A surface modification method for improving bonding strength based on the surface structure of gecko feet

Abstract

The present invention discloses a surface modification bonding strength enhancement method based on a gecko-foot-like surface structure, comprising the following steps: first, performing a first impurity removal pretreatment on a CFRP sheet and an aluminum alloy sheet; second, performing laser engraving on the bonding surfaces of the cleaned CFRP sheet and the aluminum alloy sheet using a laser engraving machine to obtain a CFRP sheet and an aluminum alloy sheet having a bonding surface morphology of a gecko-foot-like surface structure; and performing a second impurity removal treatment; third, performing a second impurity removal treatment on the obtained sheet, and evenly distributing a plurality of glass beads on the treated bonding surface; and fourth, evenly applying an adhesive on the bonding surface with the glass beads, laminating the two bonding surfaces, positioning and pressurizing the bonding sheets using a fixture after lamination, and placing the fixture and the sheet into a drying oven for curing. After curing, the fixture and the sheet are cooled to room temperature to obtain a lap joint with stable mechanical properties. By performing laser processing, the bonding strength of the lap joint is improved.

Description

Technical Field

[0001] The invention relates to a surface modification bonding strength improvement method based on a gecko foot-imitation surface structure, and belongs to the technical field of lap joint bonding processes. Background Art

[0002] Carbon fiber reinforced plastics (CFRP) and aluminum alloys have been widely used in aerospace, automotive, and other fields due to their excellent lightweight and high-strength properties. However, due to significant differences in the surface chemistry and microstructure of the two materials, lap-bonded joints are often prone to interfacial failure during tensile fracture, resulting in low bond strength and limiting their further application in high-reliability scenarios.

[0003] By precisely controlling laser parameters (such as power, line spacing, and scanning speed), the gecko-foot-like surface structure generates an interface topography with micro-nanoscale roughness. This rough structure effectively improves the wettability of the bonding surface, allowing the liquid adhesive to spread fully across the surface and penetrate into microscopic depressions, thereby increasing the contact area and significantly enhancing the mechanical locking effect and interfacial bonding strength of the bond. This simple and efficient method provides excellent interface conditions for subsequent bonding processes.

[0004] Furthermore, the gecko-foot-like structure creates a superhydrophobic property on the interface surface, thereby enhancing the bond's resistance to environmental factors such as moisture and contaminants. This superhydrophobicity effectively slows moisture intrusion and corrosion by reducing the surface area where liquids remain, providing additional protection for the bonded interface. In practical applications, this property helps extend the service life of bonded joints and further enhances their environmental adaptability. Summary of the Invention

[0005] The present invention designs and develops a surface modification bonding strength improvement method based on the surface structure imitating the gecko foot. The surface to be bonded is processed by laser technology, which can improve the bonding strength of the lap joint.

[0006] Another object of the present invention is to control the engraving parameters during the laser engraving process so that the adhesive is fully infiltrated into the bonding surface, thereby increasing the contact area to form mechanical interlocking and improve the bonding strength.

[0007] The technical solution provided by the present invention is:

[0008] A method for improving bonding strength by surface modification based on a gecko-foot-like surface structure, comprising:

[0009] Step 1: Perform the first impurity removal pretreatment on the CFRP plate and the aluminum alloy plate;

[0010] Step 2: Laser engraving the bonding surfaces of the CFRP sheet and the aluminum alloy sheet after impurity removal using a laser engraving machine to obtain CFRP sheets and aluminum alloy sheets with gecko-foot-like bonding surface morphology; and performing a second impurity removal treatment;

[0011] During laser engraving, the power of the laser engraving machine is 2.5W to 27W, the speed is 100mm / s to 1000mm / s, and the laser line spacing is 50μm to 150μm. The ablation area on the CFRP plate is a plurality of arc-shaped parallel curves, the radius of the arc is 85μm, and the spacing between each two adjacent arcs is 20μm. The ablation area on the aluminum alloy plate is a plurality of arc-shaped parallel curves, the radius of the arc is 85μm, and the spacing between each two adjacent arcs is 20μm.

[0012] Step 3: Perform a secondary impurity removal treatment on the obtained plate, and evenly distribute multiple glass beads on the treated bonding surface. During the distribution of the glass beads, preliminary fixation is required to fix the glass beads to the bonding surface;

[0013] Step 4: Apply the adhesive evenly on the bonding surface with glass beads and align the two bonding surfaces. After aligning, use a clamp to position and press the bonding plates, wipe off the excess adhesive, and place the clamp and plates in a drying oven for curing. After curing, cool to room temperature to obtain a finished lap joint.

[0014] Preferably, the first impurity removal pretreatment and the second impurity removal pretreatment have the same process, both comprising:

[0015] After wiping the CFRP plates and aluminum alloy plates clean with acetone solution, place them in an ultrasonic cleaner and use deionized water to clean them at a constant temperature of 25°C for 10 to 15 minutes. Then place them in a drying oven and dry them at 80°C for 30 to 60 minutes until the water is completely evaporated. After drying, let the plates cool naturally to room temperature.

[0016] Preferably, the CFRP plate has a sixteen-layer stacked structure, comprising:

[0017] Two layers of 3k twill carbon fiber and fourteen layers of unidirectional carbon fiber;

[0018] Wherein, in the unidirectional carbon fiber layer, the carbon fiber is T300 grade;

[0019] 3k twill carbon fiber is a FAW200 epoxy resin matrix with a matrix volume fraction of 40% and a carbon fiber volume fraction of 60%;

[0020] The unidirectional carbon fiber is a FAW150 epoxy resin matrix with a matrix volume fraction of 37% and a carbon fiber volume fraction of 63%.

[0021] Preferably, the CFRP plate is prepared by a hot pressing process, comprising:

[0022] Two layers of 3k twill carbon fiber and fourteen layers of unidirectional carbon fiber were autoclaved at a temperature of 160°C and a pressure of 20 kg / cm 2 Press for 30 min under the conditions of

[0023] The aluminum alloy plate is made by anodizing A6061-T6 aluminum alloy in a 10% H2SO4 solution at a voltage of 12V for 30 minutes.

[0024] Preferably, the diameter of the glass beads is the same as the thickness of the required adhesive layer, and the error cannot exceed ±0.2mm;

[0025] The total volume of all the glass beads cannot exceed 4% of the total volume of the glue layer.

[0026] Preferably, the adhesive in step 4 is a two-component epoxy adhesive, including a matrix resin and a curing agent, which are mixed in a mass ratio of 100:40.

[0027] Preferably, the preliminary fixing method in step three includes: preliminarily fixing the glass beads to the bonding surface by electrostatic adsorption or a light adhesive.

[0028] The beneficial effects of the present invention include: The surface modification method for improving bonding strength based on a gecko-foot-like surface structure provides a simple and precise laser process for surface treatment of the CFRP and aluminum alloy bonding surfaces. By controlling laser power, line spacing, and laser speed, a bonding morphology with a gecko-foot-like surface structure is produced. This morphology not only exhibits high surface roughness but also exhibits high wettability, allowing the adhesive to fully penetrate the bonding surface, increasing the contact area and forming a mechanical interlock, thereby improving bonding strength.

[0029] The method has a simple processing process, can improve the bonding strength and resistance to environmental moisture and heat erosion of the lap joint, and has high practical value in the direction of material bonding. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a gecko-foot-like surface structure morphology diagram of the bonding surface described in the present invention.

[0031] Figure 2 The present invention is a flow chart of the method for improving the bonding strength by surface modification based on the surface structure imitating the gecko's foot.

[0032] Figure 3 This is a schematic diagram of the dimensions of the single lap joint described in the present invention.

[0033] Figure 4This is a SEM image of the CFRP bonding surface after laser scanning according to the present invention.

[0034] Figure 5 This is a SEM image of the aluminum alloy bonding surface after laser scanning according to the present invention.

[0035] Figure 6 This is a schematic diagram comparing the moisture and heat resistance of the material before and after laser treatment according to the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0037] like Figure 1-6 As shown, the present invention provides a surface modification bonding strength improvement method based on the surface structure of a gecko's foot, which can improve the bonding strength of the lap joint by laser processing the surface to be bonded through a laser process, including:

[0038] Step 1: Perform the first impurity removal pretreatment on the CFRP plate and the aluminum alloy plate;

[0039] Among them, the CFRP plate is a sixteen-layer stacked structure, including:

[0040] Two layers of 3k twill carbon fiber and fourteen layers of unidirectional carbon fiber;

[0041] In the unidirectional carbon fiber layer, the carbon fiber is T300 grade;

[0042] CFRP sheets are produced through a hot pressing process, which includes:

[0043] Two layers of 3k twill carbon fiber and fourteen layers of unidirectional carbon fiber were autoclaved at a temperature of 160°C and a pressure of 20 kg / cm 2 Press for 30 min under the conditions of

[0044] The aluminum alloy plate was made by anodizing A6061-T6 aluminum alloy in a 10% mass concentration H2SO4 solution at a voltage of 12 V for 30 min.

[0045] 3k twill carbon fiber is a FAW200 epoxy resin matrix with a matrix volume fraction of 40% and the remaining 60% being carbon fiber volume fraction;

[0046] The unidirectional carbon fiber is a FAW150 epoxy resin matrix with a matrix volume fraction of 37% and the remaining 63% being carbon fiber volume fraction.

[0047] Step 2: Laser engraving the bonding surfaces of the CFRP sheet and the aluminum alloy sheet after impurity removal using a laser engraving machine to obtain CFRP sheets and aluminum alloy sheets with gecko-foot-like bonding surface morphology; and performing a second impurity removal treatment;

[0048] During laser engraving, the power of the laser engraving machine is 2.5W to 27W, the speed is 100mm / s to 1000mm / s, and the laser line spacing is 50μm to 150μm. The ablation area on the CFRP plate is a plurality of arc-shaped parallel curves, the radius of the arc is 85μm, and the spacing between each two adjacent arcs is 20μm. The ablation area on the aluminum alloy plate is a plurality of arc-shaped parallel curves, the radius of the arc is 85μm, and the spacing between each two adjacent arcs is 20μm.

[0049] Step 3: Perform a secondary impurity removal treatment on the obtained plate, and evenly distribute multiple glass beads on the treated bonding surface. During the distribution of the glass beads, it is necessary to initially fix the glass beads to the bonding surface by electrostatic adsorption or light adhesive;

[0050] In the present invention, as a preferred embodiment, 3M TM Super 77 TM Multipurpose spray adhesive provides initial fixation of the glass beads to the bonding surface.

[0051] The first impurity removal pretreatment process is the same as the second impurity removal pretreatment process, and both include:

[0052] After wiping the CFRP plates and aluminum alloy plates clean with acetone solution, place them in an ultrasonic cleaner and use deionized water to clean them at a constant temperature of 25°C for 10 to 15 minutes. Then place them in a drying oven and dry them at 80°C for 30 to 60 minutes until the water is completely evaporated. After drying, let the plates cool naturally to room temperature.

[0053] The diameter of the glass beads should be the same as the thickness of the required adhesive layer, and the error should not exceed ±0.2mm;

[0054] And the sum of the volumes of all the glass beads cannot exceed 4% of the total volume of the glue layer.

[0055] Step 4: Apply the adhesive evenly on the bonding surface with glass beads and align the two bonding surfaces. After aligning, use a clamp to position and press the bonding plates, wipe off the excess adhesive, and place the clamp and plates in a drying oven for curing. After curing, cool to room temperature to obtain a lap joint with stable mechanical properties.

[0056] In the present invention, the adhesive is preferably a two-component epoxy adhesive, Araldite 2015, comprising a matrix resin and a curing agent, mixed in a mass ratio of 100:40. The adhesive must be thoroughly stirred before application to ensure uniformity of the components, and the faying surfaces must be kept dry and clean before bonding to ensure a high-quality bond.

[0057] Example

[0058] Taking T300 grade 3k twill carbon fiber and A6061-T6 aluminum alloy as an example, the bonding surface is processed into a gecko foot-like surface structure through laser technology and applied in practice. The specific implementation steps are as follows:

[0059] The first step is to prepare T300 grade 3k twill carbon fiber 1 and A6061-T6 aluminum alloy 2.

[0060] The CFRP matrix is ​​composed of 3k twill (2 layers) and unidirectional (14 layers) carbon fibers (T300 grade). The 3k twill carbon fibers and unidirectional carbon fibers are based on FAW200 and FAW150 epoxy resin matrices, with the matrix volume fractions being approximately 40% and 37%, respectively. The CFRP is made up of 16 layers stacked together and is produced through a hot press molding process at 160°C and 20kg / cm 2 Press under pressure for 30 minutes.

[0061] A6061-T6 aluminum alloy was anodized in a 10% mass concentration H2SO4 solution at a voltage of 12 V for 30 min.

[0062] In the second step, the CFRP and aluminum alloy were cleaned with acetone solution, placed in an ultrasonic cleaner and cleaned with deionized water at a constant temperature of 25°C for 15 minutes, and then immediately placed in a drying oven at 80°C for 60 minutes and cooled to room temperature; the laser engraving machine was used to set the parameters of laser power (P), laser line spacing (H D ) and laser speed (V) as shown in Table 1; the arc radius was selected as 85 μm for each bonding surface, resulting in a CFRP and aluminum alloy bonding surface morphology mimicking a gecko's foot. The surfaces were then cleaned again with acetone solution, placed in an ultrasonic cleaner, and cleaned in deionized water at 25°C for 10-15 minutes. The surfaces were then immediately dried in a drying oven at 80°C for 60 minutes before cooling to room temperature.

[0063] In the third step, a confocal laser microscope (CLM, VK-X3000, KEYENCE) and a contact angle meter (CAME, 100SB, Sindatek) were used to measure the surface roughness and surface wettability of the CFRP and aluminum alloy bonding surfaces under different laser parameters. The optimal parameter group with the maximum surface roughness (Ra) and the minimum surface water contact angle (WCA) was selected. The experiments showed that the optimal parameters were 27W, 50μm, and 100mm / s for CFRP and 27W, 100μm, and 100mm / s for aluminum alloy.

[0064] Step 4: Prepare adhesive 3.

[0065] The adhesive used is Araldite 2015, a two-component epoxy adhesive. Component A is the matrix resin, and component B is the curing agent. They are mixed evenly at a mass ratio of 100:40 before use. The adhesive must be thoroughly stirred before application to ensure uniformity. To ensure a quality bond, the faying surfaces must be kept dry and clean before bonding.

[0066] In the fifth step, an appropriate amount of adhesive is applied to the bonding surfaces of the CFRP and aluminum alloy substrates (optimal parameter set) and aligned in the predetermined position to ensure complete contact. A dedicated fixture is used for the bonding process. The adhesive thickness is adjusted to approximately 0.2 mm by tightening the screw push rod. The adhesive is then pressed and cured at room temperature for 24 hours to ensure there are no bubbles or gaps between the bonding surfaces. The bonded assembly is then placed in a drying oven and cured at 80°C for 60 minutes to ensure complete curing of the adhesive. After curing, the joint is allowed to cool naturally to room temperature, resulting in a mechanically stable lap joint.

[0067] A comparative example was prepared. The bonding surface of the comparative example was not laser treated, and other treatments and bonding methods were consistent with those of the embodiment.

[0068] The optimal parameter embodiment and the comparative example were placed in a damp heat aging environment box for damp heat aging test, and the aging process was as follows: (1) the temperature was raised to 70±2°C within 30 minutes (this step is required only in the first cycle); (2) the temperature was maintained at 70±2°C within 5 hours±20 minutes, while the relative humidity was maintained above 90%; (3) the temperature was lowered to -40±3°C within 60±20 minutes; (4) the temperature was maintained at -40±3°C within 5 hours±20 minutes; (5) the temperature was raised to 70±2°C within 60±20 minutes; (6) steps (2) to (5) were repeated.

[0069] The aging time of the test samples was 1 to 8 weeks, and then the tensile failure test was carried out using an electronic universal testing machine to obtain the joint failure load data. The results are as follows: Figure 6 shown.

[0070] The joint of CFRP sheet and aluminum alloy sheet without gecko foot treatment was used as a comparison example.

[0071] The bond strength between the CFRP sheet and the aluminum alloy sheet treated with the lizard-like surface structure was significantly improved, with the joint strength after the lizard-like surface treatment increasing by 13.17% (10.4±0.32MPa) compared to the untreated joint strength (9.19±0.16MPa). After eight weeks of aging, the lap shear strength of the untreated CFRP / aluminum alloy specimens and those with the lizard-like surface structure decreased to 2.22±0.82MPa and 9.26±0.29MPa, respectively. Compared to the unaged specimens, the lap shear strength of the untreated specimen decreased by 75.84%, while the lap shear strength of the lizard-like surface structure decreased by 10.96%, significantly extending the service life of the joint.

[0072] Table 1

[0073]

[0074] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for improving the bonding strength of a surface modified by imitating the surface structure of a gecko's foot, characterized in that: include: Step 1: Perform the first impurity removal pretreatment on the CFRP plate and the aluminum alloy plate; Step 2: Laser engraving the bonding surfaces of the CFRP sheet and the aluminum alloy sheet after impurity removal using a laser engraving machine to obtain CFRP sheets and aluminum alloy sheets with gecko-foot-like bonding surface morphology; and performing a second impurity removal treatment; During laser engraving, the power of the laser engraving machine is 2.5W to 27W, the speed is 100mm / s to 1000mm / s, and the laser line spacing is 50μm to 150μm. The ablation area on the CFRP plate is a plurality of arc-shaped parallel curves, the radius of the arc is 85μm, and the spacing between each two adjacent arcs is 20μm. The ablation area on the aluminum alloy plate is a plurality of arc-shaped parallel curves, the radius of the arc is 85μm, and the spacing between each two adjacent arcs is 20μm. Step 3: Perform a secondary impurity removal treatment on the obtained plate, and evenly distribute multiple glass beads on the treated bonding surface. During the distribution of the glass beads, preliminary fixation is required to fix the glass beads to the bonding surface; Step 4: Apply the adhesive evenly on the bonding surface with glass beads and align the two bonding surfaces. After aligning, use a clamp to position and press the bonding plates, wipe off the excess adhesive, and place the clamp and plates in a drying oven for curing. After curing, cool to room temperature to obtain a finished lap joint.

2. The surface modification bonding strength improving method based on the gecko foot imitation surface structure according to claim 1, characterized in that: The first impurity removal pretreatment and the second impurity removal pretreatment processes are the same, both comprising: After wiping the CFRP plates and aluminum alloy plates clean with acetone solution, place them in an ultrasonic cleaner and use deionized water to clean them at a constant temperature of 25°C for 10 to 15 minutes. Then place them in a drying oven and dry them at 80°C for 30 to 60 minutes until the water is completely evaporated. After drying, let the plates cool naturally to room temperature.

3. The surface modification bonding strength improving method based on the gecko foot imitation surface structure according to claim 2, characterized in that: The CFRP plate has a sixteen-layer stacked structure, including: Two layers of 3k twill carbon fiber and fourteen layers of unidirectional carbon fiber; Wherein, in the unidirectional carbon fiber layer, the carbon fiber is T300 grade; 3k twill carbon fiber is a FAW200 epoxy resin matrix with a matrix volume fraction of 40% and a carbon fiber volume fraction of 60%; The unidirectional carbon fiber is a FAW150 epoxy resin matrix with a matrix volume fraction of 37% and a carbon fiber volume fraction of 63%.

4. The method for improving the bonding strength of a surface modified by imitating the gecko foot surface structure according to claim 2, wherein: The CFRP plate is prepared by a hot pressing process, including: Two layers of 3k twill carbon fiber and fourteen layers of unidirectional carbon fiber were autoclaved at a temperature of 160°C and a pressure of 20 kg / cm 2 Press for 30 min under the conditions of The aluminum alloy plate is made by anodizing A6061-T6 aluminum alloy in a 10% H2SO4 solution at a voltage of 12V for 30 minutes.

5. The method for improving the bonding strength of a surface modified by imitating the gecko foot surface structure according to claim 4, characterized in that: The diameter of the glass beads should be the same as the thickness of the required adhesive layer, and the error should not exceed ±0.2mm; The total volume of all the glass beads cannot exceed 4% of the total volume of the glue layer.

6. The method for improving the bonding strength of a surface modified by imitating the gecko foot surface structure according to claim 5, characterized in that: The adhesive in step 4 is a two-component epoxy adhesive, including a matrix resin and a curing agent, which are mixed in a mass ratio of 100:

40.

7. The method for improving the bonding strength of a surface modified by imitating the gecko foot surface structure according to claim 6, characterized in that: The preliminary fixing method in step three includes: preliminarily fixing the glass beads to the bonding surface by electrostatic adsorption or light adhesive.

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