| A series of experiments is performed for studying the effects of different contents of Co, hot-working technique, solution treatment, cold deformation or aging treatment on the hardness, electrical conductivity, tensile property softening temperature and the microstructure evolution of Cu-3.0Ni-0.75Si alloy,by using X-ray diffraction(XRD), optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectrometer (EDS).The results of the research show that the particle with high Ni, Si, Co content exist in the grain and grain boundary of Cu-3.0Ni-0.75Si-xCo alloy by hot rolling after holding lh on880℃. And the size of the particle in grain boundary is larger. The electrical conductivity of hor-rolled alloy increase rapidly at the first beginning and then decrease with the contents of Co increase.The cold rolling of60%deformation ratios is carried after950℃×1h solid solution treatment. After cold rolling the hardness increase due to working hardening effect, and the electrical conductivity decrease slightly. During single aging treatment, the electrical conductivity increase with the increase of the aging time due to the secondary phase precipitation. As a result of the pinning effect of the precipitates on the dislocations, the hardness increase with the increase of the aging time. Then the hardness decrease with the aging time continuous increasing due to overaging. The Avrami phase transformation kinetics equation were derived by use of the linearity between electrical conductivity and volume fraction of precipitates under the aging proeess.The electrical conductivity of Cu-3.0Ni-0.75Si-xCo alloy, after450℃×2h aging treatment,60%second cold rolling and two-step aging treatment, is significantly higher than a single aging process, the electrical conductivity increase rapidly at the first beginning and then level out with the increase of the two-step aging time due to solute atoms precipitate, the electrical conductivity increase rapidly at the first beginning and then decrease with the increase of the two-step aging temperature. As a result of Coarsening of the precipitated phase the hardness decrease with the increase of the two-step aging temperature.The contents of Si in copper matrix decrease due to the CoSi phase precipitation, and the electrical conductivity increase. As a result of the contents of Co continuous increasing the contents of Co in copper matrix increase, and the electrical conductivity decrease. The hardness, tensile strength and softening temperature of Cu-3.0Ni-0.75Si alloy increase with the contents of Co increase, the good properties of Cu-3.0Ni-0.75Si-0.2Co alloy can be obtained after950℃×1h solid solution treatment,60%cold rolling rate,450℃×2h aging treatment, second cold rolling and450℃×2h two-step aging treatment. The finish strip’s hardness is213HB, electric conductivity is48.7%IACS, tensile strength is816MPa, elongation is4.8%, and softening temperature is430℃. |
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