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The stress relaxation resistance of a Cu–Ni–Si alloy strip after 48 h of initial loading stress of 80% σ0.2 at 125 °C was studied. The stress relaxation curve was fitted using a model. By employing EBSD, TEM, and other techniques, this study examined the microstructural characteristics of the Cu–Ni–Si alloy strip before and after stress relaxation. This study investigated the stress relaxation mechanism of the alloy and revealed that the stress relaxation rate of the Cu–Ni–Si alloy strip was 10.82% after 48 h at 125 °C. The stress relaxation process of the alloy strip was divided into two main stages. During the first stage, there was a significant rearrangement and movement of dislocations within the alloy strip, leading to a rapid decline in the remaining stress. In the second stage, the interaction among the Ni2Si phase, twins and dislocations led to a slow decrease in the remaining stress. After the stress relaxation of the alloy strip, the precipitated phase in the microstructure grew from 67 nm to 200 nm, the recrystallization microstructure increased from 57.91% to 62.42%, and the twin boundary content decreased from 22.1% to 18.5%. These observed changes in the microstructure are anticipated to further reduce the stress relaxation resistance of the alloy strip.

Under the condition of controlling the total rolling deformation to 80.0%, the effects of multi-pass rolling, the ratio of deformation between the first and second stages in two-stage rolling, and aging parameters on the microstructural evolution and property enhancement of Cu–Ni–Si alloy were investigated. The results showed that the second-stage rolling promotes the formation of high-density dislocations, significantly enhancing dislocation strengthening. Simultaneously, the high-density dislocations facilitate the precipitation of the second phase during aging, and concurrently improving the strength and electrical conductivity of the alloy. In the two-stage rolling and aging process, a ratio of first-stage to second-stage rolling deformation less than 1 yields superior comprehensive properties. Specifically, when the first-stage rolling deformation is 35.0% and the second-stage deformation is 68.8%, the alloy achieves an optimal electrical conductivity of 49.53% IACS, hardness of 272.9 HV0.1, tensile strength of 773.0 MPa, and yield strength of 723.3 MPa. This is because a rolling ratio less than 1 results in higher dislocation density; the δ-Ni2Si precipitates have a coherent relationship with the Cu matrix, the interparticle spacing of precipitates is smaller. The average grain size is refined from 1.29 μm to 1.08 μm, significantly enhancing grain boundary strengthening. Dislocation strengthening and second-phase strengthening are the primary strengthening mechanisms of the alloy, and the calculated alloy strength agrees well with the experimental values, with errors less than 3.4%. Additionally, the Avrami equation in phase transformation kinetics was utilized to study the variation law of the volume fraction of the δ-Ni2Si phase with aging time.

Copper-silver alloy rod with high mechanical properties and stable conductivity are the key materials for the preparation of microfilaments used in endoscopy and other medical fields. In this paper, the microstructure of Cu–20Ag rod was regulated by adding trace rare earth Y in order to improve the comprehensive performance of copper-silver alloy further. and studies the distribution and existence of rare earth Y as well as the influence on the performance of copper-silver alloy rod billet. The results of research show that: rare earth Y mainly exists in the branching nodes of the eutectic organization, so that the alloy in the solidification of constitutional supercooling increases, thus refining the eutectic structure, and make it uniformly distributed. After addition of 0.01 wt%Y, Cu4Y was precipitated in the eutectic structure of the rod. After adding 0.03 wt%Y, the precipitates types increased to trace intermetallic compound AgY and nanoparticles Cu4Y. The increase of the interface between eutectic structure and Cu matrix decreases the electron scattering probability. This is the main factor to lead to the decrease of electrical conductivity. The precipitation hardening of precipitated phase and the increase of interface between eutectic structure and Cu matrix are the main factors for the increase of tensile strength of bar billet. The main factor of the decrease in the conductivity of rod billet is the increase of Ag phase dissolved in eutectic structure and the interface between eutectic structure and Cu matrix.

Interface has been often neglected in exploring micro-alloying mechanisms in polycrystalline Cu–Cr–Zr alloys. In this study, interface structure modeling and first-principles calculations were carried out to explore the segregation behaviors of micro-alloying element Zr at nano-Cr particle interfaces and a series of low-Σ (Σ ≤ 11) Cu grain boundaries (GBs) in Cu–Cr–Zr alloys. The segregation effects on interface adhesion strength were also evaluated. Our results suggested that Zr can substitute the top-most Cu atoms at most nano-Cr particle interfaces (those with the Nishiyama–Wassermann orientation relation) with the maximal coverage of 1/3 ML. The segregation to other nano-Cr interfaces with the Kurdjumov–Sachs orientation relation is, however, energetically forbidden. At almost all the low-Σ GBs (except the Σ3 (111) only), Zr segregation can be consistently favored up to a full coverage (1 ML), which can improve the GB binding by ∼30%. Based on these results, the multi-fold benefits of Zr micro-alloying were discussed.

In this paper, the prepared Cu-0.25Cr alloy and Cu-0.25Cr-0.03Ti alloy strips were treated with aging at 490 °C for different holding time. The electrical conductivity and the yield strength of the alloy were tested. The morphology, size, spacing and phase structure of Cr-rich precipitates in the copper matrix were observed by TEM. The results show that the evolution rule of Cr-rich precipitates in Cu-0.25Cr alloy is as follows: supersaturated solid solution→G. P region (Cr atom-rich region)→ Cr-rich precipitates with fcc structure→Cr-rich precipitates with ordered bcc structure. The precipitates of peak aged Cu-0.25Cr alloy consist of fcc Cr-rich precipitates and ordered bcc Cr-rich precipitates. The electrical conductivity and the yield strength is 93.5%IACS and 178 MPa, respectively. The strengthening mechanism is mainly attributed to the synergistic effect of dislocation shear and dislocation bypass. Compared with Cu-0.25Cr alloy, the yield strength of Cu-0.25Cr-0.03Ti alloy at peak aging state increases by 31.5%, while the electrical conductivity remains at 82.4%IACS. The great increase in strength is mainly attributed to the refinement of bcc Cr-rich precipitates by adding trace Ti element. The addition of Ti promotes the nucleation of Cr-rich precipitates and refines the Cr-rich precipitates of bcc structure. The interaction mechanism is that there is a strong mutual attraction between Ti and Cr atoms, which promotes the formation of clusters between Ti and Cr. This research results can provide a theoretical basis for the development of copper alloy for high-performance electrical connectors in aerospace, new energy vehicles and other fields.