A brazing method and brazed joint under simulated microgravity conditions

Abstract

The present application relates to the technical field of brazing, in particular to a brazing method and a brazing joint under simulated microgravity conditions. The method comprises the following steps: pretreating the base material and filler metal to be welded; fixing the base material to be welded on a brazing temperature control hot table module and inputting protective gas, and placing the filler metal in a ceramic tube at the lower end of the needle head section of a needle heating unit; adjusting the distance between the needle head section and the base material to be welded; first starting the needle heating unit to heat the filler metal, and then starting the brazing temperature control hot table module to heat the base material to be welded after a preset delay; triggering the tower falling and cabin free falling when both reach the welding temperature; and sequentially completing the processes of quantitative extrusion of molten filler metal under microgravity, recording liquid bridge formation and wetting spreading, inputting cooling gas for rapid solidification, and the like in time sequence during the falling. The present application realizes precise time sequence control through independent temperature control, and can quickly complete the whole brazing process of liquid filler metal extrusion, interface wetting and spreading, and solidification within the short microgravity window period of tower falling.

Description

Technical Field

[0001] This invention relates to the field of brazing technology, and more specifically, to a brazing method and brazed joint under simulated microgravity conditions. Background Technology

[0002] With the improvement of space exploration capabilities, tasks such as the on-orbit assembly of large space stations and the on-orbit repair of damaged spacecraft components have become routine, placing stringent demands on space connection technologies. Brazing, due to its strong adaptability to operating conditions, high safety factor, and ability to connect complex components, is a key process for on-orbit manufacturing and repair. Drop tower devices can effectively simulate the microgravity environment of space and are an important platform for conducting brazing ground tests.

[0003] However, current microgravity brazing experiments using a drop tower face several technical bottlenecks: First, the lack of gravity driving force in a microgravity environment prevents liquid brazing filler metal from flowing and dripping under its own weight; second, the traditional method of simultaneous heating of the base material and brazing filler metal results in a slow melting rate and long cycle, making it difficult to accurately control the timing of the melting, wetting, and spreading of the brazing filler metal; third, the effective microgravity duration of the drop tower is less than 5 seconds, and the simultaneous heating mode cannot guarantee that the melting, wetting, spreading, and solidification processes of the brazing filler metal all fall within the microgravity window period, and it is difficult to achieve precise control over the timing and quantity of material supply. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a brazing method and brazed joint under simulated microgravity conditions, solving the problems of difficulty in independently controlling the temperature of the base material and the brazing filler metal during brazing under microgravity conditions, as well as the inability to actively and quantitatively feed the brazing filler metal.

[0005] On one hand, the present invention provides a brazing method under simulated microgravity conditions, comprising the following steps: The base material and brazing filler metal to be welded are pretreated separately and coated with flux; The pretreated base material to be welded is fixed on the brazing temperature control heating platform module and a protective gas is introduced. The pretreated brazing filler metal is placed in the ceramic tube of the needle heating unit, and a needle section is formed at the lower end of the ceramic tube. Adjust the distance between the needle tip and the surface of the base material to be welded; The needle heating unit is activated to heat the brazing filler metal to obtain molten brazing filler metal, and after a preset delay, the brazing temperature control heating platform module is activated to heat the base material to be welded; When the brazing filler metal reaches the first preset welding temperature and the base material to be welded reaches the second preset welding temperature, the drop chamber containing the brazing temperature control heating platform module and the needle heating unit is triggered to fall freely. During the free fall of the descent chamber, the following operations are performed sequentially according to a preset time sequence: the molten brazing filler metal is quantitatively extruded from the needle section onto the surface of the base material to be welded, and the molten brazing filler metal forms a liquid bridge between the needle section and the surface to be welded; the wetting and spreading process of the molten brazing filler metal on the surface to be welded is recorded by high-speed camera; and cooling gas is introduced into the welding area to rapidly solidify the brazing filler metal.

[0006] Preferably, the pretreatment of the base material and the brazing filler metal includes: grinding the base material and the brazing filler metal, ultrasonic cleaning, stepwise chemical cleaning with alkaline and acidic solutions to remove the surface oxide film, and finally storing them in anhydrous ethanol.

[0007] Preferably, the flux is a paste-like flux prepared by mixing fluoride flux powder and anhydrous ethanol at a mass ratio of 2:1.

[0008] Preferably, the diameter of the needle tip is 1.5mm to 2.0mm, and the distance between the needle tip and the surface of the base material to be welded is 1mm to 3mm.

[0009] Preferably, when the temperature of the needle heating unit reaches 350-400°C, the brazing temperature control heating stage module is activated to heat the base material to be welded; the heating rate of the brazing filler metal is 5-15°C / min, and the heating rate of the base material to be welded is 20-40°C / min.

[0010] Preferably, the first preset welding temperature is the temperature at which the brazing filler metal melts; the second preset welding temperature is higher than the melting temperature of the flux and lower than the melting temperature of the base material to be welded.

[0011] Preferably, the process of recording the wetting and spreading of molten solder on the surface to be soldered by high-speed camera includes: using a backlight source and a high-speed camera, wherein the center of the lens of the high-speed camera, the center of the observation window and the center of the backlight source are collinear, and the frame rate is 100 to 300 frames / second.

[0012] Preferably, the duration of the free fall of the drop chamber is 3.6 seconds, and the preset timing is as follows: 0.2 seconds after the start of the fall, the quantitative extrusion operation of the molten brazing filler metal is started, so that the molten brazing filler metal is wetted and spread within 2.0 seconds; 2.5 seconds after the start of the fall, the operation of introducing the cooling gas is started, and the cooling gas is high-pressure nitrogen gas with an introduction pressure of 2MPa.

[0013] Preferably, the quantitative extrusion operation of the molten brazing filler metal includes: driving the ceramic rod to move linearly through a linear stroke power component to push the molten brazing filler metal out of the needle section; wherein the ceramic rod is inserted into the ceramic tube.

[0014] On the other hand, the present invention also provides a brazed joint, which is prepared by the above-mentioned drop tower experiment to simulate brazing under microgravity conditions.

[0015] The beneficial technical effects of this invention are as follows: This invention discloses a brazing method under simulated microgravity conditions, employing a time-sequential temperature control strategy: first, the brazing filler metal is heated individually by a needle-type heating unit; after a preset delay, the base material to be welded is then heated by a brazing temperature control stage. This achieves independent temperature control and zoned heating of the brazing filler metal and base material, strictly meeting the process requirements of melting the brazing filler metal and maintaining the base material in a solid state. This ensures that core processes such as brazing filler metal extrusion, wetting, and spreading are completed within the microgravity window. After the descent chamber enters microgravity, molten brazing filler metal is quantitatively extruded from the needle tip onto the surface of the base material according to a preset sequence. This active feeding mode overcomes the limitations of gravity-driven processes, allowing for precise control of the brazing filler metal extrusion timing and filling amount, achieving accurate control of the weld filling position and amount, and effectively ensuring the quality of the brazed joint. High-speed imaging during the experiment generates high-contrast interface images, clearly distinguishing the boundary between the molten brazing filler metal and the base material to be welded, fully capturing the entire process of brazing filler metal wetting and spreading, and accurately extracting key experimental data such as liquid bridge formation, wetting angle, and spreading speed. After the brazing process is completed, cooling gas can be injected into the weld area through pipelines, promoting rapid solidification of the brazing filler metal and promptly freezing the liquid-solid interface morphology under microgravity. This avoids distortion of the microstructure and free surface morphology caused by gravity recovery and mechanical vibration during the landing and recovery phase, effectively preserving the free surface morphology and microstructure formed under microgravity. In summary, the brazing method of this invention enables precise process control and dynamic observation of the entire brazing process under microgravity.

[0016] The base material to be welded is AA3003 aluminum alloy. The brazed joint obtained by the brazing method of this invention has a maximum shear strength of 78 MPa, and the weld rate remains above 90% after 20 temperature resistance cycles. The airtightness is also higher than 1×10⁻⁶. -8 Pa·m³ / s. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a brazing method under simulated microgravity conditions in one embodiment of the present invention; Figure 2 This is a diagram illustrating the wetting and spreading process of the brazing filler metal under microgravity in one embodiment of the present invention. Figure 3 This is an enlarged view of the microstructure of a brazed joint under constant gravity conditions in one embodiment of the present invention; Figure 4 This is an enlarged view of the microstructure of a brazed joint under microgravity conditions in one embodiment of the present invention; Figure 5This is a schematic diagram of a brazing experimental apparatus simulating microgravity conditions in one embodiment of the present invention; Figure 6 for Figure 5 A partial cross-sectional diagram; Figure 7 This is a schematic diagram of the structure of a brazing temperature control heating stage module in one embodiment of the present invention.

[0018] Figure labeling: 1-Brazing temperature control heating stage module; 2-Needle heating unit; 3-Braving metal extrusion mechanism; 4-Image acquisition system; 5-Controller; 6-Fixed support mechanism; 11-Temperature control box; 12-Cooling air pipe; 13-Temperature measuring element; 21-Connecting frame; 22-Needle heating steel pipe; 23-Ceramic tube; 24-Mounting base; 25-Sealing ring; 31-Linear stroke power assembly; 32-Ceramic rod; 33-Positioning sleeve; 34-Positioning cap; 41-Backlight source; 42-High-speed camera; 61-Fixed stage; 611-Fixed plate; 62-Z-axis scissor lift platform; 111-Upper top plate; 112-Lower top plate; 113-Positioning ring; 114-Observation window; 230-Needle tip section. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0020] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used only to distinguish different devices, modules, or units, and are not intended to limit the order of functions performed by these devices, modules, or units or their interdependencies.

[0021] It should be noted that the terms "a" and "a plurality of" used in this invention are illustrative rather than restrictive. Those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0022] One embodiment of the present invention provides a brazing method and a brazed joint under simulated microgravity conditions.

[0023] See Figure 1 On the one hand, the present invention provides a brazing method under simulated microgravity conditions, comprising the following steps: S1: Pre-treat the base material and brazing filler metal separately, and apply flux; Specifically, two AA3003 aluminum alloy base materials, each 6mm long, 6mm wide, and 3mm thick, were cut using a CNC machine tool. The surfaces of the AA3003 aluminum alloy base materials to be welded were sanded to remove machining oil and cutting marks. They were then ultrasonically cleaned in anhydrous ethanol for 11-21 minutes to remove any residual sandpaper particles. Next, they were cleaned sequentially with 10wt.% NaOH and 10wt.% HNO3 solutions for 3 minutes each to remove the oxide film on the aluminum alloy surface. Finally, they were stored in anhydrous ethanol to avoid prolonged exposure to air.

[0024] Weigh 120mg of AA4047 welding wire filler metal, polish it with sandpaper to remove machining oil stains on the surface, ultrasonically clean it in anhydrous ethanol for 11~21min to remove sandpaper residue particles on the surface, then clean it with 10wt.% NaOH and 10wt.% HNO3 solution for 3min to remove the oxide film on the aluminum alloy surface, and store it in anhydrous ethanol.

[0025] S2: Fix the pretreated base material to be welded to the brazing temperature control heating platform module 1 and introduce protective gas. Place the pretreated brazing filler metal in the ceramic tube 23 of the needle heating unit 2. The lower end of the ceramic tube 23 forms a needle section 230. S3: Adjust the distance between the needle tip section 230 and the surface of the base material to be welded; Specifically, the brazing temperature control heating platform module 1 is a sealed box with upper and lower dual-zone heating, and a fixture for the base material to be welded is provided inside the box. Two pre-treated AA3003 aluminum alloy base materials are placed in a butt-to-butt configuration and clamped together using the base material fixture, ensuring a gap of 0.01–0.5 mm between the two base materials. The brazing temperature control heating platform module 1 can fix and heat the base materials to be welded. The needle heating unit 2 includes a ceramic tube 23, the lower end of which has a needle section 230 with a diameter smaller than its cavity. Pre-treated AA4047 brazing wire is placed inside the cavity of the ceramic tube 23, positioned above the needle section 230. The height of the brazing temperature control heating platform module 1 is adjusted using the Z-axis scissor lift 62 to ensure the distance between the end of the needle section 230 and the surface of the base material to be welded is a preset value (e.g., 1.5 mm). After adjustment, the Z-axis scissor lift 62 is locked. The ceramic rod 32 is inserted into the upper end of the ceramic tube 23 and is connected to the linear power component 31 for transmission. When the drop chamber falls freely to the preset time point, the linear power component 31 drives the ceramic rod 32 to move downward, and extrudes the molten brazing filler metal in the ceramic tube 23 from the needle section 230 in a quantitative manner, so that the molten brazing filler metal forms a liquid bridge between the needle section 230 and the surface of the base material to be welded, and reliably transfers the droplets to the surface to be welded. S4: The start pin heating unit 2 heats the brazing filler metal to obtain molten brazing filler metal, and after a preset delay, the brazing temperature control heating platform module 1 is started to heat the base material to be welded; Specifically, the temperature control program of the needle heating unit 2 is activated to heat the brazing filler metal. When the temperature of the needle heating unit 2 reaches 370℃ (i.e., the preset delayed trigger point), the brazing temperature control heating stage module 1 is automatically activated to heat the base material to be welded. Subsequently, both the needle heating unit 2 and the brazing temperature control heating stage module 1 continue to heat up. The set target temperature for brazing filler metal heating is 600℃, and the heating rate is 10℃ / min. The set target temperature for the base material to be welded is 575℃, and the heating rate is 30℃ / min.

[0026] S5: When the brazing filler metal reaches the first preset welding temperature and the base material to be welded reaches the second preset welding temperature, the drop chamber carrying the brazing temperature control heating platform module 1 and the needle heating unit 2 is triggered to fall freely. Specifically, the heating unit 2 reaches 600°C, the brazing temperature control module 1 reaches 575°C, and the flux on the surface to be brazed is completely melted as observed by the high-speed camera 42, indicating that the initial conditions for microgravity brazing are met. An electromagnetic release command is sent via the control console, the magnetic head is de-energized, and the drop chamber inside the drop tower falls freely.

[0027] S6: During the free fall of the landing capsule, the following operations are performed in sequence according to the preset timing: molten brazing filler metal is quantitatively extruded from the needle section 230 to the surface of the base material to be welded, and a liquid bridge is formed between the needle section 230 and the surface to be welded; the wetting and spreading process of the molten brazing filler metal on the surface of the base material to be welded is recorded by a high-speed camera 42; and cooling gas is introduced into the welding area to make the brazing filler metal solidify rapidly.

[0028] Specifically, the timing zero point is set at the moment the descent begins. At 0.2 seconds of descent, the timing program triggers the linear motion power component 31 (electric push rod). The linear motion power component 31 includes a motor and a lead screw and nut mechanism. The motor rotates at 60 rpm and drives the ceramic rod 32 to move linearly through the lead screw and nut mechanism, quantitatively extruding the molten brazing filler metal in the ceramic tube 23 from the needle section 230 onto the surface of the base material to be welded. The diameter of the needle section 230 is 1.5 mm to 2.0 mm. During the period from 0.2 to 2.0 seconds, the molten brazing filler metal completes wetting and spreading on the surface of the base material to be welded. The high-speed camera 42 continuously records the spreading process at 200 frames per second. At 2.5 seconds of descent, the timing program triggers the opening of the cooling solenoid valve, introducing 2 MPa high-pressure nitrogen gas into the weld area of ​​the temperature control box 11 of the brazing temperature control hot stage module 1 through the cooling gas pipe 12, causing the molten brazing filler metal to solidify rapidly. After 3.6 seconds of descent, the capsule landed in the buffer recovery net, marking the end of the microgravity brazing experiment.

[0029] The welded sample was removed, and the image data recorded by the high-speed camera 42 was exported. Parameters such as the free surface shape of the liquid bridge, wetting angle, and spreading speed were extracted using image analysis software. The brazed joint was then subjected to CT inspection, airtightness testing, and mechanical property testing.

[0030] It should be noted that in this embodiment, the starting needle heating unit 2 is used to heat the brazing filler metal during the heating stage, and the brazing temperature control heating platform module 1 is started to heat the base material to be welded after a preset delay. This allows the brazing filler metal and the base material to be welded to undergo independent heating processes. The target heating temperature and heating rate of both can be set separately according to process requirements, thereby achieving the ideal condition of fully melting the brazing filler metal while keeping the base material to be welded in a solid state. Secondly, addressing the problem that the brazing filler metal cannot be fed by its own gravity under microgravity, this invention quantitatively extrudes the molten brazing filler metal from the needle section 230 to the surface to be welded according to a preset sequence during the free fall of the drop chamber. This active extrusion method overcomes the dependence on gravity. By controlling the start time and extrusion amount of the extrusion action (displacement or rotation speed of the electric push rod), the timing and amount of brazing filler metal filling the weld can be precisely controlled, making the joint forming quality stable and controllable. Furthermore, a high-speed camera was used to record the wetting and spreading process of the molten brazing filler metal on the surface of the base material to be welded. Backlighting created a high-contrast silhouette of the interface between the molten filler metal and the base material, clearly distinguishing the spreading front boundary. Combined with high-speed imaging, the entire spreading process could be continuously captured, thus obtaining reliable image data required for quantitative analysis of the free surface shape of the liquid bridge, wetting angle, and spreading speed. In addition, this embodiment included a step of introducing cooling gas into the welding area during the descent to rapidly solidify the filler metal (molten liquid), ensuring the entire brazing process was completed within the microgravity window. Experimental results showed that the brazed joint with AA3003 base material obtained using the invented brazing method had a CT-detected weld rate greater than 90%, and maintained a weld rate of over 90% after 20 temperature-resistant impact cycles. The joint's highest strength reached 78 MPa, and its airtightness exceeded 1×10⁻⁶. -8 Pa·m³ / s.

[0031] In one embodiment of the present invention, the pretreatment of the base material and the brazing filler metal includes: grinding the base material and the brazing filler metal, ultrasonic cleaning, stepwise chemical cleaning using alkaline solution and acidic solution to remove the surface oxide film, and finally storing them in anhydrous ethanol.

[0032] It should be noted that, as described in step S1 above, the pretreatment of the base material and brazing filler metal in this embodiment includes grinding, ultrasonic cleaning, stepwise chemical cleaning with alkaline and acidic solutions, and preservation in anhydrous ethanol. The synergistic effect of these operations provides a reliable surface foundation for the subsequent brazing process. Specifically, grinding and ultrasonic cleaning can remove machining oil, cutting marks, and residual particles from the surface of the base material and brazing filler metal, reducing the surface roughness to a level suitable for brazing filler metal wetting. The stepwise chemical cleaning first reacts the alkaline solution with the dense oxide film (Al2O3) on the aluminum alloy surface to generate soluble aluminates, and then neutralizes the residual alkaline solution with acid and removes surface ash, thereby thoroughly removing the oxide film and exposing a fresh, clean metal surface. Finally, preservation in anhydrous ethanol can effectively isolate moisture and oxygen in the air, preventing the cleaned surface from re-oxidizing during the assembly process. This series of pretreatment steps ensures that both the surface of the base material and the surface of the brazing filler metal have highly active metallic surfaces at the start of brazing heating, creating the prerequisites for the flux to effectively remove residual oxide films and promote wetting. Because the surface oxide film is fully removed, the molten filler metal can achieve a good metallurgical bond with the base material during the subsequent microgravity drop, avoiding incomplete or false welds caused by oxide film obstruction. Simultaneously, the clean surface also facilitates the escape of gases from the molten pool and the uniform spreading of the filler metal, thereby reducing the probability of porosity defects.

[0033] In one embodiment of the present invention, the flux is a paste-like flux prepared by mixing fluoride flux powder and anhydrous ethanol at a mass ratio of 2:1.

[0034] It should be noted that fluoride flux powder, such as potassium fluoroaluminate flux (e.g., NOCOLOK), melts at the brazing temperature, effectively removing the oxide film on the aluminum alloy surface. Furthermore, its post-weld residue is non-corrosive and requires no cleaning, making it suitable for scenarios like drop tower experiments where post-weld processing is difficult. Mixing the flux powder with anhydrous ethanol at a 2:1 mass ratio to form a paste ensures sufficient viscosity for uniform and firm coating onto the base material, the surface to be welded, and the surface of the filler metal, preventing it from detaching during assembly or transportation. This avoids the problems of excessive ethanol causing flux runoff and uneven distribution, or insufficient ethanol resulting in an overly thick paste that is difficult to coat. During heating, the anhydrous ethanol evaporates completely at approximately 80–100°C, leaving a dense and uniform flux layer. This flux layer begins to activate at approximately 530°C (before the filler metal melts), thoroughly removing residual oxide films from the base material and filler metal surfaces, providing a clean metal interface for the wetting and spreading of the molten filler metal under microgravity. Without flux or with other ratios, the spreading area is significantly reduced or unwetted areas appear. Therefore, a 2:1 mass ratio is one of the key features ensuring successful microgravity brazing in this embodiment. Furthermore, the paste-like form facilitates simultaneous flux coverage of the filler metal surface during extrusion at the needle tip 230, further reducing the contact angle between the molten filler metal and the base material, thereby accelerating spreading and ensuring brazing quality under microgravity.

[0035] In one embodiment of the present invention, the needle segment 230 has a diameter of 1.5 mm to 2.0 mm, and the distance between the needle segment 230 and the surface of the base material to be welded is 1 mm to 3 mm.

[0036] Furthermore, the diameter of the needle section 230 is 1.5mm to 2.0mm, and the extrusion speed and stroke are adjusted in conjunction with the mass of the molten solder droplets to ensure that the diameter of the extruded molten solder droplets is stably controlled within a certain range. Simultaneously, the inner wall of the needle section 230 should be smooth and non-wetting (e.g., using ceramic materials or a non-wetting coating) to allow the molten solder to flow freely within the inner cavity of the needle section 230 and form regular spherical droplets at the outlet, avoiding solder residue or uneven droplet size due to rough inner walls or wetting.

[0037] In one embodiment of the present invention, when the temperature of the needle heating unit reaches 350-400°C, the brazing temperature control heating stage module 1 is activated to heat the base material to be welded; the heating rate of the brazing filler metal is 5-15°C / min, and the heating rate of the base material to be welded is 20-40°C / min.

[0038] It should be noted that this embodiment uses the heating of the needle heating unit 2 to 350-400°C as the trigger condition for starting the brazing temperature control heating stage module 1. Combined with the respective heating rates of the brazing filler metal and the base material to be welded, precise control of the heating sequence is achieved, effectively solving the problem of temperature coupling between the base material and the brazing filler metal. Specifically, when the needle heating unit 2 heats up to 350-400°C, the brazing filler metal has been sufficiently preheated but has not yet melted (the melting point of brazing filler metal AA4047 is approximately 580°C). Starting the heating of the base material at this time ensures that both subsequently reach their respective welding temperatures synchronously. By setting a slower heating rate for the brazing filler metal (5-15°C / min) and a faster heating rate for the base material to be welded (20-40°C / min), the difference in their start-up times can be compensated, allowing the base material to catch up with the temperature of the brazing filler metal in a short time. This ensures that the base material reaches the preset welding temperature (530-580°C) precisely when the brazing filler metal melts. This differentiated heating rate design, on the one hand, avoids the base material being exposed to high temperatures for extended periods under overall heating, preventing overheating and softening. On the other hand, it ensures that the brazing filler metal is heated evenly and melts fully during the heating process, preventing the flux from becoming inactive due to excessive holding time after melting. Simultaneously, it ensures that the brazing experiment is completed within the microgravity window. This combination of triggering conditions and heating rate improves the brazing joint weldability and avoids reduced joint strength due to incomplete melting of the filler metal or overheating of the base material. Therefore, this embodiment, through the combined effect of temperature-triggered sequential heating and differentiated heating rates, provides an ideal temperature change path for brazing under microgravity.

[0039] In one embodiment of the present invention, the first preset welding temperature is the temperature at which the brazing filler metal melts; the second preset welding temperature is higher than the flux melting temperature and lower than the melting temperature of the base material to be welded.

[0040] It should be noted that in this embodiment, the preset welding temperature of the brazing filler metal, i.e., the first preset welding temperature, is set to 580-630°C, and the preset welding temperature of the base material to be welded, i.e., the second preset welding temperature, is set to 570-600°C. A temperature difference of about 20-70°C is formed between the two. The setting of this differentiated temperature range is the key to matching the brazing process characteristics of aluminum alloy. Specifically, the AA4047 brazing filler metal has a melting point of approximately 580°C. Setting its preset welding temperature between 580 and 610°C ensures that the filler metal melts fully, maintains good fluidity and wettability, and avoids excessive oxidation or burn-off due to overheating. The solidus temperature of the AA3003 base material to be brazed is approximately 640°C. Setting its preset welding temperature between 570 and 600°C ensures that the base material remains solid during brazing, preventing softening or grain coarsening. This temperature range also falls within the optimal activity temperature range of the flux (potassium fluoroaluminate flux), allowing it to effectively break down the oxide film and promote wetting. Therefore, the differentiated preset welding temperature settings in this embodiment are crucial process conditions for ensuring the quality of microgravity brazing.

[0041] In one embodiment of the present invention, the process of recording the wetting and spreading of molten solder on the surface to be soldered by high-speed camera includes: using a backlight source and a high-speed camera 42, wherein the center of the lens of the high-speed camera 42, the center of the observation window 114 and the center of the backlight source are collinear, and the frame rate is 100 to 300 frames / second.

[0042] It should be noted that the high-speed camera 42 can begin recording before the landing chamber descends (3 minutes before the electromagnetic release landing chamber), fully recording the core experimental process, especially for recording the wetting and spreading process of the molten solder on the surface of the base material during the landing process. The observation window 114 refers to the transparent window set on opposite sides of the brazing temperature control platform module 1 (i.e., the sealed box containing the base material, i.e., the temperature control box 11). Light emitted from the backlight source 41 enters the temperature control box 11 through one observation window 114, penetrates the interface between the molten solder and the base material, and exits through the other observation window 114, where it is received by the high-speed camera 42. The backlight source 41 is placed on the back of the base material, and the high-speed camera 42 is placed on the front, forming transmissive illumination. Due to the opacity of the molten solder and the base material to be welded, the wetting front appears as a high-contrast silhouette, eliminating the interference of metal surface reflection and high-brightness spots on the boundary under frontal illumination, allowing the pixel-level position of the spreading front to be accurately identified. The collinear arrangement of the three points ensures the alignment consistency of the geometric optical path, avoiding image distortion or measurement errors caused by viewing angle deviations, while also ensuring optical path stability and clear imaging throughout the entire descent process. The acquisition frequency of 200 frames per second enables continuous capture of every instant of the solder within the microgravity window (approximately 2 seconds of spreading) at 5-millisecond intervals, covering the complete dynamics from droplet contact with the substrate to completion of spreading. Therefore, using the optical recording scheme of this embodiment, the temporal resolution of the spreading process reaches the millisecond level, providing data support for subsequent research.

[0043] In one embodiment of the present invention, the duration of the free fall of the drop chamber is 3.6 seconds, and the preset timing is as follows: 0.2 seconds after the start of the fall, the quantitative extrusion operation of the molten brazing filler metal is started, so that the molten brazing filler metal is spread within 2.0 seconds; 2.5 seconds after the start of the fall, the operation of introducing cooling gas is started, and the cooling gas is high-pressure nitrogen gas with an introduction pressure of 2MPa.

[0044] It should be noted that the duration of the free fall of the drop chamber in this embodiment is set to 3.6 seconds (corresponding to a drop tower height of 83 meters), and a precise preset timing sequence is allocated within this microgravity window: quantitative extrusion is initiated 0.2 seconds after the start of the fall, allowing the brazing filler metal to complete its spread within 2.0 seconds; high-pressure nitrogen gas (2MPa) is introduced for cooling 2.5 seconds after the start of the fall. The design of the above timing sequence and parameters ensures the integrity and reliability of the entire microgravity brazing process. First, the 0.2-second delay in initiation of extrusion is to allow the drop chamber to fully enter a stable microgravity state (avoiding the impact of instantaneous disturbance on the droplet extrusion accuracy), while ensuring that the molten brazing filler metal has reached a completely uniform temperature at the needle tip. Subsequently, the brazing filler metal completes its spread within 2.0 seconds (i.e., from contact with the base material to the wetting front to the cessation of expansion). This duration has been experimentally determined to be sufficient time for droplet spread under microgravity conditions, ensuring both the integrity of the spread process and reserving sufficient margin for subsequent cooling. Finally, cooling is initiated after 2.5 seconds. At this point, the brazing filler metal has fully spread and is at its maximum wetting area. Introducing 2MPa high-pressure nitrogen gas rapidly removes heat, causing the filler metal to solidify quickly within the remaining 1.1 seconds. High-pressure nitrogen gas has high thermal conductivity and inert properties, enabling efficient cooling without causing oxidation. The 2MPa pressure overcomes the gas adhesion effect under microgravity, creating a directional airflow that impacts the weld area, achieving localized rapid cooling. This timing of cooling avoids premature cooling that results in incomplete spreading, and also avoids late cooling that results in the filler metal not yet solidified by the time of descent and recovery (3.6 seconds after contact with the mesh), thus preventing impact damage to the spreading morphology during descent. Therefore, the timing allocation and cooling parameters in this embodiment are crucial for achieving precise matching of spreading and solidification within the microgravity window, ensuring brazing quality.

[0045] In one embodiment of the present invention, the quantitative extrusion operation of molten solder includes: driving the ceramic rod 32 to move linearly through the linear stroke power component 31 to push the molten solder out from the needle section 230, and inserting the ceramic rod 32 into the ceramic tube 23.

[0046] It should be noted that the linear motion power component 31 (electric push rod) in this embodiment may include a motor and a lead screw and nut mechanism. The motor rotates at a speed of 60 rpm and drives the ceramic rod 32 to move linearly along the axial direction through the lead screw and nut mechanism. This quantitatively extrudes the molten brazing filler metal in the ceramic tube 23 from the needle section 230 to the surface of the base material to be welded, realizing the active, quantitative, and reliable extrusion of the brazing filler metal under microgravity conditions. This solves the problem of the difficulty in accurately controlling the timing and quantity of brazing filler metal filling the weld. Specifically, the rotation speed of 60 rpm has been experimentally verified as the optimal parameter. When the rotation speed is too low (e.g., 30 rpm), the brazing filler metal is ejected slowly, and the droplets remain at the needle section 230 for a long time. They are prone to shrinking into balls due to surface tension and cannot be detached, resulting in transfer failure. When the rotation speed is too high (e.g., 90 rpm), the brazing filler metal is sprayed at high speed, and the droplets splash or have irregular shapes, making it difficult to accurately fall onto the surface to be welded. At 60 rpm, the molten solder of a set volume can be smoothly pushed to the nozzle exit in approximately 0.2 seconds, forming regular droplets. This ensures that the droplets have appropriate kinetic energy and shape upon contact with the substrate surface. Simultaneously, the ceramic rod 32 is inserted into the ceramic tube 23 with a small gap (e.g., 0.05–0.1 mm) between them. This ensures stable transmission of extrusion pressure, prevents solder leakage from the rod wall gap, and allows the ceramic rod 32 to slide smoothly without jamming. By controlling the single downward movement distance of the ceramic rod 32, the volume of solder extruded each time can be precisely adjusted to match the distance (1.5 mm) between the nozzle 230 and the substrate surface, ensuring reliable droplet transfer. Experiments show that the 60 rpm rotation speed combined with the precise fit between the ceramic rod 32 and the container results in a high solder transfer success rate and a small extrusion volume repeatability error rate, providing a stable solder supply for the subsequent spreading process.

[0047] On the other hand, the present invention also provides a brazed joint, which is prepared by the above-mentioned drop tower experiment simulating brazing under microgravity conditions; the base material to be welded in the brazed joint is AA3003 aluminum alloy, the maximum strength of the brazed joint reaches 78MPa, and the airtightness of the brazed joint is higher than 1×10 -8 Pa·m³ / s.

[0048] It should be noted that the CT welding rate of the joint is greater than 90%, indicating that the brazing filler metal and the base material to be welded have achieved sufficient metallurgical bonding, with no obvious unfused areas or porosity defects observed. After undergoing 20 temperature cycle shock tests (simulating the severe alternating temperatures in the space service environment), the welding rate still remains above 90%, proving that the brazed joint has good resistance to thermal fatigue and aging. The highest strength of the brazed joint reaches 78 MPa, meeting the mechanical requirements of the spacecraft thermal control piping system; the airtightness is higher than 1×10⁻⁶. -8Achieving a high vacuum sealing level of Pa·m³ / s effectively prevents media leakage during on-orbit service. These performance indicators fully validate the reliability and practical value of the aforementioned brazing method in the field of microgravity brazing. The brazed joints meet the high standards of connection quality required for on-orbit manufacturing and repair in space.

[0049] The present invention will be further described below with reference to specific embodiments.

[0050] Example 1: Step 1: Pre-treatment of the base material to be welded.

[0051] Two AA3003 aluminum alloy base materials, each 6mm long, 6mm wide, and 3mm thick, were cut using a CNC machine tool. The surfaces of the AA3003 aluminum alloy to be welded were sanded with sandpaper (240#-2000#) to remove machining oil and cutting marks. The surfaces were then ultrasonically cleaned in anhydrous ethanol for 11-21 minutes to remove any residual sandpaper particles. Subsequently, the surfaces were cleaned sequentially with 10wt.% NaOH solution and 10wt.% HNO3 solution for 3 minutes each to remove the oxide film. Finally, the surfaces were stored in anhydrous ethanol to avoid prolonged exposure to air.

[0052] Step 2: Solder pretreatment.

[0053] Cut AA4047 welding wire to a length of 15mm and a diameter of 2mm. Grind it with sandpaper (240#-2000#) to remove machining oil stains from the surface. Ultrasonically clean it in anhydrous ethanol for 11-21 minutes to remove sandpaper residue particles from the surface. Then clean it in 10wt.% NaOH solution and 10wt.% HNO3 solution for 3 minutes each to remove the oxide film on the aluminum alloy surface. Store it in anhydrous ethanol.

[0054] Step 3: Flux preparation and material assembly.

[0055] Weigh 10g of NOCOLOK flux powder and mix it with anhydrous ethanol at a mass ratio of 2:1 to prepare a paste flux for later use. After cleaning the surface of the solder, coat the surface of the paste flux evenly and place the treated solder into the ceramic tube 23 of the needle heating unit 2.

[0056] Step 4: Locating.

[0057] The paste-like flux is uniformly coated onto the surface of the AA3003 aluminum alloy base material to be welded. The base material is then assembled and fixed in a base material fixture in a butt-joint configuration. The assembled base material fixture is fixed to the brazing temperature control heating platform module 1. A needle tip section 230 is formed at the lower end of the ceramic tube 23 of the needle heating unit 2. The height of the needle heating unit 2 is adjusted so that the distance between the end of the needle tip section 230 and the surface of the base material to be welded is strictly maintained at 1.5 mm, and this distance is fixed by a locking mechanism. This distance parameter is set based on the droplet transition characteristics under microgravity conditions: the diameter of the needle tip section 230 is 1.5 mm to 2.0 mm, and molten droplets are easily dripped out. Limiting the distance to 1.5 mm ensures that the molten droplets can overcome surface tension under microgravity conditions, stably contact and wet the surface to be welded, thereby avoiding liquid bridge breakage.

[0058] Step 5: Temperature measurement setup and atmosphere protection.

[0059] Place the head of the temperature sensing element 13 (thermocouple) on the side of the AA3003 base material to be welded, and ensure that the temperature sensing node avoids the area where the brazing filler metal melts, to prevent the thermocouple from coming into contact with the molten brazing filler metal and sticking together; close the furnace door of the temperature control box 11 of the brazing temperature control platform module 1, and introduce a protective gas, such as 99.999% high-purity nitrogen, to establish an inert atmosphere, thereby effectively suppressing the high-temperature oxidation of the brazing filler metal and the base material to be welded during the brazing process.

[0060] Step Six: Adjust the high-speed camera system.

[0061] Turn on the high-speed camera 42 and the backlight illumination assembly (backlight source 41). Through three-dimensional position adjustment, make the lens center of the high-speed camera 42, the geometric center of the observation window 114 of the brazing temperature control hot stage module 1, and the light source center of the backlight illumination assembly coaxial, so as to ensure that the dynamic transition morphology of the molten droplets can be collected with high fidelity during the drop tower experiment.

[0062] Step 7: Configure the temperature control system and data acquisition system.

[0063] The temperature control program of the needle heating unit 2 is started, setting the target heating temperature of the brazing filler metal to 600℃ and the heating rate to 10℃ / min; the temperature control program of the brazing temperature control hot stage module 1 is started, setting the target heating temperature of the base material to be welded to 575℃ and the heating rate to 30℃ / min. Limiting the heating temperature of the base material to be welded to 575℃ can effectively prevent the aluminum alloy base material from overheating and softening during the heating process; subsequently, the control program of the high-speed camera 42 is started, with the preset image acquisition frame rate of 200 frames / s.

[0064] Step 8: Secure the device to the landing platform.

[0065] All moving and loaded components inside the experimental device are structurally secured to eliminate swaying and vibration during the microgravity drop experiment. After the internal components of the entire system are confirmed to be secure, the experimental device is connected to the experimental drop chamber platform of the drop tower.

[0066] Step Nine: Control System Initialization and Macro-Timing Preset.

[0067] After checking the system communication interface and confirming that the signal transmission link is normal, the timing control program is started, and the linkage timing sequence of heating the base material to be welded - camera start - electromagnetic release - solder ejection - cooling trigger is preset. The specific timing parameters are configured as follows: the start node of the brazing temperature control stage module 1 is set to 35 minutes after the heating program of the needle heating unit 2 is started, and its heating rate is set to 30℃ / min. The physical mechanism of this setting is that if the holding time of the flux after melting exceeds 30 minutes, it is easy to lose its activity and cannot play a role in breaking the oxide film on the surface of the aluminum alloy, which seriously affects the experimental results. The high heating rate of 30℃ / min combined with the 35-minute delay start of the brazing temperature control stage module 1 can effectively avoid the phenomenon of flux deactivation. In combination with the data storage limit of the high-speed camera system in high frame rate mode (the longest continuous recording time is 5 minutes under 200 frames / s), the trigger node of the high-speed camera 42 is set to 3 minutes before the electromagnetic release of the tower drop, so as to ensure that the data recording window completely covers the core experimental process.

[0068] Step 10: Microscopic timing preset for the microgravity window period.

[0069] To address the 3.6-second effective microgravity window in the drop tower experiment, a microsecond-level servo timing sequence was set: 0.2 seconds after the start of the drop chamber's descent, the electric push rod was triggered, with a rotation speed of 60 rpm, ensuring the brazing filler metal began to be ejected 0.2 seconds after the start of descent and completed spreading within 2.0 seconds. Simultaneously, the cooling system's control solenoid valve was set to open 2.5 seconds after descent, introducing 2MPa high-pressure cooling gas to rapidly solidify the brazing filler metal joint, thus freezing the spreading morphology under microgravity. This ensured that the brazing filler metal was completely solidified before the drop chamber touched the wire mesh for retrieval, and that its free surface shape would not change due to wire mesh vibration or gravity recovery. This precise allocation of micro-time parameters not only allowed sufficient wetting and spreading time for the molten brazing filler metal but also ensured that the filler metal completed the solidification process before the end of the 3.6-second microgravity window.

[0070] Step 11: Lowering and sealing the cabin, hoisting and macroscopic sequential heating.

[0071] After sealing the experimental landing chamber and leveling its center of gravity, the experimental landing chamber was lifted to the top of the landing tower (83m height) using an electromagnetic suspension mechanism. The needle heating unit 2 was started and heated at a rate of 10℃ / min. When the timing program detected that the heating had been running for 35 minutes (i.e., the temperature of the needle heating unit 2 reached 370℃), the brazing temperature control heating stage module 1 was triggered to start, and the base material to be welded was heated in conjunction with the heating. When the needle heating unit 2 reached 570℃, the timing program triggered the high-speed camera 42 to start, and recorded images at a sampling rate of 200 frames / s.

[0072] Step 12: Status determination and fall trigger.

[0073] Heating continued until the needle heating unit 2 reached 600°C, at which point the brazing filler metal was fully melted. Simultaneously, images transmitted from the high-speed camera 42 confirmed that the NOCOLOK flux on the surface of the substrate to be welded had completely melted, and the temperature of the temperature control module 1 was 575°C. At this point, the system was deemed to have met the initial conditions for microgravity brazing. Subsequently, an electromagnetic release command was sent via the control console to cut off the power to the electromagnetic suspension mechanism, causing the experimental drop chamber to detach from its restraints and enter a free-falling microgravity state.

[0074] Step Thirteen: Microgravity Experiment Execution (Finite Drop, Spreading, Solidification, and Device Recovery).

[0075] The moment the experimental capsule begins its descent is taken as the zero point of the microgravity time sequence: at 0.2s, the timing program triggers the electric push rod to push the molten brazing filler metal in the needle heating unit 2 to the surface of the substrate to be welded at a speed of 60 rpm, forming a liquid bridge between the liquid brazing filler metal at the needle tip 230 and the surface of the substrate. Under microgravity conditions, the molten brazing filler metal completes wetting and spreading on the surface to be welded within 2.0s (this process is simultaneously captured by the high-speed camera 42). At 2.5s, the timing program triggers the cooling gas pipe 12 to open, supplying cooling gas (2 MPa high-purity nitrogen cooling gas), and spraying cooling gas into the welding area to achieve rapid solidification and cooling. At 3.6s, the experimental capsule falls into the deceleration and recovery net at the bottom of the drop tower, and the microgravity brazing experiment ends.

[0076] Example of Results (Analysis and Testing): The brazed joints prepared using steps one to thirteen of Embodiment 1 above exhibit the following microgravity brazing and solder wetting and spreading process: Figure 2 As shown. Figure 2 (a) shows the 0s of the wetting and spreading process, at which point the solder has not yet been ejected; approximately 0.2s after the drop chamber begins to fall, the electric push rod of the needle heating unit 2 drives the ceramic rod 32 to eject the molten solder from the needle tip section 230 at a rotation speed of 60 rpm; at the 1s mark, the solder contacts the surface of the base material to be welded and begins to wet, spread, and fill the gap, as shown in Figure 1. Figure 2As shown in (c); as the mass of the solder being pushed out increases, the solder continuously fills the gap between the mating parts under the action of capillary force, as... Figure 2 As shown in (d) to (h). The entire process lasts until approximately 2.0 seconds after the start of the descent, at which point the solder has spread, as shown in... Figure 2 (h).

[0077] 2.5 seconds after the start of the descent, the timing program triggers the cooling gas to start, and the solder begins to solidify rapidly. For example... Figure 2 As shown in (i), the brazing filler completely solidifies about 3.0s after the start of the descent, and then the descent chamber enters the recovery net (about 3.6s), causing the descent chamber to be buffered and decelerated, and generating rebound motion and mechanical disturbance, thus ending the microgravity experiment.

[0078] Microstructural analysis was performed on typical areas of the brazed joint, such as... Figure 3 It is a eutectic Al-Si phase obtained under constant gravity conditions. Figure 4 The Al-Si eutectic phase was obtained under microgravity conditions. The size of the Al-Si eutectic phase obtained under normal gravity conditions was significantly larger than that obtained under microgravity conditions, indicating that a uniform and fine brazing seam structure was more easily obtained under microgravity conditions. In addition, no obvious porosity was observed in the joint structure under microgravity conditions. This is attributed to the smaller brazing seam size under microgravity, making it difficult for bubbles to aggregate and thus preventing the formation of pores after solidification.

[0079] The airtightness testing process was strictly carried out in accordance with the GB / T36176-2018 standard "Vacuum Technology - Helium Mass Spectrometry - Vacuum Leak Detection Method", using an INFICONUL 1000 helium mass spectrometer leak detector.

[0080] Testing showed that the airtightness of the brazed joint prepared in this embodiment was higher than 1×10⁻⁶. -8 Pa·m³ / s, meeting the high vacuum sealing requirements of spacecraft thermal control piping systems.

[0081] Example 2: See Figures 5 to 7The brazing experimental apparatus for implementing the brazing method of Embodiment 1 includes a brazing temperature-controlled heating stage module 1, a needle heating unit 2, a brazing filler metal extrusion mechanism 3, an image acquisition system 4, an atmosphere system, a controller 5, and a fixed support mechanism 6, all fixedly installed within a chamber. The brazing temperature-controlled heating stage module 1 is used to load and heat the base material to be welded. The needle heating unit 2 is used to heat and melt the brazing filler metal; its needle tip is inserted into the brazing temperature-controlled heating stage module 1, and the needle tip is positioned at a preset position above the base material. The brazing filler metal extrusion mechanism 3 is installed on the needle heating unit 2 and is used to quantitatively extrude the molten brazing filler metal onto the surface of the base material to be welded. The image acquisition system 4 is used to record the wetting and spreading process of the molten brazing filler metal on the surface of the base material to be welded. The atmosphere system... The controller 5 is connected to the brazing temperature control heating stage module 1 and is used to introduce protective gas and cooling gas into the brazing temperature control heating stage module 1. The controller 5 is electrically connected to the brazing temperature control heating stage module 1, the needle heating unit 2, the brazing filler metal extrusion mechanism 3, the image acquisition system 4 and the atmosphere system respectively. The controller 5 is used to control the linkage of each unit and adopts separate heating: first heat the brazing filler metal, then heat the base material to be welded. After both reach the set temperature, the drop chamber is triggered to fall freely. During the free fall of the drop chamber, the brazing filler metal extrusion mechanism 3 is controlled to extrude the molten brazing filler metal quantitatively onto the surface of the base material to be welded, the image acquisition system 4 is controlled to record the wetting and spreading process of the molten brazing filler metal, and the atmosphere system is controlled to introduce cooling gas into the brazing temperature control heating stage module 1.

[0082] Specifically, the fixed support mechanism 6 includes a base plate, a Z-axis scissor lift platform 62, and a fixed platform 61; the base plate is connected to the bottom of the cabin; the Z-axis scissor lift platform 62 is connected to the base plate, and the top of the Z-axis scissor lift platform 62 is used to install the brazing temperature control heating platform module 1. The height of the Z-axis scissor lift platform 62 is adjustable and can be locked and fixed; the fixed platform 61 is connected to the base plate, and a fixed plate 611 is provided on the fixed platform 61. The fixed plate 611 is used to install the needle heating unit 2.

[0083] The needle heating unit 2 includes a connecting frame 21, a needle heating steel tube 22, and a ceramic tube 23. The connecting frame 21 is connected to the fixing plate 611; the upper end of the needle heating steel tube 22 is connected to the connecting frame 21, and the lower end extends into the interior of the brazing temperature control heating platform module 1; the ceramic tube 23 is coaxially disposed inside the needle heating steel tube 22, the cavity of the ceramic tube 23 is used to hold the brazing filler metal, and an electric heating wire is wound around the outside of the ceramic tube 23. The lower end of the ceramic tube 23 forms a needle tip section 230 with a diameter smaller than the diameter of its cavity, so that the bottom of the ceramic tube 23 forms a stepped structure, which matches the stepped hole at the bottom of the needle heating steel tube 22, and the needle tip section 230 extends out of the bottom end of the needle heating steel tube 22 and is locked by threads.

[0084] The brazing filler metal extrusion mechanism 3 includes a linear power assembly 31 and a ceramic rod 32. The linear power assembly 31 is mounted on the connecting frame 21. The ceramic rod 32 is driven by the linear power assembly 31, and its lower end is inserted into the ceramic tube 23. The linear power assembly 31 drives the ceramic rod 32 to move vertically to extrude molten brazing filler metal quantitatively from the bottom end of the ceramic tube 23. The brazing filler metal extrusion mechanism 3 also includes a positioning sleeve 33 and a positioning cap 34. The positioning sleeve 33 extends through the lower end of the connecting frame 21, and the upper end of the needle heating steel tube 22 is inserted into the lower end of the positioning sleeve 33. The positioning cap 34 covers the upper end of the positioning sleeve 33, and the ceramic rod 32 passes through the positioning cap 34 and extends into the ceramic tube 23.

[0085] The brazing temperature control heating platform module 1 includes a temperature control chamber 11, a temperature measuring element 13, and a cooling gas pipe 12. Heating components are respectively provided in the upper and lower parts of the temperature control chamber 11, and a protective gas inlet and outlet are opened on the side of the temperature control chamber 11. The temperature measuring element 13 is located inside the temperature control chamber 11 and is used to monitor the temperature of the base material to be welded in real time. The cooling gas pipe 12 is used to introduce cooling gas into the temperature control chamber 11, and the outlet of the cooling gas pipe 12 is located inside the temperature control chamber 11 and aligned with the weld seam of the base material to be welded. The top surface of the temperature control box 11 includes an upper top plate 111 and a lower top plate 112 spaced apart. The upper top plate 111 and lower top plate 112 have corresponding positioning holes for the needle heating steel tube 22 to pass through. A positioning ring 113 protrudes from the positioning hole of the lower top plate 111. The needle heating unit 2 also includes a mounting base 24 and a sealing ring 25. The sealing ring 25 is embedded in the mounting base 24 and wedge-shapedly engages with the inner wall of the positioning ring 113. The mounting base 24 passes through the positioning hole of the upper top plate 111 and is threadedly connected to the outer wall of the positioning ring 113. When the mounting base and the positioning ring 113 are tightened, the sealing ring 25 grips the needle heating steel tube 22. Observation windows 114 are provided on both opposite sides of the temperature control box 11. The backlight source 41, the observation windows 114, and the lens center of the high-speed camera 42 are collinear.

[0086] The temperature control box 11 is also equipped with a base material clamp, which is used to accurately position and clamp the base material to be welded in the temperature control box 11 of the brazing temperature control hot stage module 1, so as to ensure that the base material does not undergo any displacement or deflection during free fall, thereby ensuring that the molten brazing filler material squeezed from the bottom end of the ceramic tube 23 can accurately fall on the predetermined weld area on the surface of the base material.

[0087] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A brazing method simulating microgravity conditions, characterized in that, Includes the following steps: The base material and brazing filler metal to be soldered are pretreated by surface cleaning and then coated with flux. The pretreated base material to be welded is fixed on the brazing temperature control heating platform module and a protective gas is introduced. The pretreated brazing filler metal is placed in the ceramic tube of the needle heating unit, and a needle section is formed at the lower end of the ceramic tube. Adjust the distance between the needle tip and the surface of the base material to be welded; The needle heating unit is activated to heat the brazing filler metal to obtain molten brazing filler metal, and after a preset delay, the brazing temperature control heating platform module is activated to heat the base material to be welded; When the brazing filler metal reaches the first preset welding temperature and the base material to be welded reaches the second preset welding temperature, the drop chamber equipped with the brazing temperature control heating platform module and the needle heating unit is triggered to fall freely. During the free fall of the descent capsule, the following operations are performed sequentially according to a preset time sequence: the molten brazing filler metal is quantitatively extruded from the needle section to the surface to be welded of the base material, and the molten brazing filler metal forms a liquid bridge between the needle section and the surface to be welded; The process of the molten brazing filler metal wetting and spreading on the surface to be welded is recorded using a high-speed camera; and cooling gas is introduced into the welding area to rapidly solidify the brazing filler metal.

2. The brazing method under simulated microgravity conditions according to claim 1, characterized in that, The pretreatment of the base material and the brazing filler metal includes: grinding the base material and the brazing filler metal, ultrasonic cleaning, stepwise chemical cleaning with alkaline and acidic solutions to remove the surface oxide film, and finally storing them in anhydrous ethanol.

3. The brazing method under simulated microgravity conditions according to claim 1, characterized in that, The flux is a paste-like flux prepared by mixing fluoride flux powder and anhydrous ethanol at a mass ratio of 2:

1.

4. The brazing method under simulated microgravity conditions according to claim 1, characterized in that, The diameter of the needle tip is 1.5mm to 2.0mm, and the distance between the needle tip and the surface of the base material to be welded is 1mm to 3mm.

5. The brazing method under simulated microgravity conditions according to claim 1, characterized in that, When the temperature of the needle heating unit reaches 350-400℃, the brazing temperature control heating stage module is activated to heat the base material to be welded; the heating rate of the brazing filler metal is 5-15℃ / min, and the heating rate of the base material to be welded is 20-40℃ / min.

6. The brazing method under simulated microgravity conditions according to claim 5, characterized in that, The first preset welding temperature is the temperature at which the brazing filler metal melts; the second preset welding temperature is higher than the melting temperature of the flux and lower than the melting temperature of the base material to be welded.

7. The brazing method under simulated microgravity conditions according to claim 1, characterized in that, The process of recording the molten solder wetting and spreading on the surface to be soldered by high-speed camera includes: using a backlight source and a high-speed camera, wherein the center of the lens of the high-speed camera, the center of the observation window and the center of the backlight source are collinear, and the frame rate is 100 to 300 frames / second.

8. The brazing method under simulated microgravity conditions according to claim 1, characterized in that, The duration of the free fall of the drop chamber is 3.6 seconds. The preset timing sequence is as follows: 0.2 seconds after the start of the fall, the quantitative extrusion operation of the molten brazing filler metal is started, so that the molten brazing filler metal is wetted and spread within 2.0 seconds; 2.5 seconds after the start of the fall, the operation of introducing the cooling gas is started, and the cooling gas is high-pressure nitrogen gas with an introduction pressure of 2MPa.

9. The brazing method under simulated microgravity conditions according to claim 8, characterized in that, The quantitative extrusion operation of the molten brazing filler metal includes: driving the ceramic rod to move linearly through a linear stroke power component to push the molten brazing filler metal out of the needle section; wherein the ceramic rod is inserted into the ceramic tube.

10. A brazed joint, characterized in that, It was prepared by brazing under simulated microgravity conditions as described in any one of claims 1 to 9.

Images