Laser remelting modification method of copper-chromium contact and copper-chromium contact

Abstract

The application discloses a laser remelting modification method of a copper-chromium contact and the copper-chromium contact, relates to the technical field of copper alloy contacts, and comprises the following steps: performing sand blasting treatment and ultrasonic cleaning on the copper-chromium contact, laser remelting, stress relaxation and surface purification treatment through a low-temperature plasma device, and magnetic force grinding finishing. The method solves the technical problems of micro-cracks and size deformation caused by high residual stress in the surface layer of the contact after laser remelting, and the difficulty in high-consistency batch production, makes the chromium phase in the surface layer of the copper-chromium contact uniform and refined, forms a continuous and dense fine-grain layer, and the roughness and residual stress are significantly reduced. The four processes of the application work together to realize the multiple goals of "performance improvement-defect elimination-batch stability", and can directly replace the traditional old smelting process, and greatly improve the production efficiency.

Description

Technical Field

[0001] This application relates to the field of copper alloy contact technology, and in particular to a laser remelting modification method for copper-chromium contacts and copper-chromium contacts. Background Technology

[0002] Copper-chromium contacts possess excellent electrical conductivity, thermal conductivity, resistance to welding, and breaking capacity, making them core components of medium- and high-voltage vacuum circuit breakers, vacuum load switches, and vacuum contactors. In contact manufacturing, surface aging is a crucial process that determines their electrical performance and reliability.

[0003] Traditional aging is divided into current aging and voltage aging, which usually takes 7 to 8 hours and has drawbacks such as high energy consumption, low efficiency, large equipment investment, and poor consistency.

[0004] Currently, some studies employ a method of modifying copper-chromium contacts using laser remelting combined with magnetic grinding, which can refine the chromium phase and improve surface properties. Other studies use a method of modifying copper alloy surfaces using sandblasting combined with selective laser melting, which can improve laser absorption and form a fine-grained layer. However, both methods rely on rapid laser heating and cooling, resulting in high residual stress on the contact surface, which easily induces microcracks and dimensional deformation. Furthermore, due to the lack of a stress relief process, it is difficult to achieve high-consistency mass production of contacts. Summary of the Invention

[0005] The main objective of this application is to provide a laser remelting modification method for copper-chromium contacts and a copper-chromium contact, aiming to solve the technical problems existing in the prior art, such as high residual stress on the contact surface leading to microcracks and dimensional deformation, and difficulties in mass production with high consistency.

[0006] To achieve the above objectives, this application provides a laser remelting modification method for copper-chromium contacts, comprising the following steps: The copper-chromium contacts are sandblasted and ultrasonically cleaned to complete the surface pretreatment. A laser remelting system is used to remelt the pre-treated copper-chromium contacts. During the laser remelting process, the central and edge regions of the pre-treated copper-chromium contacts are scanned differently, and dynamic power compensation is performed on the edge regions. A low-temperature plasma device is used to perform plasma treatment on the copper-chromium contacts after laser remelting to achieve stress relaxation and surface purification. The plasma-treated copper-chromium contacts were then magnetically ground and dried to obtain laser-remelted modified copper-chromium contacts.

[0007] Optionally, the air pressure for the sandblasting treatment is 0.5MPa~0.7MPa; the ultrasonic cleaning uses anhydrous ethanol, the cleaning time is 10min~15min, and the drying temperature is 60℃~80℃; the mass fraction of chromium in the copper-chromium contact is 25%~55%.

[0008] Optionally, during the laser remelting process, the laser scanning power of the central region is 300W~420W, the scanning speed is 1500mm / s~2500mm / s, and the spot spacing is 0.04mm~0.08mm; The width of the edge region is 2mm to 5mm, the laser scanning power of the edge region is 10% to 25% higher than that of the center region, and the scanning speed of the edge region is 15% to 30% higher than that of the center region. The scanning paths of the central region and the edge region are interleaved raster scans with an overlap rate of 30% to 50%.

[0009] Optionally, the plasma of the cryogenic plasma device is a mixed plasma comprising argon and hydrogen, wherein the volume fraction of hydrogen is 3% to 8%. The plasma treatment is performed at a pressure of 50 Pa to 200 Pa, a temperature of 80°C to 150°C, and a time of 10 min to 25 min.

[0010] Optionally, the magnetic abrasive finishing process uses a demagnetized stainless steel abrasive needle with a diameter of 0.6mm to 1.0mm, and the abrasive time is 8min to 18min; after abrasive finishing, the abrasive is cleaned with deionized water and dried.

[0011] Optionally, the air pressure for the sandblasting process is 0.6 MPa; The ultrasonic cleaning uses anhydrous ethanol, the cleaning time is 12 minutes, and the drying temperature is 70°C. The copper-chromium contact has a chromium content of 50% by mass. The width of the edge region is 3mm, the laser scanning power of the center region is 390W, the scanning speed is 1800mm / s, and the spot spacing is 0.06mm. The laser scanning power of the edge region is 20% higher than that of the center region, and the scanning speed of the edge region is 22.5% higher than that of the center region. The overlap rate of the scanning paths of the center region and the edge region is 40%. The volume fraction of hydrogen in the low-temperature plasma device is 5%, and the gas pressure during plasma treatment is 100 Pa, the treatment temperature is 120 °C, and the treatment time is 15 min. Magnetic grinding and finishing were performed using a demagnetized stainless steel grinding needle with a diameter of 0.8 mm for 12 minutes.

[0012] Optionally, when the plasma-treated copper-chromium contact is magnetically ground and finished, the mass ratio of the grinding medium to the contact is 5:1.

[0013] Optionally, when sandblasting the copper-chromium contact, the sandblasting medium used is white corundum sand with a particle size of 80 mesh.

[0014] Optionally, the modified copper-chromium contact shall satisfy at least one of the following properties: Surface roughness Ra≤3.5μm; Electrical conductivity ≥ 22.0 Ms / m; Surface grain size ≤5μm; Residual stress is reduced by 40% to 60% compared to single laser remelting; The performance deviation between the edge region and the center region is ≤5%.

[0015] In addition, to achieve the above objectives, this application also provides a copper-chromium contact, which is prepared using the laser remelting modification method described above.

[0016] Compared with the prior art, this application has the following beneficial effects: The laser remelting modification method provided in this application solves the problems of oil stains, oxide layers, and impurities on the surface of copper-chromium contacts through pretreatment, providing a clean and rough surface for subsequent laser remelting and improving laser absorption rate. By using partitioned laser remelting and edge power compensation, it solves the core defects of edge heat accumulation and uneven remelted layer thickness in the prior art from the source, ensuring uniform overall performance of the contacts. Among them, plasma relaxation purification is the key innovation of this application, which specifically solves the problems of high residual stress and residual surface oxide adsorption layer after laser remelting, while passivating micro-cracks and preventing defect propagation. Magnetic grinding and finishing further reduce the surface roughness of copper-chromium contacts and improve the surface finish of copper-chromium contacts, providing a guarantee for the improvement of their electrical performance. Attached Figure Description

[0017] Figure 1 This is a flowchart of the laser remelting modification method in the embodiments of this application; Figure 2 The images show the chromium phase microstructure distribution on the surface of the copper-chromium contacts prepared in Example 1 and Comparative Example 1 of this application. In Example 1, A is the surface grain distribution of the copper-chromium contacts prepared in Example 1, and B is the surface grain distribution of the copper-chromium contacts prepared in Comparative Example 1. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] See Figure 1 This application provides a laser remelting modification method for copper-chromium contacts, comprising the following steps: S1. Sandblasting and ultrasonic cleaning are performed on the copper-chromium contacts to complete the surface pretreatment. S2. A laser remelting system is used to perform laser remelting on the pre-treated copper-chromium contacts. During the laser remelting process, the central and edge areas of the pre-treated copper-chromium contacts are scanned differently, and dynamic power compensation is performed on the edge areas. S3. A low-temperature plasma device is used to perform plasma treatment on the copper-chromium contacts after laser remelting to achieve stress relaxation and surface purification. S4. The plasma-treated copper-chromium contacts are magnetically ground, refined, and dried to obtain laser-remelted modified copper-chromium contacts.

[0020] In this process, the pretreatment in step S1 solves the problems of oil stains, oxide layers, and residual impurities on the surface of the copper-chromium contact, providing a clean and rough surface for subsequent laser remelting and improving laser absorption rate. The partitioned laser remelting and edge power compensation in step S2 solves the core defects of edge heat accumulation and uneven remelted layer thickness in the prior art from the source, ensuring uniform overall performance of the contact. The plasma relaxation purification in step S3 is the key innovation of this application, which specifically solves the problems of high residual stress and residual surface oxide adsorption layer after laser remelting, while passivating micro-cracks and preventing defect propagation. The magnetic grinding and finishing in step S4 further reduces the surface roughness of the copper-chromium contact and improves the surface finish of the copper-chromium contact, providing a guarantee for the improvement of its electrical performance.

[0021] This application breaks through the limitations of existing technologies that rely on single laser remelting or laser remelting plus a single post-treatment. It integrates four processes—pretreatment, zoned laser remelting, plasma relaxation purification, and magnetic polishing—into a complete modification process chain. The synergistic effect of these four processes achieves multiple objectives: performance improvement, defect elimination, and batch stabilization. This can directly replace traditional aging processes and significantly improve production efficiency.

[0022] In other embodiments, the air pressure for sandblasting in step S1 is 0.5 MPa to 0.7 MPa; the ultrasonic cleaning uses anhydrous ethanol, the cleaning time is 10 min to 15 min, and the drying temperature is 60°C to 80°C; the mass fraction of chromium in the copper-chromium contact is 25% to 55%.

[0023] In this embodiment, the air pressure during sandblasting is limited to 0.5MPa~0.7MPa. This effectively removes the surface oxide layer and impurities, creating a suitable surface roughness to improve laser absorption, while avoiding excessive pressure that could damage or deform the contact surface, or insufficient pressure that could lead to incomplete pretreatment. Anhydrous ethanol is used for ultrasonic cleaning for 10~15 minutes, which efficiently removes surface oil. The volatile nature of anhydrous ethanol leaves no residue, preventing the impact of water-based cleaning solution residue on subsequent laser remelting. The drying temperature is 60℃~80℃, which quickly dries the contact surface moisture while preventing oxidation caused by high temperatures. The chromium content is 25%~55%, covering commonly used copper-chromium contact specifications in industry (such as CuCr25, CuCr40, CuCr50), expanding the application range and ensuring that copper-chromium contacts with different chromium contents can achieve performance improvements through this method.

[0024] In other embodiments, during the laser remelting process in step S2, the laser scanning power of the central region is 300W~420W, the scanning speed is 1500mm / s~2500mm / s, and the spot spacing is 0.04mm~0.08mm; the width of the edge region is 2mm~5mm, the laser scanning power of the edge region is 10%~25% higher than that of the central region, and the scanning speed of the edge region is 15%~30% higher than that of the central region; the scanning paths of the central region and the edge region are interleaved grating scans, with an overlap rate of 30%~50%.

[0025] In this embodiment, the parameters of the central region are limited to 300W~420W, 1500mm / s~2500mm / s, and 0.04mm~0.08mm, which can achieve uniform refinement of the chromium phase and form a continuous and dense fine-grained layer. At the same time, it avoids over-melting due to excessive power and incomplete remelting due to insufficient power. The width of the edge region is 2mm~5mm, which can be adapted to copper-chromium contacts of different specifications. The laser scanning power and scanning speed of the edge region are limited (laser scanning power increased by 10%~25%, scanning speed increased by 15%~30%), which specifically solves the problems of poor heat dissipation and heat accumulation at the edge, ensuring that the thickness of the remelted layer at the edge and the center is consistent and the performance is uniform. The staggered grating scanning combined with an overlap rate of 30%~50% can avoid scanning blind spots, ensure full coverage of the remelted layer, reduce defects in the remelted layer, improve surface density, and lay a good foundation for subsequent plasma processing and magnetic polishing.

[0026] In other embodiments, the plasma of the low-temperature plasma device in step S3 is a mixed plasma including argon and hydrogen, with a hydrogen volume fraction of 3% to 8%; the gas pressure during plasma treatment is 50 Pa to 200 Pa, the treatment temperature is 80°C to 150°C, and the treatment time is 10 min to 25 min.

[0027] This embodiment clearly defines the parameters and functions of the plasma treatment process, highlighting its core value. In the argon / hydrogen mixed plasma, argon plays a protective role, preventing secondary oxidation of the copper-chromium contact surface, while hydrogen efficiently removes the surface oxide layer and adsorbed gases, and participates in the stress relaxation process. The volume fraction of hydrogen is 3%~8%, ensuring both purification and stress relief effects while avoiding safety hazards caused by excessive hydrogen content. The treatment pressure is 50Pa~200Pa, the temperature is 80℃~150℃, and the time is 10min~25min. Low-temperature plasma treatment avoids high-temperature-induced grain growth and performance degradation of the copper-chromium contact, while ensuring sufficient elimination of residual stress, complete removal of the oxide layer, and effective passivation of microcracks, further improving the electrical performance and service life of the copper-chromium contact.

[0028] In other embodiments, when performing magnetic grinding and finishing on the copper-chromium contact in step S4, a demagnetized stainless steel grinding needle with a diameter of 0.6 mm to 1.0 mm is used; the grinding time is 8 min to 18 min; and after grinding, the contact is cleaned with deionized water and dried.

[0029] This embodiment limits the parameters of the magnetic polishing process to ensure a fine finish on the copper-chromium contact surface while avoiding damage. A 0.6mm~1.0mm demagnetized stainless steel polishing needle, with moderate hardness, effectively reduces surface roughness to Ra≤3.5μm. The demagnetization process also prevents residual magnetism from affecting the electrical performance of the copper-chromium contact. The polishing time is 8min~18min, which can be flexibly adjusted according to the required surface roughness of the copper-chromium contact, ensuring the polishing effect while avoiding over-polishing that could damage the remelted layer. Deionized water rinsing and drying remove debris and residual impurities generated during polishing, ensuring a clean copper-chromium contact surface and further improving its insulation performance and withstand voltage level.

[0030] Example 1 This embodiment uses the above method to perform laser remelting modification on a copper-chromium contact (specification: diameter 50mm, thickness 10mm) with a chromium content of 50%, including the following steps: 1. Pretreatment: (1) Sandblasting: Compressed air sandblasting equipment is used. The sandblasting medium is white corundum sand (particle size is 80 mesh). The sandblasting air pressure is adjusted to 0.6MPa, the sandblasting distance is controlled to 150mm, and the sandblasting angle is 45°. The upper and lower surfaces and edges of the copper-chromium contact are uniformly sandblasted for 3 minutes to ensure that the oxide layer and impurities on the surface of the copper-chromium contact are completely removed and a uniform and rough surface is formed. (2) Ultrasonic cleaning: Place the sandblasted copper-chromium contacts in anhydrous ethanol solution and put them in an ultrasonic cleaner. Adjust the ultrasonic power to 300W, the ultrasonic frequency to 40kHz, and the ultrasonic cleaning time to 12min to ensure that the oil stains and sandblasting residues on the surface of the copper-chromium contacts are completely removed. (3) Drying: Take out the ultrasonically cleaned copper-chromium contacts and put them into a forced-air drying oven. Adjust the drying temperature to 70℃ and the drying time to 20min to ensure that there is no moisture residue on the surface of the copper-chromium contacts. After drying, take them out and cool them to room temperature for later use.

[0031] 2. Adaptive partitioned laser remelting: (1) System debugging: The fiber laser remelting system is used with a laser wavelength of 1064nm and a spot diameter of 0.1mm. The adaptive partition scanning system is turned on, and the scanning parameters of the central area and the edge area are set, wherein the width of the edge area is set to 3mm. (2) Central area scanning: The laser scanning power of the central area is adjusted to 390W, the scanning speed is adjusted to 1800mm / s, and the spot spacing is adjusted to 0.06mm; (3) Edge region scanning: The laser power in the edge region is increased by 20% compared with the center region, that is, the power in the edge region is 468W; the scanning speed is increased by 22.5% compared with the center region, that is, the scanning speed in the edge region is 2205mm / s; the spot spacing is the same as that in the center region, which is 0.06mm; (4) Scanning operation: Use an interlaced grating scanning path and adjust the scanning overlap rate to 40%. During the scanning process, keep the distance between the laser focus and the surface of the copper-chromium contact constant (e.g., 5mm) to ensure that the remelting layer thickness is uniform. After the scanning is completed, remove the copper-chromium contact, cool it to room temperature, and set it aside for later use.

[0032] 3. Low-temperature plasma relaxation purification: (1) Device debugging: A low-temperature plasma device is used, and a mixed plasma including argon and hydrogen is introduced. The volume fraction of hydrogen is adjusted to 5%, the gas pressure inside the device is adjusted to 100 Pa, and the processing temperature is adjusted to 120 °C. (2) Plasma treatment: Place the laser-remelted copper-chromium contact into the plasma treatment chamber, ensuring that the copper-chromium contact is placed evenly and without obstruction. Turn on the device to perform plasma relaxation and surface cleaning treatment for 15 minutes. During the treatment, monitor the gas pressure, temperature and gas flow rate in the chamber in real time to ensure that the parameters are stable. After the treatment is completed, turn off the device and wait for the temperature in the chamber to cool to room temperature before taking out the copper-chromium contact for later use.

[0033] 4. Magnetic grinding, finishing, and drying: (1) Magnetic grinding: Plasma-treated copper-chromium contacts are placed in a magnetic grinding machine, and demagnetized stainless steel grinding needles with a diameter of 0.8 mm are added. The mass ratio of grinding media to copper-chromium contacts is 5:1. The grinding speed is adjusted to 300 r / min and the grinding time is 12 min. (2) Cleaning and drying: After grinding, the copper-chromium contact is taken out and ultrasonically cleaned with deionized water for 5 minutes to remove surface grinding debris. Then it is placed in a forced-air drying oven and dried at 70°C for 15 minutes. After cooling to room temperature, the laser remelted modified copper-chromium contact is obtained.

[0034] Compare with Example 1 This comparative example is identical to Example 1 except that low-temperature plasma relaxation purification is not performed. The specific steps are as follows: 1. The raw material preparation, pretreatment, and adaptive partitioned laser remelting are all consistent with those in Example 1; 2. Skip the low-temperature plasma relaxation purification and directly cool the laser-remelted copper-chromium contact to room temperature before proceeding to step 4; 3. The magnetic grinding finishing and drying are the same as in Example 1, and the modified copper-chromium contact is finally obtained.

[0035] To verify the effectiveness of this method, a four-level verification system was established, and the performance of both the examples and control examples was tested according to the following methods: (1) Microscopic organization verification Equipment: Metallurgical microscope, SEM (scanning electron microscope), TEM (transmission electron microscope), XRD (X-ray diffractometer). Indicators: chromium phase refinement degree, fine grain layer continuity, defects (cracks / porosity), grain size (measured using the intercept method).

[0036] (2) Physical performance verification Roughness: Measured using a roughness tester, the average value of 5 different points on the contact surface is taken, in μm; Electrical conductivity: measured using an eddy current conductivity meter, unit Ms / m; Hardness: Measured using a Vickers hardness tester, the average value of 5 points is taken, unit HV; Residual stress: Measured using an X-ray stress meter, in MPa. The difference and reduction ratio between the residual stress and that of single laser remelting (control example) were calculated.

[0037] (3) Electrical performance verification Withstand voltage strength: Measured using a high voltage tester, unit: kV / mm; the improvement ratio compared with the control example was calculated. Power frequency withstand voltage: Tested according to GB / T 14048.1-2012 standard to determine whether it is qualified; Breaking capacity: Tested according to GB / T 14048.2-2012 standard, and the improvement ratio compared with the control example was calculated; Anti-fusion welding performance: The on / off test was used to test and the improvement ratio compared with the control example was calculated; Insulation resistance: Measured using an insulation resistance tester, unit: MΩ.

[0038] (4) Batch reliability verification Thermal cycling test: -40℃~120℃, 50 cycles, observe for cracks, deformation, and failure. Life test: Simulate switching on and off according to actual working conditions, record the service life, and calculate the extension ratio compared with the control example; Process capability: Randomly select 30 batch products, test key performance indicators, and calculate the process capability index Cpk. Cpk ≥ 1.33 is required to meet the requirements of mass production.

[0039] Example 1 employs a complete composite process of "pretreatment-zoned laser remelting-plasma relaxation purification-magnetic polishing," while Example 1 lacks the plasma relaxation purification step. The performance differences between the two are significant, as detailed in the following comparative analysis: 1. Microstructure: such as Figure 2 As shown in A, the copper-chromium contact obtained in Example 1 has a uniform and refined chromium phase on its surface, with a small grain size (approximately 3.5 μm). The fine-grained layer is continuous and dense, without obvious cracks or pores. Figure 2 As shown in B, the copper-chromium contact obtained in Comparative Example 1 has a larger surface grain size (approximately 7.8 μm), uneven chromium phase distribution, and a small number of microcracks. This is mainly due to the lack of plasma passivation, and the microcracks generated by laser remelting were not repaired.

[0040] 2. Physical properties: The copper-chromium contact obtained in Example 1 has a surface roughness Ra=3.1μm, an electrical conductivity of 22.8Ms / m, and a residual stress of only 85MPa, which is 52% lower than that of the copper-chromium contact obtained in Control Example 1 (with a residual stress of 177MPa). The copper-chromium contact obtained in Control Example 1 has a surface roughness Ra=4.8μm and an electrical conductivity of 20.3Ms / m, mainly due to the lack of plasma purification, resulting in a residual oxide layer on the surface. At the same time, the residual stress was not relaxed, affecting the conductivity and surface finish.

[0041] 3. Electrical performance: The copper-chromium contact obtained in Example 1 has a 30% higher withstand voltage, a 38% higher breaking capacity, and a 35% higher anti-welding performance than that in Control Example 1, and meets the power frequency withstand voltage requirements; the copper-chromium contact obtained in Control Example 1 has a significantly lower withstand voltage and breaking capacity and poor anti-welding performance due to the high residual oxide layer and residual stress on the surface.

[0042] 4. Batch reliability: The copper-chromium contact obtained in Example 1 showed no failures in the thermal cycling test, with a process capability index Cpk=1.42, meeting the requirements for mass production; the copper-chromium contact obtained in Control Example 1 showed a small number of microcracks after the thermal cycling test, with Cpk=0.98, failing to meet the consistency requirements for mass production.

[0043] Example 2 This embodiment uses the above method to perform laser remelting modification on a copper-chromium contact (40mm in diameter and 8mm in thickness) with a chromium content of 25%, including the following steps: 1. Pretreatment: (1) Sandblasting: Compressed air sandblasting equipment is used. The sandblasting medium is white corundum sand (particle size is 80 mesh). The sandblasting air pressure is adjusted to 0.5MPa, the sandblasting distance is controlled to 150mm, and the sandblasting angle is 45°. The upper and lower surfaces and edges of the copper-chromium contact are uniformly sandblasted. The sandblasting time is 3min to ensure that the oxide layer and impurities on the surface of the copper-chromium contact are completely removed. (2) Ultrasonic cleaning: Place the sandblasted copper-chromium contacts in anhydrous ethanol solution and put them in an ultrasonic cleaner. Adjust the ultrasonic power to 300W, the ultrasonic frequency to 40kHz, and the ultrasonic cleaning time to 10min to remove surface oil and sandblasting residue. (3) Drying: Place the ultrasonically cleaned copper-chromium contacts into a forced-air drying oven, adjust the drying temperature to 60℃, and dry for 20 minutes to ensure that there is no moisture residue on the surface. Cool to room temperature for later use.

[0044] 2. Adaptive partitioned laser remelting: (1) System debugging: The fiber laser remelting system is used with a laser wavelength of 1064nm and a spot diameter of 0.1mm. The adaptive partition scanning system is turned on, and the scanning parameters of the central area and the edge area are set, wherein the width of the edge area is set to 2mm. (2) Central area scanning: The laser scanning power of the central area is adjusted to 300W, the scanning speed is adjusted to 1500mm / s, and the spot spacing is adjusted to 0.04mm; (3) Edge region scanning: The laser power in the edge region is increased by 10% compared with the center region, that is, the power in the edge region is 330W; the scanning speed is increased by 15% compared with the center region, that is, the scanning speed in the edge region is 1725mm / s; the spot spacing is the same as that in the center region, which is 0.04mm; (4) Scanning operation: Use an interlaced grating scanning path and adjust the scanning overlap rate to 30%. During the scanning process, keep the distance between the laser focus and the surface of the copper-chromium contact constant (e.g., 5mm) to ensure that the remelting layer thickness is uniform. After the scanning is completed, remove the copper-chromium contact, cool it to room temperature, and set it aside for later use.

[0045] 3. Low-temperature plasma relaxation purification: (1) Device debugging: A low-temperature plasma device is used, and a mixed plasma including argon and hydrogen is introduced. The volume fraction of hydrogen is adjusted to 3%, the gas pressure inside the device is adjusted to 50 Pa, and the processing temperature is adjusted to 80 °C. (2) Plasma treatment: Place the laser-remelted copper-chromium contact into the plasma treatment chamber, ensuring that the copper-chromium contact is placed evenly and without obstruction. Turn on the device to perform plasma relaxation and surface cleaning treatment for 10 minutes. During the treatment, monitor the gas pressure, temperature and gas flow rate in the chamber in real time to ensure that the parameters are stable. After the treatment is completed, turn off the device and wait for the temperature in the chamber to cool to room temperature before taking out the copper-chromium contact for later use.

[0046] 4. Magnetic grinding, finishing, and drying: A demagnetized stainless steel grinding needle with a diameter of 0.6 mm was used for grinding for 8 minutes. The remaining operations were the same as in Example 1, and the laser-remelted modified copper-chromium contact was finally obtained.

[0047] Compare with Example 2 Except for the absence of low-temperature plasma relaxation purification, the steps and parameters in this comparative example are exactly the same as in Example 2, and the modified copper-chromium contact is finally obtained.

[0048] Compared with Control Example 2, Example 2 shows significant performance advantages: 1. Microstructure: The surface grain size of the copper-chromium contact obtained in Example 2 was 4.8 μm, the chromium phase was relatively uniformly distributed, the fine grain layer was continuous, and there were no cracks; the surface grain size of the copper-chromium contact obtained in Control Example 2 was 8.2 μm, with a small number of pores and microcracks, and obvious chromium phase aggregation.

[0049] 2. Physical properties: The copper-chromium contact obtained in Example 2 has a surface roughness Ra=3.4μm, an electrical conductivity of 22.1Ms / m, and a residual stress of 102MPa, which is 51% lower than that of the copper-chromium contact obtained in Control Example 2 (residual stress of 208MPa); the surface roughness Ra of Control Example 2 is 5.1μm, and the electrical conductivity is 19.8Ms / m.

[0050] 3. Electrical performance: The copper-chromium contact obtained in Example 2 has a 25% higher withstand voltage, a 32% higher breaking capacity, and a 30% higher anti-welding performance than the control example 2, and its power frequency withstand voltage is qualified. Although the copper-chromium contact obtained in control example 2 is qualified in terms of power frequency withstand voltage, its withstand voltage and breaking capacity are lower than those of the copper-chromium contact obtained in Example 2, and it cannot meet the requirements for the use of medium and high voltage vacuum switches.

[0051] 4. Batch reliability: The copper-chromium contact obtained in Example 2 showed no failures in the thermal cycling test, with Cpk=1.35, meeting the requirements for mass production; the copper-chromium contact obtained in Control Example 2 showed slight deformation after the thermal cycling test, with Cpk=0.92, indicating poor consistency.

[0052] Example 3 This embodiment uses the above method to perform laser remelting modification on a copper-chromium contact (specification: diameter 60mm, thickness 12mm) with a chromium content of 55%, including the following steps: 1. Pretreatment: (1) Sandblasting: Compressed air sandblasting equipment is used. The sandblasting medium is white corundum sand (particle size is 80 mesh). The sandblasting air pressure is adjusted to 0.7MPa, the sandblasting distance is controlled to 150mm, and the sandblasting angle is 45°. The upper and lower surfaces and edges of the copper-chromium contact are uniformly sandblasted for 3 minutes to ensure that the oxide layer and impurities on the surface of the copper-chromium contact are completely removed and a uniform and rough surface is formed. (2) Ultrasonic cleaning: Place the sandblasted copper-chromium contacts in anhydrous ethanol solution and put them in an ultrasonic cleaner. Adjust the ultrasonic power to 300W, the ultrasonic frequency to 40kHz, and the ultrasonic cleaning time to 15min to ensure that the oil stains and sandblasting residues on the surface of the copper-chromium contacts are completely removed. (3) Drying: Take out the ultrasonically cleaned copper-chromium contacts and put them into a forced-air drying oven. Adjust the drying temperature to 80℃ and the drying time to 20min to ensure that there is no moisture residue on the surface of the copper-chromium contacts. After drying, take them out and cool them to room temperature for later use.

[0053] 2. Adaptive partitioned laser remelting: (1) System debugging: The fiber laser remelting system is used with a laser wavelength of 1064nm and a spot diameter of 0.1mm. The adaptive partition scanning system is turned on, and the scanning parameters of the central area and the edge area are set, wherein the width of the edge area is set to 5mm. (2) Central area scanning: The laser scanning power of the central area is adjusted to 420W, the scanning speed is adjusted to 2500mm / s, and the spot spacing is adjusted to 0.08mm; (3) Edge region scanning: The laser power in the edge region is increased by 25% compared with that in the center region, that is, the power in the edge region is 525W; the scanning speed is increased by 30% compared with that in the center region, that is, the scanning speed in the edge region is 3250mm / s; the spot spacing is the same as that in the center region, which is 0.08mm; (4) Scanning operation: Use an interlaced grating scanning path and adjust the scanning overlap rate to 50%. During the scanning process, keep the distance between the laser focus and the surface of the copper-chromium contact constant (e.g., 5mm) to ensure that the remelting layer thickness is uniform. After the scanning is completed, remove the copper-chromium contact, cool it to room temperature, and set it aside for later use.

[0054] 3. Low-temperature plasma relaxation purification: (1) Device debugging: A low-temperature plasma device is used, and a mixed plasma including argon and hydrogen is introduced. The volume fraction of hydrogen is adjusted to 8%, the gas pressure inside the device is adjusted to 200 Pa, and the processing temperature is adjusted to 150 °C. (2) Plasma treatment: Place the laser-remelted copper-chromium contact into the plasma treatment chamber, ensuring that the copper-chromium contact is placed evenly and without obstruction. Turn on the device to perform plasma relaxation and surface cleaning treatment for 25 minutes. During the treatment, monitor the gas pressure, temperature and gas flow rate in the chamber in real time to ensure that the parameters are stable. After the treatment is completed, turn off the device and wait for the temperature in the chamber to cool to room temperature before taking out the copper-chromium contact for later use.

[0055] 4. Magnetic grinding, finishing, and drying: A demagnetized stainless steel grinding needle with a diameter of 1.0 mm was used to grind for 18 minutes. The remaining operations were the same as in Example 1, and the laser-remelted modified copper-chromium contact was finally obtained.

[0056] Compare with Example 3 Except for the absence of low-temperature plasma relaxation purification, the steps and parameters in this comparative example are exactly the same as in Example 3, and the modified copper-chromium contact is finally obtained.

[0057] Compared with Control Example 3, Example 3 shows significant performance advantages: 1. Microstructure: The surface grain size of the copper-chromium contact obtained in Example 3 was 4.2 μm, the chromium phase was uniformly and finely distributed, the fine grain layer was dense, and there were no cracks; the surface grain size of the copper-chromium contact obtained in Control Example 3 was 7.5 μm, with a small amount of oxide inclusions and microcracks, mainly due to the high laser remelting power and the lack of plasma purification and stress relief.

[0058] 2. Physical properties: The copper-chromium contact obtained in Example 3 has a surface roughness Ra=3.2μm, an electrical conductivity of 22.5Ms / m, and a residual stress of 95MPa, which is 56% lower than that of the copper-chromium contact obtained in Control Example 3 (residual stress of 216MPa); the surface roughness Ra of Control Example 3 is 4.9μm, the electrical conductivity is 20.1Ms / m, and the residual stress is too high, which can easily lead to deformation of the copper-chromium contact.

[0059] 3. Electrical performance: The copper-chromium contact obtained in Example 3 has a 28% higher withstand voltage strength, a 35% higher breaking capacity, and a 32% higher anti-welding performance than the copper-chromium contact obtained in Comparative Example 3. It also meets the requirements for power frequency withstand voltage. The copper-chromium contact obtained in Comparative Example 3 has a larger fluctuation in withstand voltage strength due to surface oxide inclusions and high residual stress, and is prone to fusion welding when breaking.

[0060] 4. Batch reliability: The copper-chromium contact obtained in Example 3 showed no failures in the thermal cycling test, with Cpk=1.38, indicating good batch consistency; the copper-chromium contact obtained in Control Example 3 showed cracks after the thermal cycling test, with Cpk=0.95, which could not meet the requirements of industrial mass production.

[0061] Example 4 This embodiment uses the above method to perform laser remelting modification on CuCr20 copper-chromium contacts (specifications: diameter 40mm, thickness 8mm) with a chromium content of 15%, including the following steps: 1. Pretreatment: (1) Sandblasting: The sandblasting air pressure is adjusted to 0.4 MPa, and the rest of the operation is the same as in Example 1; (2) Ultrasonic cleaning: The ultrasonic cleaning time is 8 minutes, and the rest of the operation is the same as in Example 1; (3) Drying: The drying temperature is 50℃, and the rest of the operation is the same as in Example 1.

[0062] 2. Adaptive partitioned laser remelting: (1) System debugging: The width of the edge area is set to 1mm, and the rest of the operation is the same as in Example 1; (2) Central area scanning: The laser scanning power of the central area is adjusted to 280W, the scanning speed is adjusted to 1400mm / s, and the spot spacing is adjusted to 0.03mm; (3) Edge region scanning: The laser power in the edge region is increased by 8% compared with the center region; the scanning speed is increased by 12% compared with the center region; the spot spacing is the same as that in the center region, which is 0.03mm; (4) Scanning operation: The scanning overlap rate is adjusted to 25%, and the rest of the operation is the same as in Example 1.

[0063] 3. Low-temperature plasma relaxation purification: (1) Device debugging: A low-temperature plasma device is used, and a mixed plasma including argon and hydrogen is introduced. The volume fraction of hydrogen is adjusted to 2%, the gas pressure inside the device is adjusted to 40 Pa, and the processing temperature is adjusted to 70 °C. (2) Plasma treatment: The treatment time is 8 minutes, and the rest of the operation is the same as in Example 1.

[0064] 4. Magnetic grinding, finishing, and drying: A demagnetized stainless steel grinding needle with a diameter of 0.5 mm was used to grind for 6 minutes. The remaining operations were the same as in Example 1, and the laser-remelted modified copper-chromium contact was finally obtained.

[0065] Compare with Example 4 Except for the absence of low-temperature plasma relaxation purification, the steps and parameters in this comparative example are exactly the same as in Example 4, and the modified copper-chromium contact is finally obtained.

[0066] The results of the comparative analysis between Example 4 and Control Example 4 are as follows: 1. Microstructure: The surface grain size of the copper-chromium contact obtained in Example 4 was 5.8 μm, the chromium phase was unevenly distributed, the fine grain layer was discontinuous, and a small number of pores were present; the surface grain size of the copper-chromium contact obtained in Control Example 4 was 9.2 μm, the number of cracks was large, the chromium phase was severely aggregated, and the performance was worse.

[0067] 2. Physical properties: The copper-chromium contact obtained in Example 4 has a surface roughness Ra=3.8μm, an electrical conductivity of 21.5Ms / m, and a residual stress of 135MPa, which is 51% lower than that of the copper-chromium contact obtained in Control Example 4 (residual stress of 278MPa); the copper-chromium contact obtained in Control Example 4 has a surface roughness Ra=5.5μm and an electrical conductivity of 18.9Ms / m, showing a significant difference in performance indicators.

[0068] 3. Electrical performance: The copper-chromium contact obtained in Example 4 has a 20% higher withstand voltage, a 25% higher breaking capacity, and a 22% higher anti-welding performance than the copper-chromium contact obtained in Comparative Example 4. However, due to the failure of surface roughness and conductivity to meet the standards, the power frequency withstand voltage is barely qualified. The copper-chromium contact obtained in Comparative Example 4 fails the power frequency withstand voltage test and cannot be put into use.

[0069] 4. Batch reliability: The copper-chromium contact obtained in Example 4 showed slight cracks after thermal cycling test, with Cpk=1.12, which did not meet the requirements for mass production (Cpk≥1.33); the copper-chromium contact obtained in Control Example 4 failed severely after thermal cycling test and could not be used.

[0070] Example 5 This embodiment uses the above method to perform laser remelting modification on a CuCr60 copper-chromium contact (specification: diameter 60mm, thickness 12mm) with a chromium content of 65%, including the following steps: 1. Pretreatment: (1) Sandblasting: The sandblasting air pressure is adjusted to 0.8 MPa, and the rest of the operation is the same as in Example 1; (2) Ultrasonic cleaning: The ultrasonic cleaning time is 18 minutes, and the rest of the operation is the same as in Example 1; (3) Drying: The drying temperature is 90℃, and the rest of the operation is the same as in Example 1.

[0071] 2. Adaptive partitioned laser remelting: (1) System debugging: The width of the edge area is set to 6mm, and the rest of the operation is the same as in Example 1; (2) Central area scanning: The laser scanning power of the central area is adjusted to 450W, the scanning speed is adjusted to 2800mm / s, and the spot spacing is adjusted to 0.09mm; (3) Edge region scanning: The laser power in the edge region is increased by 30% compared with the center region; the scanning speed is increased by 35% compared with the center region; the spot spacing is the same as that in the center region, which is 0.09mm; (4) Scanning operation: The scanning overlap rate is adjusted to 55%, and the rest of the operation is the same as in Example 1.

[0072] 3. Low-temperature plasma relaxation purification: (1) Device debugging: A low-temperature plasma device is used, and a mixed plasma including argon and hydrogen is introduced. The volume fraction of hydrogen is adjusted to 10%, the gas pressure inside the device is adjusted to 220 Pa, and the processing temperature is adjusted to 160 °C. (2) Plasma treatment: The treatment time is 30 min, and the rest of the operation is the same as in Example 1.

[0073] 4. Magnetic grinding, finishing, and drying: A demagnetized stainless steel grinding needle with a diameter of 1.2 mm was used for grinding for 20 minutes. The remaining operations were the same as in Example 1, and the laser-remelted modified copper-chromium contact was finally obtained.

[0074] Compare with Example 5 Except for the absence of low-temperature plasma relaxation purification, the steps and parameters in this comparative example are exactly the same as in Example 5, and the modified copper-chromium contact is finally obtained.

[0075] The results of the comparative analysis between Example 5 and Control Example 5 are as follows: 1. Microstructure: The surface grain size of the copper-chromium contact obtained in Example 5 was 5.5 μm. Due to the excessively high laser power, local overmelting occurred, and local fractures occurred in the fine grain layer. In contrast, the surface grain size of Control Example 5 was 8.8 μm, the overmelting phenomenon was more severe, and there were more cracks and pores.

[0076] 2. Physical properties: The copper-chromium contact obtained in Example 5 has a surface roughness Ra=3.7μm and an electrical conductivity of 22.2Ms / m, which barely meets the specified standard. The residual stress is 115MPa, which is 54% lower than that of the copper-chromium contact obtained in Control Example 5 (residual stress of 248MPa). The copper-chromium contact obtained in Control Example 5 has a surface roughness Ra=5.2μm and an electrical conductivity of 19.5Ms / m. The residual stress is too high and is prone to contact damage.

[0077] 3. Electrical performance: The copper-chromium contact obtained in Example 5 has a 23% higher withstand voltage, a 28% higher breaking capacity, and a 25% higher anti-welding performance than the copper-chromium contact obtained in Comparative Example 5. It meets the requirements for power frequency withstand voltage, but its electrical performance stability is poor due to local overmelting. The copper-chromium contact obtained in Comparative Example 5 meets the requirements for power frequency withstand voltage, but its breaking capacity and anti-welding performance are significantly insufficient, and it cannot meet the requirements for high-voltage vacuum switches.

[0078] 4. Batch reliability: The copper-chromium contact obtained in Example 5 showed local cracks after thermal cycling test, with Cpk=1.18, which did not meet the requirements for mass production; the copper-chromium contact obtained in Control Example 5 showed severe deformation and cracks after thermal cycling test and could not be used.

[0079] Table 1 shows some performance parameters of the copper-chromium contacts prepared in Examples 1-5 and the copper-chromium contacts prepared in the control example: Table 1 Performance parameters of the copper-chromium contact parts obtained in Examples 1-5 and the control example.

[0080] The laser remelting modification method provided in this application is based on a synergistic process chain of "pretreatment - adaptive zoned laser remelting - low-temperature plasma relaxation purification - magnetic polishing finishing". By precisely limiting the key parameters of each process (covering the parameter ranges of pretreatment, laser remelting, plasma treatment, and magnetic polishing), the surface performance of copper-chromium contacts is comprehensively optimized. Experimental verification shows that the optimal modification effect can be obtained when the parameters of each process are controlled at a chromium mass fraction of 25%~55%, an air pressure of 0.5MPa~0.7MPa for sandblasting, and a laser scanning power of 300W~420W in the central region. When the parameters exceed this range (too high or too low), the modification effect will decrease significantly and the expected performance standard cannot be achieved.

[0081] Among them, the adaptive partitioned laser remelting solves the problems of edge heat accumulation and uneven remelted layer in traditional laser remelting by performing differentiated scanning and dynamic power compensation on the central and edge areas of the copper-chromium contact. The low-temperature plasma relaxation purification, as the key innovation of this application, can effectively eliminate the high residual stress generated by laser remelting, remove the surface oxide adsorption layer, and passivate microcracks, making up for the core defects of the single laser remelting process. The synergistic effect of each process forms a complete modification system, which can directly replace the traditional current aging and voltage aging processes, and greatly improve production efficiency and product quality.

[0082] The method provided in Example 1 can be applied to the mass production of CuCr50 contacts for 12kV vacuum circuit breakers, replacing the traditional voltage aging process. This method is also applicable to the production of various copper-chromium contacts (covering common specifications such as CuCr25, CuCr40, and CuCr50) with a chromium content of 25% to 55% by mass. It can directly replace traditional current aging and voltage aging processes without requiring additional production steps. It can be widely used in medium and high voltage vacuum circuit breakers, load switches, contactors, and other power equipment such as 12kV and 40.5kV circuit breakers, and has broad market application prospects.

[0083] Based on the performance comparison data of the embodiments and control examples, the beneficial effects of the method provided in this application can be divided into the following four points, all of which are supported by clear experimental data and have strong practicality and industrial application value: 1. Comprehensive performance improvement and effective elimination of defects: Compared with the control example lacking the plasma process, the copper-chromium contact modified by the method of this application can control the surface grain size to ≤5μm (all of Examples 1 to 3 meet this requirement), and the residual stress is reduced by 40% to 60% compared with single laser remelting (52% reduction in Example 1 and 56% reduction in Example 3); the surface roughness Ra≤3.5μm, the conductivity≥22.0Ms / m, and the withstand voltage strength, breaking capacity, and anti-welding performance are all improved by more than 25% (breaking capacity improved by 38% in Example 1). It completely solves the defects such as edge performance degradation, micro-cracks, and surface oxidation that exist in traditional laser remelting, and the electrical and physical properties meet the requirements for use in medium and high voltage vacuum switches.

[0084] 2. The process is highly efficient and environmentally friendly, reducing production costs: The total processing time for a single batch of the method in this application is ≤40 minutes (only 32 minutes in Example 1), which is more than 10 times more efficient than the traditional aging process (7~8 hours); there is no need to use impregnation solutions such as silver salts and molybdates, and there is no waste liquid discharge, which meets environmental protection requirements; at the same time, it significantly reduces energy consumption, is compatible with automated batch production lines, and significantly improves the economics of industrial production.

[0085] 3. Excellent batch consistency and outstanding stability: Through precise parameter limitation and collaborative process design, the performance deviation between the edge region and the center region of the modified contact in this application is ≤5% (only 3.2% in Example 1), and the process capability index Cpk≥1.33 (all of Examples 1 to 3 meet this requirement), which is much higher than the control example (Cpk <1.0). This enables high-consistency batch production, solves the industry pain point of poor batch reliability of existing modification methods, and ensures stable and controllable product quality.

[0086] In summary, this application effectively solves the core bottlenecks of existing copper-chromium contact surface modification technologies through process innovation and parameter optimization, taking into account performance improvement, efficiency improvement and cost reduction. It has significant technical advantages, economic benefits and environmental benefits, and is suitable for large-scale industrial application.

[0087] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A laser remelting modification method for copper-chromium contacts, characterized in that, include: The copper-chromium contacts are sandblasted and ultrasonically cleaned to complete the surface pretreatment. A laser remelting system is used to remelt the pre-treated copper-chromium contacts. During the laser remelting process, the central and edge regions of the pre-treated copper-chromium contacts are scanned differently, and dynamic power compensation is performed on the edge regions. A low-temperature plasma device is used to perform plasma treatment on the copper-chromium contacts after laser remelting to achieve stress relaxation and surface purification. The plasma-treated copper-chromium contacts were then magnetically ground and dried to obtain laser-remelted modified copper-chromium contacts.

2. The laser remelting modification method according to claim 1, characterized in that, The air pressure for the sandblasting process is 0.5 MPa to 0.7 MPa; the ultrasonic cleaning uses anhydrous ethanol, the cleaning time is 10 min to 15 min, and the drying temperature is 60℃ to 80℃; the mass fraction of chromium in the copper-chromium contact is 25% to 55%.

3. The laser remelting modification method according to claim 1, characterized in that, During the laser remelting process, the laser scanning power of the central region is 300W~420W, the scanning speed is 1500mm / s~2500mm / s, and the spot spacing is 0.04mm~0.08mm. The width of the edge region is 2mm to 5mm, the laser scanning power of the edge region is 10% to 25% higher than that of the center region, and the scanning speed of the edge region is 15% to 30% higher than that of the center region. The scanning paths of the central region and the edge region are interleaved raster scans with an overlap rate of 30% to 50%.

4. The laser remelting modification method according to claim 1, characterized in that, The plasma of the cryogenic plasma device is a mixed plasma comprising argon and hydrogen, wherein the volume fraction of hydrogen is 3% to 8%. The plasma treatment is performed at a pressure of 50 Pa to 200 Pa, a temperature of 80°C to 150°C, and a time of 10 min to 25 min.

5. The laser remelting modification method according to claim 1, characterized in that, The magnetic abrasive finishing process uses demagnetized stainless steel abrasive needles with a diameter of 0.6mm to 1.0mm, and the abrasive time is 8min to 18min. After abrasive finishing, the needles are cleaned with deionized water and dried.

6. The laser remelting modification method according to any one of claims 1-5, characterized in that, The air pressure for the sandblasting process is 0.6 MPa; The ultrasonic cleaning uses anhydrous ethanol, the cleaning time is 12 minutes, and the drying temperature is 70°C. The copper-chromium contact has a chromium content of 50% by mass. The width of the edge region is 3mm, the laser scanning power of the center region is 390W, the scanning speed is 1800mm / s, and the spot spacing is 0.06mm. The laser scanning power of the edge region is 20% higher than that of the center region, and the scanning speed of the edge region is 22.5% higher than that of the center region. The overlap rate of the scanning paths of the center region and the edge region is 40%. The volume fraction of hydrogen in the low-temperature plasma device is 5%, and the gas pressure during plasma treatment is 100 Pa, the treatment temperature is 120 °C, and the treatment time is 15 min. Magnetic grinding and finishing were performed using a demagnetized stainless steel grinding needle with a diameter of 0.8 mm for 12 minutes.

7. The laser remelting modification method according to claim 6, characterized in that, When the plasma-treated copper-chromium contacts are magnetically ground and finished, the mass ratio of the grinding medium to the contacts is 5:

1.

8. The laser remelting modification method according to claim 6, characterized in that, When the copper-chromium contact is sandblasted, the sandblasting medium used is white corundum sand with a particle size of 80 mesh.

9. The laser remelting modification method according to claim 7 or 8, characterized in that, The modified copper-chromium contact shall satisfy at least one of the following properties: Surface roughness Ra≤3.5μm; Electrical conductivity ≥ 22.0 Ms / m; Surface grain size ≤5μm; Residual stress is reduced by 40% to 60% compared to single laser remelting; The performance deviation between the edge region and the center region is ≤5%.

10. A copper-chromium contact, characterized in that, It was prepared by the laser remelting modification method as described in any one of claims 1 to 9.

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