A method for low-temperature brazing of carbon fiber composite material and aluminum alloy and a connecting structure

Abstract

This invention belongs to the field of materials science and engineering technology, and specifically relates to a low-temperature brazing method and connection structure for carbon fiber composite materials and aluminum alloys. It includes the following steps: S1: preparing a Ti adhesion layer; S2: preparing a Ni-P barrier layer; S3: preparing a Cu wetting layer; S4: pre-applying low-temperature brazing filler metal; S5: low-temperature brazing connection. This invention uses surface treatment and metallization deposition methods to prepare a metallized transition layer on the surface of the carbon fiber composite material to be joined. This results in a brazing-compatible metallized transition layer on the surface of the carbon fiber composite material, improving the low-temperature brazing filler metal wettability of its surface without damaging the resin matrix and fiber reinforcement structure of the carbon fiber composite material. This achieves a low-temperature brazing connection between the carbon fiber composite material and the aluminum alloy, obtaining a carbon fiber composite material / aluminum alloy heterogeneous connection structure with high connection strength and service stability.

Description

Technical Field

[0001] This invention relates to the fields of materials science and engineering technology, specifically to a low-temperature brazing method and connection structure for carbon fiber composite materials and aluminum alloys. Background Technology

[0002] Carbon fiber composites possess characteristics such as high specific strength, high specific stiffness, good fatigue resistance, and significant weight reduction, and have been widely used in aerospace, rail transportation, new energy vehicles, marine equipment, and high-end sports equipment. Aluminum alloys have low density, good processing performance, and good thermal and electrical conductivity, making them one of the most mature metallic materials used in lightweight structures. As aerospace equipment, new energy vehicles, and rail transportation structures continue to develop towards lightweighting and multi-material integration, the demand for heterogeneous bonding between carbon fiber composites and aluminum alloys is increasing. For example, in structures such as vehicle body structural components, battery pack shells, rail vehicle components, and aircraft skins and reinforcements, reliable bonding between composite materials and aluminum alloys directly affects structural weight reduction, load-bearing capacity, and service safety. Therefore, developing a high-strength, corrosion-resistant bonding method suitable for carbon fiber composites and aluminum alloys has significant engineering application value.

[0003] Currently, the main methods for joining carbon fiber composites and aluminum alloys include mechanical joining, adhesive bonding, adhesive-riveting composite joining, thermocompression joining, friction welding, laser-assisted joining, and brazing. Mechanical joining is a mature technology and easy to assemble, but it usually requires drilling holes in the composite material, which can easily cut continuous fibers, introduce stress concentration, and increase the weight of the joint, hindering lightweight design. Adhesive bonding avoids damage from drilling and provides a relatively uniform stress distribution at the joint, but the connection strength and long-term reliability are easily affected by the adhesive properties. Under high temperature, humidity, salt spray, or thermal cycling conditions, the adhesive interface is prone to aging and strength degradation. While adhesive-riveting composite joining can improve the safety margin of the connection to some extent, the process is complex, the structure becomes significantly heavier, and it is difficult to completely avoid local stress concentration. Heat-assisted joining and friction joining methods can enhance interfacial bonding, but the joining process often involves high heat input and pressure, which can easily damage the resin matrix and is not very suitable for heat-sensitive composite materials.

[0004] Brazing is a common method for joining dissimilar materials. Low-temperature brazing offers advantages such as relatively low connection temperature, high joint dimensional accuracy, and suitability for complex component connections. However, direct brazing of carbon fiber composites and aluminum alloys remains significantly challenging. The surface of carbon fiber composites is primarily composed of a resin matrix and carbon fibers, which are not typical metal surfaces and are difficult to wet directly with metal brazing filler metals, making it difficult to form a continuous and stable connection interface during brazing. Furthermore, a significant potential difference exists between carbon fibers and aluminum alloys. If they come into direct contact in humid or salt spray environments, galvanic corrosion is likely to occur, leading to interface corrosion propagation and decreased joint performance. Therefore, relying solely on traditional brazing processes makes it difficult to achieve a stable connection between carbon fiber composites and aluminum alloys. To improve the connection performance between composite materials and metal materials, existing technologies typically employ methods such as surface roughening, plasma treatment, laser etching, chemical activation, and the introduction of metal plating or intermediate layers. Surface roughening and plasma treatment can increase the surface energy of composite materials and enhance mechanical interlocking to some extent, but these methods do not fundamentally solve the problem of poor wettability of low-temperature brazing filler metals on carbon fiber composites. Metallization can transform the surface of composite materials into a weldable, brazable, or conductive surface, providing an effective way to join composite materials with metals. However, existing metallization methods still have some shortcomings, such as unstable bonding between the metal layer and the composite material surface, insufficient coating continuity, easy interface cracking due to thermal expansion mismatch, lack of an effective barrier layer, and insufficient resistance to galvanic corrosion. Especially in the connection of carbon fiber composites and aluminum alloys, if the metallization layer only serves a simple wetting function for the brazing filler metal without also providing adhesion, barrier, and wetting functions, the joint may still experience interface corrosion failure during service. For low-temperature brazing filler metals to be truly used for joining carbon fiber composites and aluminum alloys, a stable metallization transition layer is also needed as a support. If the composite material surface lacks a firmly bonded adhesion layer, the metallization layer is prone to peeling off entirely during brazing or service; without a barrier layer, galvanic corrosion may still occur between the carbon fiber and the aluminum alloy; and without a good wetting layer, low-temperature brazing filler metals cannot form a continuous brazing interface on the composite material side. Therefore, how to construct a metallized transition layer on the surface of carbon fiber composite materials that combines interfacial bonding, barrier protection, and brazing performance, and how to achieve a reliable connection with aluminum alloy within a temperature range that does not significantly damage the resin matrix, is a technical challenge that urgently needs to be solved in the connection of such heterogeneous materials. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0007] A low-temperature brazing method for carbon fiber composite materials and aluminum alloys includes the following steps:

[0008] S1: Preparation of Ti adhesion layer: Select the carbon fiber composite material to be joined, clean, dry and roughen the surface of the carbon fiber composite material to be joined, and deposit a Ti adhesion layer on the pretreated carbon fiber composite material surface to be joined by magnetron sputtering. The thickness of the Ti adhesion layer is 100-300nm.

[0009] S2: Preparation of Ni-P barrier layer: Ni-P barrier layer is prepared on the surface of Ti adhesion layer by chemical plating. The Ni-P barrier layer is used to prevent carbon fiber from directly contacting aluminum alloy, reduce galvanic corrosion tendency, and serve as a continuous conductive base layer for subsequent electroplated Cu layer. The thickness of the Ni-P barrier layer is 3-10 μm.

[0010] S3: Preparation of Cu wetting layer: A Cu wetting layer is prepared on the surface of the Ni-P barrier layer by electroplating. The Cu wetting layer is used to improve the thermal conductivity of the metallization transition layer and the low-temperature solder wetting and spreading ability. The thickness of the Cu wetting layer is 3-10μm.

[0011] S4: Low-temperature solder pre-placement: Low-temperature solder is pre-placed between the carbon fiber composite material with Ti / Ni-P / Cu metallization transition layer and the aluminum alloy, wherein the thickness of the low-temperature solder is 30-150μm;

[0012] S5: Low-temperature brazing connection: The assembled carbon fiber composite material, low-temperature brazing filler metal and aluminum alloy are brazed at low temperature under argon protection. After brazing, the material is cooled to below the solidus temperature of the low-temperature brazing filler metal while maintaining pressure. Then the pressure is released and the material is cooled to room temperature.

[0013] As a preferred embodiment of the low-temperature brazing method for carbon fiber composite materials and aluminum alloys described in this invention, in step S1, during the magnetron sputtering process, the target material is a pure Ti target with a purity of not less than 99.9%; the sputtering gas is argon; the sputtering power is 100-200W; the working pressure is 0.3-0.8Pa; the substrate temperature is room temperature to 80℃; and the sputtering time is 20-40min.

[0014] As a preferred embodiment of the low-temperature brazing method for carbon fiber composite materials and aluminum alloys described in this invention, in step S2, the concentration of nickel sulfate in the chemical Ni-P plating solution is 20-40 g / L, the concentration of sodium hypophosphite is 15-40 g / L, the concentration of sodium citrate is 5-30 g / L, the concentration of sodium acetate is 5-20 g / L, the pH value of the plating solution is 4.0-6.0, the chemical plating temperature is 70-90℃, and the plating time is 10-60 min.

[0015] As a preferred embodiment of the low-temperature brazing method for carbon fiber composite materials and aluminum alloys described in this invention, in step S3, the Cu plating solution includes copper sulfate, sulfuric acid, and chloride ions, with a copper sulfate concentration of 100-250 g / L, a sulfuric acid concentration of 30-100 g / L, a chloride ion concentration of 20-100 mg / L, an electroplating temperature of 25-35℃, a current density of 1-3 A / dm², and an electroplating time of 10-20 min.

[0016] In a preferred embodiment of the low-temperature brazing method for carbon fiber composite materials and aluminum alloys described in this invention, in step S4, the low-temperature brazing filler metal is one of Sn-Bi, Sn-Bi-Ag, Sn-In, Sn-Zn, Sn-Ag-Cu, or In-Sn brazing filler metals.

[0017] A low-temperature brazing connection structure between carbon fiber composite material and aluminum alloy includes a carbon fiber composite material, a metallized transition layer, and an aluminum alloy, wherein the metallized transition layer is located between the carbon fiber composite material and the aluminum alloy.

[0018] As a preferred embodiment of the low-temperature brazing connection structure of carbon fiber composite material and aluminum alloy described in this invention, the metallization transition layer consists of a low-temperature brazing connection layer, a Cu wetting layer, a Ni-P barrier layer and a Ti adhesion layer arranged sequentially from bottom to top.

[0019] As a preferred embodiment of the low-temperature brazing connection structure of carbon fiber composite material and aluminum alloy described in this invention, the low-temperature brazing connection layer is a continuous and dense brazing layer.

[0020] As a preferred embodiment of the low-temperature brazing connection structure of carbon fiber composite material and aluminum alloy described in this invention, the lap shear strength of the low-temperature brazing connection structure of carbon fiber composite material and aluminum alloy is not less than 29 MPa, and after 72 h of salt spray test, the lap shear strength retention rate after corrosion is not less than 80%.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention prepares a metallized transition layer on the surface of the carbon fiber composite material to be joined by surface treatment and metallization deposition methods, and obtains a metallized transition layer with brazing performance on the surface of the carbon fiber composite material. Without damaging the resin matrix and fiber reinforcement structure of the carbon fiber composite material, the low-temperature brazing wettability of its surface is improved, realizing the low-temperature brazing connection between the carbon fiber composite material and the aluminum alloy, avoiding galvanic corrosion caused by direct contact between the carbon fiber composite material and the aluminum alloy, and obtaining a carbon fiber composite material / aluminum alloy heterogeneous connection structure with high connection strength and service stability. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0023] Figure 1 This is a schematic diagram illustrating the principle of the low-temperature brazing connection process between carbon fiber composite material and aluminum alloy of the present invention;

[0024] Figure 2 This is a schematic diagram of the heterogeneous connection interface structure of carbon fiber composite material / metallized transition layer / aluminum alloy of the present invention;

[0025] Figure 3 This invention relates to a heterogeneous connection structure interface between carbon fiber composite material and aluminum alloy.

[0026] In the figure: 1-carbon fiber composite material, 2-metallized transition layer, 3-aluminum alloy. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0030] This invention prepares a Ti / Ni-P / Cu metallization transition layer on the surface of a carbon fiber composite material to be joined. The Ti adhesion layer enhances the bonding strength between the metallization layer and the carbon fiber composite surface; the Ni-P barrier layer prevents direct contact between the carbon fiber and the aluminum alloy and reduces galvanic corrosion; and the Cu wetting layer improves the wetting and spreading ability of the low-temperature brazing filler metal on the surface of the metallization transition layer. Subsequently, a low-temperature brazing filler metal is pre-placed between the carbon fiber composite material with the metallization transition layer and the aluminum alloy, and low-temperature pressure brazing is performed under argon protection to form a continuous and dense low-temperature brazed connection layer between the two materials.

[0031] The core technologies of this invention are: (1) a metallized transition layer on the surface of carbon fiber composite material; (2) achieving low-temperature brazing between carbon fiber composite material with metallized transition layer and aluminum alloy under conditions lower than the obvious thermal damage temperature of carbon fiber composite resin matrix, thereby obtaining a carbon fiber composite material / aluminum alloy heterogeneous connection structure with high connection strength and resistance to galvanic corrosion.

[0032] like Figure 1 As shown, a low-temperature brazing method for carbon fiber composite materials and aluminum alloys includes the following steps:

[0033] The first step is to prepare the Ti adhesion layer. The carbon fiber composite material 1 to be joined is selected, and its surface is cleaned, dried, and roughened. A Ti adhesion layer is then deposited on the pretreated surface of the carbon fiber composite material 1 using magnetron sputtering. The Ti adhesion layer is used to improve the interfacial bonding strength between the metallization transition layer 2 and the surface of the carbon fiber composite material 1. The thickness of the Ti adhesion layer is 100-300 nm. During magnetron sputtering, the target material is a pure Ti target with a purity of not less than 99.9%; the sputtering gas is argon; the sputtering power is 100-200 W; the working pressure is 0.3-0.8 Pa; the substrate temperature is room temperature to 80℃; and the sputtering time is 20-40 min.

[0034] The second step is to prepare a Ni-P barrier layer. A Ni-P barrier layer is prepared on the surface of the Ti adhesion layer using a chemical plating method. The Ni-P barrier layer prevents direct contact between the carbon fiber and the aluminum alloy, reduces the tendency for galvanic corrosion, and serves as a continuous conductive base layer for subsequent Cu electroplating. The thickness of the Ni-P barrier layer is 3-10 μm. In the chemical Ni-P plating solution, the concentrations are: nickel sulfate 20-40 g / L, sodium hypophosphite 15-40 g / L, sodium citrate 5-30 g / L, sodium acetate 5-20 g / L, pH 4.0-6.0, plating temperature 70-90℃, and plating time 10-60 min.

[0035] The third step is to prepare the Cu wetting layer. A Cu wetting layer is prepared on the surface of the Ni-P barrier layer using electroplating. This Cu wetting layer improves the thermal conductivity of the metallization transition layer 2 and the wetting and spreading ability of the low-temperature solder. The thickness of the Cu wetting layer is 3-10 μm. The Cu electroplating solution includes copper sulfate, sulfuric acid, and chloride ions. The concentration of copper sulfate is 100-250 g / L, the concentration of sulfuric acid is 30-100 g / L, and the concentration of chloride ions is 20-100 mg / L. The electroplating temperature is 25-35℃, the current density is 1-3 A / dm², and the electroplating time is 10-20 min.

[0036] The fourth step is the pre-placement of low-temperature solder. A low-temperature solder is pre-placed between the carbon fiber composite material 1 with the Ti / Ni-P / Cu metallization transition layer and the aluminum alloy 3. The low-temperature solder is one of the following: Sn-Bi, Sn-Bi-Ag, Sn-In, Sn-Zn, Sn-Ag-Cu, or In-Sn. The thickness of the low-temperature solder is 30-150 μm.

[0037] Step 5: Low-temperature brazing. The assembled carbon fiber composite material 1, low-temperature brazing filler metal, and aluminum alloy 3 are brazed under argon protection. The brazing temperature is 140-220℃, the holding time is 5-30 min, the brazing pressure is 0.05-0.8 MPa, and the heating rate is 3-10℃ / min. After brazing, the material is cooled to below the solidus temperature of the low-temperature brazing filler metal while maintaining pressure, then the pressure is released and the material is cooled to room temperature.

[0038] Example (see example) Figure 2-3 ):

[0039] Example 1: A low-temperature brazing method for carbon fiber composite materials and aluminum alloys includes the following process steps:

[0040] The first step is to prepare the Ti adhesion layer. The carbon fiber composite material 1 to be joined is selected, and its surface is cleaned, dried, and roughened. A Ti adhesion layer is then deposited on the pretreated surface of the carbon fiber composite material 1 using magnetron sputtering. The Ti adhesion layer is used to improve the interfacial bonding strength between the metallization transition layer 2 and the surface of the carbon fiber composite material 1. The Ti adhesion layer thickness is 200 nm. During magnetron sputtering, the target material is a pure Ti target with a purity of not less than 99.9%; the sputtering gas is argon; the sputtering power is 150 W; the working pressure is 0.5 Pa; the substrate temperature is 40 °C; and the sputtering time is 30 min.

[0041] The second step involved preparing a Ni-P barrier layer. A Ni-P barrier layer was prepared on the Ti adhesion layer surface using a chemical plating method. This Ni-P barrier layer prevents direct contact between the carbon fiber and the aluminum alloy 3, reducing the tendency for galvanic corrosion, and serves as a continuous conductive base layer for subsequent Cu electroplating. The Ni-P barrier layer thickness was 5 μm. The Ni-P electroplating solution contained 30 g / L nickel sulfate, 20 g / L sodium hypophosphite, 20 g / L sodium citrate, and 10 g / L sodium acetate. The pH of the solution was 5.0, the electroplating temperature was 80℃, and the plating time was 30 min.

[0042] The third step is to prepare the Cu wetting layer. A Cu wetting layer is prepared on the surface of the Ni-P barrier layer using electroplating. This Cu wetting layer improves the thermal conductivity of the metallization transition layer 2 and the wetting and spreading ability of the low-temperature solder. The thickness of the Cu wetting layer is 5 μm. The Cu electroplating solution includes copper sulfate, sulfuric acid, and chloride ions. The concentration of copper sulfate is 150 g / L, the concentration of sulfuric acid is 60 g / L, and the concentration of chloride ions is 60 mg / L. The electroplating temperature is 30℃, the current density is 2 A / dm², and the electroplating time is 15 min.

[0043] The fourth step is the pre-placement of low-temperature solder. A low-temperature solder, Sn-57Bi-1Ag, is pre-placed between the carbon fiber composite material 1 with the Ti / Ni-P / Cu metallization transition layer 2 and the aluminum alloy 3. The thickness of the low-temperature solder is 100 μm.

[0044] Step 5: Low-temperature brazing. The assembled carbon fiber composite material 1, low-temperature brazing filler metal, and aluminum alloy 3 are brazed under argon protection at a temperature of 180℃ for 15 minutes, a brazing pressure of 0.2 MPa, and a heating rate of 5℃ / min. After brazing, the material is cooled to below the solidus temperature of the low-temperature brazing filler metal while maintaining pressure, then the pressure is released and the material is cooled to room temperature.

[0045] Example 2: A low-temperature brazing method for carbon fiber composite materials and aluminum alloys includes the following process steps:

[0046] The first step is to prepare the Ti adhesion layer. The carbon fiber composite material 1 to be joined is selected, and its surface is cleaned, dried, and roughened. A Ti adhesion layer is then deposited on the pretreated surface of the carbon fiber composite material 1 using magnetron sputtering. The Ti adhesion layer is used to improve the interfacial bonding strength between the metallization transition layer 2 and the surface of the carbon fiber composite material 1. The Ti adhesion layer thickness is 200 nm. During magnetron sputtering, the target material is a pure Ti target with a purity of not less than 99.9%; the sputtering gas is argon; the sputtering power is 150 W; the working pressure is 0.5 Pa; the substrate temperature is 40 °C; and the sputtering time is 30 min.

[0047] The second step involved preparing a Ni-P barrier layer. A Ni-P barrier layer was prepared on the Ti adhesion layer surface using a chemical plating method. This Ni-P barrier layer prevents direct contact between the carbon fiber and the aluminum alloy 3, reducing the tendency for galvanic corrosion, and serves as a continuous conductive base layer for subsequent Cu electroplating. The Ni-P barrier layer thickness was 5 μm. The Ni-P electroplating solution contained 30 g / L nickel sulfate, 20 g / L sodium hypophosphite, 20 g / L sodium citrate, and 10 g / L sodium acetate. The pH of the solution was 5.0, the electroplating temperature was 80℃, and the plating time was 30 min.

[0048] The third step is to prepare the Cu wetting layer. A Cu wetting layer is prepared on the surface of the Ni-P barrier layer using electroplating. This Cu wetting layer improves the thermal conductivity of the metallization transition layer 2 and the wetting and spreading ability of the low-temperature solder. The thickness of the Cu wetting layer is 5 μm. The Cu electroplating solution includes copper sulfate, sulfuric acid, and chloride ions. The concentration of copper sulfate is 150 g / L, the concentration of sulfuric acid is 60 g / L, and the concentration of chloride ions is 60 mg / L. The electroplating temperature is 30℃, the current density is 2 A / dm², and the electroplating time is 15 min.

[0049] The fourth step is the pre-placement of low-temperature solder. A low-temperature solder, Sn-58Bi, is pre-placed between the carbon fiber composite material 1 with the Ti / Ni-P / Cu metallization transition layer 2 and the aluminum alloy 3. The thickness of the low-temperature solder is 100 μm.

[0050] Step 5: Low-temperature brazing. The assembled carbon fiber composite material 1, low-temperature brazing filler metal, and aluminum alloy 3 were brazed under argon protection at a temperature of 170℃ for 15 minutes, a brazing pressure of 0.2 MPa, and a heating rate of 5℃ / min. After brazing, the material was cooled to below the solidus temperature of the low-temperature brazing filler metal while maintaining pressure, then the pressure was released and the material was cooled to room temperature.

[0051] Example 3: A low-temperature brazing method for carbon fiber composite materials and aluminum alloys includes the following process steps:

[0052] The first step is to prepare the Ti adhesion layer. The carbon fiber composite material 1 to be joined is selected, and its surface is cleaned, dried, and roughened. A Ti adhesion layer is then deposited on the pretreated surface of the carbon fiber composite material 1 using magnetron sputtering. The Ti adhesion layer is used to improve the interfacial bonding strength between the metallization transition layer 2 and the surface of the carbon fiber composite material 1. The Ti adhesion layer thickness is 200 nm. During magnetron sputtering, the target material is a pure Ti target with a purity of not less than 99.9%; the sputtering gas is argon; the sputtering power is 150 W; the working pressure is 0.5 Pa; the substrate temperature is 40 °C; and the sputtering time is 30 min.

[0053] The second step involved preparing a Ni-P barrier layer. A Ni-P barrier layer was prepared on the Ti adhesion layer surface using a chemical plating method. This Ni-P barrier layer prevents direct contact between the carbon fiber and the aluminum alloy 3, reducing the tendency for galvanic corrosion, and serves as a continuous conductive base layer for subsequent Cu electroplating. The Ni-P barrier layer thickness was 5 μm. The Ni-P electroplating solution contained 30 g / L nickel sulfate, 20 g / L sodium hypophosphite, 20 g / L sodium citrate, and 10 g / L sodium acetate. The pH of the solution was 5.0, the electroplating temperature was 80℃, and the plating time was 30 min.

[0054] The third step is to prepare the Cu wetting layer. A Cu wetting layer is prepared on the surface of the Ni-P barrier layer using electroplating. This Cu wetting layer improves the thermal conductivity of the metallization transition layer 2 and the wetting and spreading ability of the low-temperature solder. The thickness of the Cu wetting layer is 5 μm. The Cu electroplating solution includes copper sulfate, sulfuric acid, and chloride ions. The concentration of copper sulfate is 150 g / L, the concentration of sulfuric acid is 60 g / L, and the concentration of chloride ions is 60 mg / L. The electroplating temperature is 30℃, the current density is 2 A / dm², and the electroplating time is 15 min.

[0055] The fourth step is the pre-placement of low-temperature solder. A low-temperature solder, Sn-52In, is pre-placed between the carbon fiber composite material 1 with the Ti / Ni-P / Cu metallization transition layer 2 and the aluminum alloy 3. The solder thickness is 100 μm.

[0056] Step 5: Low-temperature brazing. The assembled carbon fiber composite material 1, low-temperature brazing filler metal, and aluminum alloy 3 were brazed under argon protection at a temperature of 155℃ for 20 minutes, a brazing pressure of 0.15 MPa, and a heating rate of 5℃ / min. After brazing, the material was cooled to below the solidus temperature of the low-temperature brazing filler metal while maintaining pressure, then the pressure was released and the material was cooled to room temperature.

[0057] Example 4: A low-temperature brazing method for carbon fiber composite material 1 and aluminum alloy 3 includes the following process steps:

[0058] The first step is to prepare the Ti adhesion layer. The carbon fiber composite material 1 to be joined is selected, and its surface is cleaned, dried, and roughened. A Ti adhesion layer is then deposited on the pretreated surface of the carbon fiber composite material 1 using magnetron sputtering. The Ti adhesion layer is used to improve the interfacial bonding strength between the metallization transition layer 2 and the surface of the carbon fiber composite material 1. The Ti adhesion layer thickness is 200 nm. During magnetron sputtering, the target material is a pure Ti target with a purity of not less than 99.9%; the sputtering gas is argon; the sputtering power is 150 W; the working pressure is 0.5 Pa; the substrate temperature is 40 °C; and the sputtering time is 30 min.

[0059] The second step involved preparing a Ni-P barrier layer. A Ni-P barrier layer was prepared on the Ti adhesion layer surface using a chemical plating method. This Ni-P barrier layer prevents direct contact between the carbon fiber and the aluminum alloy 3, reducing the tendency for galvanic corrosion, and serves as a continuous conductive base layer for subsequent Cu electroplating. The Ni-P barrier layer thickness was 5 μm. The Ni-P electroplating solution contained 30 g / L nickel sulfate, 20 g / L sodium hypophosphite, 20 g / L sodium citrate, and 10 g / L sodium acetate. The pH of the solution was 5.0, the electroplating temperature was 80℃, and the plating time was 30 min.

[0060] The third step is to prepare the Cu wetting layer. A Cu wetting layer is prepared on the surface of the Ni-P barrier layer using electroplating. This Cu wetting layer improves the thermal conductivity of the metallization transition layer 2 and the wetting and spreading ability of the low-temperature solder. The thickness of the Cu wetting layer is 5 μm. The Cu electroplating solution includes copper sulfate, sulfuric acid, and chloride ions. The concentration of copper sulfate is 150 g / L, the concentration of sulfuric acid is 60 g / L, and the concentration of chloride ions is 60 mg / L. The electroplating temperature is 30℃, the current density is 2 A / dm², and the electroplating time is 15 min.

[0061] The fourth step is the pre-placement of low-temperature solder. A low-temperature solder, Sn-35Bi-1Ag, is pre-placed between the carbon fiber composite material 1 with the Ti / Ni-P / Cu metallization transition layer 2 and the aluminum alloy 3. The solder thickness is 100 μm.

[0062] Step 5: Low-temperature brazing. The assembled carbon fiber composite material 1, low-temperature brazing filler metal, and aluminum alloy 3 are brazed under argon protection at a temperature of 200℃ for 20 minutes, a brazing pressure of 0.3 MPa, and a heating rate of 5℃ / min. After brazing, the material is cooled to below the solidus temperature of the low-temperature brazing filler metal while maintaining pressure, then the pressure is released and the material is cooled to room temperature.

[0063] Example 5: A low-temperature brazing method for carbon fiber composite material 1 and aluminum alloy 3 includes the following process steps:

[0064] The first step is to prepare the Ti adhesion layer. The carbon fiber composite material 1 to be joined is selected, and its surface is cleaned, dried, and roughened. A Ti adhesion layer is then deposited on the pretreated surface of the carbon fiber composite material 1 using magnetron sputtering. The Ti adhesion layer is used to improve the interfacial bonding strength between the metallization transition layer 2 and the surface of the carbon fiber composite material 1. The Ti adhesion layer thickness is 200 nm. During magnetron sputtering, the target material is a pure Ti target with a purity of not less than 99.9%; the sputtering gas is argon; the sputtering power is 150 W; the working pressure is 0.5 Pa; the substrate temperature is 40 °C; and the sputtering time is 30 min.

[0065] The second step involved preparing a Ni-P barrier layer. A Ni-P barrier layer was prepared on the Ti adhesion layer surface using a chemical plating method. This Ni-P barrier layer prevents direct contact between the carbon fiber and the aluminum alloy 3, reducing the tendency for galvanic corrosion, and serves as a continuous conductive base layer for subsequent Cu electroplating. The Ni-P barrier layer thickness was 5 μm. The Ni-P electroplating solution contained 30 g / L nickel sulfate, 20 g / L sodium hypophosphite, 20 g / L sodium citrate, and 10 g / L sodium acetate. The pH of the solution was 5.0, the electroplating temperature was 80℃, and the plating time was 30 min.

[0066] The third step is to prepare the Cu wetting layer. A Cu wetting layer is prepared on the surface of the Ni-P barrier layer using electroplating. This Cu wetting layer improves the thermal conductivity of the metallization transition layer 2 and the wetting and spreading ability of the low-temperature solder. The thickness of the Cu wetting layer is 5 μm. The Cu electroplating solution includes copper sulfate, sulfuric acid, and chloride ions. The concentration of copper sulfate is 150 g / L, the concentration of sulfuric acid is 60 g / L, and the concentration of chloride ions is 60 mg / L. The electroplating temperature is 30℃, the current density is 2 A / dm², and the electroplating time is 15 min.

[0067] The fourth step is the pre-placement of low-temperature solder. A low-temperature solder, Sn-8Zn-3Bi, is pre-placed between the carbon fiber composite material 1 with the Ti / Ni-P / Cu metallization transition layer 2 and the aluminum alloy 3. The solder thickness is 100 μm.

[0068] Step 5: Low-temperature brazing. The assembled carbon fiber composite material 1, low-temperature brazing filler metal, and aluminum alloy 3 were brazed under argon protection at a temperature of 205℃ for 15 minutes, a brazing pressure of 0.4 MPa, and a heating rate of 5℃ / min. After brazing, the material was cooled to below the solidus temperature of the low-temperature brazing filler metal while maintaining pressure, then the pressure was released and the material was cooled to room temperature.

[0069] The technical specifications achieved by the low-temperature brazing connection structure of carbon fiber composite material and aluminum alloy connected according to the above process steps are as follows:

[0070] (1) The lap shear strength of the carbon fiber composite / aluminum alloy connection structure is 29-34 MPa, which is high strength;

[0071] (2) The carbon fiber composite material / aluminum alloy connection structure retains 80%-90% of its strength after 72h salt spray corrosion, and has excellent corrosion resistance.

[0072] Table 1: Structural Performance Indicators of Carbon Fiber Composite Materials / Aluminum Alloys

[0073]

[0074] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A low-temperature brazing method for carbon fiber composite materials and aluminum alloys, characterized in that, Includes the following steps: S1: Preparation of Ti adhesion layer: Select the carbon fiber composite material to be joined, clean, dry and roughen the surface of the carbon fiber composite material to be joined, and deposit a Ti adhesion layer on the pretreated carbon fiber composite material surface to be joined by magnetron sputtering. The thickness of the Ti adhesion layer is 100-300nm. S2: Preparation of Ni-P barrier layer: Ni-P barrier layer is prepared on the surface of Ti adhesion layer by chemical plating. The Ni-P barrier layer is used to prevent carbon fiber from directly contacting aluminum alloy, reduce galvanic corrosion tendency, and serve as a continuous conductive base layer for subsequent electroplated Cu layer. The thickness of the Ni-P barrier layer is 3-10 μm. S3: Preparation of Cu wetting layer: A Cu wetting layer is prepared on the surface of the Ni-P barrier layer by electroplating. The Cu wetting layer is used to improve the thermal conductivity of the metallization transition layer and the low-temperature solder wetting and spreading ability. The thickness of the Cu wetting layer is 3-10μm. S4: Low-temperature solder pre-placement: Low-temperature solder is pre-placed between the carbon fiber composite material with Ti / Ni-P / Cu metallization transition layer and the aluminum alloy, wherein the thickness of the low-temperature solder is 30-150μm; S5: Low-temperature brazing connection: The assembled carbon fiber composite material, low-temperature brazing filler metal and aluminum alloy are brazed at low temperature under argon protection. After brazing, the material is cooled to below the solidus temperature of the low-temperature brazing filler metal while maintaining pressure. Then the pressure is released and the material is cooled to room temperature.

2. The low-temperature brazing method for carbon fiber composite materials and aluminum alloys according to claim 1, characterized in that, In S1, during the magnetron sputtering process, the target material is a pure Ti target with a purity of not less than 99.9%; the sputtering gas is argon; the sputtering power is 100-200W; the working pressure is 0.3-0.8Pa; the substrate temperature is room temperature to 80℃; and the sputtering time is 20-40min.

3. The low-temperature brazing method for carbon fiber composite materials and aluminum alloys according to claim 1, characterized in that, In S2, the concentration of nickel sulfate in the electroless Ni-P plating solution is 20-40 g / L, the concentration of sodium hypophosphite is 15-40 g / L, the concentration of sodium citrate is 5-30 g / L, the concentration of sodium acetate is 5-20 g / L, the pH value of the plating solution is 4.0-6.0, the electroless plating temperature is 70-90℃, and the plating time is 10-60 min.

4. The low-temperature brazing method for carbon fiber composite materials and aluminum alloys according to claim 1, characterized in that, In step S3, the Cu plating solution includes copper sulfate, sulfuric acid, and chloride ions. The concentration of copper sulfate is 100-250 g / L, the concentration of sulfuric acid is 30-100 g / L, the concentration of chloride ions is 20-100 mg / L, the plating temperature is 25-35℃, the current density is 1-3 A / dm², and the plating time is 10-20 min.

5. The low-temperature brazing method for carbon fiber composite materials and aluminum alloys according to claim 1, characterized in that, In S4, the low-temperature solder is one of Sn-Bi, Sn-Bi-Ag, Sn-In, Sn-Zn, Sn-Ag-Cu, or In-Sn solder.

6. The low-temperature brazing method for carbon fiber composite materials and aluminum alloys according to claim 1, characterized in that, In S5, the brazing temperature is 140-220℃, the holding time is 5-30min, the brazing pressure is 0.05-0.8MPa, and the heating rate is 3-10℃ / min.

7. A low-temperature brazing connection structure between carbon fiber composite material and aluminum alloy, manufactured using the low-temperature brazing method for carbon fiber composite material and aluminum alloy as described in any one of claims 1-6, characterized in that, It includes a carbon fiber composite material, a metallized transition layer, and an aluminum alloy, wherein the metallized transition layer is located between the carbon fiber composite material and the aluminum alloy.

8. The low-temperature brazing connection structure of carbon fiber composite material and aluminum alloy according to claim 7, characterized in that, The metallization transition layer consists of, from bottom to top, a low-temperature brazing connection layer, a Cu wetting layer, a Ni-P barrier layer, and a Ti adhesion layer.

9. The low-temperature brazing connection structure of carbon fiber composite material and aluminum alloy according to claim 8, characterized in that, The low-temperature brazing connection layer is a continuous and dense brazing layer.

10. The low-temperature brazing connection structure of carbon fiber composite material and aluminum alloy according to claim 7, characterized in that, The lap shear strength of the low-temperature brazed connection structure between the carbon fiber composite material and the aluminum alloy is not less than 29 MPa, and after a 72-hour salt spray test, the lap shear strength retention rate after corrosion is not less than 80%.

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