A method for non-equilibrium brazing connection of graphene and aluminum alloy

Abstract

The present application relates to the technical field of dissimilar material connection, and particularly relates to a non-equilibrium state brazing connection method of graphene and aluminum alloy. The method comprises the following steps: step one, cleaning and drying the high-thermal-conductivity graphene block, rapid heating element, the welding surface of aluminum alloy, and brazing filler metal foil; step two, assembling the above materials in the assembly mode of aluminum alloy / brazing filler metal foil / rapid heating element / brazing filler metal foil / graphene block / brazing filler metal foil / rapid heating element / brazing filler metal foil / aluminum alloy to form a brazing assembly, and the distance between the rapid heating element and the welding surface of the graphene block is less than the distance between the rapid heating element and the aluminum alloy on the same side; step three, heating the brazing assembly through a special heating mode to ensure that a non-equilibrium state temperature field is formed on both sides of the joint, and the joint is naturally cooled to room temperature after holding, and the brazing is completed. The above scheme can solve the technical problem of high residual stress concentration in the existing welding of graphene material and aluminum alloy.

Description

Technical Field

[0001] This invention relates to the field of dissimilar material joining technology, specifically to a non-equilibrium brazing joining method for graphene and aluminum alloy. Background Technology

[0002] Graphene bulk materials assembled from single-layer graphene exhibit in-plane thermal conductivity exceeding 1200 W / (m·K), making them an ideal choice for high thermal conductivity cores in solid-state vapor chambers. However, graphene bulk materials have poor mechanical properties. Therefore, connecting high thermal conductivity graphene bulk materials with thermally conductive aluminum alloys, which offer better processing performance and mechanical strength, to form a heterostructure can overcome the problems of easy breakage and wrinkling of graphene bulk materials, potentially achieving lightweight, high-strength, and rapid high-temperature thermal conductivity. Currently, common bonding methods for graphene materials are adhesive bonding and mechanical bonding. Mechanical bonding interfaces have numerous micropores, resulting in extremely high thermal resistance, while thermally conductive adhesives have low thermal conductivity, significantly limiting the thermal conductivity of graphene. To achieve good interfacial thermal conductivity, graphene and aluminum alloys need to form interatomic bonds. Brazing, as an advanced solid-phase bonding method, is the most reliable way to achieve interatomic bonding at the interface of metals in a non-molten state. However, conventional brazing methods require uniform heating of the entire base material. The thermal properties of aluminum alloy and graphene differ significantly, with their coefficients of thermal expansion differing by approximately one order of magnitude. This makes them highly susceptible to generating substantial residual stress, which can lead to joint cracking. Therefore, there is an urgent need to develop an efficient welding method that can alleviate the residual stress in brazed joints between graphene bulk and aluminum alloy materials. Summary of the Invention

[0003] To address the technical problem of high residual stress concentration in heterogeneous joints during existing graphene-aluminum alloy welding, this invention provides a non-equilibrium brazing method for graphene and aluminum alloy.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A non-equilibrium brazing method for joining graphene and aluminum alloy comprises the following steps:

[0006] Step 1: Clean the high thermal conductivity graphene block and the fast heating element until clean. Polish the aluminum alloy surface to be soldered and the solder foil, and then clean and dry them.

[0007] Step 2: Assemble the cleaned and dried aluminum alloy base material, graphene block, brazing foil, and fast heating element into a brazing assembly according to the assembly method of aluminum alloy / brazing foil / fast heating element / brazing foil / graphene block / brazing foil / fast heating element / brazing foil / aluminum alloy, and ensure that the contact surfaces are completely aligned, and the distance between the fast heating element and the surface of the graphene block to be brazed is less than the distance between the fast heating element and the aluminum alloy on the same side.

[0008] Step 3: Transfer the assembled components to be brazed to the workbench, evacuate the brazing working environment and introduce reducing protective gas, and heat the fast-heating elements in the components through a special heating method to ensure that a non-equilibrium temperature field is formed on both sides of the joint. After the heat preservation is completed, let the joint cool naturally to room temperature, and the brazing is completed.

[0009] Furthermore, in step one, the rapid heating element is made of a material with a high melting point, high thermal conductivity, and no damage to the weld performance, preferably carbon fiber braid or graphene film.

[0010] Further, in step one, the solder foil is one of AgCuTi solder, AgCuInTi solder, TiZrNiCu solder, TiCu solder, AgCu solder, SnAgCu solder, BNi2 solder, or BNi5 solder.

[0011] Further, in step one, the graphene block has a length of 1-100 mm, a width of 1-100 mm, and a thickness of 0.5-10 mm; the rapid heating element has a length of 20-200 mm, a width of 20-200 mm, and a thickness of 0.05-0.3 mm; the aluminum alloy has a length of 1-100 mm, a width of 1-100 mm, and a thickness of 0.5-10 mm; and the single-layer solder foil has a thickness of 0.05-0.3 mm.

[0012] Further, in step one, the process of cleaning the high thermal conductivity graphene block and the rapid heating element until clean, and polishing and cleaning the aluminum alloy surface to be soldered and the solder foil, and then drying them, specifically involves: the graphene block and the rapid heating element being cleaned by rinsing with anhydrous ethanol and then drying them with a hairdryer on a cool setting; the aluminum alloy and the solder foil being polished with 240# to 2000# SiC sandpaper and then ultrasonically cleaned in anhydrous ethanol for 15 minutes.

[0013] Furthermore, in step two, in the assembly method, the number of solder foil layers between the aluminum alloy on one side of the graphene block and the fast heating element on the same side is 3 to 5, and the total thickness of the solder foil is 0.15 mm to 1.5 mm. The number of solder foil layers between the graphene block and the fast heating element is 1, and the total thickness of the solder foil is 0.05 mm to 0.3 mm.

[0014] Furthermore, in step three, the vacuuming step has a vacuum level of 10. -2 ~10 -4 Pa.

[0015] Furthermore, in step three, the protective gas used is a mixture of one or more of hydrogen, nitrogen, and methane.

[0016] Furthermore, in step three, the special heating method is to raise the temperature of the rapid heating element to above the melting point of the solder in a short time through an external directional heating method and then hold it at that temperature briefly. Resistance heating or laser heating is preferred.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] This invention alleviates the high stress concentration caused by thermal expansion mismatch between dissimilar base materials by constructing a non-equilibrium temperature field, forming a good stress gradient in the weld, and improving the strength of the welded joint. The specific beneficial effects are as follows:

[0019] 1. This invention uses externally oriented, short-term localized heating to make the fast-heating elements in the brazing assembly the heat source for brazing. Compared with the global environmental heating under traditional vacuum brazing, it requires less energy, which helps to save energy, reduce production costs, and improve energy utilization.

[0020] 2. This invention can complete the construction of a non-equilibrium temperature field and the entire welding process of heating-holding-cooling in a short time, and the operation is simpler and the welding efficiency is much higher than that of traditional brazing methods such as vacuum brazing.

[0021] 3. This invention reduces thermal expansion mismatch by introducing a non-equilibrium temperature field, while also preventing damage to the intrinsic properties of the aluminum alloy base material due to excessively high welding temperatures. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the assembly method for the non-equilibrium brazing connection of graphene bulk and aluminum alloy according to the present invention;

[0023] Figure 2 This is an actual finished product image of the brazed joint prepared using the brazing connection method of the present invention in Example 1;

[0024] Figure 3 This is a comparison of the finite element simulation results of residual stress concentration between the brazed joint prepared by the brazing method of the present invention in Example 1 and the brazed joint prepared under a uniform temperature field. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] The inventive mechanism of this invention is as follows:

[0027] This invention introduces a non-equilibrium temperature field to assist in the brazing of high thermal conductivity graphene and aluminum alloy. This method introduces a non-equilibrium temperature field within the heterogeneous base materials at the interface by controlling the structure and distance between the heat source and the heterogeneous base materials. The temperature gradient, from high to low, is: graphene bulk > brazing filler metal > aluminum alloy. This places the base material with a lower coefficient of thermal expansion at a relatively high temperature and the base material with a higher coefficient of thermal expansion at a relatively low temperature. This specific regulation of the thermal expansion of the heterogeneous base materials reduces the difference in thermal expansion, thereby alleviating residual stress and improving the strength of the welded joint.

[0028] This invention provides a non-equilibrium brazing connection method for graphene and aluminum alloy, which is carried out according to the following steps:

[0029] Step 1: Clean the high thermal conductivity graphene block and the fast heating element until clean. Polish the aluminum alloy surface to be soldered and the solder foil, and then clean and dry them.

[0030] Among them, the rapid heating element is made of a material with a high melting point, high thermal conductivity and no damage to the weld performance, preferably carbon fiber braid or graphene film.

[0031] The solder foil is one of AgCuTi solder, AgCuInTi solder, TiZrNiCu solder, TiCu solder, AgCu solder, SnAgCu solder, BNi2 solder, or BNi5 solder.

[0032] The graphene bulk material has a length of 1–100 mm, a width of 1–100 mm, and a thickness of 0.5–10 mm; the rapid heating element has a length of 20–200 mm, a width of 20–200 mm, and a thickness of 0.05–0.3 mm; the aluminum alloy has a length of 1–100 mm, a width of 1–100 mm, and a thickness of 0.5–10 mm; and the single-layer solder foil has a thickness of 0.05–0.3 mm.

[0033] In step one, the graphene block and the fast heating element are cleaned by rinsing with anhydrous ethanol and then drying with a hairdryer on a cool setting; the aluminum alloy and brazing foil are polished with 240# to 2000# SiC sandpaper and then ultrasonically cleaned in anhydrous ethanol for 15 minutes.

[0034] Step 2: Assemble the cleaned and dried aluminum alloy base material, graphene block, brazing foil, and fast heating element into a brazing assembly according to the assembly method of aluminum alloy / brazing foil / fast heating element / brazing foil / graphene block / brazing foil / fast heating element / brazing foil / aluminum alloy, and ensure that the contact surfaces are completely aligned, and that the distance between the fast heating element and the surface of the graphene block to be brazed is less than the distance between the fast heating element and the aluminum alloy on the same side.

[0035] In the assembly method, the number of solder foil layers between the aluminum alloy on one side of the graphene block and the fast heating element on the same side is 3 to 5, and the total thickness of the solder foil is 0.15 mm to 1.5 mm. The number of solder foil layers between the graphene block and the fast heating element is 1, and the total thickness of the solder foil is 0.05 mm to 0.3 mm.

[0036] Step 3: Transfer the assembled components to be brazed to the workbench, evacuate the brazing working environment and introduce reducing protective gas, and heat the fast-heating elements in the components through a special heating method to ensure that a non-equilibrium temperature field is formed on both sides of the joint. After the heat preservation is completed, let the joint cool naturally to room temperature, and the brazing is completed.

[0037] In the vacuuming step, the vacuum level is 10. -2 ~10 -4 Pa.

[0038] The protective gas used is a mixture of one or more of hydrogen, nitrogen, and methane.

[0039] The special heating method is to raise the temperature of the rapid heating element to above the melting point of the solder in a short time through external directional heating and then hold it at that temperature briefly. Resistance heating and laser heating are preferred.

[0040] Example:

[0041] Example 1:

[0042] A non-equilibrium brazing method for joining graphene and aluminum alloy comprises the following steps:

[0043] 1. Rinse the surfaces of a 50×50×2mm graphene block and a 100×80×0.1mm carbon fiber braid with anhydrous ethanol and dry them with a hairdryer on the cool setting. Use the 50×50mm surface of the 6063 aluminum alloy base material (50×50×2mm) as the surface to be soldered and polish it sequentially with 240# SiC sandpaper, 500# SiC sandpaper, and 1000# SiC sandpaper. Polish the upper and lower surfaces of the 50×50×0.1mm AgCuTi solder foil sequentially with 240# SiC sandpaper, 1000# SiC sandpaper, and 2000# SiC sandpaper until they are shiny. Place the polished base material and AgCuTi solder foil in anhydrous ethanol for ultrasonic cleaning for 15 minutes and then put them into an oven to dry. Set the drying process parameters to 80℃ / 2h.

[0044] 2. The cleaned and dried aluminum alloy base material, graphene block, brazing foil and carbon fiber braid are assembled into a component to be brazed. The assembly method is 6063 aluminum alloy / AgCuTi brazing foil / carbon fiber braid / AgCuTi brazing foil / graphene block / AgCuTi brazing foil / carbon fiber braid / AgCuTi brazing foil / 6063 aluminum alloy.

[0045] In the assembly method, the number of solder layers between the 6063 aluminum alloy on one side of the graphene block and the carbon fiber braid on the same side is 3, with a total thickness of 0.3mm, and the number of solder layers between the graphene block and the carbon fiber braid on one side is 1, with a thickness of 0.1mm.

[0046] 3. Transfer the assembled brazed components to the operating table in the DC electrothermal shock chamber. Fix both ends of the carbon fiber braided body in conductive clamps, and connect the clamps at both ends to a DC power supply. After closing the chamber, evacuate to 10°C. -2 After Pa, hydrogen gas is introduced as a protective gas. The preset power parameters are: current intensity 15A, power-on time 3s. Turn on the power to pass DC current into the carbon fiber braid, and use the heating element as the brazing heat source. After the heat preservation is completed, turn off the power directly. After the welded part cools down, take it out. The brazing is complete.

[0047] The highest surface temperature of the carbon fiber braid during DC electrothermal shock brazing was 1300℃, and it was held at this temperature for 3 seconds.

[0048] Figure 1 This is a schematic diagram of the assembly method for non-equilibrium brazing connection of graphene bulk and aluminum alloy according to the present invention. As shown in the figure, the method introduces a non-equilibrium temperature field by controlling the structure and distance between the heat source (rapid heating element in the present invention) and the heterogeneous base material during the brazing process. Since the thermal expansion coefficient of graphene bulk is much lower than that of aluminum alloy, the graphene bulk will shrink significantly during the brazing cooling process, while the shrinkage of aluminum alloy is relatively reduced, thereby alleviating the residual stress caused by thermal mismatch.

[0049] Figure 2 The image shows the actual finished product of the brazed joint prepared by the brazing connection method of the present invention in Example 1. As can be seen from the image, the welding effect is good.

[0050] Figure 3 The figure shows a comparison of the finite element simulation results of the brazed joint prepared by the brazing connection method of the present invention in Example 1 and the brazed joint prepared under a uniform temperature field. As can be seen from the figure, the non-equilibrium temperature field can effectively reduce the residual stress of the joint and alleviate stress concentration.

[0051] Example 2: This example is basically the same as Example 1, except that the aluminum alloy used in this example is 6061. Example 3: This example is basically the same as Example 1, except that the brazing filler metal used in this example is AgCuInTi. Example 4: This example is basically the same as Example 1, except that the rapid heating element used in this example is a graphene film.

[0052] Example 5: This example is basically the same as Example 1, except that the size of the graphene block is 30×10×3mm, the size of the carbon fiber braid is 80×40×0.2mm, and the size of the 6063 aluminum alloy is 30×10×3mm. Example 6: This example is basically the same as Example 1, except that in this example, the number of solder layers between the 6063 aluminum alloy and its single-sided carbon fiber braid is 4, with a total thickness of 0.8mm, while the number of solder layers between the graphene block and its single-sided carbon fiber braid is 1, with a thickness of 0.2mm.

[0053] Example 7: This example is basically the same as Example 1, except that in this example, the highest temperature on the surface of the carbon fiber braid is 1100℃ during the DC electrothermal shock brazing process in step 3, and it is held at this temperature for 5 seconds.

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A non-equilibrium brazing method for joining graphene and aluminum alloy, characterized in that... Follow these steps: Step 1: Clean the high thermal conductivity graphene block and the fast heating element until clean. Polish the aluminum alloy surface to be soldered and the solder foil, and then clean and dry them. Step 2: Assemble the cleaned and dried aluminum alloy base material, graphene block, brazing foil, and fast heating element into a brazing assembly according to the assembly method of aluminum alloy / brazing foil / fast heating element / brazing foil / graphene block / brazing foil / fast heating element / brazing foil / aluminum alloy, and ensure that the contact surfaces are completely aligned, and the distance between the fast heating element and the surface of the graphene block to be brazed is less than the distance between the fast heating element and the aluminum alloy on the same side. In the assembly method, the number of brazing foil layers between the aluminum alloy on one side of the graphene block and the fast heating element on the same side is 3 to 5, and the total thickness of the brazing foil is 0.15 mm to 1.5 mm. The number of brazing foil layers between the graphene block and the fast heating element is 1, and the total thickness of the brazing foil is 0.05 mm to 0.3 mm. Step 3: Transfer the assembled components to be brazed to the workbench, evacuate the brazing working environment and introduce reducing protective gas, and heat the fast-heating elements in the components through a special heating method to ensure that a non-equilibrium temperature field is formed on both sides of the joint. After the heat preservation is completed, let the joint cool naturally to room temperature, and the brazing is completed. The special heating method involves using external directional heating to raise the temperature of the rapid heating element above the melting point of the solder in a short time and then briefly maintaining the temperature.

2. The non-equilibrium brazing connection method between graphene and aluminum alloy according to claim 1, characterized in that, In step one, the rapid heating element is made of a material with a high melting point, high thermal conductivity, and no damage to the weld performance.

3. The non-equilibrium brazing connection method between graphene and aluminum alloy according to claim 2, characterized in that, The rapid heating element is a carbon fiber braid or a graphene film.

4. The non-equilibrium brazing connection method between graphene and aluminum alloy according to claim 1, characterized in that, In step one, the solder foil is one of AgCuTi solder, AgCuInTi solder, TiZrNiCu solder, TiCu solder, AgCu solder, SnAgCu solder, BNi2 solder, or BNi5 solder.

5. The non-equilibrium brazing connection method between graphene and aluminum alloy according to claim 1, characterized in that, In step one, the graphene block has a length of 1-100mm, a width of 1-100mm, and a thickness of 0.5-10mm; the rapid heating element has a length of 20-200mm, a width of 20-200mm, and a thickness of 0.05-0.3mm; the aluminum alloy has a length of 1-100mm, a width of 1-100mm, and a thickness of 0.5-10mm; and the single-layer solder foil has a thickness of 0.05-0.3mm.

6. The non-equilibrium brazing connection method between graphene and aluminum alloy according to claim 1, characterized in that, In step one, the high thermal conductivity graphene block and the rapid heating element are cleaned until clean, and the aluminum alloy surface to be soldered and the solder foil are polished and cleaned and then dried. Specifically, the graphene block and the rapid heating element are cleaned by rinsing with anhydrous ethanol and then drying with a hair dryer in cold air; the aluminum alloy and the solder foil are polished with 240# to 2000# SiC sandpaper and then ultrasonically cleaned in anhydrous ethanol for 15 minutes.

7. The non-equilibrium brazing connection method between graphene and aluminum alloy according to claim 1, characterized in that, In step three, the vacuum level during the vacuuming process is 10. -2 ~10 -4 Pa.

8. The non-equilibrium brazing connection method between graphene and aluminum alloy according to claim 1, characterized in that, In step three, the protective gas used is one or a mixture of hydrogen, nitrogen, and methane.

9. The non-equilibrium brazing connection method between graphene and aluminum alloy according to claim 1, characterized in that, In step three, the special heating method is resistance heating or laser heating.

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