Effect of several metal elements on silver-based electrical contact materials

The effect of prime has been described in terms of meaning.

Silver-based Electrical Contact Metal Elemental Additive Function National Scientific and Technological Innovation (No.: 201BA326C) and Yunnan Science and Technology (No.: 2B3-01) Jointly-sponsored Project E-mail 0 Foreword Electrical contacts, also known as contacts or contacts, are high. Low-voltage electrical appliances play a role in making, breaking, diverting, and isolating currents. They are one of the key components of high- and low-voltage electrical appliances.

Its performance directly affects the switch electrical capacity, life and reliability. The early electrical contacts used more pure silver, but the hardness of silver is not high, the anti-weldability and wear resistance are poor, and the electrical life is low. For the purpose of improving the performance of the electrical contacts and saving silver, a series of silver-based electrical contact materials have been developed, including AgCdO, AgSnOz, AgZnO, AgNi, AgW, AgC, and the like. In these silver-based electrical contact materials, the addition of various metals or metal oxides has an important influence on the performance of the material. "21, making the material's performance gradually meet the requirements of the electrical industry for electrical contact materials. Several metal elements are introduced below. The effect on the performance of the electrical contact material.

1 non-silver metal on the electrical contacts in the silver-based electrical contact materials, and some metal elements can be used as the main component of the material, such as AgCdO, AgSn2 materials, Cd, Sn, and some are to improve performance or Improve the process of adding ingredients, with less. Now introduce the main ingredients and additives.

1.1 Main component elements AgCdO material has good resistance to electrical wear, resistance to welding and low and stable contact resistance. It was widely used in medium-power appliances in the 1970s and 1980s. The material has good performance and The role of Cd (specifically, the role of CdO) is inseparable from the role of Cd is: CdO particle dispersion strengthening can improve the mechanical properties; dispersed cadmium oxide particles can increase the viscosity of the molten material and reduce metal splash loss; Under the arc, the cadmium oxide decomposes, sublimates from the solid state to the gaseous state (decomposition temperature is about 900x.), generates violent evaporation, plays the role of blowing arc, and cleans the surface of the contact; cadmium oxide absorbs a large amount of heat when it decomposes. Conducive to the cooling and quenching of the arc; cadmium oxide has high volatility and low contact resistance (.

01.5ncm), therefore, no conductive layer is formed on the surface of the contact, so that the contact resistance is low and stable.

The cadmium oxide content of 12% 15% can maintain the best performance. Although AgCdO material has good performance, but with the increase in the number of switching operations, CdO sublimation will cause the oxide to be consumed, the formation of an AgCd alloy layer on the contact surface will reduce the material's resistance to arc erosion and resistance to welding, making CdO The advantages of the use are reduced. To improve the properties of the material, additives must be added.

Sn2 has good chemical and thermal stability, sublimation and high decomposition temperature (divided into 180 (TC and 225 °C) and other characteristics, Sn02 particles in the Ag molten pool to increase its viscosity, the molten metal is easy to produce splash, arc The erosion is small and the thermal stability of Sn2 is high. After multiple arcs, the Sn02 component can still remain on the surface of the contact, so that the viscosity of the bath is not reduced due to multiple effects of the arc, and the arc erosion can be maintained for a long time. In addition, Sn02 has brittleness and is not easily decomposed by the arc, so it has good resistance to welding and stability. However, Sn2 is a brittle reinforcing phase with high hardness and high shear modulus, resulting in strong dispersion strengthening effect. The AgSnO2 material is difficult to plastically deform.The contact resistance and temperature of the AgSnO2 material are higher than that of the AgCdO material in practical applications. This is due to the fact that the D-SnOz particles cannot be excreted by the Ag and form a metal oxide after the Ag condenses. The layer, which makes contact resistance and temperature rise, is improved by adding additives to improve wetting.

The silver zinc oxide electrical contact materials have the characteristics of strong resistance to welding, good resistance to electrical wear, small contact resistance and stability. The role of Zn in the material is mainly ZnO melting point and decomposition temperature are about 2000 °C under the action of short-circuit current and strong arc, ZnO is not easy to decompose, can maintain its strong "skeleton" role. ZnO diffusely distributed in the Ag matrix, can decompose Ag into many small "regions", making the current distributed in many small "regions" and not concentrated in a face Bu, properly reduce the r current density, thereby reducing / contact melting Welding tendency.

During the on-off process of the switch, ZnO prevents the silver in the molten state from being blown by the arc, thereby avoiding a large amount of metal scattering and flying spurs, making the material resistant to electrical wear.

1.2 The role of additives Many electrical contact materials with excellent properties, such as AgCdO, AgSn02, etc., are obtained by adding appropriate amount of additive components. A lot of experimental and operating experience tells us that different materials are used in the electrical contact materials. Additives and the use of different manufacturing methods will have a major impact on the performance of the material. The effect of different additives is now described as follows.

In cattle: If it is to play a role in the internal oxidation of AgSnO2 material in the alloy, the pure silver-tin alloy is not easy to produce silver tin oxide material by internal oxidation of the alloy. This is because the dense oxide layer on the surface of the tin hinders the oxygen atoms from entering the interior of the material. Diffusion reason. At this time, indium may be added. From the viewpoint of chemical thermodynamics, the free energy and thermal effect of indium-forming oxides are greater than that of tin. However, when the silver-tin-indium alloy is oxidized, since indium is more easily oxidized than tin, it can act as a nucleus while indium The oxides are relatively loose, so that the oxygen atoms facilitate diffusion to form a silver-tin oxide-indium oxide precipitation-strengthening material. When the indium content is less than 2wt%, the effect is not obvious, and the total amount of tin indium before the internal oxidation is not more than 12wt% In order to save rare metal indium, 3. Indium is added in an amount of 8-°. In addition, the addition of indium also changes the microstructure, so that ordered oxides are formed in the vertical direction of the switch face, limiting the arc The activity generated by the action also plays a role in mechanical fixation, so that the internal oxidation of AgSn02ln203 material has better burn resistance.

The rare-earth (RE) high-purity Ag has a natural recovery at room temperature, which reduces the strength properties and resistivity, and affects the use of silver. The RE element has solid solution strengthening and expansion lattices, pinning dislocations, and reduced dislocation energy. Refine the role of grains, make dislocations in a more stable state and increase the grain boundary area, which has a significant hindrance to dislocation climbing and grain boundary migration, unfavorable lattice recovery and recrystallization nucleation grow, Delay it to a higher temperature. In addition, the RE element shows a significant strengthening effect on precious metals, including increasing hardness, room temperature strength, high temperature instantaneous and permanent strength, creep life, and elastic modulus U4). In the alloy smelting process, rare earth elements have the effect of purifying impurities. The role of rare earth elements on the electrical contact materials is mainly to: under the premise of maintaining the excellent conductivity and thermal conductivity of the base metal, the rare earth elements have a significant strengthening effect on the matrix; refine the crystal grains and increase the recrystallization temperature, thereby improving the material Stability; increased resistance to electrical erosion and blocking resistance.

Dielectric contacts containing dilute materials have been widely used. In some applications, Ag-CdO materials have been successfully replaced. This has important implications for reducing pollution and reducing costs.

The addition of a suitable amount of germanium in the AgSnO2 electrical contact material can improve the wettability of the liquid Sn with the Sn02 particles and prevent the precipitation of SnO2 at the grain boundaries. When the Ag is solidified, Sn(I): is not ejected to the surface to form an oxide layer. Instead, they are redistributed in the matrix to form a cellular structure, so that under the action of the arc, the indicators that are beneficial to the performance of the operation will be greatly improved. In addition, the addition of niobium will result in the formation of a yellow-green structure Bi2Sn07. Sublimation, significantly improve the resistance to welding and wear resistance, improve the wear resistance of sliding contacts.

The addition of Bi in the AgCdO electrical contact material can significantly reduce the electrical erosion of the material.

The addition of Sb to the AgSnO2 material prevents the abnormal loss of the contact material.

Due to the effects of arc and Joule heat on the contact material, the surface temperature of the contact that generates the arc is the highest, from the surface to the inside, and the temperature gradually decreases from the center of the arc region outward.

In the process of frequent opening and closing, the contact is subjected to the alternating heat caused by heating and cooling. In the case of coarse crystal grains, the contact may be distorted and the abnormal loss of the crack may be caused. In general, the contact surface has a suitable oxide evaporation, which can play a role in purification and heat absorption. Sb203 has a relatively high vapor pressure at a relatively low temperature, and Sn02 has a relatively low vapor pressure at a relatively low temperature and a relatively high vapor pressure at a high temperature. Ln203 vapor pressure is also lower at high temperatures. The only component in the contact is high vapor pressure at high temperatures. Its loss is intense under the arc. Instead, it only contains oxides with low vapor pressure at high temperatures. There is no purification or endothermic effect. Sb203 is added so that the contacts contain Sn02, 103, and Sb203 at the same time, so that there is an appropriate volatilization from the formation of the arc to the extinction of the arc. Keep the contact surface clean and have a proper endothermic effect. After the addition of Sb, the contact material grain is very fine 50150fn, while the AgCdO grain is generally 150 (Vm. Therefore. The internal oxidation of the body effect residual distortion is present in the grain boundary, the development of numerous micro cracks, absorption Alternating thermal stress due to contact work avoids abnormal loss of twisting and cracking of the contacts resulting in shedding.

The role of alkali metals remains controversial. Some studies have shown that the addition of alkali metals such as K, Na, Li, etc. in the amount of 100 pprn or more in AgCdO can lead to slightly increased arc erosion of the material, and a slight decrease in the ability of closed fusion welding. The addition of U can cause grain refinement. , To improve the resistance to welding and electrical loss. U can also promote oxidation, shorten the internal oxidation time, while Ll20 has a broken arc, can improve Ag-SnCVInzO;. Breaking performance.

The impact of energy. As a result, it was found that in the Ag-SnO2-In203 material added with Li, there was no sheet-like structure that was detrimental to the contact performance, and the oxidized material dots were distributed in clusters and the SnOhln/ICV 'symbiotic' together, making the material arc selective. The erosion is weakened, Ag melted and no longer formed due to selective erosion, forming beading and gasification spurs to form honeycomb cavities, and the tiny contact points with even surface and metallic luster on the contact surface are evenly distributed, with no melting beads. Melt-like and honeycomb-like cavities.

The contact resistance and temperature rise of AgSnO2 produced by powder sintering and squeezing are relatively high. Adding additives such as WO or M03 can significantly improve the temperature rise characteristics of the contacts when they are closed, plus Mn can improve the uniformity of the oxidized structure and improve the resistance to welding. However, the amount can not be added too much. When AgSnO2 is prepared by internal oxidation of alloys, addition of Te can improve the internal oxidation of Ag-Sn alloys, increase the internal oxidation rate, and obtain uniform microstructure and fine particles. The addition of trace amounts of Mn in AgCdO material can improve the resistance to erosion and soldering, and the contact resistance is low and stable. Adding appropriate amounts of Ge2 and Ta205 to AgCdO materials can improve the resistance to welding and the arcing of the contact surfaces. Erosive 32'33".

3 Summary Non-silver metal elements (or their oxides) play an important role in silver-based contact materials and have become an indispensable component of contact materials. Silver-based contact materials have been produced in various series and applied in different fields. In each series of materials of these contact materials, there are more or less additive components, which can improve the deficiencies of contact materials. Does not affect its good performance. In the contact industry, silver-based contact products will not change too much, but the addition of trace elements will be very different in different studies. This requires us to further study and explore to find the most suitable Add ingredients.