A stainless steel flat tube for a liquid cooling radiator and a manufacturing process thereof

Abstract

This application relates to the field of liquid-cooled tubing, specifically disclosing a stainless steel flat tube for liquid-cooled radiators and its manufacturing process, including the following steps: S1, fabricating the flat tube body and flat tube sealing cap using a MIM process; S2, performing plasma cleaning on the welding areas of the flat tube body and flat tube sealing cap, then applying copper solder paste to the welding area and placing copper solder sheets, followed by vacuum brazing; S3, post-processing to obtain the stainless steel flat tube; this application also discloses the stainless steel tubing produced using the above manufacturing process. This application features a stainless steel flat tube with excellent sealing and leak-proof performance to meet the requirements of liquid-cooled radiators.

Description

Technical Field

[0001] This application relates to the field of liquid cooling tubing, and more specifically, to a stainless steel flat tube for liquid cooling radiators and its manufacturing process. Background Technology

[0002] With the rapid development of electronic information technology, the integration and computing speed of electronic devices such as servers and high-performance computing equipment are constantly improving, leading to a sharp increase in their power consumption density. Traditional air cooling methods are gradually failing to meet the demand for efficient heat dissipation. Liquid cooling technology, with its advantages of high heat capacity and high heat transfer efficiency, has become an effective way to solve the heat dissipation problem of high-power components.

[0003] Stainless steel flat tubes, as a key heat transfer element, play a crucial role in high-performance liquid cooling systems due to their compact structure, high strength, and corrosion resistance. A stainless steel flat tube typically consists of a flat tube body and a sealing cap welded to both sides or one end of the tube body. The tube body, as the main part of the stainless steel flat tube, forms the internal coolant flow channels, serving as the core heat dissipation pathway. The sealing cap is used to seal these channels, making it a key structural component for achieving a tight seal. As a critical component of radiators, the stability and precision of the manufacturing process of the stainless steel flat tube directly affect the final performance and reliability of the radiator. The manufacturing process of the stainless steel flat tube directly influences its performance, especially its sealing and leak-proof performance, which is crucial for its practical application. Summary of the Invention

[0004] In order to obtain a stainless steel flat tube with excellent sealing and leak-proof performance to meet the requirements of liquid cooling radiators, this application provides a stainless steel flat tube for liquid cooling radiators and its manufacturing process.

[0005] In a first aspect, this application provides a manufacturing process for a stainless steel flat tube used in a liquid-cooled radiator, employing the following technical solution: A manufacturing process for a stainless steel flat tube used in a liquid-cooled heat sink includes the following steps: S1. Flat tube body and flat tube sealing cap are manufactured separately by MIM process; S2. Plasma cleaning is performed on the welding area of ​​the flat tube body and the flat tube sealing cap. Then, copper solder paste is applied to the welding area and copper solder sheets are placed there. Then, vacuum brazing is performed. S3. Post-processing to obtain stainless steel flat tubes.

[0006] By adopting the above technical solution, this application uses a combination of copper solder paste and copper solder sheet. The copper solder paste melts at high temperature, filling the tiny gaps between the stainless steel flat tube and the copper solder sheet, and filling the voids between the welding surfaces, ensuring complete contact. Furthermore, atomic diffusion occurs between the molten copper solder paste, the stainless steel substrate, and the copper solder sheet, forming a strong metallurgical bond for reliable connection and a dense weld layer. This seals potential leak points in the coolant flow channel inside the stainless steel flat tube. The copper solder sheet connects the flat tube body and the flat tube sealing cap. During vacuum brazing, the melted copper solder paste spreads along the copper solder sheet, filling the welding gap between the flat tube body and the flat tube sealing cap, forming a dense weld. Ultimately, the copper solder sheet serves as a welding transition layer, and the copper solder paste fills the gap between the cap and the tube body, achieving a sealed weld. The copper solder sheet and copper solder paste together constitute a sealed weld layer, ensuring the airtightness of the coolant flow channel meets the helium leak detection rate and gas leak detection rate requirements.

[0007] Optionally, in step S2, the parameters for vacuum brazing are: evacuate to 10... -8 Pa-10 -4 Pa, then raise the temperature from room temperature to 400-450℃ at a rate of 2-5℃ / min and hold for 10-15 min; then raise the temperature to 820-880℃ at a rate of 5-8℃ and hold for 8-12 min; finally, lower the temperature to 600-650℃ at a rate of 1-3℃ and hold for 20-30 min before cooling to room temperature with the furnace.

[0008] By adopting the above technical solution, the vacuum brazing in this application uses a segmented heating process. First, it is kept at a lower temperature to allow the organic binder in the copper solder paste to decompose and volatilize, avoiding the presence of organic residue that could cause porosity in the weld. Then, it is brazed at a high temperature. After the copper solder paste melts, it spreads along the copper solder sheet, filling the flat tube body and the flat tube sealing cap. The copper-iron primary diffusion forms a metallurgical bond. Finally, it is first cooled and kept at a higher temperature, and then cooled again to achieve a slow cooling process. In this way, the physical state of the brazing filler metal changes in an orderly manner, reducing thermal stress, and the diffusion layer changes uniformly, avoiding the formation of microcracks due to rapid cooling.

[0009] Optionally, the material of the copper solder sheet in step S2 is copper.

[0010] Optional, the solder paste comprises the following ingredients by weight percentage: The composition is 68-75% low-temperature copper solder paste, 5-10% silver, 3-5% Ti powder, 0.3-0.8% Ce, 0.5-1% B and the balance being nano-TiC, wherein the metallic composition of the low-temperature copper solder paste is Cu74.8P5Sn16Ni4.2.

[0011] By adopting the above technical solution, this application uses low-temperature copper solder paste as the main component. Its low-temperature processing window helps reduce the brazing temperature and minimizes the impact of high temperatures on flat tube deformation. In addition, this application also adds Ti powder, which reacts with the chromium oxide passivation film on the stainless steel surface, transforming the dense oxide film into a wettable Ti-Cr-O mixed layer, facilitating the wetting and spreading of the copper solder paste. Ce element removes tin oxide and residual oxygen, reducing the tin oxide content with large wetting angles and improving wetting performance. The addition of B element reacts with chromium oxide to form a boron oxide film, which is dissolved during brazing. The addition of nano-titanium carbide can, on the one hand, [further enhance the brazing performance]. It acts as a thixotropic thickener. On the other hand, it is evenly dispersed in the weld to hinder misalignment. The addition of silver powder improves the spreading performance and reduces the enrichment of Sn. In this application, titanium carbide plays a role in filling and preventing flow, boron plays a role in destroying the lubricating film, and titanium helps with wetting. In the low-temperature copper solder paste, P and Sn affect the melting point, which reduces the impact on flat tube deformation during low-temperature brazing. The combination of boron, ce and titanium helps to destroy the chromium oxide layer and reduces the reduction in wetting effect caused by competition of boron for titanium. In the end, the wettability of the copper solder paste is improved, thereby improving the sealing performance and leakage prevention performance.

[0012] Optionally, the raw materials for the flat tube body and the flat tube sealing cap in step S1 include 316L powder and nano titanium carbide, and the amount of nano titanium carbide added is 0.5-1 wt% of 316L powder.

[0013] By adopting the above technical solution, when nano-titanium carbide is added to the flat tube raw material, it agglomerates on the surface during sintering, forming a self-lubricating brazing interface, which helps to improve the wettability of the brazing paste, thereby improving the sealing and leak-proof performance.

[0014] Optionally, in step S1, the sintering temperature of the MIM process is 1280-1380℃, the holding time is 3-5h, and the sintering atmosphere is a mixed gas of nitrogen and hydrogen mixed in a volume ratio of (95-97): (3-5).

[0015] Optionally, the post-processing in step S3 includes a dehydrogenation treatment and a nickel plating treatment performed sequentially, wherein the dehydrogenation treatment parameters are: holding at 180-220℃ for 2-4 hours.

[0016] By adopting the above technical solutions, hydrogen removal treatment removes hydrogen absorbed by the stainless steel substrate during vacuum brazing, preventing hydrogen embrittlement and hydrogen-induced microcracks in the weld area, and nickel plating treatment applies nickel to the surface of the flat tube to improve corrosion resistance.

[0017] Optional, the specific steps for nickel electroplating are as follows: 1) First, degrease and wash with water, then acid pickling and activation; 2) Then, in an activation solution of 180-240 g / L nickel chloride and 100-120 mL / L, at a concentration of 3-5 A / dm³ 2 Nickel plating at current density for 2-4 minutes; 3) In a plating bath containing 130-140 g / L nickel sulfamate, 25-35 g / L boric acid, and 15-20 g / L nickel chloride, at a concentration of 2-4 A / dm 2 Nickel plating at current density for 10-20 minutes, with a pH of 4-4.5 and a temperature of 40-55℃. 4) After washing with water and drying, it is then kept at 200-220℃ for 2-4 hours for dehydrogenation treatment.

[0018] By adopting the above technical solution, the first step is to perform degreasing treatment, followed by water washing and acid activation, which helps the coating to adhere. Then, pre-plating is performed before nickel plating, resulting in good coating adhesion.

[0019] Optionally, during nickel electroplating, the degreasing treatment in step 1) is carried out at a temperature of 80-95℃ for 20-30 minutes, and in an alkaline degreasing solution comprising the following raw materials: 60-75 g / L sodium hydroxide, 25-30 g / L sodium carbonate, 30-40 g / L trisodium phosphate dodecahydrate, 25-35 g / L sodium silicate nonahydrate, 1-2 g / L emulsifier, and the balance water.

[0020] Secondly, this application provides a stainless steel flat tube for a liquid-cooled radiator, employing the following technical solution: A stainless steel flat tube for liquid cooling radiators is manufactured using the aforementioned manufacturing process.

[0021] By adopting the above technical solution and the manufacturing process provided in this application, the stainless steel flat tube has excellent sealing and leak-proof performance, meeting the requirements of liquid-cooled radiators.

[0022] In summary, this application has the following beneficial effects: 1. In this application, a combination of copper solder paste and copper solder sheet is used. The copper solder sheet serves as a welding transition layer, and the copper solder paste fills the gap between the cap and the tube body to achieve a sealed weld. The copper solder sheet and copper solder paste together constitute a sealed weld layer to ensure that the airtightness of the coolant flow channel meets the helium leak detection rate and gas leak detection rate. 2. In this application, the copper solder paste melts at high temperature, filling the tiny gaps between the stainless steel flat tube and the copper solder sheet, and filling the voids between the welding surfaces to ensure complete contact. Moreover, atomic diffusion occurs between the molten copper solder paste, the stainless steel substrate, and the copper solder sheet, forming a strong metallurgical bond, achieving a reliable connection, and forming a dense weld layer that blocks potential leakage points in the coolant flow channels inside the stainless steel flat tube, thus playing a sealing role. The copper solder sheet connects the flat tube body and the flat tube sealing cap. During vacuum brazing, the melted copper solder paste spreads along the copper solder sheet, filling the welding gap between the flat tube body and the flat tube sealing cap, forming a dense weld. 3. In this application, vacuum brazing adopts a segmented heating process. First, it is kept at a lower temperature to allow the organic binder in the copper solder paste to decompose and volatilize, avoiding the presence of organic residue that could cause porosity in the weld. Then, it is brazed at a high temperature. After the copper solder paste melts, it spreads along the copper solder sheet, filling the flat tube body and the flat tube sealing cap. The copper-iron diffusion forms a metallurgical bond. Finally, it is first cooled and kept at a higher temperature, and then cooled again to achieve a slow cooling process. In this way, the physical state of the brazing filler metal changes in an orderly manner, reducing thermal stress, and the diffusion layer changes uniformly, avoiding the formation of microcracks due to rapid cooling.

[0023] 4. This application uses low-temperature copper solder paste as the main component. Its low-temperature processing window helps to reduce the brazing temperature and reduce the impact of high temperature on flat tube deformation. In addition, this application also adds Ti powder, which reacts with the chromium oxide passivation film on the stainless steel surface to form a wettable Ti-Cr-O mixed layer, which helps the copper solder paste to wet and spread. Ce element removes tin oxide and residual oxygen, reduces the content of tin oxide with large wetting angle, and improves wetting performance. The addition of B element reacts with chromium oxide to form a boron oxide film, which is dissolved during brazing. The addition of nano titanium carbide can play a thixotropic thickening role on the one hand, and on the other hand, it is uniformly dispersed in the weld to hinder misalignment movement. The addition of silver powder improves the spreading performance and reduces the enrichment of Sn. 5. In this application, titanium carbide plays a role in filling and preventing flow, boron plays a role in disrupting the lubricating film, and titanium (Ti) helps with wetting. In the low-temperature copper solder paste, phosphorus (P) and sn affect the melting point, which reduces the impact of brazing on flat tube deformation at low temperatures. The combination of boron, ce, and titanium (B, Ce, and Ti) breaks down the chromium oxide layer, which helps with wetting. At the same time, it reduces the reduction in wetting effect caused by competition between phosphorus (P) and titanium (Ti), ultimately improving the wettability of the copper solder paste, thereby improving the sealing performance and leakage prevention performance. Detailed Implementation

[0024] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0025] In the following examples, the low-temperature copper solder paste used is the low-temperature copper solder paste of Shanxi Weilang New Material Co., Ltd., which has a metal content of 85-90%, a polymer carrier of 10-15%, and a metal composition of Cu74.8P5Sn16Ni4.2.

[0026] In the following examples, the 316L stainless steel powder used was selected from Hebei Huazuan Alloy Welding Materials Co., Ltd. Example

[0027] A manufacturing process for a stainless steel flat tube used in a liquid-cooled heat sink includes the following steps: S1. Using 316L stainless steel powder and nano titanium carbide powder as raw materials, the amount of nano titanium carbide added is 0.8wt% of 316L powder. Flat tube body and flat tube sealing cap are made by MIM process. The sintering temperature of MIM process is 1200℃, the holding time is 4h, and the sintering atmosphere is a mixed gas of nitrogen and hydrogen in a volume ratio of 95:5. S2. Plasma cleaning is performed on the welding area of ​​the flat tube body and the flat tube sealing cap (cleaning parameters are helium pressure 200Kpa, cleaning time 50s, cleaning power 350W). Then, copper solder paste is applied to the welding area and copper solder sheet is placed. Then, vacuum brazing is performed to weld the flat tube body and the flat tube sealing cap to obtain the flat tube blank. Specifically, the copper solder sheet is selected from pure copper (T2) copper solder sheet, and the copper solder paste is prepared by mixing the following raw materials in the following mass percentages: It contains 72% low-temperature copper solder paste, 8% silver, 4% Ti powder, 0.5% Ce, 0.8% B and the balance nano TiC, wherein the metallic composition of the low-temperature copper solder paste is Cu74.8P5Sn16Ni4.2; The specific steps for vacuum brazing are as follows: evacuate to 10⁻³Pa, then heat from room temperature to 420℃ at a heating rate of 3℃ / min and hold for 12min; then heat to 850℃ at a heating rate of 6℃ and hold for 10min; finally, cool to 620℃ at a cooling rate of 2℃ and hold for 25min before cooling to room temperature with the furnace. S3. Post-processing, specifically including sequential dehydrogenation and nickel plating, with the following steps: S3-1, Dehydrogenation treatment: First, the flat tube blank obtained after step S2 is kept at 200℃ for 3 hours. S3-2, Electroplating nickel treatment, specifically including the following operations: 1) The flat tube blank after step S3-1 is first degreased in an alkaline degreasing solution. The degreasing temperature is 85℃ and the treatment time is 25min. The alkaline degreasing solution is made from the following raw materials: 65g / L sodium hydroxide, 28g / L sodium carbonate, 35g / L trisodium phosphate dodecahydrate, 30g / L sodium silicate nonahydrate, 1.5g / L emulsifier OP-10 and water to make up to 1L. Then, after washing three times with water, it is activated by soaking in 1 mol / L hydrochloric acid at a temperature of 30°C for 8 minutes. 2) The flat tube blank treated in step 2) is placed in an activation solution of 200 g / L nickel chloride and 110 mL / L, at a concentration of 4 A / dm³. 2 Nickel plating at current density for 3 minutes; 3) Then, in a plating solution containing 135 g / L nickel sulfamate, 30 g / L boric acid, and 18 g / L nickel chloride, at a concentration of 3 A / dm 2 Nickel plating was performed at a current density of 15 min, with the pH of the plating solution at 4 and the temperature at 50℃. 4) After washing and drying, the tube is then kept at 210℃ for 3 hours to remove hydrogen, thus obtaining a stainless steel flat tube. Example

[0028] A manufacturing process for a stainless steel flat tube used in a liquid-cooled heat sink includes the following steps: S1. Using 316L stainless steel powder and nano titanium carbide powder as raw materials, the amount of nano titanium carbide added is 0.5wt% of 316L powder. Flat tube body and flat tube sealing cap are made by MIM process. The sintering temperature of MIM process is 1280℃, the holding time is 5h, and the sintering atmosphere is a mixed gas of nitrogen and hydrogen in a volume ratio of 95:5. S2. Plasma cleaning is performed on the welding area of ​​the flat tube body and the flat tube sealing cap (cleaning parameters are helium pressure 200Kpa, cleaning time 40s, cleaning power 400W). Then, copper solder paste is applied to the welding area and copper solder sheet is placed. Then, vacuum brazing is performed to weld the flat tube body and the flat tube sealing cap to obtain the flat tube blank. Specifically, the copper solder sheet is selected from pure copper (T2) copper solder sheet, and the copper solder paste is prepared by mixing the following raw materials in the following mass percentages: The composition consists of 68% low-temperature copper solder paste, 10% silver, 5% Ti powder, 0.8% Ce, 1% B, and the balance being nano-TiC. The metallic composition of the low-temperature copper solder paste is Cu74.8P5Sn16Ni4.2. The specific operation steps of vacuum brazing are as follows: evacuate to 10⁻³Pa, then heat from room temperature to 400℃ at a heating rate of 2℃ / min and hold for 15min; then heat to 820℃ at a heating rate of 5℃ and hold for 12min; finally, cool to 600℃ at a cooling rate of 1℃ and hold for 30min before cooling to room temperature with the furnace. S3. Post-processing, specifically including sequential dehydrogenation and nickel plating, with the following steps: S3-1, Dehydrogenation treatment: First, the flat tube blank obtained after step S2 is kept at 180℃ for 4 hours. S3-2, Electroplating nickel treatment, specifically including the following operations: 1) The flat tube blank after step S3-1 is first degreased in an alkaline degreasing solution. The degreasing temperature is 80℃ and the treatment time is 30min. The alkaline degreasing solution is made from the following raw materials: 60g / L sodium hydroxide, 25g / L sodium carbonate, 30g / L trisodium phosphate dodecahydrate, 25g / L sodium silicate nonahydrate, 1g / L emulsifier OP-10 and water to make up to 1L. Then, after washing three times with water, it is activated by soaking in 1 mol / L hydrochloric acid at a temperature of 25°C for 10 minutes. 2) The flat tube blank treated in step 2) is placed in an activation solution of 180 g / L nickel chloride and 100 mL / L, at a concentration of 3 A / dm³. 2 Nickel plating at current density for 4 minutes; 3) Then, in a plating solution containing 130 g / L nickel sulfamate, 25 g / L boric acid, and 15 g / L nickel chloride, at a concentration of 2 A / dm 2 Nickel plating was performed at a current density of 20 min, with the pH of the plating solution at 4 and the temperature at 40℃. 4) After washing and drying, the tube is then kept at 200℃ for 4 hours to remove hydrogen, thus obtaining a stainless steel flat tube. Example

[0029] A manufacturing process for a stainless steel flat tube used in a liquid-cooled heat sink includes the following steps: S1. Using 316L stainless steel powder and nano titanium carbide powder as raw materials, the amount of nano titanium carbide added is 1wt% of 316L powder. Flat tube body and flat tube sealing cap are made by MIM process. The sintering temperature of MIM process is 1380℃, the holding time is 3h, and the sintering atmosphere is a mixed gas of nitrogen and hydrogen in a volume ratio of 97:3. S2. Plasma cleaning is performed on the welding area of ​​the flat tube body and the flat tube sealing cap (cleaning parameters are helium pressure 200Kpa, cleaning time 60s, cleaning power 300W). Then, copper solder paste is applied to the welding area and copper solder sheet is placed. Then, vacuum brazing is performed to weld the flat tube body and the flat tube sealing cap to obtain the flat tube blank. Specifically, the copper solder sheet is selected from pure copper (T2) copper solder sheet, and the copper solder paste is prepared by mixing the following raw materials in the following mass percentages: 75% low-temperature copper solder paste, 10% silver, 5% Ti powder, 0.8% Ce, 1% B and the balance nano TiC, wherein the metal composition of the low-temperature copper solder paste is Cu74.8P5Sn16Ni4.2; The specific steps for vacuum brazing are as follows: evacuate to 10⁻ 4 Pa, then raise the temperature from room temperature to 450℃ at a heating rate of 5℃ / min and hold for 10min; then raise the temperature to 880℃ at a heating rate of 8℃ and hold for 8min; finally, lower the temperature to 650℃ at a cooling rate of 3℃ and hold for 30min before cooling to room temperature with the furnace. S3. Post-processing, specifically including sequential dehydrogenation and nickel plating, with the following steps: S3-1, Dehydrogenation treatment: First, the flat tube blank obtained after step S2 is kept at 220℃ for 2 hours. S3-2, Electroplating nickel treatment, specifically including the following operations: 1) The flat tube blank after step S3-1 is first degreased in an alkaline degreasing solution. The degreasing temperature is 95℃ and the treatment time is 20min. The alkaline degreasing solution is made from the following raw materials: 75g / L sodium hydroxide, 30g / L sodium carbonate, 40g / L trisodium phosphate dodecahydrate, 35g / L sodium silicate nonahydrate, 2g / L emulsifier OP-10 and water to make up to 1L. Then, after washing three times with water, it is activated by soaking in 1 mol / L hydrochloric acid at a temperature of 35℃ for 5 minutes. 2) The flat tube blank treated in step 2) is placed in an activation solution of 240 g / L nickel chloride and 120 mL / L, at a concentration of 5 A / dm³. 2 Nickel plating at current density for 2 minutes; 3) Then, in a plating solution containing 140 g / L nickel aminosulfonate, 35 g / L boric acid, and 20 g / L nickel chloride, at a concentration of 4 A / dm 2 Nickel plating was performed at a current density of 20 min, with the pH of the plating solution at 4.5 and the temperature at 55℃. 4) After washing and drying, the tube is then kept at 220℃ for 2 hours to remove hydrogen, thus obtaining a stainless steel flat tube. Example

[0030] A manufacturing process for a stainless steel flat tube for a liquid-cooled radiator is carried out according to the method in Example 1, except that the vacuum brazing parameters in step S2 are: evacuate to 10⁻³Pa, then heat from room temperature to 850°C at a heating rate of 5°C / min, hold at that temperature for 30 minutes, and then cool to room temperature with the furnace. Example

[0031] A manufacturing process for a stainless steel flat tube for a liquid cooling radiator is carried out according to the method in Example 1, except that Ti powder is not added to the copper solder paste in step S2. Example

[0032] A manufacturing process for a stainless steel flat tube for a liquid cooling radiator is carried out according to the method in Example 1, except that TiC is not added to the copper solder paste in step S2. Example

[0033] A manufacturing process for a stainless steel flat tube for a liquid cooling radiator is carried out according to the method in Example 1, except that Ce is not added to the copper solder paste in step S2. Example

[0034] A manufacturing process for a stainless steel flat tube for a liquid cooling radiator is carried out according to the method in Example 1, except that B is not added to the copper solder paste in step S2. Example

[0035] A manufacturing process for a stainless steel flat tube for a liquid cooling radiator is carried out according to the method in Example 1, except that nano-titanium carbide is not added to the raw materials of the flat tube body and the flat tube sealing cap in step S1.

[0036] Comparative Example 1 A manufacturing process for a stainless steel flat tube for a liquid cooling radiator is carried out according to the method in Example 1, except that no copper solder sheet is placed at the welding part in step S2.

[0037] Comparative Example 2 A manufacturing process for a stainless steel flat tube for a liquid cooling radiator is carried out according to the method in Example 1, except that copper solder paste is not applied to the welding area in step S2.

[0038] Performance testing The flat tube blanks obtained in step S3-1 of the above embodiments and comparative examples were tested for helium leakage rate (helium pressure 200KPa, pressure holding for 60s, in accordance with GB / T 15171) and gas leakage rate (350KPa charging pressure, pressure holding for 120s, pressure rise on the leakage side, in accordance with HB 5460). The test results are shown in Table 1.

[0039] Table 1:

[0040] Based on the test results in Table 1 above, it can be seen that the stainless steel flat tube prepared in the embodiments of this application has good sealing and leak-proof performance. Based on the test results of Embodiments 1 and 4, it can be seen that in Embodiment 4, the conventional brazing process is used. Compared with the three-stage heating method in Embodiment 1, the helium leak detection rate and gas leak detection rate in Embodiment 4 are both increased. Compared with the stepped heating process in Embodiment 1, its sealing and leak-proof performance is reduced. Based on the test results of Embodiments 1 and 5, when titanium powder is not added to the copper solder paste in Embodiment 5, its helium leak detection rate and gas leak detection rate are increased, and its sealing and leak-proof performance is reduced. In Example 6, the sealing and leak-proof performance was reduced when titanium carbide was not added. This may be because nano-titanium carbide hinders misalignment movement, affecting the welding performance of the welding area and thus the sealing performance. In Examples 7 and 8, the sealing and leak-proof performance was reduced when Ce or B was not added. The addition of Ce and B to the copper solder paste affects the spreading and wetting properties of the copper solder paste, thereby affecting the final sealing performance. In Example 9, the sealing performance was also reduced when nano-titanium carbide was not added to the raw materials in the MIM process. Adding nano-titanium carbide to the base material helps the copper solder paste wettability.

[0041] Combining the test results of Example 1 and Comparative Examples 1 and 2, it can be seen that when no copper solder sheet or copper solder paste was added in Comparative Examples 1 and 2, or when only one of them was added, the sealing performance was significantly reduced. The synergistic effect of copper solder paste and copper solder sheet has a significant effect on sealing performance. The absence of key components in copper solder paste will also affect the leakage rate and thus affect sealing performance.

[0042] In addition, the stainless steel flat tubes prepared in Examples 1-3 of this application were subjected to flow resistance testing (using a UNF7 / 16 connector to connect to a flow resistance tester), and their flow resistance was <0.4H (unit pressure drop), which meets the requirements.

[0043] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A manufacturing process for a stainless steel flat tube used in a liquid-cooled radiator, characterized in that, Includes the following steps: S1. Flat tube body and flat tube sealing cap are manufactured separately by MIM process; S2. Plasma cleaning is performed on the welding area of ​​the flat tube body and the flat tube sealing cap. Then, copper solder paste is applied to the welding area and copper solder sheets are placed there. Then, vacuum brazing is performed. S3. Post-processing to obtain stainless steel flat tubes.

2. The manufacturing process of a stainless steel flat tube for a liquid-cooled radiator according to claim 1, characterized in that: In step S2, the parameters for vacuum brazing are: evacuate to 10... -8 Pa-10 -4 Pa, then raise the temperature from room temperature to 400-450℃ at a rate of 2-5℃ / min and hold for 10-15 min; then raise the temperature to 820-880℃ at a rate of 5-8℃ and hold for 8-12 min; finally, lower the temperature to 600-650℃ at a rate of 1-3℃ and hold for 20-30 min before cooling to room temperature with the furnace.

3. The manufacturing process of a stainless steel flat tube for a liquid-cooled radiator according to claim 1, characterized in that: The material of the copper solder sheet in step S2 is copper.

4. The manufacturing process of a stainless steel flat tube for a liquid-cooled radiator according to claim 1, characterized in that: The copper solder paste comprises the following ingredients by weight percentage: The composition is 68-75% low-temperature copper solder paste, 5-10% silver, 3-5% Ti powder, 0.3-0.8% Ce, 0.5-1% B and the balance being nano-TiC, wherein the metallic composition of the low-temperature copper solder paste is Cu74.8P5Sn16Ni4.

2.

5. The manufacturing process of a stainless steel flat tube for a liquid-cooled radiator according to claim 1, characterized in that: In step S1, the raw materials for the flat tube body and the flat tube sealing cap include 316L powder and nano titanium carbide, and the amount of nano titanium carbide added is 0.5-1 wt% of 316L powder.

6. The manufacturing process of a stainless steel flat tube for a liquid-cooled radiator according to claim 1, characterized in that: In step S1, the sintering temperature of the MIM process is 1280-1380℃, the holding time is 3-5h, and the sintering atmosphere is a mixture of nitrogen and hydrogen in a volume ratio of (95-97): (3-5).

7. The manufacturing process of a stainless steel flat tube for a liquid-cooled radiator according to claim 1, characterized in that: The post-processing in step S3 includes a dehydrogenation treatment and a nickel electroplating treatment performed sequentially. The dehydrogenation treatment parameters are: holding at 180-220℃ for 2-4 hours.

8. The manufacturing process of a stainless steel flat tube for a liquid-cooled radiator according to claim 7, characterized in that: The specific steps for nickel electroplating are as follows: 1) First, degrease and wash with water, then acid pickling and activation; 2) then in 180-240 g / L nickel chloride, 100-120 mL / L of activating solution, at 3-5 A / dm 2 current density 2-4 min; 3) In a plating bath containing 130-140 g / L nickel sulfamate, 25-35 g / L boric acid, and 15-20 g / L nickel chloride, at a concentration of 2-4 A / dm 2 Nickel plating at current density for 10-20 minutes, with a pH of 4-4.5 and a temperature of 40-55℃. 4) After washing with water and drying, it is then kept at 200-220℃ for 2-4 hours for dehydrogenation treatment.

9. The manufacturing process of a stainless steel flat tube for a liquid-cooled radiator according to claim 8, characterized in that: During nickel electroplating, the degreasing treatment in step 1) is carried out at a temperature of 80-95℃ for 20-30 minutes in an alkaline degreasing solution, which includes the following raw materials: 60-75 g / L sodium hydroxide, 25-30 g / L sodium carbonate, 30-40 g / L trisodium phosphate dodecahydrate, 25-35 g / L sodium silicate nonahydrate, 1-2 g / L emulsifier, and the balance water.

10. A stainless steel flat tube for liquid-cooled radiators, characterized in that: It is produced by the manufacturing process described in any one of claims 1-9.

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