A method for preparing a low temperature coefficient silver-doped tin indium oxide contact material

Abstract

A preparation method of a low-temperature-rise silver / tin-doped indium oxide contact material, comprising the following steps: (1) smelting; (2) ingot casting; (3) surface treatment; (4) sintering; (5) extrusion forming; (6) welding; (7) hot rolling; (8) cold rolling; (9) annealing; (10) internal oxidation: oxygen is introduced, the oxygen pressure is controlled to be 0.7-0.9 MPa, then the temperature is raised to 720-780 DEG C, and the temperature is kept for 25-35 hours, and the silver / tin-doped indium oxide composite sheet is obtained. The silver block, tin block and indium block are directly used as raw materials, the pre-alloyed powder or oxide powder with a higher price is replaced, the material cost is reduced from the source, through high-temperature smelting and controllable internal oxidation, the complete alloying and uniform solidification of silver, tin and indium are realized, the uniform dispersion distribution of the oxide in the silver matrix is realized, the micro defect aggregation caused by uneven powder mixing in the powder metallurgy method is effectively avoided, and the consistency, stability and reliability of the material structure are improved.

Description

Technical Field

[0001] This invention belongs to the field of electrical materials technology, specifically relating to a method for preparing silver oxide-tin oxide-indium oxide contact materials for electrical contact materials used in switching devices. Background Technology

[0002] Electrical contact materials are the core components of switching devices, enabling circuit switching and continuous conductivity. During the switching process, if the electrical conditions exceed the material's arc-initiating limit, a high-temperature arc will be generated, leading to melting, evaporation, splashing, and material transfer at the contact surface. This is the main cause of electrical contact failure. To meet reliable service requirements, electrical contact materials should possess comprehensive properties such as high conductivity, good chemical corrosion resistance and oxidation resistance, excellent plasticity and machinability, low and stable contact temperature rise, strong resistance to welding, and resistance to arc erosion. Silver oxide-indium oxide (AgSnO2In2O3) electrical contact materials are widely used in contactors, relays, and low-voltage switches due to their good thermal stability, strong resistance to arc erosion, and excellent resistance to welding.

[0003] Currently, the preparation of silver oxide, tin oxide, and indium oxide (AgSnO2In2O3) electrical contact materials in industry often employs powder metallurgy or smelting-internal oxidation methods.

[0004] Powder metallurgy involves mixing silver powder with tin oxide and indium oxide powder in a mixing tank using a powder mixer to ensure uniform dispersion of oxide particles within a silver matrix. The uniformly mixed powder is then loaded into a mold and isostatically pressed under high pressure to create a blank with a predetermined shape and density. The blank is then sintered at high temperature in a protective atmosphere. During sintering, silver particles diffuse and bond to form a continuous metal matrix, while oxide particles are uniformly distributed within the silver matrix. Sintering temperature, time, and atmosphere are key control parameters that directly affect the material's density and microstructure. Subsequent processes such as punching and finishing then shape the material into contacts of specified dimensions.

[0005] The smelting-internal oxidation method involves melting silver, tin, and indium ingots in a furnace to form a homogeneous silver-tin-indium (Ag-Sn-In) liquid alloy, which is then cast into an alloy ingot. The silver-tin-indium alloy undergoes high-temperature oxidation under specific oxygen pressure conditions. During this process, the tin and indium elements diffuse from the interior to the surface, reacting with oxygen in the atmosphere to generate fine SnO2 and In2O3 particles in situ, which are dispersed within the silver matrix. After oxidation, the material can be rolled and heat-treated as needed to further control the alloy's microstructure and properties, and processed into the desired contact shape.

[0006] The preparation of silver-tin-indium oxide (AgSnO2In2O3) electrical contact materials using powder metallurgy requires the purchase of high-purity silver powder, tin oxide powder, and indium oxide powder. This results in high raw material costs, and uneven mixing of the silver, tin oxide, and indium oxide powders is prone to occur during the mixing process. Uneven mixing can lead to the aggregation of defects in the microstructure of the material, affecting its contact performance. Furthermore, substandard semi-finished products from intermediate processes cannot be recycled, directly increasing the production cost of silver-tin-indium oxide materials. The smelting-internal oxidation method requires high precision in oxidation process control; both insufficient and excessive oxidation can negatively impact its electrical properties. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing low-temperature silver oxide-indium oxide contact material with low raw material cost, and the resulting silver oxide-indium oxide contact material has good microstructure uniformity.

[0008] The technical solution adopted by the present invention to solve its technical problem is as follows:

[0009] A method for preparing a low-temperature silver-indium oxide contact material includes the following steps:

[0010] (1) Smelting:

[0011] Place silver, tin and indium ingots in a melting furnace, control the furnace temperature at 1250–1300℃, and hold for 25–30 minutes (to ensure that the alloy is completely melted and homogenized) to obtain silver-tin-indium alloy melt.

[0012] Studies have shown that by strictly controlling the furnace temperature and holding time, and through high-temperature melting and full alloying, the uniformity of the microstructure of silver-tin-indium alloys can be guaranteed.

[0013] If the furnace temperature is too low, the following adverse effects will occur:

[0014] Incomplete melting: Uneven temperature inside the furnace. Low temperature zones may cause high melting point components (silver) to fail to melt completely, resulting in unmelted solid silver particles inside the furnace.

[0015] Poor fluidity: Too low a temperature will cause the alloy melt to have excessive viscosity and poor fluidity. This is not conducive to the self-homogenization of the melt in the furnace, and in the subsequent casting process, it will lead to defects such as cold shuts or incomplete casting due to insufficient filling capacity.

[0016] Compositional segregation: Because the melt does not reach a state of sufficient convection, the denser silver may settle at the bottom of the furnace, resulting in inconsistent composition between the upper and lower parts of the melt, i.e., severe compositional segregation, which leads to uneven performance of different parts of the final product.

[0017] Adverse effects of excessively high furnace temperature:

[0018] At high temperatures, the solubility of gases in the melt increases. Upon cooling, the gases precipitate out and easily form pores in the ingot.

[0019] Energy waste and equipment wear and tear: Excessive temperature increases energy consumption and accelerates the aging and damage of refractory materials and heating elements in smelting furnaces.

[0020] Adverse effects of insufficient heat preservation time:

[0021] Inhomogeneous alloying: The main purpose of heat preservation is to achieve composition homogenization through atomic diffusion. If the heat preservation time is too short, the diffusion process is not yet complete, resulting in compositional fluctuations in microscopic regions of the melt. In the solidified structure after casting, dendritic segregation (intragranular segregation) is prone to occur, meaning that the chemical composition within a single grain is not uniform, leading to unstable physical and chemical properties of the alloy. If the melt is removed from the furnace immediately after heating, a temperature gradient may exist within the melt. In the lower temperature regions, the alloy may crystallize prematurely, affecting casting quality.

[0022] Adverse effects of prolonged heat preservation time:

[0023] Increased gas and inclusion content: As the holding time increases, the melt has more opportunities to absorb gas, and at the same time, oxide inclusions may continue to accumulate or form in the melt, reducing the purity of the alloy liquid.

[0024] Increased energy consumption and reduced production efficiency: Unnecessarily extending the holding time wastes energy and reduces the turnover rate of the smelting furnace, thereby affecting overall production efficiency.

[0025] (2) Casting:

[0026] The silver-tin-indium alloy melt obtained in step (1) is cast into silver-tin-indium alloy ingots;

[0027] (3) Surface treatment: The silver-tin-indium alloy ingot cast in step (2) is subjected to surface treatment to remove inclusions, cracks, pores and other defects on the outer surface.

[0028] (4) Sintering: The silver-tin-indium alloy ingot after surface treatment in step (3) is sintered;

[0029] (5) Extrusion molding: The silver-tin-indium alloy ingot sintered in step (4) is extruded into silver-tin-indium sheet;

[0030] (6) Welding:

[0031] The silver-tin-indium plate extruded in step (5) is welded to a pure silver plate of the same specifications on both sides to obtain a silver / silver-tin-indium composite plate.

[0032] (7) Hot rolling: The silver / silver-tin-indium composite plate obtained in step (6) is hot rolled;

[0033] Hot rolling is performed in one step. For silver / silver-tin-indium composite plates with welded perimeters, a reduction of more than 50% during a single hot rolling process will ensure that the composite interface strength between the silver plate and the silver-tin-indium plate reaches the specified bonding strength.

[0034] (8) Cold rolling:

[0035] The hot-rolled silver / silver-tin-indium composite plate is cold-rolled (the dimensions are controlled according to the stamping drawings) to obtain the cold-rolled silver / silver-tin-indium composite sheet.

[0036] (9) Annealing: Anneal the cold-rolled silver / silver-tin-indium composite sheet;

[0037] (10) Internal oxidation:

[0038] The silver / silver tin indium composite sheet processed in step (9) is placed into a container, oxygen is introduced into the container, and the oxygen pressure is controlled at 0.7–0.9 MPa. Then the temperature is raised to 720–780 ℃ (more preferably 760–780 ℃) and kept at the temperature for 25–35 hours to obtain the silver / silver tin indium oxide composite sheet.

[0039] This internal oxidation step allows tin and indium to be fully oxidized within the silver matrix, forming dispersed oxides. The key process conditions for internal oxidation significantly improve the consistency of the material's microstructure and the stability of its properties. The internal oxidation temperature directly affects the final hardness of the material. To obtain ideal microstructure and properties, a higher oxidation temperature should be used within the limits of equipment and process specifications.

[0040] The final hardness of silver oxide, tin oxide, and indium oxide mainly comes from the nanoscale oxide particles of tin oxide and indium oxide formed after internal oxidation. These particles are dispersed in the silver matrix, hindering dislocation movement and thus increasing hardness.

[0041] At lower internal oxidation temperatures (below 720℃), the atomic diffusion rate is slow, leading to incomplete internal oxidation or a small number of unevenly distributed oxide particles. In this case, the dispersion strengthening effect is weak, severely impacting the electrical properties of silver-tin-indium oxide materials, and the material hardness is also low.

[0042] Increased internal oxidation temperature (720–780℃): As the temperature increases, the oxidation reaction is complete, generating a large number of fine oxide particles. The precipitation strengthening effect is significant, and the electrical properties of silver oxide, tin oxide, and indium oxide materials can meet the design requirements. The material hardness increases accordingly.

[0043] A relatively high internal oxidation temperature (close to 780℃) ensures that alloying elements are fully and uniformly oxidized, eliminating unoxidized solid solution regions and resulting in a stable and homogeneous microstructure. However, if the temperature is too high (significantly exceeding 780℃), although the oxidation reaction accelerates, the oxide particles will coarsen, and the interparticle spacing will increase. According to the dispersion strengthening theory, the hindering effect of coarse particles on dislocations decreases, leading to a decrease in material hardness (over-aging softening).

[0044] Oxygen pressure too low:

[0045] The low partial pressure of oxygen reduces its solubility in silver, resulting in insufficient diffusion driving force. This prevents the sufficient oxidation of tin and indium in deeper regions, creating oxide-depleted zones and causing inconsistencies in the material's internal and external properties. For thicker sheets, a dense oxide layer may preferentially form on the surface, hindering oxygen diffusion and leading to insufficient oxidation in the core.

[0046] Oxygen pressure too high:

[0047] High-temperature, high-pressure oxygen environments are extremely dangerous, requiring equipment with high pressure resistance. Leaks or contact with grease can easily cause fires or explosions. It may also lead to excessive surface oxidation: a thick oxide scale or grain boundary oxidation may form on the silver sheet surface, affecting surface quality and subsequent processing (such as welding performance). Increased energy consumption: high pressure resistance requirements for equipment increase manufacturing and operating costs.

[0048] Temperature too low:

[0049] Incomplete oxidation: As mentioned earlier, there is a large amount of residual tin and indium solid solution and insufficient oxides. The grains are fine but not uniform, resulting in large fluctuations in the electrical and mechanical properties of the material.

[0050] Too high temperature:

[0051] Oxide coarsening: Nanoscale oxide particles grow to submicron or even micron size, significantly reducing dispersion strengthening and softening the material. Silver grains grow rapidly at high temperatures; according to the Hall-Petch relation, coarse grains lead to decreased material strength. High temperatures place high demands on heating elements and furnace materials, shortening equipment lifespan.

[0052] (11) Cleaning and drying:

[0053] Cleaning and drying are existing technologies, and the specific operations are as follows:

[0054] Soak the silver / silver tin oxide indium oxide composite sheet in a 10–15% sulfuric acid aqueous solution for 8–10 minutes. Rinse 2–3 times with water. Place the silver / silver tin oxide indium oxide composite sheet in a planetary tumble polisher and tumble polish it at low speed with tap water for 10 minutes. Dry it in a heated spin dryer for 10 minutes. Place the silver / silver tin oxide indium oxide composite sheet in a stainless steel basin and dry it in an oven at 300±20℃ for 1 hour under air atmosphere. The desired silver tin oxide indium oxide contact raw material is then obtained.

[0055] Furthermore, in step (1), the mass percentages of silver ingots, tin ingots and indium ingots are 87-89%, 7-9%, and 3-5%, respectively (more preferably 88%, 8%, and 4%).

[0056] Furthermore, in step (1), a medium-frequency induction melting furnace is used for melting.

[0057] Furthermore, in step (1), during the smelting process, the cooling water pressure of the induction coil is ≥0.2 MPa; the cooling water pressure of the power supply and capacitor compartment is ≥0.1 MPa; and the working power of the medium-frequency induction smelting furnace is ≤55 kW.

[0058] Furthermore, in step (2), a mold (preferably Φ108×260 mm) is used for casting. Before casting, the mold is polished, preheated to 200–250°C, and then uniformly coated with machine oil as a lubricant. During casting, the molten silver-tin-indium alloy is poured into the gate, using a speed control method that starts fast and then slows down to ensure that casting is completed within 45 seconds to 1 minute.

[0059] Furthermore, in step (3), turning is preferred. For locally deep defects, the method of first digging deeper and then turning the arc transition on both sides is used to eliminate them.

[0060] Furthermore, in step (3), the diameter of the alloy ingot should be controlled between 80 mm and 95 mm.

[0061] Here, since the extrusion furnace diameter is 100mm, the alloy ingot diameter should be controlled between 80mm and 95mm. First, ensure smooth loading (avoid jamming): If the ingot diameter is too close to (or even exceeds) the furnace diameter, due to thermal expansion or the ingot's own curvature, it is prone to getting stuck in the furnace after heating, unable to move forward, or requiring enormous thrust to move, which is impractical in actual production. The reserved gap ensures smooth feeding. Second, allow reasonable upsetting deformation: In the initial stage of extrusion, the ingot will upset inside the furnace under the thrust of the extrusion shaft, i.e., its diameter increases until it fills the entire furnace. The advantage of moderate upsetting: This process can break up the oxide scale and segregation layer on the ingot surface, exposing fresh metal that adheres tightly to the inner wall of the extrusion cylinder. This is beneficial for the subsequent formation of a stable extrusion lubricating film, improving the surface quality of the extruded material. Third, form an effective thermal barrier and lubrication conditions: The air (or protective atmosphere, lubricant) present in the gap has a certain insulating effect, helping to control the temperature rise rate of the ingot surface and preventing surface overheating. During the extrusion process, the lubricant flows with the billet and forms a lubricating film between the billet and the extrusion cylinder, which greatly reduces friction.

[0062] If the billet diameter is too large, leaving only a very small gap, the following problems will mainly occur:

[0063] Feeding difficulties and surface scratches: The friction between the billet and the furnace wall is extremely high, making feeding difficult. Even if it is forced in, the oxide scale, burrs, or hard particles on the surface of the billet will severely scratch the inner wall of the extrusion cylinder, which will damage the expensive extruder in the long run.

[0064] Overheating and uncontrolled temperature rise in the extrusion cylinder: Due to excessively small gaps and rapid heat conduction, the temperature of the extrusion cylinder will rise rapidly. While the billet is waiting to be extruded, its surface may overheat due to excessive heat absorption, leading to a sharp deterioration in surface quality (cracks or craters appearing).

[0065] Lubrication failure and abnormal increase in extrusion pressure: The lubricant cannot be evenly distributed in the gap, which leads to "dry friction" at the beginning of extrusion. The required extrusion pressure will increase sharply, which not only increases energy consumption, but may also cause periodic cracks on the surface of the extruded material due to local adhesion (adhesion-slip phenomenon).

[0066] Surface defects cannot be eliminated: If the upsetting deformation is too small, the original casting defects of the billet (such as microcracks, porosity, inclusions) cannot be improved through the upsetting process, and may instead be directly retained on the surface of the extruded material.

[0067] If the billet diameter is too small, although feeding is very easy, it is prone to folding and compression tailing: During extrusion, the billet is first thickened under pressure, attempting to fill the large-diameter extrusion cylinder. The metal flows outwards and then forwards through the die orifice. This intense radial flow causes oxide scale, gas, and impurities from the billet surface to be drawn into the center or front of the billet, forming subcutaneous folds or internal lamellar cracks. In the later stages of extrusion, due to the turbulent metal flow along the cylinder wall, a funnel-shaped defect called "extrusion compression tailing" (central shrinkage tail or annular shrinkage tail) is easily formed at the tail of the extruded product, leading to the scrapping of the entire product.

[0068] Furthermore, in step (4), sintering is carried out using a muffle furnace. The power of the muffle furnace is preferably 60 kW.

[0069] Furthermore, in step (4), the furnace temperature is initially set to 400-500℃ before sintering.

[0070] Furthermore, in step (4), the sintering temperature is 700–800°C and the sintering time is 1–2 hours (more preferably 1.5 hours).

[0071] Furthermore, in step (4), an ammonia decomposition atmosphere is used for protection throughout the sintering process.

[0072] Furthermore, in step (5), a 1250-ton extruder is used to extrude the sintered alloy ingot.

[0073] Furthermore, in step (5), the extrusion molding temperature is 450-500℃.

[0074] Furthermore, in step (5), the mold specifications are 5 mm × 72 mm.

[0075] Furthermore, in step (5), the extrusion speed is controlled to be 2-3 mm / s.

[0076] Furthermore, in step (6), welding is performed by composite peripheral argon arc welding.

[0077] Further, in step (7), the silver / silver-tin-indium composite plate obtained in step (6) is placed in a muffle furnace, heated to 800–850°C and held for 2–2.5 hours.

[0078] Furthermore, in step (7), a 15 kW muffle furnace is used for hot rolling.

[0079] Furthermore, in step (7), the reduction amount during the first hot rolling must be greater than 50% to ensure the bonding strength of the composite interface.

[0080] Furthermore, in step (9), the cold-rolled silver / silver-tin-indium composite sheet is placed in a nitrogen atmosphere at 600–650°C for 1.5–2 hours and then cooled to below 100°C by air cooling.

[0081] Furthermore, in step (9), the annealing is performed using a muffle furnace, more preferably a 15 kW muffle furnace.

[0082] Furthermore, in step (10), the internal oxidation is carried out in an oxidation furnace.

[0083] This invention employs a casting-internal oxidation method, focusing on the synergistic optimization of oxidation process conditions. Specifically, it systematically matches and controls three key parameters: oxidation time, oxidation temperature, and oxygen pressure, thereby improving the stability and consistency of material properties. Compared to traditional powder metallurgy methods for preparing silver-tin-indium oxide (AgSnO2In2O3) materials, this invention offers the following significant advantages:

[0084] 1. Significantly reduced raw material costs: Silver, tin, and indium blocks are used directly as raw materials to replace more expensive pre-alloyed powders or oxide powders, thereby reducing material costs at the source.

[0085] 2. Better microstructure uniformity: Through high-temperature melting and controlled internal oxidation, complete alloying and uniform solidification of silver, tin and indium are achieved, and the oxides are uniformly dispersed in the silver matrix. This effectively avoids the aggregation of micro-defects caused by uneven powder mixing in powder metallurgy, thereby improving the consistency, stability and reliability of the material structure.

[0086] 3. High process repeatability and improved material utilization: In the casting-internal oxidation process, substandard semi-finished products generated due to process reasons can be remelted in the furnace. This process not only maintains the purity of the silver matrix, but also realizes the recycling of silver materials, ensuring the purity of raw materials and reducing material loss, thereby effectively controlling the overall production cost.

[0087] The core technological innovations of this invention can be summarized in the following three aspects:

[0088] 1. Optimization of internal oxidation process parameters: Key internal oxidation process conditions were established and solidified: oxygen pressure 0.7–0.9 MPa, oxidation temperature 720–780 ℃, and oxidation time 25–35 hours. This process significantly improved the consistency of the material's microstructure and the stability of its properties.

[0089] 2. The casting process achieves dual optimization of cost and microstructure: the furnace temperature is controlled at 1250–1300℃ during the melting stage, and held for 25–30 minutes. This process not only reduces raw material costs, but also ensures the uniformity of the microstructure of the silver-tin-indium alloy through high-temperature melting and full alloying.

[0090] 3. Recyclable preparation and cost control: Based on the process characteristics of the internal oxidation method, unqualified semi-finished products generated during the production process can be remelted multiple times, realizing the recycling of silver materials. While ensuring the purity of raw materials, material loss is reduced, and production costs are effectively controlled. Attached Figure Description

[0091] Figure 1 Metallographic image (50X) of the silver oxide-tin oxide-indium oxide material prepared in Example 1 of this invention; 50X indicates a magnification of 50 times, the same applies below;

[0092] Figure 2 Metallographic image (50X) of the silver oxide-tin oxide-indium oxide material prepared in Example 2 of the present invention;

[0093] Figure 3 Metallographic image (50X) of the silver oxide-tin oxide-indium oxide material prepared in Example 3 of the present invention;

[0094] Figure 4 Metallographic image (50X) of the silver oxide-tin oxide-indium oxide material prepared in Comparative Example 1 of the present invention.

[0095] Figure 5 Metallographic image (50X) of the silver oxide-tin oxide-indium oxide material prepared in Comparative Example 2 of the present invention.

[0096] Figure 6 Metallographic image (50X) of the silver oxide-tin oxide-indium oxide material prepared in Comparative Example 3 of the present invention.

[0097] Figure 7 The image shows a metallographic image (50X) of the silver oxide-tin oxide-indium oxide material prepared in Comparative Example 4 of this invention. Detailed Implementation

[0098] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0099] The performance test data results obtained in the tables of each embodiment in this specification are based on the national standards GB / T13397-2008 and GB / T 14048.4-2020.

[0100] Example 1

[0101] The preparation method of the low-temperature silver-indium oxide contact material in this embodiment includes the following steps:

[0102] (1) Smelting:

[0103] Silver ingots, tin ingots and indium ingots are placed in a medium-frequency induction melting furnace, the furnace temperature is controlled at 1250℃, and the temperature is held for 30 minutes (to ensure that the alloy is completely melted and homogenized) to obtain silver-tin-indium alloy melt.

[0104] In step (1), the mass percentages of silver ingots, tin ingots, and indium ingots are 88%, 8%, and 4%, respectively.

[0105] In step (1), during the smelting process, the cooling water pressure of the induction coil is 0.2 MPa; the cooling water pressure of the power supply and capacitor compartment is 0.1 MPa; and the working power of the medium frequency induction smelting furnace is 55 kW.

[0106] (2) Casting:

[0107] The silver-tin-indium alloy melt obtained in step (1) is cast into silver-tin-indium alloy ingots;

[0108] In step (2), a mold (preferably Φ108×260 mm) is used for casting. Before casting, the mold is polished, preheated to 200°C, and then uniformly coated with machine oil as a lubricant. During casting, the molten silver-tin-indium alloy is poured into the gate, and a speed control method of fast at first and then slow is adopted to ensure that the casting is completed within 1 minute.

[0109] (3) Surface treatment: The silver-tin-indium alloy ingot cast in step (2) is subjected to surface treatment to remove inclusions, cracks, pores and other defects from the outer surface. Turning is used. For localized deep defects, the defects are first removed by digging and then turning the edges to form arc transitions. In step (3), the diameter of the alloy ingot should be controlled between 80 mm and 95 mm.

[0110] (4) Sintering: The silver-tin-indium alloy ingots after surface treatment in step (3) are sintered in a 60 kW muffle furnace;

[0111] In step (4), the furnace temperature is initially set to 400℃ before sintering.

[0112] In step (4), the sintering temperature is 750℃ and the sintering time is 1.5 hours.

[0113] In step (4), an ammonia decomposition atmosphere is used for protection throughout the sintering process.

[0114] (5) Extrusion molding: The silver-tin-indium alloy ingot sintered in step (4) is extruded into silver-tin-indium sheet using a 1250-ton extruder;

[0115] In step (5), the extrusion molding temperature is 450-500℃.

[0116] In step (5), the mold specifications are 5 mm × 72 mm.

[0117] In step (5), the extrusion speed is controlled to be 2 mm / s.

[0118] (6) Welding:

[0119] The silver / silver-tin-indium composite plate is obtained by double-sided welding of the silver-tin-indium plate extruded in step (5) and the pure silver plate of the same specification through composite peripheral argon arc welding.

[0120] (7) Hot rolling:

[0121] The welded silver / silver-tin-indium composite plate obtained in step (6) is placed in a 15 kW muffle furnace, heated to 800–850℃ and held for 2–2.5 hours for hot rolling.

[0122] During the first hot rolling, the reduction must be greater than 50% to ensure the bonding strength of the composite interface.

[0123] (8) Cold rolling:

[0124] The hot-rolled silver / silver-tin-indium composite plate is cold-rolled to obtain a cold-rolled silver / silver-tin-indium composite sheet.

[0125] (9) Annealing:

[0126] The cold-rolled silver / silver-tin-indium composite sheet was placed in a 15 kW muffle furnace and annealed at 600–650°C in a nitrogen atmosphere for 1.5–2 hours, and then cooled to below 100°C by air cooling.

[0127] (10) Internal oxidation:

[0128] The silver / silver tin indium composite sheet processed in step (9) is placed into an oxidation furnace, oxygen is introduced into the oxidation furnace, the oxygen pressure is controlled at 0.7 MPa, and then the temperature is raised to 720℃ and held for 35 hours to obtain the silver / silver tin indium oxide composite sheet.

[0129] (11) Cleaning and drying:

[0130] Cleaning and drying are existing technologies, and the specific operations are as follows:

[0131] Soak the silver / silver tin oxide indium oxide composite sheet in a 15% sulfuric acid solution for 8 minutes. Rinse three times with water. Place the silver / silver tin oxide indium oxide composite sheet in a planetary tumble polisher and tumble polish it at low speed with tap water for 10 minutes. Dry it in a heated spin dryer for 10 minutes. Place the silver / silver tin oxide indium oxide composite sheet in a stainless steel basin, adjust the temperature of the furnace to 300±20 ℃, and dry it for 1 hour in an air atmosphere. The desired silver tin oxide indium oxide contact raw material is then obtained.

[0132] Figure 1 The image shows a metallographic image (50X) of the silver-tin-indium oxide material prepared in Example 1 of this invention; 50X indicates a magnification of 50 times. The physical properties of the silver-tin-indium oxide obtained in Example 1 are shown in Table 1, and the temperature rise and electrical life test data of the 32A relay prepared from the obtained material are shown in Table 2.

[0133] Table 1 Physical property parameters of silver oxide, tin oxide, and indium oxide obtained in Example 1

[0134]

[0135] Table 2. Temperature rise and electrical life test data of the 32A relay prepared from the material obtained in Example 1.

[0136]

[0137] Depend on Figure 1 As shown in Tables 1 and 2 above, the silver-tin-indium oxide material prepared in this embodiment exhibits a uniform and dense microstructure with no obvious defects, as revealed by metallographic analysis. Tests indicate that the material's physical and electrical properties meet national standards.

[0138] Example 2

[0139] In this embodiment, except for the following conditions, all other operations and parameters are the same as in Embodiment 1:

[0140] Step (1) Melting step: control the furnace temperature at 1280℃ and hold for 28 minutes; Step (10) Internal oxidation: control the oxygen pressure at 0.8 MPa, then raise the temperature to 760℃ and hold for 30 hours.

[0141] Figure 2 The image shows a metallographic image (50X) of the silver-tin-indium oxide material prepared in Example 2 of this invention; 50X indicates a magnification of 50 times. The physical properties of the silver-tin-indium oxide obtained in Example 2 are shown in Table 3, and the temperature rise and electrical life test data of the 32A relay prepared from the obtained material are shown in Table 4.

[0142] Table 3 Physical property parameters of silver oxide, tin oxide, and indium oxide obtained in Example 2

[0143]

[0144] Table 4. Temperature rise and electrical life test data of the 32A relay prepared from the material obtained in Example 2.

[0145]

[0146] Depend on Figure 2 As shown in Tables 3 and 4 above, the silver-tin-indium oxide material prepared in this embodiment exhibits a uniform and dense microstructure with no obvious defects, as revealed by metallographic analysis. Tests indicate that the material's physical and electrical properties meet national standards.

[0147] Example 3

[0148] In this embodiment, except for the following conditions, all other operations and parameters are the same as in Embodiment 1:

[0149] Step (1) Melting step: control the furnace temperature at 1300℃ and hold for 25 minutes; Step (10) Internal oxidation: control the oxygen pressure at 0.9 MPa, then raise the temperature to 780℃ and hold for 25 hours.

[0150] Figure 3 The image shows a metallographic image (50X) of the silver-tin-indium oxide material prepared in Example 3 of this invention; 50X indicates a magnification of 50 times. The physical properties of the silver-tin-indium oxide obtained in Example 3 are shown in Table 5, and the temperature rise and electrical life test data of the 32A relay prepared from the obtained material are shown in Table 6.

[0151] Table 5 Physical property parameters of silver oxide, tin oxide, and indium oxide obtained in Example 3

[0152]

[0153] Table 6. Temperature rise and electrical life test data of the 32A relay prepared from the material obtained in Example 3.

[0154]

[0155] Depend on Figure 3 As shown in Tables 5 and 6 above, the silver-tin-indium oxide material prepared in this embodiment exhibits a uniform and dense microstructure with no obvious defects, as revealed by metallographic analysis. Tests indicate that the material's physical and electrical properties meet national standards.

[0156] Comparative Example 1

[0157] In this comparative example, except for the following conditions, all other operations and parameters are the same as in Example 1:

[0158] In step (10), internal oxidation is performed, and the oxygen pressure is controlled at 0.5 MPa.

[0159] Figure 4 The metallographic image (50X) of the silver-tin-indium oxide material prepared in Comparative Example 1 is shown below; 50X indicates a magnification of 50 times. The physical properties of the silver-tin-indium oxide obtained in Comparative Example 1 are shown in Table 7, and the temperature rise and electrical life test data of the 32A relay prepared from the obtained material are shown in Table 8.

[0160] Table 7 Physical property parameters of silver oxide, tin oxide, and indium oxide obtained in Comparative Example 1

[0161]

[0162] Table 8. Temperature rise and electrical life test data of the 32A relay prepared from the material obtained in Comparative Example 1

[0163]

[0164] Depend on Figure 4 As shown in Tables 7 and 8 above, metallographic analysis of the silver-tin-indium oxide material prepared in this comparative example reveals unoxidized alloy portions and a small number of oxide-deficient regions in its microstructure, indicating insufficient internal oxidation. Tests show that the physical and electrical properties of the material are inferior to those of Examples 1, 2, and 3 of this invention.

[0165] Comparative Example 2

[0166] In this comparative example, except for the following conditions, all other operations and parameters are the same as in Example 1:

[0167] In step (10), internal oxidation is performed, and the oxygen pressure is controlled at 1.1 MPa.

[0168] Figure 5 The image shown is a metallographic image (50X) of the silver-tin-indium oxide material prepared in Comparative Example 2 of this invention; 50X indicates a magnification of 50 times. The physical properties of the silver-tin-indium oxide obtained in Comparative Example 2 are shown in Table 9, and the temperature rise and electrical life test data of the 32A relay prepared from the obtained material are shown in Table 10.

[0169] Table 9 Physical property parameters of silver oxide, tin oxide, and indium oxide obtained in Comparative Example 2

[0170]

[0171] Table 10 Temperature rise and electrical life test data of the 32A relay prepared from the material obtained in Comparative Example 2

[0172]

[0173] Depend on Figure 5 As shown in Tables 9 and 10 above, the metallographic analysis of the silver-tin-indium oxide material prepared in this comparative example reveals a peroxidized region in the central part of its microstructure, along with a small number of pores. Tests indicate that the physical and electrical properties of this material are inferior to those of Examples 1, 2, and 3 of this invention.

[0174] Comparative Example 3

[0175] In this comparative example, except for the following conditions, all other operations and parameters are the same as in Example 1:

[0176] Oxidation in step (10) involves heating to 680 °C.

[0177] Figure 6The image shown is a metallographic image (50X) of the silver-tin-indium oxide material prepared in Comparative Example 3 of this invention; 50X indicates a magnification of 50 times. The physical properties of the silver-tin-indium oxide obtained in Comparative Example 3 are shown in Table 11, and the temperature rise and electrical life test data of the 32A relay prepared from the obtained material are shown in Table 12.

[0178] Table 11 Physical property parameters of silver oxide, tin oxide, and indium oxide obtained in Comparative Example 3

[0179]

[0180] Table 12 Temperature rise and electrical life test data of the 32A relay prepared from the material obtained in Comparative Example 3

[0181]

[0182] Depend on Figure 6 As shown in Tables 11 and 12 above, metallographic analysis of the silver-tin-indium oxide material prepared in this comparative example reveals unoxidized alloy portions and a small number of oxide-deficient regions in its microstructure, indicating insufficient internal oxidation. Tests show that the physical and electrical properties of the material are inferior to those of Examples 1, 2, and 3 of this invention.

[0183] Comparative Example 4

[0184] In this comparative example, except for the following conditions, all other operations and parameters are the same as in Example 1:

[0185] In step (10), internal oxidation is carried out and the temperature is raised to 820°C.

[0186] Figure 7 The image shown is a metallographic image (50X) of the silver-tin-indium oxide material prepared in Comparative Example 4 of this invention; 50X indicates a magnification of 50 times. The physical properties of the silver-tin-indium oxide obtained in Comparative Example 4 are shown in Table 13, and the temperature rise and electrical life test data of the 32A relay prepared from the obtained material are shown in Table 14.

[0187] Table 13 Physical property parameters of silver oxide, tin oxide, and indium oxide obtained in Comparative Example 4

[0188]

[0189] Table 14 Temperature rise and electrical life test data of 32A relays prepared from the materials obtained in Comparative Example 4

[0190]

[0191] Depend on Figure 7As shown in Tables 13 and 14 above, metallographic analysis of the silver-tin-indium oxide material prepared in this comparative example reveals a peroxidized region in the central part of its microstructure, along with a small number of pores. Tests indicate that the physical and electrical properties of this material are inferior to those of Examples 1, 2, and 3 of this invention.

Claims

1. A method for preparing a low-temperature silver-tin-indium oxide contact material, characterized in that, Includes the following steps: (1) Smelting: Silver ingots, tin ingots and indium ingots are placed in a melting furnace, the furnace temperature is controlled at 1250–1300℃, and the temperature is held for 25–30 minutes to obtain a silver-tin-indium alloy melt. (2) Casting: The silver-tin-indium alloy melt obtained in step (1) is cast into silver-tin-indium alloy ingots; (3) Surface treatment: The silver-tin-indium alloy ingot cast in step (2) is subjected to surface treatment; (4) Sintering: The silver-tin-indium alloy ingot after surface treatment in step (3) is sintered; (5) Extrusion molding: The silver-tin-indium alloy ingot sintered in step (4) is extruded into silver-tin-indium sheet; (6) Welding: The silver-tin-indium plate extruded in step (5) is welded to a pure silver plate of the same specifications on both sides to obtain a silver / silver-tin-indium composite plate. (7) Hot rolling: The welded silver / silver-tin-indium composite plate obtained in step (6) is hot rolled. (8) Cold rolling: The hot-rolled silver / silver-tin-indium composite plate is cold-rolled to obtain a cold-rolled silver / silver-tin-indium composite sheet. (9) Annealing: Anneal the cold-rolled silver / silver-tin-indium composite sheet; (10) Internal oxidation: The silver / silver tin indium composite sheet processed in step (9) is placed into a container, oxygen is introduced into the container, and the oxygen pressure is controlled at 0.7–0.9 MPa. Then the temperature is raised to 720–780 ℃ and kept at that temperature for 25–35 hours to obtain the silver / silver tin oxide indium oxide composite sheet.

2. The method for preparing the low-temperature silver-tin oxide-indium oxide contact material according to claim 1, characterized in that, In step (1), the mass percentages of silver ingots, tin ingots and indium ingots are 87-89%, 7-9% and 3-5%, respectively; and / or, in step (1), a medium-frequency induction melting furnace is used for melting; and / or, in step (1), during the melting process, the cooling water pressure of the induction coil is ≥0.2 MPa; the cooling water pressure of the power supply and capacitor compartment is ≥0.1 MPa; and the working power of the medium-frequency induction melting furnace is ≤55 kW.

3. The method for preparing the low-temperature silver-tin-oxide-indium oxide contact material according to claim 1 or 2, characterized in that, In step (3), turning is used; and / or, in step (3), the diameter of the alloy ingot should be controlled between 80 mm and 95 mm.

4. The method for preparing the low-temperature silver-tin oxide-indium oxide contact material according to claim 1 or 2, characterized in that, In step (4), a muffle furnace is used for sintering; and / or, in step (4), the sintering temperature is 700–800℃ and the sintering time is 1–2 hours; and / or, in step (4), an ammonia decomposition atmosphere is used for protection throughout the sintering process.

5. The method for preparing the low-temperature silver-tin-oxide-indium oxide contact material according to claim 1 or 2, characterized in that, In step (5), the extrusion temperature is 450-500℃; and / or, in step (5), the extrusion speed is controlled to be 2-3 mm / s.

6. The method for preparing the low-temperature silver-tin-oxide-indium oxide contact material according to claim 1 or 2, characterized in that, In step (6), welding is performed by composite peripheral argon arc welding.

7. The method for preparing the low-temperature silver-tin-oxide-indium oxide contact material according to claim 1 or 2, characterized in that, In step (7), the silver / silver-tin-indium composite plate obtained in step (6) is placed in a muffle furnace, heated to 800–850°C and held for 2–2.5 hours.

8. The method for preparing the low-temperature silver-tin-oxide-indium oxide contact material according to claim 1 or 2, characterized in that, In step (9), the cold-rolled silver / silver-tin-indium composite sheet is placed in a nitrogen atmosphere at 600–650°C for 1.5–2 hours and then cooled to below 100°C by air cooling.

9. The method for preparing the low-temperature silver-tin-oxide-indium oxide contact material according to claim 1 or 2, characterized in that, The silver / silver-tin-indium composite sheet processed in step (9) is placed into a container, oxygen is introduced into the container, and the temperature is raised to 760-780℃.

10. The method for preparing the low-temperature silver-tin-oxide-indium oxide contact material according to claim 1 or 2, characterized in that, In step (10), the internal oxidation is carried out in an oxidation furnace.

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