Effect Of Cr And Co Microalloying On Microstructure And Machining Properties Of Cu-Ni-Si Alloy

Cu-Ni-Si series alloy is a typical representative of the second generation of lead frame materials,but the hardness,conductivity and other aspects still can not meet the market demand well.For this reason,balancing and optimizing its mechanical properties is currently the direction of many scholars'efforts.In this experiment,micro-alloying and deformation heat treatment process were used to systematically study the influence of trace Cr and Co on the microstructure and properties of Cu-Ni-Si alloy,besides the evolution of the alloy microstructure and the influencing factors of the properties under different processing techniques such as solution treatment,aging,and recrystallization are discussed respectively,The effect of cold deformation and subsequent heat treatment on Cu-Ni-Si-Cr-Co alloy was mainly analyzed,It aims to find out better process parameters and provide effective theoretical basis for further optimization of alloy process routes and parameters in the future.The main results of this study are as follows:?1?The addition of Cr or Co elements can reduce the secondary dendrite spacing of the as-cast Cu-Ni-Si alloy,and the addition of Cr can also promote the dissolution of Si atoms,but the addition of Cr will increase the dendrite segregation of the matrix and its segregation structure Contains high concentration of Cr.The addition of Cr and Co alloys can significantly reduce the grain size,from about 80?m to 40?m,which is reduced by 50%,and with the cooling process,new Ni₂Si,Co₂Si,Cr₃Si compounds will be precipitated,besides the microhardness and the conductivity can reach 139.1HV and 33.0%IACS respectively.?2?Through the study of the recrystallization behavior of the alloy with a deformation of 70%,it was found that the Cr₃Si and Co₂Si phases will hinder the movement of grain boundaries and dislocations and prolong the recrystallization process,that is,the recrystallization temperature of the Cu-2Ni-0.5Si alloy is around720?,the recrystallization temperature of the Cu-2Ni-0.5Si-0.2Cr alloy is 750°C,and that of the Cu-2Ni-0.5Si-0.2Cr-0.2Co alloy is 750?800?.In addition,the higher the temperature,the more complete the atomic diffusion,and the faster the recrystallization rate of the alloy,it needs to be kept at 700?for 9 hours to complete the recrystallization.it takes only 5 hours to heat at 750?,and only 20 minutes to complete the recrystallization at 800?.?3?The addition of traces of Cr and Co will significantly delay the solution process and increase the optimal solution temperature.Comprehensive consideration,after holding for 1h,the better solution temperature range of Cu-2Ni-0.5Si alloy is about 840?880?,Cu-2Ni-0.5Si-0.2Cr-0.2Co alloy is about 980?.In addition,the addition of Cr and Co will slow down the diffusion rate of alloy elements,and higher temperatures are required to achieve obvious aging strengthening effect,that is,after holding for 1h,the 70%deformed Cu-2Ni-0.5Si alloy reaches a peak hardness of232.9HV at 450?,while the same deformation variable Cu-2Ni-0.5Si-0.2Cr-0.2Co alloy needs to be heated to 500?to obtain the maximum hardness value of 250HV.?4?After Cu-2Ni-0.5Si-0.2Cr-0.2Co alloy undergoes 0?70%cold rolling,then heated at 450?,and kept at 0.5?11h aging treatment,it was found that pre-cold deformation would increase the number of dislocations and increase lattice distortion energy.it can provide energy and nucleation position for the new phase precipitation,thereby promoting the aging precipitation rate,improving the hardness and other properties,but does not contribute much to the conductivity Comprehensive comparison,in this experiment,the preferred combination process of the deformation heat treatment of Cu-2Ni-0.5Si-0.2Cr-0.2Co alloy is 70%cold deformation+aging450?×3h,that is,the microhardness is 269.5HV,and the conductivity 44.2%IACS.?5?In the study of the precipitation kinetics of the new phase of the aging Cu-Ni-Si-Cr-Co alloy,the relationship between the conductivity and the holding time was obtained,and calculated the 50%deformation Cu-2Ni-0.5Si,Cu-2Ni-0.5Si-0.2Cr and Cu-2Ni-0.5Si-0.2Cr-0.2Co alloy aging time at heating 450?is 133.35 min,168.44min and 211.49min,which further shows that trace amounts of Cr and Co can affect the atom diffusion rate and prolong the aging precipitation time.