Laser joining method of metal and carbon fiber composite materials based on intermediate layer design

Abstract

The present invention discloses a laser connection method for metal and carbon fiber composite materials based on an intermediate layer design, comprising: designing a metal mesh with an intersecting curved structure; removing oil stains or oxide films on the surfaces of the metal plate, carbon fiber composite material, and the metal mesh; placing the metal mesh as an intermediate layer between the metal plate and the carbon fiber composite material and fixing it; and performing a laser connection process while keeping the three tightly connected, completing the laser connection of the three to obtain a reinforced joint. Advantages of this method: By designing a woven structure with intersecting curved surfaces, the surface presents a form of alternating solid-hole contact, so that during the laser welding process, the surface of the carbon fiber composite material changes from continuous heating to alternating heating, thereby reducing the thermal decomposition of the resin and extending the cooling time, achieving a deeper pinning depth, and realizing the in-situ construction of the interface "interlocking + bonding" structure, forming a multi-scale mosaic and multi-chemical bond connection interface to improve the connection strength of the metal-carbon fiber composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber composite material processing, and in particular to a laser connection method of metal and carbon fiber composite material based on an intermediate layer design. Background Art

[0002] Carbon fiber composites, with their excellent mechanical properties, light weight, and high corrosion resistance, are increasingly being used in aircraft, automobiles, rail transit, and sports equipment. Titanium alloys, with their high strength, stiffness-to-weight ratio, good fatigue life, and relatively low price, have been widely used in aerospace, power generation, and other fields. To meet stringent CO2 emission limits and high fuel costs, aircraft often utilize multi-material structures, including carbon fiber composites and titanium alloys. Every kilogram of weight reduction in an aircraft results in nearly 120 liters of fuel spare parts. For example, the A-320 reduced its total weight by 1.1 metric tons by replacing some metal with a multi-material structure made of carbon fiber composites and titanium. Compared to traditional joining methods such as bonding and mechanical fastening, laser welding offers advantages such as short cycle times, high precision, and excellent flexibility, making it increasingly popular for joining carbon fiber composites to metals.

[0003] The interface strength between composite materials and metals determines the fatigue life, safety and reliability of composite structures. The connection between metal and carbon fiber composite materials is limited by the large differences in their thermophysical properties, such as melting point, thermal conductivity and linear expansion coefficient. Achieving high-quality welding between carbon fiber composite materials and metals by laser welding is still a technical bottleneck for the application of this technology in the manufacturing industry. In existing studies to enhance the strength of laser connection joints between carbon fiber composites and metals, most of the methods used are to prepare fine pit structures on the metal surface by laser etching or anodizing to enhance the intercalation with the molten resin on the surface of the carbon fiber composite material and the chemical reaction between the metal surface oxide film and the internal elements of the resin to form chemical bonds, so as to enhance the strength of the connection between carbon fiber composite materials and metals by enhancing mechanical bonding or chemical bonding. However, there are two problems with the above methods: first, the process time for sample surface treatment is long; second, the cost required for processing is high and cannot meet the needs of industrial production. Summary of the Invention

[0004] In view of this, the present invention provides a laser joining method for metal and carbon fiber composite materials based on an intermediate layer design, comprising the following steps:

[0005] S1. Design a metal mesh with an intersecting curved structure;

[0006] S2. Removing oil stains or oxide films on the surfaces of the metal plate, carbon fiber composite material, and the metal mesh;

[0007] S3, placing the metal mesh as an intermediate layer between the metal plate and the carbon fiber composite material and fixing them;

[0008] S4. Perform the laser connection process while keeping the three parts tightly connected, and complete the laser connection of the three parts to obtain a reinforced joint.

[0009] Furthermore, the metal mesh is a grid with a square hole diameter of 0.4 mm obtained by weaving 304 stainless steel wire with a diameter of 0.05 mm.

[0010] Furthermore, the carbon fiber composite material is a composite material with carbon fiber as reinforcement and polyamide resin as matrix.

[0011] Furthermore, the metal plate is TC4 titanium alloy.

[0012] Furthermore, the laser connection process has a laser power of 450W-675W and a laser scanning speed of 800mm / min-1000mm / min.

[0013] The beneficial effects brought about by the technical solution provided by the present invention are:

[0014] The present invention provides a metal-carbon fiber composite laser connection method based on the design of an intermediate layer. The intermediate layer geometry and composition design are used to achieve in-situ construction of an interface "interlocking + bonding" structure, forming a multi-scale interlocking and multi-chemical bond connection interface to improve the connection strength between the metal and carbon fiber composite. The heterogeneous interlayer with an intersecting curve structure converts the continuous heating of the carbon fiber composite surface into alternating heating, resulting in less resin pyrolysis, a deeper pinning depth, extended cooling time, and promoted full resin filling and interfacial chemical reaction. The components of the intermediate layer are chemically active for both metal and carbon fiber composites, generating chemical bonds at high temperatures, thereby improving the bonding strength of the laser connection between the metal plate and the carbon fiber composite plate. Compared with existing metal and carbon fiber composite laser connection processes, the present invention has a shorter time for laser connection pre-processing because only a metal mesh needs to be added between the metal and carbon fiber composite, which is less expensive and the resulting joint has a higher strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the laser connection method of metal and carbon fiber composite material based on the intermediate layer design of the present invention, wherein a and b are schematic diagrams of the morphology and size of the metal mesh in Example 1 of the present invention, and c is a schematic diagram of the laser connection process in Example 1 of the present invention;

[0016] Figure 2 This is a diagram showing the mechanism of formation of the TC4 / CF-PA linker prepared in Example 1 of the present invention;

[0017] Figure 3 Schematic diagram of the dimensions of the TC4 / CF-PA connector prepared in Example 1 of the present invention;

[0018] Figure 4 Schematic diagram of the force applied to the TC4 / CF-PA joint prepared in Example 1 of the present invention in a tensile testing machine;

[0019] Figure 5 This is an ultra-depth-of-field microscope image of the metal surface weld of the TC4 / CF-PA joint prepared in Example 1 of the present invention;

[0020] Figure 6 Ultra-depth-of-field microscopy images of the cross section and cross section of the TC4 / CF-PA joint prepared in Example 1 of the present invention, where a is an ultra-depth-of-field microscopy image of the cross section of the joint, b is an ultra-depth-of-field microscopy image of the cross section of the joint, divided into c: fusion zone (FZ) and d: heat-affected zone (HAZ);

[0021] Figure 7 : This is the SEM element distribution image of the cross section FZ of the TC4 / CF-PA joint prepared in Example 1 of the present invention;

[0022] Figure 8 This is the SEM element distribution image of the HAZ of the TC4 / CF-PA joint cross section prepared in Example 1 of the present invention;

[0023] Figure 9 This is the XRD test curve of the TC4 / CF-PA joint weld prepared in Example 1 of the present invention;

[0024] Figure 10 This is the XPS spectrum fitting curve of the cross section of the TC4 / CF-PA joint prepared in Example 1 of the present invention;

[0025] Figure 11 FIG1 is a COMSOL physical field simulation model diagram of the TC4 / CF-PA joint prepared in Example 1 of the present invention;

[0026] Figure 12 It is the surface temperature cloud map and curve diagram of carbon fiber composite material;

[0027] Figure 13 1 is a graph showing the tensile performance curve of the TC4 / CF-PA joint prepared in Examples 1 and 2 of the present invention;

[0028] Figure 14 3D surface topography of the cross section of the TC4 / CF-PA joint prepared in Example 1 of the present invention, where a and b are the 3D topography of the Ti plate and CFRTP surface, respectively, and c is a surface topography curve diagram;

[0029] Figure 15 This is a 3D morphology image of the cross section of the TC4 / CF-PA joint prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0031] Example 1

[0032] This embodiment provides a laser joining method for metal and carbon fiber composite materials based on an intermediate layer design, and completes the laser joining of TC4 titanium alloy and carbon fiber reinforced polyamide (CF-PA). The method specifically includes the following steps:

[0033] S1. Design a metal mesh with an intersecting curve structure. The metal mesh is a mesh with a square hole diameter of 0.4 mm obtained by weaving 304 stainless steel wire with a diameter of 0.05 mm. The schematic diagram of the specific mesh morphology is as follows Figure 1 As shown in a and b, Figure 1 Schematic diagram of the laser connection method of metal and carbon fiber composite materials based on the intermediate layer design of the present invention, wherein a and b are schematic diagrams of the morphology and size of the metal mesh in Example 1 of the present invention.

[0034] The metal mesh designed in this embodiment is intended to play two roles. On the one hand, by pre-setting an intermediate layer with a cross-curve structure, the connection between the metal and the resin is transformed into an alternating connection of "solid + void", so that the surface of the carbon fiber composite material is changed from continuous heating to alternating heating, thereby improving the maximum heat input tolerance of the carbon fiber composite material and extending the interface cooling time; this helps to form a deeper pinning depth and sufficient filling of the resin. On the other hand, by selecting a heterogeneous intermediate layer that is chemically active to both the carbon fiber composite material and the metal, the interfacial reaction is further enhanced, and the generated chemical bonds can further improve the strength of the joint.

[0035] S2. Remove the oil or oxide film on the surface of the metal plate, carbon fiber composite material and the metal mesh, polish the surface of the TC4 titanium alloy plate to be connected with 400 mesh sandpaper to remove the oxide film on the metal surface, and then place the stainless steel mesh, carbon fiber composite material and TC4 titanium alloy polished with sandpaper into a beaker filled with deionized water and ultrasonically clean them for 5 minutes. After the ultrasonic cleaning, wash them with deionized water and alcohol and dry them.

[0036] S3, placing the metal mesh obtained in S2 as an intermediate layer between the metal plate and the carbon fiber composite material and fixing them according to a certain overlap area;

[0037] S4. After maintaining a tight connection between the three parts under a certain pressure, a continuous laser process is used to connect the two parts, completing the laser connection of the three parts to obtain a reinforced joint. The specific laser connection process is a laser power of 675W and a laser scanning speed of 800mm / min.

[0038] The laser deflection angle was 30°, the side-blowing protective gas was N2, the gas flow rate was 5 L / min, and the sample was taken out of the fixture after being naturally cooled at room temperature for 5 minutes.

[0039] Laser is used to directly heat the TC4 surface, heating from the TC4 surface to the steel mesh and then to the carbon fiber composite surface. After heating, the resin on the carbon fiber composite surface melts and is embedded into the gaps between the stainless steel mesh and the TC4 metal plate surface under pressure. The metal mesh will also react chemically with the resin and TC4 under the action of heat to form bonds. The specific interface formation mechanism is as follows: Figure 2 As shown, Figure 2 The mechanism of the TC4 / CF-PA joint formed in Example 1 of the present invention is as follows: nitrogen is used as the shielding gas on the TC4 surface. After welding, the lap joint is cooled under the fixture for a few minutes to achieve the connection between TC4 and carbon fiber composite material. Figure 3 , Figure 3 Schematic diagram of the dimensions of the TC4 / CF-PA connector prepared in Example 1 of the present invention.

[0040] In this embodiment, the heat source is the heat generated by the continuous laser on the surface of TC4. However, due to the good thermal conductivity of metal, high heat will also be generated at the interface. Controlling the laser power and scanning speed can avoid excessive heating of CF-PA to produce pore defects and cracking, and insufficient heating to cause loose connection.

[0041] The joint obtained in the above steps is placed in a universal tensile testing machine and the shear strength of the joint is tested at a speed of 1 mm / min, as shown in the figure. Figure 4 , Figure 4 Schematic diagram of the force applied to the TC4 / CF-PA joint prepared in Example 1 of the present invention in a tensile testing machine.

[0042] Figure 5 This is an ultra-depth microscope image of the metal surface weld of the TC4 / CF-PA joint prepared in Example 1 of the present invention. Figure 5 It can be seen that after welding, the joint surface is well formed without defects such as ablation and pores.

[0043] Figure 6Ultra-depth microscopy images of a cross section and a cross section of the TC4 / CF-PA joint prepared in Example 1 of the present invention. (a) Ultra-depth microscopy image of the cross section, (b) Ultra-depth microscopy image of the cross section, divided into (c) fusion zone (FZ) and (d) heat-affected zone (HAZ). It is found that CF-PA and TC4 form a deep pinning interlocking effect in the FZ, while the interlocking effect in the HAZ is relatively weak. The interlocking structures of different scales in the two zones significantly enhance the mechanical interlocking effect of the joint interface.

[0044] Figure 7 : This is the SEM element distribution image of the cross section FZ of the TC4 / CF-PA joint prepared in Example 1 of the present invention; Figure 8 This is the SEM element distribution image of the HAZ of the TC4 / CF-PA joint cross section prepared in Example 1 of the present invention; Figure 7 and Figure 8 The SEM element mapping results qualitatively analyzed the distribution of elements among the three layers, which helped to further clarify the geometric characteristics of the interface. Figure 7 The element mapping shown shows that layer II is mainly C and O, and layer III is Ti, Al, and V. From the SEM, the resin is white and rough, so it can be inferred that layer I in the FZ is resin, layer II is carbon fiber, and layer III is titanium alloy. Figure 8 From the element mapping of the HAZ, we can see that the I and III layers are mainly C and O, and the II layer is mainly Fe, Cr, and Ni. Therefore, in the HAZ, the first and third layers are resin, and the second layer is steel mesh. It can be inferred that the steel mesh in the FZ melts and diffuses into the titanium alloy, while the steel mesh in the HAZ does not melt. Figure 6 、 Figure 7 and Figure 8 It can be seen that the gaps caused by the intersecting curved structures between the carbon fiber composite, TC4, and the interlayer are completely filled with resin. This indicates that there is a large amount of molten resin that fills the voids between the steel mesh and TC4 surface before solidification.

[0045] Figure 9 This is the XRD test curve of the TC4 / CF-PA joint weld prepared in Example 1 of the present invention. Figure 10 is the XPS spectrum fitting curve of the cross section of the TC4 / CF-PA joint prepared in Example 1 of the present invention; Figure 7 and Figure 8 Analysis shows that the steel mesh reacts with the carbon fiber composite at the interface between the FZ and HAZ, forming an Fe-O compound. The steel mesh melts in the FZ and diffuses into the titanium alloy, forming an Fe-Ti intermetallic compound. This chemical bond at the joint interface enhances joint strength.

[0046] In order to explore the heating form of the carbon fiber composite surface, the COMSOL multi-physics simulation software was used to simulate the heating of the carbon fiber composite surface. A Gaussian surface heat source was set on the surface of the titanium alloy model to simulate laser heating. The specific situation is as follows: Figure 11 and Figure 12 As shown, Figure 11 FIG1 is a COMSOL physical field simulation model diagram of the TC4 / CF-PA joint prepared in Example 1 of the present invention; Figure 12 The temperature cloud and curve of the carbon fiber composite surface are shown in Figure 2. The heating method of the carbon fiber composite surface is changed from traditional continuous heating to alternating heating.

[0047] Example 2

[0048] This embodiment provides a laser joining method for metal and carbon fiber reinforced thermoplastic composite materials without an intermediate layer, and uses this method to complete the laser joining of TC4 titanium alloy and carbon fiber reinforced polyamide (CF-PA), which specifically includes the following steps:

[0049] S1. Remove oil stains or oxide films from the surfaces of metal plates and carbon fiber composite materials. Polish the surface of the TC4 titanium alloy plates to be connected with 400-grit sandpaper to remove the oxide film on the metal surface. Then, place the carbon fiber composite material and the sanded TC4 titanium alloy in a beaker filled with deionized water and ultrasonically clean them for 5 minutes. After the ultrasonic cleaning, rinse them with deionized water and alcohol and dry them.

[0050] S2. Fixing the metal plate and the carbon fiber composite material obtained in S1 according to a certain overlap area.

[0051] S3. After maintaining a tight connection between the two under a certain pressure, a continuous laser process is used to connect the two, completing the laser connection and obtaining a reinforced joint. The laser connection process specifically includes a laser power of 675W, a laser scanning speed of 800mm / min, a laser deflection angle of 30°, and a side-blowing shielding gas of nitrogen at a gas flow rate of 5L / min. The parts are then naturally cooled at room temperature for 5 minutes before being removed from the fixture.

[0052] Comparing the two embodiments, the joint strength of TC4 titanium alloy / CF-PA with a metal mesh added in the middle layer is greater than the strength of the joint without the middle layer, nearly twice as strong.

[0053] refer to Figure 13 、 Figure 14 and Figure 15 , Figure 13 1 is a graph showing the tensile performance curve of the TC4 / CF-PA joint prepared in Examples 1 and 2 of the present invention; Figure 143D surface topography of the cross section of the TC4 / CF-PA joint prepared in Example 1 of the present invention, where a and b are the 3D topography of the Ti plate and CFRTP surface, respectively, and c is a surface topography curve diagram; Figure 15 This is a 3D morphology image of the cross section of the TC4 / CF-PA joint prepared in Example 2 of the present invention.

[0054] Compared with the joint without an intermediate layer that fractures at the interface (fracture between resin and metal), in the case of an intermediate layer, the fracture interface shows a gradient fixing effect including deep and shallow pinning, and the cross-section is complete without defects such as pores. In addition, there are a large number of carbon fibers in the HZ area of ​​the TC4 surface and resin in the HAZ area, which further illustrates that the degree of interlocking in the HZ area is deep and the fracture occurs in the carbon fiber layer inside the CFRTP.

[0055] By designing a woven structure with intersecting curved surfaces, the surface presents an alternating contact between solid and hole. During the laser welding process, the surface of the carbon fiber composite material changes from continuous heating to alternating heating, thereby reducing the thermal decomposition of the resin and extending the cooling time, achieving a deeper pinning depth, and realizing the in-situ construction of the interface "interlocking + bonding" structure, forming a multi-scale mosaic and multi-chemical bond connection interface to improve the connection strength of the metal-carbon fiber composite material.

[0056] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A laser joining method of metal and carbon fiber composite materials based on an intermediate layer design, characterized in that: The following steps are involved: S1. Designing a metal mesh having an intersecting curved structure, wherein the metal mesh is chemically active towards both carbon fiber composite materials and metals; S2. Removing oil stains or oxide films on the surfaces of the metal plate, carbon fiber composite material, and the metal mesh; S3, placing the metal mesh as an intermediate layer between the metal plate and the carbon fiber composite material and fixing them; S4. Perform the laser connection process while keeping the three parts tightly connected, and complete the laser connection of the three parts to obtain a reinforced joint.

2. The laser joining method of metal and carbon fiber composite materials based on intermediate layer design according to claim 1 is characterized in that: The metal mesh is a grid with a square hole diameter of 0.4 mm obtained by weaving 304 stainless steel wire with a diameter of 0.05 mm.

3. The laser joining method of metal and carbon fiber composite materials based on intermediate layer design according to claim 1 is characterized in that: The carbon fiber composite material is a composite material with carbon fiber as reinforcement and polyamide resin as matrix.

4. The laser joining method of metal and carbon fiber composite materials based on intermediate layer design according to claim 1 is characterized in that: The metal plate is made of TC4 titanium alloy.

5. The laser joining method of metal and carbon fiber composite materials based on intermediate layer design according to claim 1 is characterized in that: The laser connection process has a laser power of 450W-675W and a laser scanning speed of 800mm / min-1000mm / min.

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