Silver tin oxide electric contact material and preparation method and application thereof

Abstract

The invention provides a silver tin oxide electric contact material and a preparation method and application thereof, and relates to the technical field of silver-based electric contact materials. The silver tin oxide electric contact material is prepared into a wire rod through raw material proportioning, atomization powder preparation, constant-pressure low-temperature-to-high-temperature powder internal oxidation treatment, vacuum cold isostatic pressing forming, sintering extrusion and drawing. The raw material comprises the following elements by weight percent: 6wt.%-12wt.% of Sn, 0.3 wt.%-1.5 wt.% of additive elements and the balance of Ag. The additive element is at least one of Cu, Bi, Te, Sb, Ni and Ce. Compared with a conventional method, the preparation method of the silver tin oxide electric contact material has the advantages that the production period is remarkably shortened, the yield is improved, the production cost is reduced, the preparation process is green and environment-friendly, and no harm is caused to the environment and human health. The silver tin oxide electric contact material is uniform in metallographic structure distribution, has good wire processing performance, rivet manufacturing performance, breaking performance, fusion welding resistance and moderate hardness, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of silver-based electrical contact materials, in particular to a silver tin oxide electrical contact material and a preparation method and application thereof. Background Art

[0002] Silver-based electrical contact materials are important electronic device materials, widely used in various switches for low-voltage electrical appliances, household appliances, aerospace appliances, and automotive appliances. Among them, silver-cadmium oxide (STO) materials are the most widely used in low-voltage electrical appliances due to their excellent arc erosion resistance, strong resistance to welding, and low and stable contact resistance. However, during the production and use of STO materials, they inevitably generate cadmium vapor, which is not only harmful to human health but also pollutes the environment. Furthermore, with the development of low-voltage electrical appliances towards miniaturization, long life, and high reliability, STO materials are no longer able to meet the arc erosion and welding resistance requirements. Extensive research and practice have demonstrated that silver-tin oxide (STO) electrical contact materials, prepared using a conventional powder internal oxidation method, exhibit excellent arc erosion resistance and welding resistance, making them a leading alternative to cadmium oxide electrical contact materials.

[0003] The powder internal oxidation method is a common method for preparing silver tin oxide electrical contact materials. However, when using this method to prepare silver tin oxide electrical contact materials, as the high-temperature and high-pressure oxidation process progresses, powder agglomeration becomes serious. This increases the density between the powders and hinders the diffusion of oxygen atoms into the powder interior. This results in uneven metallographic structure distribution of the silver tin oxide electrical contact material, with obvious silver-based bright bands and oxide aggregation. This affects the processing and electrical properties of the silver tin oxide electrical contact material, resulting in a low product yield and increased production costs.

[0004] In addition, when the tin content is ≥6% by mass, the conventional powder internal oxidation method cannot completely oxidize the silver tin oxide powder. For this reason, indium is usually added as an oxygen aid or ultra-high pressure energy of 10MPa or above is used to achieve smooth oxidation of the silver tin powder. However, indium is relatively expensive and is a rare metal. From the perspective of cost savings and protection of rare metals, its use should be avoided as much as possible. Silver tin oxide electrical contact materials prepared using ultra-high pressure energy of 10MPa or above have defects such as poor arc erosion resistance, lower conductivity than conventional internal oxidation materials, and unstable contact resistance.

[0005] Therefore, it is necessary to develop a new preparation process for silver tin oxide electrical contact materials in order to reduce the production cost of silver tin oxide electrical contact materials, simplify the production process, and thus improve the production efficiency of silver tin oxide electrical contact materials. Summary of the Invention

[0006] In light of this, the present invention provides a silver tin oxide electrical contact material, its preparation method, and its application. This invention utilizes a constant-pressure, low-temperature to high-temperature internal oxidation process to overcome the severe powder agglomeration problem of conventional powder internal oxidation methods. This method achieves the preparation of high-quality silver tin oxide electrical contact materials without adding expensive indium and using ultrahigh pressure energy exceeding 10 MPa.

[0007] The silver tin oxide electrical contact material of the present invention is made into a wire through raw material proportioning, atomization powder making, constant pressure low temperature to high temperature powder internal oxidation treatment, vacuum cold isostatic pressing, sintering and extrusion. The elemental composition of the raw materials is:

[0008] Sn 6wt.%~12wt.%, added elements 0.3wt.%~1.5wt.%, the balance is Ag;

[0009] The added element is at least one of Cu, Bi, Te, Sb, Ni, and Ce.

[0010] Preferably, the added element is Bi.

[0011] The present invention provides a method for preparing a silver tin oxide electrical contact material, comprising the following steps:

[0012] S1. Weigh the raw materials in proportion, grind them into powder, dry them, cool them, and sieve them to obtain silver-tin alloy powder;

[0013] S2, subjecting the -100 mesh silver-tin alloy powder to a constant pressure low-temperature to high-temperature powder internal oxidation treatment, cooling the powder, and sieving the powder to obtain a -100 mesh silver-tin oxide powder;

[0014] S3, forming the silver tin oxide powder by vacuum cold isostatic pressing to obtain a silver tin oxide ingot;

[0015] S4. The silver tin oxide ingot is sintered, extruded, and drawn to obtain a silver tin oxide electrical contact material.

[0016] In an embodiment of the present invention, the constant pressure low temperature to high temperature internal oxidation of the silver-tin alloy powder in step S2 is carried out in three stages: the first stage is low temperature oxidation, in which the alloy powder is kept at 400°C and an oxygen pressure of 0.12MPa to 0.15MPa for 4h to 5h; the second stage is powder crushing, in which the silver tin oxide powder after low temperature oxidation is crushed; the third stage is high temperature oxidation, in which the crushed silver tin oxide powder is kept at 650°C to 680°C and an oxygen pressure of 0.12MPa to 0.15MPa for 6h to 10h, and then cooled to below 50°C and taken out of the furnace.

[0017] In an embodiment of the present invention, after the constant pressure low temperature to high temperature internal oxidation treatment, the powder is cooled to below 50° C. and then passed through a 100 mesh sieve to obtain -100 mesh silver tin oxide powder.

[0018] In an embodiment of the present invention, the forming pressure of the vacuum cold isostatic pressing in step S3 is 300 MPa to 400 MPa, the holding time is 2 min to 5 min, and the diameter of the silver tin oxide ingot is 90 mm to 100 mm.

[0019] In an embodiment of the present invention, the sintering temperature in step S4 is 850° C. to 880° C., the sintering time is 5 h to 6 h, and then the sintering is immediately followed by extrusion: the extrusion ratio is 260 to 360, and the extruded wire specification is Φ5 mm to Φ6 mm.

[0020] In an embodiment of the present invention, the extruded wire is further drawn into wires of different specifications to meet different application requirements.

[0021] Application of a silver tin oxide electrical contact material in switch manufacturing, wherein the silver tin oxide electrical contact material is the silver tin oxide electrical contact material described in the above technical solution.

[0022] In an embodiment of the present invention, the switch is a switch in low-voltage electrical appliances, household appliances, aerospace electrical appliances, and automotive electrical appliances.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] After internal oxidation, the powder of the present invention will not form hard agglomerates, but only a small amount of loose powder balls, which can be crushed and finely compressed with a powder crushing tool for screening, without the need for ball milling and subsequent screening. The production cycle of each batch is shortened by about 20%, thereby improving the capital turnover rate of the production process; and the yield rate of the process is increased by 4.5% to 5.0%. Based on the current silver price, the production cost per kilogram is reduced by 90 to 100 yuan.

[0025] In the preparation process of the present invention, low-cost metal elements are selected to replace indium elements as oxygen-promoting agents, which not only reduces production costs but also protects rare metal indium.

[0026] After internal oxidation, the oxide particles are evenly distributed in the silver matrix, and the metallographic structure is evenly distributed, so the prepared silver tin oxide electrical contact material has good wire processing performance, rivet making performance, excellent breaking performance, anti-welding performance and moderate hardness.

[0027] The preparation process of the present invention is green and environmentally friendly and will not cause harm to the environment and human health. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] Figure 1 This is a 100-fold horizontal metallographic image of the finished product line of Example 1 of the present invention;

[0030] Figure 2 This is a metallographic image of the finished product wire of Example 1 of the present invention at a 100-fold magnification in the longitudinal direction;

[0031] Figure 3 This is a metallographic image of the finished product line of Example 1 of the present invention at a horizontal magnification of 500 times;

[0032] Figure 4 This is a metallographic image of the finished wire of Example 1 of the present invention at a magnification of 500 times in the longitudinal direction;

[0033] Figure 5 This is a metallographic image of the finished product line of Example 2 of the present invention at a horizontal scale of 100 times;

[0034] Figure 6 This is a metallographic image of the finished product wire of Example 2 of the present invention at a 100-fold magnification in the longitudinal direction;

[0035] Figure 7 This is a metallographic image of the finished product line of Example 2 of the present invention at a horizontal magnification of 500 times;

[0036] Figure 8 This is a metallographic image of the finished wire of Example 2 of the present invention at a magnification of 500 times in the longitudinal direction;

[0037] Figure 9 This is a 100-fold horizontal metallographic image of the finished product line of Comparative Example 1 of the present invention;

[0038] Figure 10 This is a metallographic image of the finished product line of Comparative Example 1 of the present invention at a 100-fold magnification in the longitudinal direction;

[0039] Figure 11 This is a 500-fold horizontal metallographic image of the finished product line of Comparative Example 1 of the present invention;

[0040] Figure 12 This is a metallographic image of the finished product line of comparative example 1 of the present invention at a horizontal scale of 500 times.

[0041] Figure 13 This is a 100-fold horizontal metallographic image of the finished product line of Comparative Example 2 of the present invention;

[0042] Figure 14 This is a metallographic image of the finished product line of comparative example 2 of the present invention at a 100-fold magnification in the longitudinal direction;

[0043] Figure 15 This is a 500-fold horizontal metallographic image of the finished product line of Comparative Example 2 of the present invention;

[0044] Figure 16 This is a metallographic image of the finished wire of Comparative Example 2 of the present invention at a magnification of 500 times in the longitudinal direction. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] The present invention provides a silver tin oxide electrical contact material, a preparation method thereof, and an application thereof. The process has high production efficiency, short cycle, and low cost. Without adding the rare metal indium element as an oxygen promoter, the metallographic structure of the silver tin alloy powder after oxidation can be uniformly distributed, thereby enabling the material to obtain good processing performance, moderate hardness, excellent breaking performance, and anti-welding performance.

[0047] The silver tin oxide electrical contact material of the present invention is processed through raw material proportioning, atomization powder making, constant pressure low temperature to high temperature internal oxidation treatment, vacuum cold isostatic pressing, sintering and extrusion, and then drawn into wires of different specifications to meet different application requirements. The elemental composition of the raw materials is:

[0048] Sn 6wt.% to 12wt.%, added elements 0.3wt.% to 1.5wt.%, the balance is Ag;

[0049] The added element is at least one of Cu, Bi, Te, Sb, Ni, and Ce, preferably Bi.

[0050] The present invention adopts other elements with significantly lower prices than indium as oxygen-promoting agents, and the prepared silver tin oxide electrical contact material has uniform metallographic structure distribution, excellent processing performance and electrical properties, and has good application prospects.

[0051] The present invention provides a method for preparing a silver tin oxide electrical contact material, comprising the following steps:

[0052] S1. Weigh the raw materials in proportion, grind them, dry them, and sieve them to obtain alloy powder;

[0053] S2, subjecting the alloy powder to a constant pressure low-temperature to high-temperature internal oxidation treatment, followed by cooling and sieving to obtain silver tin oxide powder;

[0054] S3, forming the silver tin oxide powder by vacuum cold isostatic pressing to obtain a silver tin oxide ingot;

[0055] S4. Sintering the silver tin oxide ingot and then cooling it to obtain a silver tin oxide electrical contact material.

[0056] The first step of the present invention is to pretreat the raw materials to obtain alloy powder. In some specific embodiments of the present invention, after powdering in step S1, the powder is dried at 180°C ± 20°C for 4 to 5 hours, then cooled to 50°C and passed through a 100-mesh sieve to obtain a -100-mesh silver-tin alloy powder.

[0057] Step S1 obtains silver-tin alloy powder through a powder making process, so that each element is evenly distributed in the subsequent process, ensuring that the final prepared silver tin oxide electrical contact material has uniform composition and stable performance. The present invention does not strictly limit the powder making method, but in some preferred embodiments, the powder making process in step S1 is atomization powder making, and the powder making process is carried out in a medium frequency atomizing furnace. This process can improve the uniformity and dispersibility of the alloy powder, ensure the uniform distribution of the material components and provide a particle size and surface area powder suitable for internal oxidation treatment, thereby improving oxidation efficiency and material performance. Drying can remove moisture from the powder, avoid agglomeration or uneven oxidation problems during subsequent oxidation treatment, and improve the fluidity and screening effect of the powder. Screening can control the powder particle size, ensure that the alloy powder particle size is uniform, and is suitable for subsequent internal oxidation and vacuum cold isostatic pressing steps.

[0058] The second step of the present invention is to perform a constant-pressure, low-temperature-to-high-temperature powder internal oxidation treatment on the alloy powder. In some specific embodiments of the present invention, the constant-pressure, low-temperature-to-high-temperature internal oxidation treatment in step S2 is carried out in three stages. The first stage is low-temperature oxidation, and the steps are: keeping the alloy powder at 400°C and an oxygen pressure of 0.12MPa to 0.15MPa for 4 to 5 hours; the second stage is powder crushing, and the steps are: crushing the silver tin oxide powder after low-temperature oxidation; the third stage is high-temperature oxidation, and the steps are: keeping the crushed silver tin oxide powder at 650°C to 680°C and an oxygen pressure of 0.12MPa to 0.15MPa for 6 to 10 hours; after the constant-pressure, low-temperature-to-high-temperature internal oxidation treatment, the powder is cooled to below 50°C and passed through a 100-mesh sieve to obtain a -100-mesh silver tin oxide powder.

[0059] This invention utilizes a constant-pressure, low-temperature-to-high-temperature internal oxidation process for powders, strictly controlling the process parameters involved. Combined with the crushing step, this process achieves complete oxidation of the alloy powder. This overcomes the problems of powder agglomeration seen with conventional internal oxidation, as well as the inability to oxygen-permeate the silver-tin powder when the tin content is ≥6%. After low-temperature oxidation, the powder produced by this invention forms only a small, loose mass, rather than a hard agglomerate. This mass can be crushed and sieved using a common powder crushing spoon, eliminating the need for ball milling and subsequent sieving, thus shortening the production cycle.

[0060] The novel constant-pressure low-temperature to high-temperature powder internal oxidation process of the present invention aims to: effectively avoid frequent thermal motion of alloy atoms caused by high-temperature oxidation in the low-temperature oxidation stage (i.e., the first stage), thereby accelerating the oxidation rate and forming a dense oxide film on the alloy surface, which affects the subsequent internal oxidation effect of the alloy; crushing the small amount of loose powder formed in the process with a spoon in the powder crushing stage (i.e., the second stage), which is conducive to oxygen permeation of the alloy powder that has not been completely oxidized in the high-temperature oxidation stage (i.e., the third stage), and no hard agglomerates are formed after the oxidation is completed. The oxygen permeability of the silver tin oxide powder is determined based on the silver content of the silver oxide powder after high-temperature oxidation being within the range of ±0.5% of the design value and the uniform distribution of the metallographic structure of the final product silver tin oxide; and constant-pressure-controlled oxidation is used for both low-temperature and high-temperature oxidation, effectively avoiding the formation of oxide-rich or oxide-poor areas caused by oxygen pressure fluctuations, thereby improving the processing performance and electrical properties of the final product silver tin oxide electrical contact material.

[0061] The third step of the present invention is to form a silver tin oxide ingot by vacuum cold isostatic pressing the alloy powder. In some specific embodiments of the present invention, the vacuum cold isostatic pressing in step S3 is performed at a pressure of 300 MPa to 400 MPa, with a holding time of 2 to 5 minutes. The diameter of the silver tin oxide ingot is 90 mm to 100 mm. The vacuum level is controlled by a vacuum gauge.

[0062] The fourth step of the present invention is to sinter the silver tin oxide ingot to obtain the silver tin oxide electrical contact material. In some specific embodiments of the present invention, the sintering temperature in step S4 is 850° C. to 880° C., and the sintering time is 5 hours to 6 hours.

[0063] In a specific embodiment of the present invention, a silver tin oxide ingot is sintered and extruded to produce a silver tin oxide extruded wire, which is then drawn as needed into wires of varying specifications to meet different application requirements. In a preferred embodiment of the present invention, the extrusion ratio is 260 to 360, and the wire has a specification of 5 mm to 6 mm.

[0064] The present invention provides an application of a silver tin oxide electrical contact material in switch manufacturing. The silver tin oxide electrical contact material is the silver tin oxide electrical contact material described in the above technical solution. The switch is a switch used in low-voltage electrical appliances, household appliances, aerospace electrical appliances, and automotive electrical appliances.

[0065] The present invention adopts an innovative process of constant temperature low temperature to high temperature powder internal oxidation to prepare silver tin oxide electrical contact materials with a tin oxide mass content of 8% to 14.5% (including 0.3% to 1.5% of the mass of added elements). The difficulty of its preparation increases with the increase of tin oxide content. In order to facilitate the promotion and application of the present invention, the inventors selected silver tin oxide (12) with the greatest market demand as Example 1 and silver tin oxide (14.5) with the greatest preparation difficulty as Example 2 to illustrate the specific implementation process of the present invention; and used conventional internal oxidation process to prepare comparative examples 1 and comparative examples 2 with the same composition as Examples 1 and 2 of the present invention to demonstrate the advantages of the present invention. The details are as follows:

[0066] Example 1 A method for preparing silver tin oxide (12), comprising the following steps:

[0067] S1. Take 2.18 kg of tin ingot, 0.18 kg of bismuth ingot, and 0.0375 kg of nickel element in proportion (because the solubility of nickel in silver is only 0.15%, to ensure that nickel is fully dissolved in silver, this embodiment uses 0.375 kg of silver nickel 10 to replace nickel, and the weight of silver contained in it needs to be included in the silver ratio weight). 22.273 kg (22.61 kg - 0.337 kg) of silver ingot is atomized and powdered in an intermediate frequency furnace. The preparation method is as follows:

[0068] Under nitrogen protection, silver ingots and silver nickel (10) are added to a medium frequency furnace, heated to 1100° C. to completely melt them, and then tin ingots and bismuth ingots are added, heated to 1350° C. to completely melt the added elements and stirred evenly to spray silver-tin alloy powder, and then the alloy powder is dried at 180° C. for 4.5 hours, cooled to below 50° C., and passed through a 100-mesh sieve to obtain -100-mesh silver-tin alloy powder (particle size ≤ 0.15 mm);

[0069] S2. Place the silver-tin alloy powder in the material rack, and then use a crane to lift it into the pit-type internal oxidation furnace, flush it with 0.13MPa pure oxygen, and keep it at 400℃ for 4.5h to complete the low-temperature oxidation stage. Low-temperature oxidation is used in this stage, which effectively avoids the frequent thermal motion of alloy atoms caused by high-temperature oxidation and accelerates the oxidation rate, thereby forming a dense oxide film on the surface of the alloy, affecting the subsequent internal oxidation effect of the alloy; after reducing the oxygen pressure to 0MPa, use a crane to lift out the silver-tin oxide powder that has not been oxygenated, and then use a spoon to form the low-temperature oxidation The small amount of loose powder is crushed and compacted, which is conducive to the high-temperature oxidation stage (i.e., the third stage) to oxygenate the alloy powder that has not been completely oxidized, thereby obtaining silver tin oxide (12) powder with uniform metallographic structure distribution and uniform composition, see S4 for details, completing the powder crushing stage; the crushed powder is hoisted into the pit-type internal oxidation furnace again, and when the temperature reaches 680°C, it is rushed into an oxygen pressure of 0.13MPa, and after the internal oxidation with heat and pressure maintenance for 7.5h, the oxygen pressure is reduced to 0MPa, and the temperature is reduced to below 50°C before being taken out of the furnace, completing the high-temperature oxidation stage;

[0070] After being taken out of the furnace, it was found that the silver tin oxide powder did not form hard agglomerates, but only a small amount of loose powder lumps. The powder lumps can be crushed and finely compressed with a spoon without ball milling, which shortens the production cycle and reduces production costs. At the same time, it also improves the yield rate of the internal oxidation process (see S3 of Example 1 for details); whether it is low-temperature oxidation or high-temperature oxidation, constant pressure control is adopted, which effectively avoids the occurrence of oxide-enriched or oxide-depleted zones caused by oxygen pressure fluctuations (see S4 of Example 1 for details), thereby improving the processing performance (see S7 and S8 of Example 1 for details) and electrical properties (see electrical life tests of Example 1, Example 2 and Comparative Example 1 and Comparative Example 2 for details) of the final finished silver tin oxide electrical contact material;

[0071] S3, after the silver tin oxide powder is taken out of the furnace, the powder can be crushed and finely compacted with a spoon, and the powder can be screened without ball milling, which shortens the production cycle and reduces the production cost; after the crushed silver tin oxide powder is passed through a 100-mesh sieve, the sieve-surface material accounts for 0.1% of the total weight and is treated as waste; the sieve-surface material is the obtained -100-mesh silver tin oxide (12) powder (particle size ≦ 0.15mm), accounting for 99.9% of the total weight. Compared with the 95.2% yield rate of silver tin oxide (12) powder obtained by internal oxidation of conventional powder, ball milling and then screening (see comparative example 1 for details), the internal oxidation process alone can increase the yield rate of silver tin oxide (12) powder by 4.5%;

[0072] S4. Powders at 6 different locations were then taken for metallographic observation and composition analysis: no oxide-poor or oxide-enriched micro-regions were found at each point, indicating that the metallographic distribution of the powder after oxidation was uniform; the silver mass content test results of each point were 88.06%, 87.88%, 88.00%, 88.05%, 87.80%, and 88.10%, respectively, all within the theoretical design value of 87.98% ± 0.50%, and very close to the design value of 87.98%, indicating that the silver tin oxide (12) composition of the powder after oxidation was uniform;

[0073] S5. The silver tin oxide powder is subjected to vacuum cold isostatic pressing to obtain a silver tin oxide ingot with a diameter of 95 mm. The molding pressure is 350 MPa, the holding time is 3 min, and the vacuum degree is controlled by a vacuum gauge;

[0074] S6. Sintering the silver tin oxide ingot at 850° C. for 5.5 h, and extruding it into a Φ5.5 mm wire at an extrusion ratio of 300 when sintered to temperature;

[0075] S7, the wire is drawn into finished wires of various specifications, and there is no wire breakage during the drawing process, indicating that the silver tin oxide (12) wire prepared by the present invention has good processing performance;

[0076] S8, rivets with specifications of SR8Φ4.8*1.55(0.55)-Φ2.5*1.25 were made on the 2.35mm finished wire, and the rivet cracking rate was less than 0.2%, and the flattening cracking rate was less than 0.4%, indicating that the silver tin oxide (12) wire prepared by the present invention has good rivet processing performance;

[0077] S9, the hardness (HV0.3) of the finished wire samples was tested, and the results were 106, 104, and 105, with an average value of 105.3, which was between the hardness (HV0.3) ≤ 100 prepared by the mixed powder method and the hardness (HV0.3 ≥ 110 prepared by the conventional internal oxidation method, indicating that the silver tin oxide (12) wire prepared by the present invention has moderate hardness;

[0078] S10, take samples of the silver tin oxide (12) finished product line prepared by the present invention for metallographic observation, the metallographic images are as follows: Figure 1 、 Figure 2 As shown: It can be seen that the metallographic structure is evenly distributed and there is no silver-based bright band defect; the metallographic structure is as follows at 500 times the horizontal and vertical dimensions. Figure 3 、 Figure 4 As shown: The oxide particle size is evenly distributed and there is no oxide aggregation defect.

[0079] Example 2 Preparation method of silver tin oxide (14.5), the steps are:

[0080] S1. Take 2.53 kg of tin ingot, 0.34 kg of bismuth ingot, 0.0375 kg of nickel element, and 21.763 kg of silver ingot and prepare -100 mesh silver-tin alloy powder (particle size ≤ 0.15 mm) according to the process of S1 in Example 1;

[0081] S2. Compared with Example 1, the internal oxidation in Example 2 adds 2.5% of oxides on the basis of Example 1. Under the condition that the other oxidation conditions remain unchanged, the high-temperature oxidation time is extended by 2h to complete the high-temperature oxidation: after being taken out of the furnace, it is found that the silver tin oxide powder does not form hard agglomerates, but only a small amount of loose powder balls. The powder balls can be crushed and finely pressed with a spoon without ball milling, which shortens the production cycle, reduces production costs, and improves the yield of the internal oxidation process (see S3 of Example 2 for details); whether it is low-temperature oxidation or high-temperature oxidation, constant pressure-controlled oxidation is adopted, which effectively avoids the occurrence of oxide-enriched or oxide-poor zones caused by oxygen pressure fluctuations (see S4 of Example 2 for details), thereby improving the processing performance (see S7 and S8 of Example 2 for details) and electrical properties (see electrical life tests of Example 1, Example 2 and Comparative Example 1 and Comparative Example 2 for details) of the final finished silver tin oxide electrical contact material;

[0082] S3. The crushed silver tin oxide powder was passed through a 100-mesh sieve to obtain -100-mesh (particle size ≦ 0.15 mm) silver tin oxide (14.5) powder with a yield of 99.88%, which was 4.96% higher than the yield of 94.92% of silver tin oxide (14.5) powder obtained by ball milling and sieving after internal oxidation of conventional powder (see Comparative Example 1 for details).

[0083] S4. Powders were then taken from six different locations for metallographic observation and composition analysis: no oxide-depleted or oxide-enriched micro-regions were found at any of the locations, indicating that the metallographic distribution within the powder after oxidation was uniform. The silver mass content at each location was 85.52%, 85.34%, 85.65%, 85.73%, 85.59%, and 85.42%, respectively, all within the theoretical design value of 85.48% ± 0.50%, and very close to the design value of 85.48%, indicating that the powder had good compositional uniformity after oxidation.

[0084] S5-S6 are exactly the same as in Example 1;

[0085] S7. No wire breakage occurs during the drawing of the wire into finished wires of various specifications, indicating that the silver tin oxide (14.5) wire of the present invention has good processing performance;

[0086] S8. Rivets with specifications of SR8Φ4.8*1.55(0.55)-Φ2.5*1.25 were made on the 2.35mm finished wire. The rivet cracking rate was less than 0.22%, and the flattening cracking rate was less than 0.46%, indicating that the wire had good rivet processing performance;

[0087] S9. The hardness (HV0.3) of the finished wire samples was tested, and the results were 108, 105, and 107, with an average value of 106.6, which was between the hardness (HV0.3) ≤ 100 prepared by the mixed powder method and the hardness (HV0.3 ≥ 110 prepared by the conventional internal oxidation method, indicating that the silver tin oxide (14.5) wire prepared by the present invention has moderate hardness;

[0088] S10, take samples of the silver tin oxide (14.5) finished product line prepared by the present invention for metallographic observation, the metallographic structure is as follows: Figure 5 、 Figure 6 As shown: It can be seen that the metallographic structure is evenly distributed and there is no silver-based bright band defect; the metallographic structure is as follows at 500 times the horizontal and vertical magnification: Figure 7 、 Figure 8 As shown: It can be seen that the oxide particle size is evenly distributed and there is no oxide aggregation defect.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that Comparative Example 1 adopts a conventional powder internal oxidation process, and the specific preparation steps are:

[0091] S1 is the same as Example 1;

[0092] S2, -100 mesh silver-tin alloy powder is placed in a rack, and when the furnace temperature reaches 720 ° C, the rack containing the powder is hoisted into a pit-type internal oxidation furnace, 0.3 MPa of pure oxygen is poured into it, and high-temperature and high-pressure internal oxidation is carried out for 14 hours. When the oxidation is completed, the oxygen pressure is reduced to 0 MPa, and the temperature is reduced to 50 ° C. After being taken out of the furnace, a silver tin oxide powder is obtained, and it is found that the powder is severely agglomerated; this is mainly because when the conventional powder internal oxidation method is used to prepare the silver tin oxide electrical contact material, as the high-temperature and high-pressure oxidation time advances, the powder agglomeration phenomenon is serious, which increases the density between the powders, is not conducive to the diffusion of oxygen atoms into the interior of the powder, and causes the silver tin oxide electrical contact material to have an uneven metallographic structure (see S4 of Example 1 for details), with obvious silver-based bright bands and oxide aggregation, affecting the processing performance (see S7 of Example 1 for details) and electrical properties (see Example 1, Example 2 and Comparative Example 1, Comparative Example 2 electrical life test for details) of the silver tin oxide electrical contact material, resulting in a low product yield (see S3 of Example 1 for details), which increases the production cost of the silver tin oxide electrical contact material;

[0093] S3. Due to the serious agglomeration of silver tin oxide powder, ball milling is required. The process is: powder: bead = 1:1, and ball milling is carried out for 1.5 hours. After ball milling, the powder is passed through a 100-mesh sieve to obtain -100-mesh silver tin oxide (12) powder (particle size ≤ 0.15 mm), and the yield rate is 95.2%;

[0094] S4. Metallographic observation and composition analysis of powders at six different locations revealed distinct oxide-depleted and oxide-enriched microregions at each location, indicating poor metallographic distribution uniformity within the powder after oxidation. The silver mass content at each location was 88.44%, 87.51%, 88.36%, 88.09%, 87.55%, and 88.45%, respectively. Although the composition at each location was within the theoretical design value of 87.98% ± 0.50%, the deviation from the design value of 87.98% was relatively large, indicating poor composition uniformity within the powder after oxidation.

[0095] S5-S6 are exactly the same as in Example 1;

[0096] S7. During the process of drawing the wire into finished wires of various specifications, it was found that the comparative example 1 had a wire breakage phenomenon, indicating that the processing performance of the silver tin oxide (12) wire prepared by the conventional powder pre-oxidation process was relatively poor;

[0097] S8. The hardness (HV0.3) of the finished wire samples was tested. The results were 115, 114, and 118, with an average value of 115.7, indicating that the wire hardness was relatively high, which is also one of the main reasons for wire breakage during the processing of the finished wire.

[0098] S9. The rivet manufacturing process of 2.35mm finished wire with the specification of SR8Φ4.8*1.55(0.55)-Φ2.5*1.25 was verified. The results showed that the rivet cracking rate was greater than 0.3%, and the flattening cracking rate was greater than 0.8%. The high hardness and poor composition uniformity of silver tin oxide wire were the main reasons for the poor rivet processing performance.

[0099] S10, take samples of the finished product line of silver tin oxide (12) prepared by conventional powder internal oxidation process for metallographic observation, the metallographic images are as follows: Figure 9 、 Figure 10 As shown: It can be seen that the metallographic structure is unevenly distributed and there are defects of silver-based bright bands; the metallographic structure is as follows at 500 times the horizontal and vertical magnification: Figure 11 、 Figure 12 As shown: It can be seen that the size distribution of the oxide particles is uneven, and there are defects of oxide aggregation.

[0100] Comparative Example 2

[0101] The difference from Example 2 is that a conventional powder internal oxidation process is adopted, and the specific preparation steps are as follows:

[0102] S1 is the same as Example 2;

[0103] S2. Silver-tin alloy powder is placed in a rack. When the furnace temperature reaches 720° C., the rack containing the powder is hoisted into a pit-type internal oxidation furnace, and 0.3 MPa of pure oxygen is injected. The powder is oxidized at high temperature and high pressure for 18 hours. When the oxidation is completed, the oxygen pressure is reduced to 0 MPa, and the temperature is reduced to 50° C. before the powder is removed from the furnace to obtain silver tin oxide powder. It is found that the powder agglomerates more severely than in Comparative Example 1 (this is mainly due to the fact that the oxidation time is extended by 4 hours under the same oxygen pressure and temperature as in Comparative Example 1; if the oxidation time is the same as in Comparative Example 1, the powder cannot be oxygenated; this is because Comparative Example 2 adds 2.5% tin oxide to Comparative Example 1. As the tin content increases, the oxidation time needs to be increased accordingly under the condition that other conditions remain unchanged). The powder cannot be crushed and finely divided with a spoon, and the agglomerated silver tin oxide powder must be ground and finely divided by a ball milling process. See S3 for details.

[0104] S3. Since the silver tin oxide powder is severely agglomerated, it needs to be ball milled. The process is powder: bead = 1:1, and the ball milling is carried out for 1.5 hours. After ball milling, it is passed through a 100 mesh sieve to obtain -100 mesh silver tin oxide (12) powder (particle size ≤ 0.15 mm), and the yield rate is 94.92%;

[0105] S4. Metallographic observation and composition analysis of powders at six different locations revealed distinct oxide-depleted and oxide-enriched microregions at each location, indicating poor metallographic distribution uniformity within the powder after oxidation. The silver content at each location was 85.01%, 85.88%, 85.14%, 85.91%, 85.23%, and 85.79%, respectively. Although the composition at each location was within the theoretical design value of 85.48% ± 0.50%, the deviation from the design value of 85.48% was relatively large, indicating poor composition uniformity within the powder after oxidation.

[0106] S5-S6 are exactly the same as in Example 2;

[0107] S7. During the process of drawing the wire into finished wires of various specifications, it was found that there was no wire breakage in Comparative Example 12, indicating that the processing performance of the silver tin oxide (14.5) wire prepared by the conventional powder pre-oxidation process was relatively poor;

[0108] S8. The hardness (HV0.3) of the finished wire samples was tested, and the results were 119, 115, and 118, with an average of 117.3, indicating that the wire hardness is relatively high, which is also one of the main reasons for wire breakage during the processing of the finished wire. S9. The rivet punching verification of the 2.35mm finished wire with the specification of SR8Φ4.8*1.55(0.55)-Φ2.5*1.25 was conducted. The results showed that the rivet cracking rate was greater than 0.4%, and the flattening cracking rate was greater than 0.82%. The high hardness of the silver tin oxide wire and the poor uniformity of its composition are the main reasons for the poor rivet processing performance.

[0109] S10, take samples of the finished product line of silver tin oxide (14.5) prepared by conventional powder internal oxidation process for metallographic observation, the metallographic images are as follows: Figure 13 、 Figure 14 As shown: It can be seen that the metallographic structure is unevenly distributed and there are defects of silver-based bright bands; the metallographic structure is as follows at 500 times the horizontal and vertical magnification: Figure 15 、 Figure 16 As shown: there is an uneven distribution of oxide particle size and defects of oxide aggregation.

[0110] Comparative test of the electrical life of the silver tin oxide electrical contact material of the present invention and conventional silver tin oxide electrical contact material:

[0111] In order to compare the electrical performance of silver tin oxide electrical contact materials prepared by the innovative process of constant pressure low temperature to high temperature powder internal oxidation of the present invention and the conventional powder internal oxidation process, SR8 Φ4.8*1.55(0.55)-Φ2.5*1.25 rivets of the same specifications were made using Example 1, Example 2, and Comparative Example 1 and Comparative Example 2, all with the same wire diameter of Φ2.35mm. The rivets were assembled in a 40A / 220VAC magnetic latching relay of the same specifications, and three groups were assembled for electrical performance testing.

[0112] Test conditions: Contact type, 1 normally open contact; Load type, resistive load; Rated load, 40A / 220VAC; Coil voltage, 24VDC; Test frequency, 15ops / min (on:off=1s:3s); Test environment, normal temperature and pressure.

[0113] Test requirements: Electrical life ≥ 50,000 times, and within the target number of times, it cannot fail for 3 consecutive times or 5 times cumulatively. The test results are detailed in Table 1:

[0114] Table 1 Electrical life test results

[0115]

[0116] It can be seen from Table 1 that although Examples 1 and 2 and Comparative Examples 1 and 2 can all meet the electrical life requirement of 50,000 switching cycles, Comparative Examples 1 and 2 have the undesirable phenomenon of continuous bonding for 2 times or cumulative bonding for 3-4 times, while Examples 1 and 2 have no bonding phenomenon when the switching reaches 50,000 times, indicating that the silver tin oxide electrical contact material prepared by the innovative process of constant pressure low temperature to high temperature powder internal oxidation of the present invention has better breaking performance and anti-welding performance than the silver tin oxide electrical contact material prepared by the conventional powder internal oxidation process.

[0117] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A silver tin oxide electrical contact material, characterized in that: The silver tin oxide electrical contact material is made into a wire by raw material proportioning, atomization powder making, constant pressure low temperature to high temperature powder internal oxidation treatment, vacuum cold isostatic pressing, sintering and extrusion, and then drawing. The elemental composition of the raw materials is: Sn 6wt.% to 12wt.%, added elements 0.3wt.% to 1.5wt.%, the balance is Ag; The added element is at least one of Cu, Bi, Te, Sb, Ni, and Ce.

2. A method for preparing the silver tin oxide electrical contact material according to claim 1, characterized in that: The following steps are involved: S1. Weigh the raw materials in proportion, grind them into powder, dry them, cool them, and sieve them to obtain silver-tin alloy powder; S2, subjecting the -100 mesh silver-tin alloy powder to a constant pressure low-temperature to high-temperature powder internal oxidation treatment, cooling the powder, and sieving the powder to obtain a -100 mesh silver-tin oxide powder; S3, forming the silver tin oxide powder by vacuum cold isostatic pressing to obtain a silver tin oxide ingot; S4. The silver tin oxide ingot is sintered, extruded, and drawn to obtain a silver tin oxide electrical contact material.

3. The preparation method according to claim 2, characterized in that The drying temperature in step S1 is 180°C ± 20°C, and the drying time is 4h to 5h.

4. The preparation method according to claim 2, characterized in that In step S2, the constant pressure low temperature to high temperature internal oxidation of the silver-tin alloy powder is carried out in three stages: the first stage is low temperature oxidation, in which the alloy powder is kept at 400°C and an oxygen pressure of 0.12MPa to 0.15MPa for 4h to 5h; the second stage is powder crushing, in which the silver tin oxide powder after low temperature oxidation is crushed; the third stage is high temperature oxidation, in which the crushed silver tin oxide powder is kept at 650°C to 680°C and an oxygen pressure of 0.12MPa to 0.15MPa for 6h to 10h, and then cooled to below 50°C and taken out of the furnace.

5. The preparation method according to claim 2, characterized in that In step S3, the vacuum cold isostatic pressing process is performed at a pressure of 300 MPa to 400 MPa and a holding pressure of 2 to 5 minutes. After forming, the diameter of the silver tin oxide ingot is 90 mm to 100 mm.

6. The preparation method according to claim 2, characterized in that The sintering and extrusion temperature in step S4 is 850° C. to 880° C., and the sintering time is 5 h to 6 h.

7. The preparation method according to claim 2, characterized in that After step S4, the process further includes drawing the silver tin oxide extruded wire into wires of different specifications.

8. Application of a silver tin oxide electrical contact material in switch manufacturing, characterized in that: The silver tin oxide electrical contact material is the silver tin oxide electrical contact material according to claim 1 or the silver tin oxide electrical contact material prepared by the method according to any one of claims 2 to 7.

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