The effect of thermomechanical treatments on the microstructures and properties of Cu–2.1Ni–0.5Si–0.2Zr alloy was investigated. The hot‐rolled plates were solution treated at 920 °C for 1.5 h, quenched into water, cold rolled by 70 % reduction in thickness, and then aged at 400, 450 and 500 °C for various times. The variation in tensile strength and electrical conductivity of the alloy was measured as a function of the aging time. The results show the peak strength value of 665 MPa for the alloy aged at 450 °C for 2 h. However, the electrical conductivity is observed to reach a maximum of 47 % IACS aged at 450 °C for 8 h. OM, SEM, and TEM were used for microstructural inspection of the alloy. Precipitation occurs preferentially at deformation bands in the cold‐rolled alloy. Properties behavior is discussed in the light of microstructural features.

Cu-Ni-Si alloy with a different Co content was prepared by inductive melting and hot rolling. The alloy was solution treated at 950 °C for 1.5 h and aged at 450 °C, 500 °C, and 550 °C for different times. The phase diagram calculation and transmission electron microscopy was used to investigate the effect of Co addition on the aging precipitation behavior of the Cu-Ni-Si alloy. The phase transformation kinetics equation was calculated as well. The results show that, with the increase of aging temperature, the two-phase region of Fcc + Ni₂Si in the Cu-Ni-Si ternary diagram would get wider. Some Ni_xSi_y phases would also form in the Cu-rich isothermal section. The addition of Co would replace part of Ni to form the (Ni, Co)₂Si phase, which inhibits the spinodal decomposition process of the Cu-Ni-Si alloy during the aging process. The precipitated phase of the Cu-Ni-Si alloy with a high content of the Co element is more likely to grow with the extension of aging time. The phase transformation kinetic equations of the Cu-Ni-Si alloy at 450 °C and 500 °C showed good agreement with the experimental results. Furthermore, it can be seen from the precipitation kinetic curve the addition of the Co element accelerates precipitation in the aging process.

The crystallography and morphology of precipitate particles of Cu-Cr-Zr alloys with varying Zr contents were studied by transmission electron microscopy (TEM) after solution treatments at 950 ℃ for 1 h and aging treatments at 500 ℃ for different times ranged from 0.5 h to 24 h. The microhardness and electrical conductivity of Cu-Cr-Zr alloys after various aging process were tested. The results show that the microhardness and electrical conductivity rapidly increased at first, then the microhardness decreased slowly after reaching the peak, while the conductivity continues to increase. Nano-scaled precipitates exhibit two kinds of morphology (coffee bean and ellipse shaped). With increasing Zr content, the Zr-containing precipitation sequence of Cu-Cr-Zr alloys at peak-ageing is Heusler CrCu2Zr → Cu5Zr → Cu4Zr. The Heusler CrCu2Zr phase decomposed into fine and homogeneous Cr and Cu4Zr, resulting in improved alloy properties.