Electrical contacts are the key contact components for connecting and disconnecting circuits and load currents in various switching appliances and instruments. Their performance directly affects the performance and quality of switching appliances. Silver metal oxide electrical contact material is one of the most widely used electrical contact materials with excellent performance. It is widely used in various low-voltage switching appliances. This type of electrical contacts mainly include: AgCdO electrical contacts, AgSnO2 electrical contacts, AgZnO electrical contacts, etc. This type of electrical contact material is currently mainly manufactured using processes such as alloy internal oxidation and powder metallurgy.

    Since the 1930s, various countries have conducted in-depth and detailed research on AgCdO electrical contact materials. The notable feature of this material is that it is suitable for a wide range of current and voltage. It is the preferred electrical contact material for low-voltage appliances with breaking currents of 100~3000A. The material has excellent electrical and thermal conductivity, arc corrosion resistance, strong resistance to welding, and low and stable contact resistance. Therefore, it is widely used in AC contactors, relays, circuit breakers.

    Before the 1970s, the factors affecting the performance of contact materials were mainly studied. The effects of added elements on the physical and mechanical properties, metallographic structure and electrical properties of AgCdO electrical contact materials were found. Methods for improving the material processing performance, resistivity, hardness, electrical properties were found. The hardness, plasticity, metallographic structure and other properties can be controlled through appropriate addition of elements and processing technology.

    The AgCdO material manufactured by the powder metallurgy pressing and sintering process has poor uniformity, a large electrical wear rate, and abnormal losses when breaking large currents. It is generally rarely used in AC contactors. The AgCdO material produced by powder isostatic pressing and extrusion can make the CdO particles tend to form needle-like or fiber-like distribution in the silver matrix. The cross-section perpendicular to the extrusion direction is used as the working surface, which greatly improves the electrical life of the material, especially It is suitable for automatic cold heading machines to manufacture rivet-shaped AgCdO contacts or AgCdO/Cu bimetal composite electrical contacts. The latter greatly saves silver, can reduce costs, and is in line with the national resource conservation policy.

    The AgCdO electrical contact material using the internal oxidation method of the alloy has excellent electrical wear resistance and no abnormal loss when breaking large currents. At present, mainly uses the internal oxidation method to manufacture AgCdO electrical contacts.  The contact welding surface can be compounded with a pure silver layer with a thickness of about 0.2mm to facilitate soldering of the contacts.

    After the 1970s, many countries have conducted many studies on issues such as arc erosion, material migration, composite technology, and the toxicity and protection of Cd. In order to save silver, double-layer composite or multi-layer composite contacts are often used. AgCdO/Cu composite contacts, AgCdO/Ni composite contacts, AgCdO/CuNi alloy composite contacts are used in production, and the silver saving rate can reach 30 %~70%.

——The content of the article comes from the Internet