Correlation Between Compositions And Properties Of High Strength And Conductive Cu-Ni-Si Alloys

High strength and conductive Cu-Ni-Si alloy is widely used in electronic components,especially suitable for lead frames and connector joints.However,The strength and electrical conductivity of the alloy are quite composition sensitive,and industry standards often give a very wide range of composition,such as the most widely used C7025 alloy,the alloying elements are:2.2?4.2 wt.%Ni,0.25?1.2 wt.%Si,0.05?0.3 wt.%Mg,and the composition range of some elements is even greater than the absolute content of the element.However,on the premise of meeting the above broad composition range,the industry often adopts more strict composition ratio,which leads to different composition formulas and product properties.Therefore,the industry urgently needs to find a quantitative composition design method suitable for Cu-Ni-Si alloy.Considering that the heat treatment process of this alloy is solid solution plus aging,and the structure of solid solution is characterized by chemical short-range order(CSRO),this essay uses the cluster-plus-glue-atom model to describe the solid solution to understand and design the alloy composition.In this model,the CSRO structure of the solid solution alloy is simplified into a structural unit covering the first nearest neighbor and the next nearest neighbor,which consists of the first nearest neighbor coordination polyhedron clusters and several connected atoms located in the second nearest neighbor.Based on this model,the relationship between composition and performance of series Cu-Ni-Si alloys was designed,and the series of quarternary and quinary Cu-Ni-Si alloys were researched and developed,and how to set the Ni and Si atomic ratios of different composition ranges was determined,so as to achieve the accurate and quantitative design of alloy composition and correlate composition,structure and performance.The main conclusions are as follows:In the concentrated solute region where the content of Cu is less than 95 at.%,the alloy composition is designed using the single cluster model[M-Cu,2](Cu)1?6;in the dilute solute region where the content of Cu is greater than or equal to 95 at.%,the dual cluster mixture model is used,The dual cluster structure includes solute structural unit {[M-Cu,2](Cu)3} and pure Cu matrix structural unit {[Cu-Cu12](Cu)3},and M is alloyed element In the Cu-Ni-Si ternary alloy system,M represents Ni and Si.According to the precipitation phase structure of 8-Ni2Si,the cluster formula reflecting the precipitation phase is determined as[Ni-Ni8Si5]Ni,where the cluster in square brackets is the main cluster of the phase,so M=Ni10/15Si5/15.On this basis,we also carried out microalloying of Fe,Cr,Mo and Zr.The absolute mixing enthalpy of these elements with Si was greater than that of Cu and Si.Therefore,in order to form precipitated phase elements,these elements were classified as Ni elements,Replace Ni in the above composition formula,namely M=(Ni,Fe,Cr,Mo,Zr)10/15Si5/15.According to the different proportions of the two clusters[(Ni10/15Si5/15)-Cu12)Cu3} and[Cu-Cu12]Cu3,we designed Cu-Ni-Si series ternary alloy whose simplified composition is(Ni10/15Si5/15)mCun,and the total number of solute atoms is m.Samples through the preparation of copper mold casting,and after solid solution(at 950? for 1 hour)and aging(at 450? for 4 hour)treatment,through the characterization of organization,hardness,electrical conductivity.we reveal a 95?95.8 at.%Cu composition sensitive area,there isn't the regular change of this sensitive area between the composition and hardness,electrical conductivity.Through precise process control performance is hard,so the alloy composition try to avoid a fall in the composition sensitive area.The uncontrollability of this sensitive area is in sharp contrast to the alloys outside the constitutive sensitive region:solute concentrations are higher and lower than those in this sensitive area,and the hardness of the alloys meets HV=-12.6×(at.%Cu)+1362.7 and HV=-26.2×(at.%Cu)+2722.3,respectively,the electrical conductivity of the alloys meets ?=0.2×(at.%Cu)+28.6 and ?=5.2×(at.%Cu)-466.In order to further improve the strength of Cu-Ni-Si ternary alloy,a series of concentrated solute zone Cu93,75(Ni/Zr)3.75Si2.08(Cr/Fe/Mo)0.42 alloy of[M-Cu12]Cu3 clusters were designed by microalloying and adding Ni-like elements Cr,Fe,Mo and Zr on the basis of ternary Cu-Ni-Si alloy.After the 950? for 1 hour solid solution water quenching and 450? for 4 hours aging water quenching treatment,the Vickers hardness of the alloy exceeds 250 kgf/mm2,its tensile strength is equivalent to 825 MPa,while maintaining the conductivity not less than 35%IACS.Especially the hardness of Cu93.75Ni3.54Si2.08Fe0.42Zr0.21 alloy(272 kgf/mm2,tensile strength is 900 MPa)is equivalent to that of KLFA85,electrical conductivity stayed above 35%IACS.When the composition of Cu-Ni-Si alloy is designed,if the electrical conductivity of the alloy becomes the main factor of consideration,the atomic ratio of Ni and Si is designed as 2 in the composition range of 90<at.%Cu<95.63;the atomic ratio of Ni and Si is designed as 2.5 in the range of 95.63 ? at.%Cu<97.5;and the atomic ratio of Ni and Si can be designed according to any value of 2,2.5 or 3 in the range of at.%Cu>97.5,and there is almost no difference in performance.If the strength of the alloy is the main cause of the composition design,the atomic ratio of Ni and Si is designed as 2,2.5,3,2.5,2,and any value of 2,2.5 or 3 in the corresponding composition ranges of 90<at.%Cu<93.93,93.93 ? at.%Cu<94.34,94.34 ? at.%Cu<95.63,95.63 ? at.%Cu<96.12,96.12 ? at.%Cu<97.5,and at.%Cu?97.5,respectively.