Si alloys were discussed,and a good balance between strength and electrical conductivity was finally obtained.The main conclusions of this paper can be summarized as follows.(1)Microstructure of as-cast Cu-Ni-Si alloys consists of solution matrix ?-Cu(Ni,Si),netted structure of Ni31Si12 phase on grain boundaries and Ni2Si precipitations in solution matrix.Hot forging can destroy the netted structure of Ni31Si 12 phase,resulting in well dispersed sphere-like or plate-like Ni31Si12 phase and refined matrix grains.At the same time,Ni2Si phase gradually decomposes in to Ni and Si atoms,and then dissolves into Cu matrix,since the temperature of hot aging is beyond the precipitation temperature of Ni2Si phase.(2)With the increase of hot forging pass,the electrical conductivity of Cu-Ni-Si alloys increases significantly followed by slight decrease,while the hardness increases continuously.The increase of electrical conductivity can be attributed to the disintegration of netted grain boundary phase,while the decrease of electrical conductivity is the result of the decomposition Ni2Si phase and solid solution of its products.On the other hand,both the previous two factor can result in the improvement of hardness.(3)Microstructure of hot forged + aged sample mainly consists of matrix grains a-Cu(Ni,Si),micron-scaled Ni31Si12 phase on grain boundaries of matrix grains,and submicron-scaled precipitations Ni2Si.Compared with the hot forged sample,aging treatment is benefit to the improvement of both electrical conductivity and hardness,since Ni and Si solution atoms can precipitation as Ni2Si during aging process.(4)Cu-Ni-Si alloys have good performance during rolling process after hot forging +aging treatment.With the increase of the relative rolling ratio,electrical conductivity increased first and then decreased,the rolling deformation degree has little influence on tensile strength.When the relative rolling ratio is 85%,the sample after hot forging + aging + rolling + aging treatment has a best electrical conductivity of 57.96%IACS and tensile strength of 450MPa.(5)After hot forging + aging + rolling + aging + rolling treatment,Cu-Ni-Si alloy has a good combination properties,tensile strength is 592MPa,elongation is 16.5%and electrical conductivity is 48.28%IACS.Strength mechanisms include grain refining strengthening,secondary phase strengthening,precipitation strengthening and deformation strengthening.