Silver metal oxide electrical contact material prepared by internal oxidation method and preparation method of silver metal oxide electrical contact material

Abstract

The invention relates to an internal oxidation method silver metal oxide electrical contact material and a preparation method thereof. The internal oxidation method silver metal oxide electrical contact material comprises the following components in percentage by mass: 75-85% of silver; 7-16% of cadmium oxide; 4-9% of tin oxide; 1-3% of indium oxide and the balance of 0-0.5% of one or more of nickel oxide, bismuth oxide and copper oxide.

Description

Technical Field

[0001] The invention relates to an internal oxidation silver metal oxide electric contact material and a preparation method thereof, belonging to the field of electric contact materials. Background Art

[0002] In the field of electrical contact materials, silver metal oxide materials are widely used in low-voltage electrical appliances due to their good resistance to arc erosion, resistance to welding and electrical conductivity. At present, the mainstream production processes of silver metal oxide materials include internal oxidation, pre-oxidation and powder metallurgy. Among them, the internal oxidation method has an advantage in production cost because most of the scraps produced before the internal oxidation process can be directly recycled. In addition, cost reduction can also be achieved by saving silver. Patent CN112831681A reports a powder metallurgy silver cadmium oxide electrical contact material. The anti-adhesion performance of the material is improved by adding silver tungstate powder and silver molybdate powder. The silver content of this material is 75-85%, that is, the material cost is reduced by saving silver, but there is no advantage in production cost.

[0003] Internal oxidation silver metal oxide electrical contact materials with low silver content are not uncommon in the current market because of their low production and material costs. For example, patent CN104404419A discloses an internal oxidation silver cadmium oxide electrical contact material with a silver content of 75-82%. However, internal oxidation silver cadmium oxide electrical contact materials are rarely used under conditions of high current levels. This is mainly because the electrical performance of silver cadmium oxide materials is not as good as that of silver tin oxide materials under high current conditions. The principles of arc erosion resistance of the two are different. Cadmium oxide in silver cadmium oxide materials will sublimate or decompose into gaseous state under the action of arc, which can reduce arc energy; silver tin oxide materials mainly resist arc erosion through the segregation of tin oxide after arc melting the contact surface. Therefore, in theory, a higher content of tin oxide can be added to the silver cadmium oxide material. On the one hand, the high temperature decomposition of cadmium oxide can be used to reduce the arc energy to reduce the increase in contact resistance, and on the other hand, the thermal stability of tin oxide can be used to reduce material loss and improve electrical life.

[0004] Since silver metal oxide has excellent resistance to fusion welding, it is difficult to weld with other components. Usually, a layer of pure silver needs to be compounded before oxidation in the contact to improve the wettability of the welding surface and the solder, which is convenient for welding with other components. However, the internal oxidation method silver metal oxide electrical contact material with low silver content has the problem of contact failure caused by oxide aggregation at the composite silver interface (the interface between the silver metal oxide layer and the silver layer). Because the lower the silver content, the higher the solute element content, the greater the concentration difference of solute atoms at the composite silver interface, the faster the diffusion speed of solute atoms outward, and when it is close to or even equal to the diffusion speed of oxygen inward, the solute atoms will be oxidized in situ at the composite silver interface to form aggregation. This problem will be more serious in materials containing tin oxide and indium oxide (catalyzing tin oxide oxidation), because the atomic radius of tin and indium is smaller than that of cadmium, the diffusion speed is faster, and it is easier to reach diffusion equilibrium with oxygen, and it is also easier to be oxidized in situ to form aggregation. After the silver-complex interface forms aggregation, the bonding strength between the welding silver layer and the silver oxide will be reduced, which can easily lead to point drop. In severe cases, alloy interlayers will be produced during oxidation inside the contact, resulting in a large amount of production waste. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide an internal oxidation silver metal oxide electrical contact material and a preparation method thereof.

[0006] An internal oxidation silver metal oxide electrical contact material comprises the following components and their mass percentages: 75% to 85% silver; 7% to 16% cadmium oxide; 4% to 9% tin oxide; 1% to 3% indium oxide; and the balance is 0% to 0.5% of one or more of nickel oxide, bismuth oxide and copper oxide.

[0007] Silver, as the preferred component of the conductive material (75% to 85%), provides excellent conductivity, ensuring efficient transmission of current in the contact material, and is suitable for electrical applications of various frequencies and loads. The added cadmium oxide, tin oxide and indium oxide have good wear resistance and oxidation resistance, which can effectively extend the service life of the contact material and maintain stable working performance under high temperature and harsh environment. Cadmium oxide and tin oxide can improve the structural stability of the electrical contact material under high temperature conditions and prevent cracks or failures caused by uneven thermal expansion. An appropriate amount of indium oxide can enhance the mechanical strength of the material and enhance its durability under frequent switching and high load conditions, adapting to more demanding application scenarios. The flexible combination of nickel oxide, bismuth oxide and copper oxide can further enhance the electrical contact characteristics and comprehensive performance of the material, providing a variety of optimization options. By reasonably controlling the proportion of oxides, it is possible to maintain economy while taking into account the material performance, thereby reducing production costs and being suitable for large-scale applications. Silver oxide contacts made by the internal oxidation method can improve the transient current carrying capacity of the material, reduce the sparks and noise generated by electrical contact, and improve the stability of the equipment.

[0008] The present invention also provides a method for preparing a silver metal oxide electrical contact material by an internal oxidation method. The method is used to prepare the electrical contact material, and comprises the following steps:

[0009] (1) Melting: According to the composition of the above materials, weigh the corresponding weight of silver ingots, cadmium ingots, tin ingots, indium ingots and trace additive metals, melt and cast them into silver alloy ingots;

[0010] (2) Extrusion: heating the silver alloy ingot and extruding it into a long strip-shaped plate;

[0011] (3) Three-layer composite hot rolling: the silver alloy plate is welded with the intermediate layer strip and the silver plate. After the silver alloy plate, the intermediate layer strip and the silver plate are welded and fixed, a three-layer composite strip is formed by hot rolling;

[0012] (4) Cold rolling: The three-layer composite strip is subjected to multiple cold rolling passes to be rolled into a strip of required thickness;

[0013] (5) Punching: Punching the cold-rolled strip into sheet-shaped semi-finished contacts;

[0014] (6) Internal oxidation: performing internal oxidation treatment on the semi-finished sheet contact to obtain a silver metal oxide semi-finished sheet contact;

[0015] (7) Surface treatment: The silver metal oxide sheet semi-finished contact is subjected to surface treatment to obtain an internal oxidation method silver metal oxide electrical contact material.

[0016] The smelting step fully mixes the components by melting at high temperature to ensure that the silver, cadmium, tin, indium and trace additives in the alloy are evenly distributed, thereby improving the overall performance of the material. After the extrusion and hot rolling steps, the microstructure of the silver alloy is optimized, the density and uniformity of the material are enhanced, thereby improving the fatigue strength and wear resistance of the electrical contact. In the three-layer composite hot rolling process, the welding of the silver alloy layer with the intermediate layer and the silver plate provides a more complex composite structure for the material, which helps to improve the comprehensive performance of the material, including strength, conductivity and abrasion resistance. The rolling step can accurately control the thickness of the material through multiple rolling passes to meet the requirements of making electrical contacts of different specifications and improve the processing accuracy. The punching process processes the material strip into a sheet-like semi-finished contact with neat edges and stable shape, laying a good foundation for subsequent internal oxidation treatment and surface treatment. The internal oxidation step introduces an oxidized phase into the material, improves its antioxidant ability in a high temperature environment, and ensures the stability and reliability of the electrical contact under long-term high load. The final surface treatment process can effectively improve the surface finish of the electrical contact, improve its electrical contact characteristics, enhance its interaction with the contact medium, and improve the performance of the electrical contact. Through the overall design of multiple processes, the process and parameters can be flexibly adjusted according to market demand and technological progress, making the adaptability and controllability of material production higher. The overall process design reduces material waste and production costs. At the same time, the application of composite materials and the use of internal oxidation technology help reduce the impact on the environment.

[0017] Preferably, in step (1), the trace additive metal is composed of at least one metal element selected from the group consisting of nickel, bismuth and copper.

[0018] Trace additions of nickel, bismuth or copper can improve the mechanical properties and electrical conductivity of silver alloys. For example, nickel helps to increase the corrosion resistance and strength of the alloy, bismuth can improve the oxidation resistance, and copper helps to improve the conductivity. The addition of these metal elements can optimize the microstructure of the material, promote the interaction between different components, enhance the density and uniformity of the material, and improve the overall performance. Appropriate amounts of nickel and bismuth can increase the wear resistance of the material, reduce the wear rate, and ensure the long life of the electrical contact under high frequency and high load conditions. The addition of copper and nickel helps to improve the stability of the material at high temperatures, enhance the oxidation resistance, and ensure the reliability of the material in harsh environments. Nickel, bismuth and copper are relatively common and low-cost, which can optimize performance while controlling production costs and improving the economic benefits of the material. By flexibly selecting suitable trace metals, functional customization can be performed for specific electrical contact applications to meet special needs. This technical feature enhances the application adaptability of the alloy in different environments (such as humid, corrosive atmospheres, etc.) and expands the application range of electrical contacts. The rational use of trace additive metals can reduce losses caused by material brittleness or failure, thereby improving the stability and reliability of the production process.

[0019] Preferably, in step (3), the intermediate layer strip is made by a smelting-extrusion-cold rolling process, and its composition is 84% ​​to 94% silver; 6% to 15% cadmium, and the balance is 0% to 1% of one or more of tin, nickel, bismuth, and copper. After compounding, the thickness of the intermediate layer accounts for 0.05% to 4% of the thickness of the three-layer composite strip.

[0020] The design of the middle layer strip ensures the stability of the three-layer composite structure and enhances the ability of the material to resist external pressure and thermal stress during use. The middle layer is mainly composed of silver and cadmium, which ensures good electrical conductivity, helps to improve the conductivity and response speed of the electrical contact, and adapts to the requirements of high load current. The cadmium component of the middle layer improves the material's wear resistance, extends the service life of the electrical contact under frequent operation, and adapts to various harsh environments. By rationally configuring the composition of the middle layer, the thermal conductivity can be improved, so that the material exhibits excellent thermal stability under high temperature working conditions and reduces the risk of thermal failure. By controlling the thickness of the middle layer (accounting for 0.05% to 4%), moderate lightweight can be achieved while ensuring structural strength, thereby improving the overall performance of the product. Appropriate trace elements (such as tin, nickel, bismuth, and copper) can promote the toughness of the alloy due to their characteristics, reduce the risk of failure of the material due to brittle cracks, and thus improve durability. Using the smelting-extrusion-cold rolling process, the production process can be efficiently controlled, material waste can be reduced, thereby reducing production costs and improving overall economic benefits. The presence of the middle layer increases the contact area between silver and other layers, improves the bonding strength between layers, and further enhances the overall fatigue resistance of the material. The composition and thickness of the middle layer can be flexibly adjusted according to specific application requirements, providing full adaptability for the application of electrical contacts in different scenarios.

[0021] Furthermore, the plate fixed by three-layer welding is heated to 550-800° C. and then hot-rolled for 5 minutes to 3 hours.

[0022] High-temperature hot rolling can promote the recrystallization and refinement of grains, help eliminate stress and defects generated during welding, and improve the mechanical properties and toughness of materials. At high temperatures, metal atoms can diffuse more easily, enhance the bonding strength between layers, form a stronger composite interface, and improve the structural integrity of the overall material. Through proper heat treatment, the resistance of the material can be reduced, the conductivity of the electrical contact can be improved, and the effective conduction of current can be ensured, thereby improving the operating efficiency of the equipment. During the hot rolling process, a dense microstructure will be formed on the surface of the material, thereby improving wear resistance and extending the service life of the electrical contact. By controlling the heating temperature and time, the thermal conductivity of the material can be effectively adjusted, making its performance more stable in a high temperature environment and reducing the risk of thermal failure. According to different electrical application requirements, the heating parameters (temperature and time) can be adjusted to obtain the required material properties to adapt to various working conditions. The hot rolling process can promote the uniformity of the material, make the composition distribution of each layer of material more uniform, and improve the consistency and reliability of the product. The surface of the material after hot rolling is smoother, which helps to improve the contact performance of the electrical contact, reduce the resistance of the contact point, and reduce heat and energy loss. Through the composite treatment of hot rolling, the stability of the material in different environments (such as high humidity, high temperature, low temperature, etc.) is enhanced, and its application range is expanded.

[0023] The beneficial effects of the present invention are as follows: 1. The silver metal oxide electrical contact material provided by the present invention is made by an internal oxidation method, which is simple to make and has low production cost;

[0024] 2. The internal oxidation silver metal oxide electrical contact material provided by the present invention has a silver content of 75% to 85%, which saves silver and has low material cost;

[0025] 3. The internal oxidation silver metal oxide electrical contact material provided by the present invention improves the arc erosion resistance of the material under high current by increasing the content of tin oxide and indium oxide, thereby solving the problem of poor electrical performance of the internal oxidation silver metal oxide electrical contact material under high current and heavy load conditions;

[0026] 4. The three-layer composite hot rolling method of the present invention utilizes a silver-cadmium alloy intermediate layer strip with a relatively high silver content as a buffer, thereby reducing the difference in solute atom concentration between the working layer and the welding silver layer, and solving the defect of oxide aggregation at the composite silver interface of the internal oxidation method silver metal oxide electrical contact material with a low silver content. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0028] Figure 1 is a process flow chart of the preparation method of the material of the present invention;

[0029] Figure 2 This is the metallographic diagram of the material prepared without the three-layer composite hot rolling process;

[0030] Figure 3 This is a metallographic diagram of the material prepared in Example 1 of the present invention;

[0031] Figure 4 This is a metallographic image of the composite silver interface of the material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0033] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. The subsequent embodiments will not explain this one by one.

[0034] The directions and positions mentioned in the present invention, such as "upper", "lower", "front", "back", "left", "right", "inside", "outside", "top", "bottom", "side", etc., are only for reference to the directions or positions of the drawings. Therefore, the directions and positions used are for explaining and understanding the present invention, but not for limiting the scope of protection of the present invention.

[0035] An internal oxidation silver metal oxide electrical contact material comprises the following components and their mass percentages: 75% to 85% silver; 7% to 16% cadmium oxide; 4% to 9% tin oxide; 1% to 3% indium oxide; and the balance is 0% to 0.5% of one or more of nickel oxide, bismuth oxide and copper oxide.

[0036] See also Figure 1-4 The present invention provides an embodiment of a method for preparing a silver metal oxide electrical contact material by an internal oxidation method, which is used to prepare the above-mentioned electrical contact material, comprising the following steps:

[0037] Embodiment 1:

[0038] (1) Melting: According to the composition of the above materials, weigh 23.57 kg of silver ingot, 2.8 kg of cadmium ingot, 1.6 kg of tin ingot, 0.5 kg of indium ingot and 0.03 kg of nickel sheet, and melt and cast them into silver alloy ingots;

[0039] (2) Extrusion: After heating the silver alloy ingot, it is extruded into a long strip-shaped plate;

[0040] (3) Three-layer composite hot rolling: The silver alloy plate is welded with the intermediate layer strip and the silver plate. After the silver alloy plate-intermediate layer strip-silver plate are welded, they are heated to 700°C for 5 minutes using a medium frequency induction furnace and hot rolled to form a three-layer composite strip. The intermediate layer strip is made by a smelting-extrusion-cold rolling process, and its composition is 86.5% silver, 13% cadmium, and 0.5% tin. After the composite, the thickness of the intermediate layer accounts for 3% of the thickness of the three-layer composite strip;

[0041] (4) Cold rolling: The three-layer composite strip is subjected to multiple cold rolling passes to be rolled into a strip of required thickness;

[0042] (5) Punching: Punching the cold-rolled strip into sheet-shaped semi-finished contacts;

[0043] (6) Internal oxidation: performing internal oxidation treatment on the semi-finished sheet contact to obtain a silver metal oxide semi-finished sheet contact;

[0044] (7) Surface treatment: The silver metal oxide sheet-shaped semi-finished contact is subjected to surface treatment to obtain an internal oxidation method silver metal oxide electrical contact material.

[0045] The finished product of the silver metal oxide electrical contact material prepared by the internal oxidation method in this embodiment contains 10.1% of cadmium oxide, 6.8% of tin oxide, 1.9% of indium oxide, and the remainder is silver and a trace amount of nickel oxide.

[0046] Embodiment 2:

[0047] (1) Melting: According to the composition of the above materials, weigh 22.23 kg of silver ingot, 4.15 kg of cadmium ingot, 1.58 kg of tin ingot, 0.52 kg of indium ingot and 0.02 kg of copper sheet, and melt and cast them into silver alloy ingots;

[0048] (2) Extrusion: After heating the silver alloy ingot, it is extruded into a long strip-shaped plate;

[0049] (3) Three-layer composite hot rolling: The silver alloy sheet is welded with the intermediate layer strip and the silver plate. After the silver alloy sheet-intermediate layer strip-silver plate is welded, it is heated to 800°C for 8 minutes in a medium frequency induction furnace and hot rolled to form a three-layer composite strip. The intermediate layer strip is made by a smelting-extrusion-cold rolling process, and its composition is 84% ​​silver, 15% cadmium, 0.5% tin, and 0.5% copper. After the composite, the thickness of the intermediate layer accounts for 4% of the thickness of the three-layer composite strip;

[0050] (4) Cold rolling: The three-layer composite strip is subjected to multiple cold rolling passes to be rolled into a strip of required thickness;

[0051] (5) Punching: Punching the cold-rolled strip into sheet-shaped semi-finished contacts;

[0052] (6) Internal oxidation: performing internal oxidation treatment on the semi-finished sheet contact to obtain a silver metal oxide semi-finished sheet contact;

[0053] (7) Surface treatment: The silver metal oxide sheet semi-finished contact is subjected to surface treatment to obtain an internal oxidation method silver metal oxide electrical contact material.

[0054] The finished product of the silver metal oxide electrical contact material prepared by the internal oxidation method in this embodiment contains 15.5% of cadmium oxide, 6.7% of tin oxide, 2.0% of indium oxide, and the remainder is silver and a trace amount of copper oxide.

[0055] Embodiment three:

[0056] (1) Melting: According to the composition of the above materials, weigh 23.68 kg of silver ingot, 2.1 kg of cadmium ingot, 2 kg of tin ingot, 0.7 kg of indium ingot and 0.02 kg of nickel sheet, and melt and cast them into silver alloy ingots;

[0057] (2) Extrusion: After heating the silver alloy ingot, it is extruded into a long strip-shaped plate;

[0058] (3) Three-layer composite hot rolling: The silver alloy sheet is welded with the intermediate layer strip and the silver plate. After the silver alloy sheet-intermediate layer strip-silver plate is welded, it is heated to 650°C for 2.5 hours in a resistance furnace and hot rolled to form a three-layer composite strip. The intermediate layer strip is made by a smelting-extrusion-cold rolling process, and its composition is 89% silver, 10% cadmium, 0.5% tin, and 0.5% nickel. After the composite, the thickness of the intermediate layer accounts for 0.15% of the thickness of the three-layer composite strip;

[0059] (4) Cold rolling: The three-layer composite strip is subjected to multiple cold rolling passes to be rolled into a strip of required thickness;

[0060] (5) Punching: Punching the cold-rolled strip into sheet-shaped semi-finished contacts;

[0061] (6) Internal oxidation: performing internal oxidation treatment on the semi-finished sheet contact to obtain a silver metal oxide semi-finished sheet contact;

[0062] (7) Surface treatment: The silver metal oxide sheet semi-finished contact is subjected to surface treatment to obtain an internal oxidation method silver metal oxide electrical contact material.

[0063] The finished product of the silver metal oxide electrical contact material prepared by the internal oxidation method in this embodiment contains 7.5% of cadmium oxide, 8.5% of tin oxide, 2.8% of indium oxide, and the remainder is silver and a trace amount of nickel oxide.

[0064] Embodiment 4:

[0065] (1) Melting: According to the composition of the above materials, weigh 23.3 kg of silver ingot, 3.8 kg of cadmium ingot, 1.1 kg of tin ingot and 0.3 kg of indium ingot, melt and cast them into silver alloy ingots;

[0066] (2) Extrusion: After heating the silver alloy ingot, it is extruded into a long strip-shaped plate;

[0067] (3) Three-layer composite hot rolling: The silver alloy sheet is welded with the intermediate layer strip and the silver plate. After the silver alloy sheet-intermediate layer strip-silver plate is welded, it is heated to 550°C for 3 hours in a resistance furnace and hot rolled to form a three-layer composite strip. The intermediate layer strip is made by a smelting-extrusion-cold rolling process, and its composition is 94% silver and 6% cadmium. After the composite, the thickness of the intermediate layer accounts for 0.05% of the thickness of the three-layer composite strip;

[0068] (4) Cold rolling: The three-layer composite strip is subjected to multiple cold rolling passes to be rolled into a strip of required thickness;

[0069] (5) Punching: Punching the cold-rolled strip into sheet-shaped semi-finished contacts;

[0070] (6) Internal oxidation: performing internal oxidation treatment on the semi-finished sheet contact to obtain a silver metal oxide semi-finished sheet contact;

[0071] (7) Surface treatment: The silver metal oxide sheet semi-finished contact is subjected to surface treatment to obtain an internal oxidation method silver metal oxide electrical contact material.

[0072] The finished product of the silver metal oxide electrical contact material prepared by the internal oxidation method in this embodiment contains 14.1% of cadmium oxide, 4.6% of tin oxide, 1.1% of indium oxide, and the balance is silver.

[0073] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

[0074] Although the invention has been described with reference to several specific embodiments, it should be understood that the invention is not limited to the specific embodiments disclosed. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An internal oxidation method silver metal oxide electrical contact material, characterized in that: The components and their mass percentages are: 75% to 85% silver; 7% to 16% cadmium oxide; 4% to 9% tin oxide; 1% to 3% indium oxide, and the balance is 0% to 0.5% of one or more of nickel oxide, bismuth oxide and copper oxide.

2. A method for preparing a silver metal oxide electrical contact material by an internal oxidation process, characterized in that: The method is used to prepare the electrical contact material in claim 1, comprising the following steps: (1) Melting: According to the composition of the above materials, weigh the corresponding weight of silver ingots, cadmium ingots, tin ingots, indium ingots and trace additive metals, melt and cast them into silver alloy ingots; (2) Extrusion: heating the silver alloy ingot and extruding it into a long strip-shaped plate; (3) Three-layer composite hot rolling: the silver alloy plate is welded with the intermediate layer strip and the silver plate. After the silver alloy plate, the intermediate layer strip and the silver plate are welded and fixed, a three-layer composite strip is formed by hot rolling; (4) Cold rolling: The three-layer composite strip is subjected to multiple cold rolling passes to be rolled into a strip of required thickness; (5) Punching: Punching the cold-rolled strip into sheet-shaped semi-finished contacts; (6) Internal oxidation: performing internal oxidation treatment on the semi-finished sheet contact to obtain a silver metal oxide semi-finished sheet contact; (7) Surface treatment: The silver metal oxide sheet-shaped semi-finished contact is subjected to surface treatment to obtain an internal oxidation method silver metal oxide electrical contact material.

3. The method for preparing the silver metal oxide electrical contact material by internal oxidation method as claimed in claim 2, characterized in that: In step (1), the trace additive metal is composed of at least one metal element selected from the group consisting of nickel, bismuth and copper.

4. The method for preparing the silver metal oxide electrical contact material by internal oxidation method as claimed in claim 2, characterized in that: In step (3), the intermediate layer strip is made by a smelting-extrusion-cold rolling process, and its composition is 84% ​​to 94% silver; 6% to 15% cadmium, and the balance is 0% to 1% of one or more of tin, nickel, bismuth, and copper. After compounding, the thickness of the intermediate layer accounts for 0.05% to 4% of the thickness of the three-layer composite material strip.

5. The method for preparing the silver metal oxide electrical contact material by internal oxidation method as claimed in claim 2, characterized in that: In step (3), the plate fixed by three-layer welding is heated to 550-800°C and then hot-rolled for 5 minutes to 3 hours.

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