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Vacuum interrupters are important components to ensure the safety of medium and high-voltage power transmission, and contact material is an important factor affecting the performance of vacuum interrupters. CuCr contact materials have been used in most commercial vacuum interrupters. This paper summarizes the research status of the electrical properties of CuCr contacts used in vacuum interrupters, analyses the factors influencing the electrical properties of CuCr contacts, and summarizes the relevant mechanisms, which point out the direction for improving the properties of CuCr alloys and promotes the development of subsequent research on the electrical properties of CuCr contacts. Finally, the electrical properties of CuCr contacts prepared by self-propagating metallurgy based on the Al–CuO–Cr2O3 reaction system are summarized.

Microalloying is an effective approach to improve the performance of CuCr alloys. This paper presents a new idea for the preparation of CuCrFe alloys by self-propagation reduction in-situ microalloying. It is found that the addition of Fe alloying components reduces the Gm and ΔGm of the CuCr melt, which inhibits the occurrence of the liquid phase decomposition process. When the Fe content of CuCrFe alloy is 1.5%, compared with the Cr-rich phase of CuCr alloy, the second phase undergoes significant refinement, the average particle size refined from 21.7 μm to 19.3 μm and the standard deviation reduced from 10.59 to 8.73, and the addition of Fe is beneficial to the spheroidization and refinement of the Cr-rich phase. Fe is mainly combined with Cr, and CuCrFe alloy still exists in the form of two phases. After solution + aging treatment, the average particle size of the second phase in CuCr alloy decreases from 21.8 μm to 17.9 μm, and that in CuCrFe alloy decreases from 19.6 μm to 18.6 μm. The conductivity of CuCrFe alloy increases from 10.5 MS m−1 to 15.9 MS m−1, and the hardness increases from 95.0 HB to 117.0 HB. After heat treatment, the nano-spherical are present in the Cr-rich phase of the CuCrFe alloy, while Fe is completely solid-soluble in the Cr-rich phase; the Cu-rich matrix shows a diffuse distribution of fine second phases, which play a role in strengthening the second phase in the matrix.

A homogeneous CuCr50 alloy ingot prepared in situ by thermite reduction-electromagnetic casting is a type of nonequilibrium solidification structure with a Cu matrix supersaturated with Cr. In this study, the effects of heat treatment on the microstructure of the CuCr50 alloy were studied using scanning electron microscopy (SEM), metallography microscopy and transmission electron microscopy (TEM), and the conductivity, macrohardness and tensile strength of the CuCr50 alloy were measured. The obtained results show that the optimal heat treatment conditions are solution treatment (975 °C for 1 h) and aging treatment (500 °C for 2 h), for which the hardness, conductivity, and tensile strength of the CuCr50 alloy are the best; the macrohardness is 103.33 HB, the conductivity is 18.60 MS/m, and the tensile strength is 199.72 MPa. TEM characterization showed that nanosized Cr particles were precipitated and dispersed in the Cu matrix after the aging treatment; the relationship between the precipitates and the Cu matrix was incoherent, and Cu dissolved into the Cr phase in the form of a solid solution to strengthen the second Cr phase.

The high-efficiency separation of alloy and slag is fundamental to obtain high-performance CuCr alloys by self-propagating high temperature synthesis metallurgy. In this paper, Cr2O3 can determine the basic composition of CuCr alloy through the reduction efficiency, and also participates in the slagging process, which determines the separation effect of slag and alloy. Therefore, the reduction behavior and slagging effect of Cr2O3 during the in-situ synthesis of CuCr alloy by aluminothermic reduction is investigated. The results show that the Cr content of the prepared CuCr alloy is 41.3 wt.%∼42.0 wt.% according to the theoretical stoichiometric ratio, and the Cr2O3 content in the slag is 16.2 wt.%∼17.0 wt.%. When the Cr2O3 dosage is 50% over the theoretical stoichiometric ratio, the Cr content of the prepared CuCr alloy and the Cr2O3 content in the slag increases to 47.0%∼47.6 wt.% and 28.4 wt.%∼29.2 wt.%, respectively. With the increase of Cr2O3 dosage in the ingredients, the effect of alloy-slag separation is better, the inclusion in the alloy changes from Al2O3 inclusion to Cr2O3 inclusion, and the relative density of prepared CuCr alloy increases from 90.9% to 98.5%. The overall composition is evenly distributed among the different parts of the alloy. The conductivity of CuCr alloy reaches 15.69 MS m−1, and hardness reaches 95.1 H B.

CuCr contact material, whose mass fraction of Cr is generally in the range of 25% to 50%, is one of the most desirable contact materials for medium- and high-voltage vacuum switches. The homogeneity and denseness of CuCr alloy are the keys to its application. The infiltration and powder sintering have defects, such as uneven distribution of Cr phase, and great difficulties in preparing high-performance CuCr alloys with low gas content; the equipment investment in the vacuum consumable arc melting method is large and the production cost is high, while mechanical alloying, vacuum induction melting, and laser-selective melting as new technologies are still in the laboratory stage. From the perspective of surface modification treatment and multicomponent alloying, refinement of Cr phase grains can improve the properties of CuCr alloy. The new process of aluminothermic reduction-electromagnetic coupling refining-water and gas composite rapid cooling takes oxides as raw material and obtains a fully miscible CuCr alloy melt by aluminothermic reduction theoretically at 2848K, followed by secondary refining under electromagnetic field coupling and water-gas composite cooling and casting, which can obtain alloy ingots of 50 mm in diameter and 10 mm in height. The density and hardness of CuCr alloy prepared by this process as vacuum contact material are better than the requirements of GB/T 26867-2011, so this process has the potential to become a new-generation preparation method for large-size homogeneous high-performance CuCr alloy.