Non-equilibrium brazing connection method for graphene and aluminum alloy

Abstract

The invention relates to the technical field of dissimilar material connection, in particular to a non-equilibrium brazing connection method for graphene and aluminum alloy. The method comprises the steps that firstly, a high-thermal-conductivity graphene block, a rapid heating element, a to-be-welded face of aluminum alloy and brazing filler metal foil are cleaned and then dried; secondly, the materials are assembled into a to-be-brazed assembly according to the assembling 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, and the distance between the rapid heating element and the to-be-brazed face of the graphene block is smaller than the distance between the rapid heating element and the aluminum alloy on the same side; and thirdly, the assembly to be brazed is heated in a special heating mode so as to ensure that non-equilibrium temperature fields can be formed on the two sides of the connector, after heat preservation is finished, the connector is naturally cooled to the room temperature, and brazing is completed. By the adoption of the scheme, the technical problem of high residual stress concentration of a heterogeneous joint in welding of an existing graphene material and aluminum alloy can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of connecting dissimilar materials, and in particular to a non-equilibrium brazing connection method of graphene and aluminum alloy. Background Art

[0002] The in-plane thermal conductivity of the graphene block material assembled from a single layer of graphene is as high as 1200W / (m·K) or more, making it an ideal choice for the high thermal conductivity core of a solid-state heat spreader. However, the mechanical properties of the graphene block material are poor. Therefore, the high thermal conductivity graphene block is connected to a good thermal conductive aluminum alloy material with better processing performance and mechanical strength to form a heterostructure. This can overcome the problems of easy breakage and wrinkling of the graphene block material, and is expected to achieve lightweight, high-strength, high-temperature rapid thermal conduction. At present, the commonly used connection methods for graphene materials are gluing and mechanical connection. There are a large number of micro-gaps at the mechanical connection interface with extremely high thermal resistance, while the thermal conductivity of the thermal conductive glue is low, which greatly limits the thermal conductivity of graphene. In order to form good interfacial thermal conductivity, graphene and aluminum alloy need to form an atomic bond connection. Brazing, as an advanced means of solid-phase connection, is the most reliable way to achieve interatomic bonding between metal interfaces in a non-melting state. However, conventional brazing requires that the entire base material be heated uniformly. The thermal properties of aluminum alloy and graphene material are very different, and the thermal expansion coefficients between the two differ by about one order of magnitude, which can easily generate huge residual stress and cause joint cracking. Therefore, it is urgent to develop an efficient welding method that can relieve the residual stress of the brazed joint between graphene block and aluminum alloy material. Summary of the invention

[0003] In order to solve the technical problem of high residual stress concentration in heterogeneous joints in the existing welding of graphene materials and aluminum alloys, the present invention provides a non-equilibrium brazing connection method for graphene and aluminum alloys.

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

[0005] A non-equilibrium brazing connection method for graphene and aluminum alloy is carried out according to the following steps:

[0006] Step 1: clean the high thermal conductivity graphene block and the fast heating element, polish the aluminum alloy surface to be welded and the solder foil, clean them and dry them;

[0007] Step 2: Assemble the cleaned and dried aluminum alloy base material, graphene block, solder foil, and rapid heating element in the following manner: aluminum alloy / solder foil / rapid heating element / solder foil / graphene block / solder foil / rapid heating element / solder foil / aluminum alloy to form a component to be brazed, and ensure that the contact surfaces are completely aligned, and that the distance between the rapid heating element and the surface to be brazed of the graphene block is less than the distance between the rapid 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, heat the fast heating elements in the components by special heating methods to ensure that a non-equilibrium temperature field is formed on both sides of the joint, and after the insulation is completed, wait for the joint to 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 weld performance, preferably a carbon fiber braid or a graphene film.

[0010] Furthermore, 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] Furthermore, in step one, the graphene block has a length of 1 to 100 mm, a width of 1 to 100 mm, and a thickness of 0.5 to 10 mm; the rapid heating element has a length of 20 to 200 mm, a width of 20 to 200 mm, and a thickness of 0.05 to 0.3 mm; the aluminum alloy has a length of 1 to 100 mm, a width of 1 to 100 mm, and a thickness of 0.5 to 10 mm; and the thickness of the single-layer solder foil is 0.05 to 0.3 mm.

[0012] Furthermore, in step one, the high thermal conductivity graphene block and the fast heating element are cleaned, and the surface to be welded of the aluminum alloy and the solder foil are polished and dried after cleaning. Specifically, the graphene block and the fast heating element are cleaned by rinsing with anhydrous ethanol and then drying with a hair dryer; 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.

[0013] Furthermore, in step 2, in the assembly method, the number of solder foil layers between the aluminum alloy on one side of the graphene block and the rapid heating element on the same side is 3 to 5 layers, 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 rapid heating element is 1 layer, and the total thickness of the solder foil is 0.05 mm to 0.3 mm.

[0014] Furthermore, in step 3, in the vacuuming step, the vacuum degree is 10 -2 ~10 -4 Pa.

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

[0016] Furthermore, in step three, the special heating method is to increase the temperature of the fast heating element to above the melting point of the solder in a short time and keep it warm for a short time through an external directional heating method, preferably resistance heating or laser heating.

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

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

[0019] 1. The present invention uses external directional short-time local heating to make the fast heating element in the brazing assembly as a heat source for brazing. Compared with the global environmental heating under traditional vacuum brazing, the energy consumption required is lower, which helps to save energy, reduce production costs and improve energy utilization.

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

[0021] 3. The present invention not only introduces a non-equilibrium temperature field to reduce thermal expansion mismatch, but also avoids the damage to the intrinsic properties of the aluminum alloy base material due to excessively high welding temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the assembly mode of the non-equilibrium brazing connection method of the graphene block and the aluminum alloy of the present invention;

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

[0024] Figure 3 It is a comparison diagram of the simulation results of the finite element residual stress concentration 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. DETAILED DESCRIPTION

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

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

[0027] The present invention assists in brazing high thermal conductivity graphene and aluminum alloy by introducing a non-equilibrium temperature field. The method introduces a non-equilibrium temperature field in the heterogeneous parent material in the interface region by controlling the structure and distance between the heat source and the heterogeneous parent material, so that the temperature gradient from high to low is: graphene block> brazing material> aluminum alloy, so that the parent material with a small thermal expansion coefficient is at a relatively high temperature, and the parent material with a large thermal expansion coefficient is at a relatively low temperature, specifically regulating the thermal expansion of the heterogeneous parent material, reducing the thermal expansion difference, thereby relieving residual stress and improving the strength of the welded joint.

[0028] The present invention provides a non-equilibrium brazing connection method of 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 they are clean, polish the aluminum alloy surface to be welded and the solder foil, clean them and then dry them.

[0030] Among them, the rapid heating element is a material with high melting point, high thermal conductivity and no damage to weld performance, preferably a carbon fiber braid or a 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 length of the graphene block is 1 to 100 mm, the width is 1 to 100 mm, and the thickness is 0.5 to 10 mm; the length of the rapid heating element is 20 to 200 mm, the width is 20 to 200 mm, and the thickness is 0.05 to 0.3 mm; the length of the aluminum alloy is 1 to 100 mm, the width is 1 to 100 mm, and the thickness is 0.5 to 10 mm; the thickness of the single-layer solder foil is 0.05 to 0.3 mm.

[0033] In step 1, the graphene block and the fast heating element are cleaned by rinsing with anhydrous ethanol and then drying with a hair dryer; the aluminum alloy and solder 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, solder foil, and rapid heating element according to the assembly method of aluminum alloy / solder foil / rapid heating element / solder foil / graphene block / solder foil / rapid heating element / solder foil / aluminum alloy to form a component to be brazed, and ensure that the contact surfaces are completely aligned and the distance between the rapid heating element and the surface to be brazed of the graphene block is less than the distance between the rapid heating element and the aluminum alloy on the same side.

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

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

[0037] Among them, in the vacuum step, the vacuum degree is 10 -2 ~10 -4 Pa.

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

[0039] The special heating method is to increase the temperature of the fast heating element to above the melting point of the solder in a short time through an external directional heating method and to keep it warm for a short time, preferably resistance heating or laser heating.

[0040] Example:

[0041] Embodiment 1:

[0042] A non-equilibrium brazing connection method for graphene and aluminum alloy is carried out according to the following steps:

[0043] 1. Rinse the graphene block with a size of 50×50×2mm and the surface of the carbon fiber braid with a size of 100×80×0.1mm with anhydrous ethanol and then dry it with a hair dryer in cold air mode. Use the surface of the base material 6063 aluminum alloy with a size of 50×50×2mm with an area of ​​50×50mm as the welding surface and polish it with 240#SiC sandpaper, 500#SiC sandpaper, and 1000#SiC sandpaper in turn. Polish the upper and lower surfaces of the AgCuTi solder foil with a size of 50×50×0.1mm with 240#SiC sandpaper, 1000#SiC sandpaper, and 2000#SiC sandpaper in turn until it is bright. Place the polished base material and AgCuTi solder foil in anhydrous ethanol for ultrasonic cleaning for 15 minutes and then send them into an oven for drying. The drying process parameters are set to 80℃ / 2h;

[0044] 2. Assemble the cleaned and dried aluminum alloy base material, graphene block, solder foil and carbon fiber braid into a component to be brazed, and the assembly method is 6063 aluminum alloy / AgCuTi solder foil / carbon fiber braid / AgCuTi solder foil / graphene block / AgCuTi solder foil / carbon fiber braid / AgCuTi solder foil / 6063 aluminum alloy;

[0045] Among them, 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 single-sided carbon fiber braid is 1, with a thickness of 0.1mm.

[0046] 3. Transfer the assembled brazing components to the operating table in the DC thermal shock operating box, fix the two ends of the carbon fiber braid in the conductive clamps, connect the clamps at both ends to the DC power supply, close the box and evacuate to 10 -2 After Pa, hydrogen is introduced as a protective gas, and the preset power-on parameters are: current intensity 15A, power-on time 3s, turn on the power to pass direct current into the carbon fiber braided body, and use the electric heating element as the brazing heat source. After the insulation is completed, turn off the power directly, wait for the welded parts to cool down and take them out, and the brazing is completed.

[0047] Among them, the highest temperature of the carbon fiber braid surface during the DC thermal shock brazing process is 1300℃, and it is kept at this temperature for 3s.

[0048] Figure 1 It is a schematic diagram of the assembly method of the non-equilibrium brazing connection method of the graphene block and aluminum alloy of the present invention. As can be seen from the figure, the method introduces a non-equilibrium temperature field by controlling the structure and distance between the heat source (the rapid heating element in the present invention) and the heterogeneous base material during the brazing process. Since the thermal expansion coefficient of the graphene block is much lower than that of the aluminum alloy, during the brazing cooling process, the graphene block will produce a large contraction while the contraction of the aluminum alloy will be relatively reduced, thereby alleviating the residual stress caused by thermal mismatch.

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

[0050] Figure 3 This is a comparison chart of the finite element residual stress concentration 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. It can be seen from the figure that the non-equilibrium temperature field can effectively reduce the residual stress of the joint and alleviate stress concentration.

[0051] Embodiment 2: This embodiment is basically the same as Embodiment 1, except that in this embodiment, the aluminum alloy model is 6061. Embodiment 3: This embodiment is basically the same as Embodiment 1, except that in this embodiment, the solder is AgCuInTi. Embodiment 4: This embodiment is basically the same as Embodiment 1, except that in this embodiment, the rapid heating element is a graphene film.

[0052] Example 5: This example is basically the same as Example 1, except that in this example, 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 in the assembly method is 4, with a total thickness of 0.8mm, and the number of solder layers between the graphene block and the single-sided carbon fiber braid is 1, with a thickness of 0.2mm.

[0053] Embodiment 7: This embodiment is basically the same as Embodiment 1, except that in this embodiment, the maximum surface temperature of the carbon fiber braid during the direct current electric thermal shock brazing process described in step 3 is 1100° C., and is maintained at this temperature for 5 seconds.

[0054] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A non-equilibrium brazing connection method for graphene and aluminum alloy, characterized in that Follow these steps: Step 1: clean the high thermal conductivity graphene block and the fast heating element, polish the aluminum alloy surface to be welded and the solder foil, clean them and dry them; Step 2: Assemble the cleaned and dried aluminum alloy base material, graphene block, solder foil, and rapid heating element in the following manner: aluminum alloy / solder foil / rapid heating element / solder foil / graphene block / solder foil / rapid heating element / solder foil / aluminum alloy to form a component to be brazed, and ensure that the contact surfaces are completely aligned, and that the distance between the rapid heating element and the surface to be brazed of the graphene block is less than the distance between the rapid heating element and the aluminum alloy on the same side; Step 3: Transfer the assembled components to be brazed to the workbench, evacuate the brazing working environment and introduce reducing protective gas, heat the fast heating elements in the components by special heating methods to ensure that a non-equilibrium temperature field is formed on both sides of the joint, and after the insulation is completed, wait for the joint to cool naturally to room temperature, and the brazing is completed.

2. The non-equilibrium brazing connection method of 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 weld performance, preferably a carbon fiber braid or a graphene film.

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

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

5. The non-equilibrium brazing connection method of graphene and aluminum alloy according to claim 1, characterized in that: In step one, the high thermal conductivity graphene block and the fast heating element are cleaned, and the surface to be welded of the aluminum alloy and the solder foil are polished and cleaned before drying. Specifically, the graphene block and the fast heating element are cleaned by rinsing with anhydrous ethanol and then drying with a hair dryer; 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.

6. The non-equilibrium brazing connection method of graphene and aluminum alloy according to claim 1, characterized in that: In step 2, in the assembly method, the number of solder foil layers between the aluminum alloy on one side of the graphene block and the rapid 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 rapid heating element is 1, and the total thickness of the solder foil is 0.05 mm to 0.3 mm.

7. The non-equilibrium brazing connection method of graphene and aluminum alloy according to claim 1, characterized in that: In step 3, in the vacuuming step, the vacuum degree is 10 -2 ~10 -4 Pa.

8. The non-equilibrium brazing connection method of graphene and aluminum alloy according to claim 1, characterized in that: In step 3, the protective gas used is one or a mixture of hydrogen, nitrogen and methane.

9. The non-equilibrium brazing connection method of graphene and aluminum alloy according to claim 1, characterized in that: In step three, the special heating method is to increase the temperature of the fast heating element to above the melting point of the solder in a short time through an external directional heating method and keep it warm for a short time, preferably resistance heating or laser heating.

Images