Thermomechanical Treatment On Cu-Cr-Zr-Ni-Si Alloy Microstructure And Properties

A high strength, high electrical conductivity Cu-0.39Cr-0.14Zr-0.12Ni-0.027Si alloy with excellent softening resistance have been developed in this paper. The mechanical property, electrical conductivity, microstructure of phase under different thermalmechanical treatments have been investigated by means of mechanical and conductivity properties measurement, OM, SEM, TEM, HRTEM observation and select-area electron diffraction. The main conclusions have been gained and were listed as following:1. The hot slab of Cu-Cr-Zr-Ni-Si alloy prepared after homogeneous treated at920℃for5h+online hot rolling-quenching (HR-Q) process has a higher supersaturated solid solution rate and fine uniform microstructure. The hardness and the conductivity of alloy under HR-Q process are higher than those of alloy under the solution treatment at the same temperature. The high er hardness relates to the sub-structure such as dislocation cells and subgrain which are formed under the large deformation in the HR-Q process; And the increase of the conductivity stems from the loss of the solid solution during the HR-Q process.2. The appropriate temperature of HR-Q process of Cu-Cr-Zr-Ni-Si alloy is920℃. The Cu-Cr-Zr-Ni-Si alloys under solution treatment state and those after HR-Q process both show a strong age hardening reaction when aged at450℃. The alloy under solution treatment+cold-rolled process has a higher aging hardness peak while the corresponding conductivity is about6%IACS lower. Aging at the same temperature shows substantially the same amount of precipitation, although there is a slight difference in solution rate between the two process.3. Cold deformation has significant hardening effect on Cu-Cr-Zr-Ni-Si alloys. This influence on alloys under the solution treatment state is more apparent than alloys under HR-Q process. However, the cold deformation increases the rate of distortion and defects in crystal lattice, leading to the decline in the conductivity of the alloy. After the secondary cold deformation, the conductivity of the Cu-Cr-Zr-Ni-Si alloy decreases linearly as the amount of deformation increases.4. The precipitated phase of Cu-Cr-Zr-Ni-Si alloy of peak-aged state is nano-Cr particle with a bcc structure and coherent with the matrix. The crystal orientation relationship between the precipitates and copper matrix were determined as:[110]Cu//[001]Cr,(111)Cu//(110)Cr. The precipitated phase of Cu-Cr-Zr-Ni-Si alloy of Overageing state is also Cr particle which has a larger size of20nm. It maintains the N-W orientation relationship with the matrix. The precipitated phase in the early stage of the secondary aging is Cr phase whose size is less than5nm, the precipitation has a fcc structure and has a cubic-cubic orientation relationship with the matrix.5. After HR-Q+80%cold rolling+Peak aging+60%cold rolling+Two-step aging at450℃, a Cu-Cr-Zr-Ni-Si alloy with a relatively high hardness(192HV) and modestly high conductivity(75.1%IACS) is obtained; After HR-Q+80%cold rolling+Overageing+60%cold rolling+Two-step aging at450℃, a Cu-Cr-Zr-Ni-Si alloy with a relatively high conductivity(85.3%IACS) and lower hardness(144HV) is obtained. The two kinds of Cu-Cr-Zr-Ni-Si alloys have very stable properties and excellent softening resistance performance. After annealed at450℃for4h, the decline in hardness were only7.6%,12.4%, respectively.