A strong magnetic field assisted brazing method based on wetting property regulation

Abstract

The application discloses a strong magnetic field assisted brazing method based on wetting regulation, and belongs to the field of brazing. The method is that: clean, dry and fixed assembled workpieces to be welded are placed in a magnetic field, heated to a brazing temperature for brazing, and the position of the workpieces to be welded in the magnetic field, the strength of the strong magnetic field and the direction of the magnetic field are adjusted according to requirements during the brazing process; after brazing, the workpieces are kept warm, then the magnetic field is turned off after the workpiece temperature is lower than the melting point of the filler metal; the workpieces are continuously cooled to room temperature, taken out, and brazed workpieces are obtained; the strong magnetic field used in the method has a significant influence on the wetting of the brazing base material and the filler metal, and can change the energy state of the material system and the solute diffusion behavior in the liquid / solid system. Therefore, the wetting between the filler metal and the brazing base material and the reaction and mutual diffusion between the filler metal and the brazing base material are regulated by means of the strong magnetic field, the microstructure of the welded joint can be controlled, and the brazing quality can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of brazing, specifically relating to a strong magnetic field-assisted brazing method based on wettability control. Background Technology

[0002] Brazing, as a material joining method, is now widely used in non-heavy-duty precision connections such as electronic packaging, precision instruments, and medical devices. During brazing, the wettability between the molten filler metal and the base metal determines the filler metal's effect on the weld joint, thus playing a decisive role in the brazing quality. This wettability is even more crucial for irregularly shaped or irregularly shaped brazed joints. Furthermore, the reaction and interdiffusion of elements at the molten filler metal / base metal interface also play a vital role in brazing quality. For systems with significantly different physical properties, such as metal base materials or dissimilar metal and ceramic base materials, strict control of the brazing process is necessary to obtain good brazed joints. Otherwise, brittle phases, large internal stresses, porosity, and other welding defects can easily form at the interface, severely impairing the mechanical properties of the brazed joint.

[0003] In recent years, numerous studies have addressed these issues and improved brazing quality by adjusting brazing temperature, altering filler metal composition, and applying flux. However, increasing temperature leads to severe interfacial reactions and significant joint thermal stress; altering filler metal composition introduces various elements that have uncertain effects on the weld joint and increase costs; and applying flux can cause toxic side effects on personnel and is difficult to clean. Therefore, it is extremely difficult to improve wettability while simultaneously controlling the interfacial reaction.

[0004] Strong magnetic fields, as non-contact physical fields, can produce various strong force, magnetic, and energy coupling effects on matter. Based on this, researchers have conducted extensive fundamental and applied research on strong magnetic fields in materials science, physics, metallurgy, chemistry, and medicine. However, there is no research on how to use strong magnetic fields to solve the problem of brazing wettability. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide a strong magnetic field-assisted brazing method based on wettability control. This method utilizes the various force, energy, and magnetic coupling effects of a strong magnetic field to control the wettability of the molten filler metal and alter the interfacial reaction and element diffusion between the molten filler metal and the base metal, thereby obtaining the desired interfacial microstructure and significantly improving brazing quality. This method can achieve brazing of high-quality, high-value-added, and difficult-to-braze systems. The strong magnetic field used in this invention significantly affects the wettability of the molten filler metal and the base metal, and also alters the energy state of the material system and the solute diffusion behavior within the liquid / solid system. Therefore, by using a strong magnetic field to control the wettability between the molten filler metal and the base metal, as well as their reaction and mutual diffusion, it is possible to control the microstructure of the weld joint and effectively improve brazing quality.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides a strong magnetic field-assisted brazing method based on wettability control, comprising the following steps:

[0008] (1) After degreasing, cleaning and drying the surface of the base material to be welded and the surface of the brazing filler metal, assemble and fix them according to the welding process of the workpiece to be welded;

[0009] (2) Place the assembled and fixed workpiece in a magnetic field, heat it to the brazing temperature and braze it. Adjust the position, magnetic field strength and magnetic field direction of the workpiece in the magnetic field according to the requirements during the brazing process. After the brazing is completed, keep it at the temperature and then cool it with the furnace until the workpiece temperature is lower than the melting point of the brazing filler metal. Then turn off the magnetic field. Continue to cool it to room temperature and take it out to obtain the brazed workpiece. The magnetic field strength is a strong magnetic field.

[0010] In step (1), the brazing base material is preferably a hard brazing material system (brazing temperature ≥450℃), more specifically alumina, titanium alloy, aluminum alloy, tungsten cobalt hard alloy, and the brazing filler metal is preferably an aluminum-based brazing filler metal, silver-based brazing filler metal, copper-based brazing filler metal, manganese-based brazing filler metal or nickel-based brazing filler metal. The materials of the brazing base material and the brazing filler metal can be the same or different.

[0011] In step (1), the drying is carried out by blowing or drying, specifically by blowing with cold air or drying with hot air.

[0012] In step (1), chemical reagents are used for cleaning.

[0013] In step (2), the heating source used to raise the temperature to the brazing temperature is one or a combination of electron beam, laser beam, electric arc, resistance furnace or induction furnace.

[0014] In step (2), the heating rate is 5 to 800 °C / min.

[0015] In step (2), the brazing temperature is determined according to the material of the brazing base material, preferably ≥450℃, and the holding time is preferably 10~20min.

[0016] In step (2), before heating to the brazing temperature, the temperature is first raised to 300-350°C below the brazing temperature for impurity removal and isothermal process. During this process, the holding time is 20-30 minutes.

[0017] In step (2), the welded joint is placed in a magnetic field, preferably a uniform magnetic field region. The position of the welded joint in the magnetic field and the angle between the welded joint and the direction of the magnetic field are adjusted accordingly based on the microstructure of the welded workpiece and the performance requirements of the joint.

[0018] In step (2), the magnetic field is a continuously adjustable steady magnetic field, the magnetic induction intensity B is continuously adjustable within the range of 0 < B ≤ 30 T, and the direction of the steady magnetic field is longitudinal or transverse; preferably, for a brazing base material of titanium alloy and a filler metal of Ag-Cu, the magnetic induction intensity B is 4 - 30 T.

[0019] In step (2), the magnetic field is provided by a magnet, and the magnet is an electromagnet or a permanent magnet. <*

[0020] Among them, the shape of the magnet is one of an annular magnet, a horseshoe magnet, a bar magnet, an opposed magnet or a single-sided magnet.

[0021] In step (2), the brazing process is carried out in one of the atmospheres of air, vacuum or protective gas.

[0022] In step (2), the vacuum degree range of the vacuum atmosphere is 10 -1 ~10 -8 Pa, and the gas concentration of the protective gas atmosphere is 99.9% - 99.999%.

[0023] In step (2), the furnace cooling can also be replaced by a cooling method with a cooling rate of 15 - 400 °C / min.

[0024] When using a strong magnetic field-assisted brazing method based on wettability regulation of the present invention, when the brazing base material is titanium alloy and the filler metal is Ag-72Cu, and the magnetic induction intensity is above 4 T, two layers of structures are formed at the joint interface of the brazed workpiece, which are (α + βTi) + (TiCu) respectively, and the total thickness of the interface diffusion layer is greater than 38 μm.

[0025] The advantages of the present invention are as follows: By means of the multiple magnetic, force and energy coupling effects of the strong magnetic field, the wettability between the molten filler metal and the brazing base material can be regulated, and the spreading speed of the molten filler metal can also be regulated, which is beneficial to the filling of the filler metal into the weld seam; at the same time, the magnetic field can also be used to regulate the speed and degree of the interface reaction between the molten filler metal and the brazing base material and the degree and direction of element diffusion, reduce or even eliminate the formation of phases that damage the welding quality, thereby improving the welding quality; reduce the welding time required, improve the welding efficiency, and effectively achieve energy conservation and emission reduction.

[0026] Compared with the existing technology of adding a magnetic field during the welding process, the present invention can be applied to the composite brazing between the same or different materials with large differences in physical and chemical properties, the base material cannot withstand a high brazing temperature, and the welding quality requirements are extremely high, etc., and has no dependence on the material system. In addition, the present invention can regulate the wettability between the molten filler metal and the brazing base material, and can control the reaction degree and the type of reaction products at the interface, and significantly improves the brazing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of a magnetic field-assisted brazing method based on wettability control;

[0028] Figure 2 The curves show the contact angle of molten silver-copper (Ag-72Cu) eutectic solder on a titanium alloy (TC4) substrate under strong magnetic fields of 0T and 6T as a function of time. The figure includes morphological images at the beginning and end of the observation.

[0029] Figure 3 These are morphological images of the dynamic wetting behavior of α-Al2O3 on the substrate under strong magnetic fields of 0T and 6T (525 to 750℃) during continuous heating.

[0030] Figure 4 The microstructure of the Ag-Cu / TC4 interface is shown at 860℃ under a 0T strong magnetic field.

[0031] Figure 5 The microstructure of the Ag-Cu / TC4 interface is shown under a strong magnetic field of 2T at 860℃.

[0032] Figure 6 The microstructure of the Ag-Cu / TC4 interface is shown under a strong magnetic field of 4T at 860℃.

[0033] Figure 7 The microstructure of the Ag-Cu / TC4 interface is shown under a strong magnetic field of 6T at 860℃.

[0034] Figure 1 In the diagram: 1 is the magnet, 2 is the heating source, 3 is the first brazing base material, 4 is the brazing filler metal, 5 is the second brazing base material, and 6 is the brazing atmosphere. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0036] Example 1

[0037] Before the experiment, the brazing filler metal Ag-72Cu (Ag: 28%; Cu: 72%) and the TC4 substrate (brazing base material) were ultrasonically cleaned three times in acetone solution to remove impurities adhering to the sample surface. Each cleaning session lasted 3 minutes, followed by drying with cold air. After cleaning, the TC4 substrate was placed on the stage, and the brazing filler metal Ag-72Cu was positioned in the center of the TC4 substrate. The stage was leveled using a spirit level, and the vacuum chamber was closed. During the experiment, a mechanical pump was used to pre-evacuate the vacuum. Once the vacuum level reached below 5.0 Pa, the turbomolecular pump was turned on, and the furnace vacuum was evacuated to 4.0 × 10⁻⁶ Pa at room temperature. -4Pa was applied, and then the strong magnetic field device was turned on, applying a magnetic induction intensity of 0T (control group) and 6T. The furnace power was then turned on, and the heating program was started. The sample was heated at a rate of 15℃ / min with a temperature control accuracy of ±0.1℃. When the temperature reached 525℃, it was held for 20 minutes to remove moisture and impurities from the furnace and ensure that the surface and core temperatures of the experimental material were consistent. Heating was then continued at the same rate (15℃ / min) to 840℃, and held for 20 minutes. The dynamic wetting behavior during the holding process was observed in real time using a CCD camera, and the sample morphology was recorded. The obtained image data was directly transmitted to the computer and saved. After the experiment, when the temperature inside the furnace was 100℃ below the metal melting point, the strong magnetic field was turned off. The furnace was allowed to cool naturally to room temperature, the turbomolecular pump and mechanical pump were turned off, and the sample was removed.

[0038] The changes in contact angle and wetting behavior of molten Ag-72Cu eutectic solder on TC4 substrate under strong magnetic fields of 0T and 6T at 840℃ are as follows: Figure 2 As shown, after applying a 6T strong magnetic field, the initial contact angle of the Ag-Cu melt on the TC4 substrate is smaller than that under a 0T strong magnetic field, and the morphology of the Ag-Cu melt on the TC4 substrate under the 6T strong magnetic field is closer to a hemispherical shape. After applying a 6T strong magnetic field, the Ag-Cu melt spreads rapidly on the TC4 substrate, and the contact angle reaches a stable stage approximately 720 seconds earlier than when no strong magnetic field is applied. The final stable contact angles under the 0T and 6T strong magnetic fields are not significantly different, and the morphology of the metal melt is also relatively similar. Therefore, applying a strong magnetic field can significantly promote the wettability of the Ag-Cu melt on the TC4 substrate, facilitating its rapid spreading.

[0039] In summary, applying a strong magnetic field to a brazing system can significantly improve the wettability between the molten filler metal and the base material, and also increase the spreading rate of the molten filler metal on the base substrate. This effectively enhances the filling effect of the molten filler metal in the weld, ultimately having a crucial impact on the performance of the brazed joint. Furthermore, brazing time will be significantly reduced, welding efficiency will be greatly improved, and energy conservation and emission reduction will be promoted.

[0040] Example 2

[0041] Before the experiment, the Al solder and the α-Al₂O₃ substrate (brazing base material) were ultrasonically cleaned three times in acetone solution to remove impurities adhering to the sample surface. Each cleaning session lasted 3 minutes, followed by drying with cold air. After cleaning, the substrate was placed on the stage, and the Al solder was positioned in the center of the α-Al₂O₃ substrate. The stage was leveled using a spirit level, and the vacuum chamber was closed. During the experiment, a mechanical pump was used to pre-evacuate the vacuum. Once the vacuum level reached below 5.0 Pa, the turbomolecular pump was turned on, and the furnace vacuum was evacuated to 4.0 × 10⁻⁶ Pa at room temperature.-4 Pa was applied, and then the strong magnetic field device was turned on, with magnetic induction intensities of 0T (control group) and 6T. The furnace power was then turned on, and the heating program was started. The sample was heated at a rate of 15℃ / min, with a temperature control accuracy of ±0.1℃. When the temperature reached 525℃, it was held for 20 minutes to remove moisture and impurities from the furnace and to ensure a uniform temperature between the surface and core of the experimental material. Heating continued at the same rate (15℃ / min) to 750℃. The dynamic wetting behavior during the entire continuous heating process was observed and the sample morphology was recorded in real time using a CCD camera. The obtained image data was directly transferred to the computer and saved. After the experiment, when the temperature inside the furnace was 100℃ below the metal melting point, the strong magnetic field was turned off. The furnace was allowed to cool naturally to room temperature before the turbomolecular pump and mechanical pump were turned off, and the sample was removed.

[0042] The dynamic morphological changes of metallic Al on an α-Al₂O₃ substrate during continuous heating under strong magnetic fields of 0T and 6T are as follows: Figure 3 As shown in the figure, there are significant differences in the melting process and dynamic wetting behavior of metallic Al on the α-Al₂O₃ substrate under 0T and 6T strong magnetic fields during continuous heating. Under 0T strong magnetic field, metallic Al exhibits a tendency to detach from the substrate and rise during melting, but this phenomenon is not observed under 6T strong magnetic field. Under 6T strong magnetic field, Al melts and deforms at a furnace temperature of 720℃, and the molten Al spreads more quickly and approaches wetting equilibrium on the α-Al₂O₃ substrate. Under 0T strong magnetic field, metallic Al gradually melts from an initial cylindrical solid, eventually spreading into symmetrical spherical droplets with a contact angle of 121°. However, under a 6T strong magnetic field, it spreads into symmetrical hemispherical droplets with a contact angle of 86°, exhibiting better wettability. It is evident that applying a strong magnetic field during continuous heating significantly alters the melting and wetting behavior of metallic Al on the α-Al₂O₃ substrate.

[0043] In summary, applying a strong magnetic field to the brazing system can significantly affect the entire heating process, which is beneficial to the melting of the brazing filler metal, accelerates the spread of the molten filler metal in the weld, and significantly promotes wettability, ultimately having a significant impact on brazing.

[0044] Example 3

[0045] First, remove oil and stains from the surfaces of two 2cm×2cm×5mm titanium alloy (TC4) substrates to be soldered and a 2cm×2cm×0.5mm Ag-72Cu (Ag: 28%; Cu: 72%) brazing filler metal. After removing the oxide film from the surfaces with hydrochloric acid, and drying with cold air, assemble the workpieces in a "sandwich" configuration (with brazing filler metal 4 placed between the first and second brazing base materials 3 and 5). A schematic diagram of the strong magnetic field-assisted brazing method based on wettability control is shown below. Figure 1 In this embodiment, magnet 1 is a toroidal superconducting strong magnet. The "sandwich-shaped" workpiece is placed in a brazing atmosphere 6, and a heating source 2 and magnet 1 are arranged around the "sandwich-shaped" workpiece. The workpiece is positioned within a uniform region of the strong magnetic field provided by magnet 1, with the weld seam parallel to the direction of the magnetic field. Then, the magnetic field strength of the superconducting magnet is set to 0T (control group), 2T, 4T, and 6T, respectively. At a vacuum degree of 10... -5 Under Pa environment (brazing atmosphere 6), the resistance heating furnace is turned on as heating source 2, and the temperature is set to 860℃. After the furnace temperature reaches 860℃, it is held at that temperature for 10 minutes. After the holding period, the heating furnace is turned off and allowed to cool down. When the furnace temperature drops to 150℃ below the metal melting point, the magnetic field is returned to zero. After cooling, the workpiece is removed, and the welding is completed.

[0046] Appendix Figure 4 , Figure 5 , Figure 6 and Figure 7 The microstructure of one side of the weld interface is shown at 860℃ under applied magnetic fields of 0T, 2T, 4T, and 6T. The results show that compared to the 0T strong magnetic field, the wavy interface reaction layer is significantly thicker and element diffusion is significantly enhanced after applying a stronger magnetic field. The total thickness of the interface reaction layer under strong magnetic fields of 0, 2, 4, and 6T ranges from 6.4 to 11.5 μm, 18.1 to 20.1 μm, 38.1 to 97.3 μm, and 46.0 to 119.4 μm, respectively, indicating that the thickness of the interface diffusion layer increases with increasing magnetic induction intensity. When strong magnetic fields of 0T and 2T are applied, the reaction products formed at the interface are divided into four layers, with the four layers structured from top to bottom as (α+βTi)+(Ti₂Cu)+(TiCu)+(TiCu₂). When strong magnetic fields of 4T and 6T are applied, the reaction products formed at the interface are divided into two layers, with the two layers structured from top to bottom as (α+βTi)+(TiCu). With the increase of the strong magnetic field strength, the thickness of each reaction layer at the interface increases significantly overall. In addition, the weld interface is good, and no welding defects such as cracks or porosity are observed.

[0047] In summary, applying a strong magnetic field can influence the interdiffusion of elements and interfacial reactions between the brazing filler metal and the base metal, thereby altering the type and quantity of reaction products formed at the interface. The type and quantity of these reaction products have a significant impact on the performance of the weld joint. Therefore, during brazing, the type and quantity of reaction products at the interface can be controlled by applying external strong magnetic fields of varying intensities, ultimately achieving control over the brazing quality.

[0048] Example 4

[0049] This embodiment provides a method for brazing ceramics with a strong magnetic field assisted by wettability control. The specific steps are largely the same as those in Embodiment 3, except that:

[0050] Silica ceramics were brazed using titanium-based brazing filler metal (Ti: 42%, Ni: 38%, Zr: 9%, Cu: 11%) under a 5T strong magnetic field, with the weld seam perpendicular to the magnetic field direction. The brazing temperature was 1400℃, the holding time was 20min, and the brazing atmosphere was argon.

[0051] Example 5

[0052] This embodiment provides a method for brazing cemented carbide using a strong magnetic field assisted by wettability control. The specific steps are largely the same as those in Embodiment 3, except that:

[0053] Tungsten-cobalt cemented carbide (WC: 94%, Co: 6%) was brazed using pure copper brazing filler metal under a 4T strong magnetic field at a temperature of 1100℃ for 20 minutes in a hydrogen atmosphere.

[0054] Example 6

[0055] This embodiment provides a method for brazing aluminum alloys with a strong magnetic field assisted by wettability control. The specific steps are largely the same as those in Embodiment 3, except that:

[0056] Al-Mn alloy (LF21) was brazed using aluminum-silicon (Al: 88%, Si: 12%) brazing filler metal under a 2T strong magnetic field. The direction of the weld was at a 45° angle to the direction of the magnetic field. The brazing temperature was 590℃, the holding time was 15min, and the brazing atmosphere was argon.

[0057] The technical solutions of the present invention are not limited to the specific embodiments described above. Without departing from the scope and spirit of the described embodiments, many modifications and changes will be obvious to those skilled in the art. Any technical modifications made within the spirit and principles of the present invention are within the protection scope of the present invention.

Claims

1. A strong magnetic field-assisted brazing method based on wettability control, characterized in that, During the brazing process, a magnetic field is applied. The magnetic field is a continuously adjustable steady magnetic field, with the magnetic induction intensity B continuously adjustable within the range of 0 < B ≤ 30 T, and the direction of the steady magnetic field is longitudinal or transverse. The material of the brazing base metal is a hard brazing material system; the material of the filler metal is an aluminum-based filler metal, a silver-based filler metal, a copper-based filler metal, a manganese-based filler metal or a nickel-based filler metal. Applying a strong magnetic field affects the element interdiffusion and interface reaction between the filler metal and the base metal. By applying strong magnetic fields with different magnetic induction intensities, the type and quantity of reaction products at the interface are regulated, and thus the wettability is regulated, and finally the control of the brazing quality is achieved. When two titanium alloy substrates are welded with an Ag-Cu filler metal and a 2 T strong magnetic field is applied, the reaction products formed at the interface are divided into four layers. From top to bottom, the four-layer structure is (α + βTi) + (Ti2Cu) + (TiCu) + (TiCu2). When 4 T and 6 T strong magnetic fields are applied, the reaction products formed at the interface are divided into two layers. From top to bottom, the two-layer structure is (α + βTi) + (TiCu).

2. The strong magnetic field-assisted brazing method based on wettability control according to claim 1, characterized in that, It includes the following steps: (1) After degreasing, cleaning and drying the surfaces to be welded of the brazing base metal and the filler metal, assemble and fix them according to the welding process of the workpiece to be welded. ((2) Place the assembled and fixed workpiece to be welded in a magnetic field, heat it up to the brazing temperature for brazing, and adjust the position, magnetic induction intensity and magnetic field direction of the workpiece to be welded in the magnetic field during the brazing process according to requirements. After the brazing is completed, keep it warm, and then cool it in the furnace until the temperature of the workpiece is lower than the melting point of the filler metal, and then turn off the magnetic field; continue to cool it to room temperature, take it out, and obtain the brazed workpiece; the magnetic induction intensity mentioned is a strong magnetic field.

3. The strong magnetic field-assisted brazing method based on wettability control according to claim 2, characterized in that, In the step (2), the heating source used to heat up to the brazing temperature is one or a combination of an electron beam, a laser beam, an arc, a resistance furnace or an induction furnace, and the heating rate is 5 - 800 °C / min.

4. The strong magnetic field-assisted brazing method based on wettability control according to claim 2, characterized in that, In the step (2), the brazing temperature is determined according to the material of the brazing base metal, and the holding time is 10 - 20 min.

5. The strong magnetic field-assisted brazing method based on wettability control according to claim 2, characterized in that, In the step (2), before heating up to the brazing temperature, first heat it up to 300 - 350 °C lower than the brazing temperature for impurity removal and isothermal process. During this process, the holding time is 20 - 30 min.

6. The strong magnetic field-assisted brazing method based on wettability control according to claim 2, characterized in that, In the step (2), when placed in the magnetic field, it is a uniform magnetic field region, and the position of the workpiece placed in the magnetic field and the angle between the welding joint and the magnetic field direction are adjusted accordingly according to the requirements of the microstructure of the workpiece to be welded and the performance of the joint. The magnetic field is provided by a magnet, and the magnet is an electromagnet or a permanent magnet. Among them, the shape of the magnet is one of an annular magnet, a horseshoe magnet, a bar magnet, an opposed magnet or a single-sided magnet.

7. The strong magnetic field-assisted brazing method based on wettability control according to claim 2, characterized in that, In step (2), the brazing process is carried out in one of the following atmospheres: atmospheric atmosphere, vacuum atmosphere, or protective gas atmosphere; the vacuum level of the vacuum atmosphere is within the range of 10. -1 ~10 -8 Pa, the concentration of the protective gas atmosphere is 99.9%~99.999%.

8. The strong magnetic field-assisted brazing method based on wettability control according to claim 2, characterized in that, In the step (2), the cooling in the furnace is replaced by a cooling method with a cooling rate of 15 - 400 °C / min.

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