Effect Of Cold-rolling On Precipitation Behavior Of δ-Ni₂Si Phase In Cu-Ni-Si Alloy

Cu-Ni-Si alloy has been used in lead frame manufacturing because of its high strength,high conductivity and non-magnetic properties.With the development of electronic information technology,the performance of lead frame materials is becoming more and more demanding.In this paper,the selection of powder metallurgy,using elemental powder as raw material to prepare Cu-Ni-Si alloy sample,in the control of cold deformation process before the same premise,through the cold rolling way to obtain different rolling deformation,explore the alloy in the aging process of the structure and properties of the change law.In addition,the precipitation process of Ni2Si phase during aging was dynamically studied with static water quenching method,and the information of physical properties and microstructure evolution was measured.The isothermal precipitation behavior of precipitated Ni2Si phase was discussed with JMA equation,and the influence of cold rolling on precipitation behavior was clarified.The Ni2Si phase in the peaking alloy was analyzed by TEM,and the size and position of the precipitated phase and the orientation relationship between the precipitated phase and the matrix were observed,which further clarified the influence of cold rolling on the precipitation behavior and mechanism of Cu-Ni-Si alloy.In this paper,the effect of high-density dislocation introduced by cold rolling on the precipitate behavior during aging is studied by combining experiment and theoretical calculation.It will greatly enrich the existing alloy strengthening and conductivity regulation mechanism,and provide ideas for the preparation of high-performance IC lead frame Cu-Ni-Si alloy sheet.The main conclusions of this paper are as follows:1)Taking Cu-Ni-Si alloy as the initial state,the yield strength of 75%deformed alloy is increased from 154MPa to 525MPa after cold rolling.The microstructure of the alloy was observed,and the average grain size was reduced from 4.38μm to 2.81μm.The dislocation density of the alloy increases from 2.168×1014m-2 to 13.790×1014m-2 The texture orientation shows a gradually stronger Brass texture,and the proportion of small corner grain boundary increases with the increase of deformation.2)After aging treatment at 400℃,450℃,500℃ and 550℃,the hardness and conductivity of the alloy are improved.At the aging temperature of 500℃,it can have high strength and maintain good conductivity in the peak aging state.The aging temperature is too low,the precipitation power is insufficient,the atomic diffusion ability is weak,the conductivity rises slowly and the peak value is not high.When the aging temperature is too high,the alloy grains will be coarsened in the late aging period,resulting in a significant decrease in hardness,and the higher the deformation,the more obvious the decrease.Therefore,the aging temperature of 500℃was selected as the optimal aging temperature.3)The deformation heat treatment process to achieve the best properties of the alloy:solution at 900℃ for 2h+cold rolling at 75%+aging at 500℃ for 1h.Its comprehensive performance is the best:the hardness is 245HV,the conductivity is 38.18%IACS,the yield strength and tensile strength are 705MPa and 770MPa respectively,and the elongation after fracture is 9.5%.The average grain size of δ-Ni2Si phase is 20.94nm under TEM,which is in semi-coherent relationship with the matrix.4)For 75%cold deformation alloy aged at 500℃ for 1 h,the contributions of work hardening,solution strengthening,fine crystal strengthening and aging strengthening to the yield strength of the alloy are 255.59MPa,25.89MPa,107.38MPa and 260.28MPa,respectively.The calculated yield strength of 701MPa is in good agreement with the experimental result of 705MPa.5)The corresponding transformation kinetics equation and conductivity equation were calculated by Avrami’s empirical equation of phase transition kinetics,and the transformation kinetics S curves of Cu-Ni-Si alloy with different cold-rolled deformation at different aging temperatures were obtained.The apparent activation energy Q of the alloy during aging process was calculated as 29.46kJ/mol.The larger the deformation,the higher the aging temperature,the larger the precipitation force and the earlier the precipitation process begins.When the aging temperature is 500℃,the n value is about 0.5,so it can be considered that the precipitation mechanism of 8-Ni2Si precipitate is the thickening of large flake precipitate,and with the aging time,the precipitate eventually grows into a disc shape.