Study On The Microstructures And Properties Of Rapid Solidified CuNiSiCrZn Alloys

The traditional preparation technology of lead frame materials of Cu-Ni-Si alloys is‘Melting-Casting-Forging-Heat treatment-Rolling–Sheet’. This process is not only thehigh producing cost, heavy pollution, and the prepared Cu-Ni-Si alloys is not up to therequirements on the performance of the lead frame materials. This project aims to improvethis process by rapid solidification technology, because of fast cooling speed; rapidsolidification technology can save ‘forging-solid solution treatment’ and directly rolling.We want to improve the process by rapid solidification technology to reduce productioncosts and improve production efficiency, and also its comprehensive performance can meetthe requirements of the lead frame of Cu-Ni-Si alloys.In this paper，Cu-2.4Ni-0.46Si-0.22Cr-0.33Zn alloys which respectively produced byas-casting method and copper-mould casting method, can get optimal comprehensiveperformance after a series of heat treatments. We study the effect of different preparationmethod on the micro-structure and performance of alloys it concludes that：1) Compared with the conventional solid solution, rapid solidification technology hasimproved liquid metal cooling capacity, the nucleation rate increases, it then obtains theprimary fine grain; At the same time, solid solution is supersaturated solid solution in thematrix, the distortion of crystal lattice is increased, and due to fine grain strengthening andsolid solution strengthening，the micro-hardness is significantly improve. On the other hand,rapid cooling rate destroyed the equilibrium solidification, there are lots of latticedistortions、dislocation and vacancy retained, they decreases the conductivity of the alloys.2) Compared with the traditional solid solution and aging treatment ","the rapidsolidification and ageing treatment" makes the micro-hardness and conductivity of thealloys increased. In the process of rapid solidification, a large number of vacancies,sub-grain boundaries and other crystal defects are retained, they provide more "channel" forthe precipitation of precipitates, the strengthening phase is dispersed on the surface of thesubstrate faster and more uniformly, and fine grain strengthening effect, the micro-hardnessof the alloys increased more, the solute atoms precipitated extent make the conductivity ofalloys enhanced.3) The SEM spectrum and EDS spectrum analysis can concludes that: The dicty-strengthening phase Ni2Si is distributed in the boundary of matrix. In addition, the strengthening phase of Cr3Si also is distributed in the surface of matrix. The solute Cr isadded for strengthening phase Cr3Si precipitated in Cu-2.4Ni-0.46Si-0.22Cr-0.33Zn alloys;a small amount of residual Ni atoms makes up of Cu0.81Ni0.19in matrix. Therefore, the mainstrengthening phase in Cu-2.4Ni-0.46Si-0.22Cr-0.33Zn alloy is Ni2Si phase and Cr3Siphase, and also some residual Ni in the matrix.4) Cold deformation before ageing makes lattice defects of vacancy, dislocationincreased, they provides more "channel" for the precipitation of solute atoms, which makesstrengthening phase precipitated faster and more uniformly, it further improves themicro-hardness of the alloys; At the same time, cold deformation also can make the residualsolute atoms further precipitated in the matrix. The degree of lattice distortion is greatlyreduced, it makes the conductivity recovered quickly.5) After40%cold deformation and ageing treatment at500℃, conventional solidsolution gets to the ageing peak in3h: the micro-hardness of225.64HV, the conductivity of38%IACS; rapid solidified1#alloy reaches the ageing peak in1h: the micro-hardness of268.07HV, the conductivity of32%IACS; rapid solidified2#alloy reaches the ageing peakin2h,micro-hardness of248HV, the conductivity of33%IACS; rapid solidified3#alloyreach the ageing peak in2h.