Method for joining metals to cfrp based on interfacial chemical strengthening layer

Abstract

The application provides a connecting method for connecting metal and CFRP based on an interface chemical strengthening layer, and steps include: preparing a reaction solution of the chemical strengthening layer, selecting or configuring a silane coupling treatment solution, performing surface treatment on a metal plate, then spraying the silane coupling treatment solution to the surface of the metal plate until the silane treatment solution is solidified on the surface of the metal plate, uniformly spraying the reaction solution of the chemical strengthening layer to the surface of a CFRP plate to form a chemical strengthening layer, clamping the metal plate and the CFRP plate, starting a welding device to weld and connect the metal plate and the CFRP plate together, and cooling and solidifying at room temperature. The original interface temperature range is greatly widened by the scheme of the application, the implementation difficulty is significantly reduced, and the industrial application is more beneficial.

Description

Technical Field

[0001] This invention belongs to the field of joining technology of dissimilar materials, specifically relating to a welding joining method for joining metal and CFRP (resin) based on an interface chemical reinforcement layer. Background Technology

[0002] For joining dissimilar materials like metal and CFRP, existing literature CN2016108089101 discloses a method for joining metal materials and resin-based composite materials using friction stir welding (FSW). This method employs an integrated shoulder / stirring pin FSW welding fixture, with the metal plate on top and the resin-based composite material below. The stirring pin penetrates the metal plate without entering the FRP material, thus initially achieving a connection between the metal and FRP. However, the resin material is still squeezed out at the interface due to heat and pressure, resulting in limited connection strength. Existing literature CN2019102250377 discloses a method suitable for joining metal and polymers, which uses a static shoulder and an auxiliary heat source to improve the joint quality of FSLW, offering some reference value. However, this method is only applicable to clamping configurations with the FRP plate on top and the metal material below, and requires an external auxiliary heat source, making real-time, quantitative control via a welding machine difficult.

[0003] To achieve high-strength bonding at the interface of metal / CFRP composite structures, the previously developed friction stir welding method for bonding metal and resin materials (reference CN117139817A) involves coating the surface of the metal sheet to be welded in the central bonding zone with a chemical film layer (such as a silane coupling agent) that can chemically bond the metal and resin, and creating a surface microtexture on the surface of the metal sheet in the outer bonding zone, before finally forming a weld joint. However, this approach requires a relatively high interface temperature range (240-280℃) to achieve effective bonding between the metal and CFRP, which is not conducive to industrial application. Therefore, it is necessary to develop a method that can achieve effective bonding between metal and CFRP in a lower interface temperature range. Summary of the Invention

[0004] This invention provides a method for connecting metal and CFRP (resin) based on an interface chemical reinforcement layer, which can at least broaden the interface temperature range for effective connection between metal materials and CFRP.

[0005] The present invention adopts the following technical solution.

[0006] The method for joining metals and CFRP based on an interface chemical reinforcement layer includes the following steps:

[0007] Step 1: Preparation of the reaction solution for the chemically reinforced layer. Vinylpyrrolidone monomer, acrylic acid monomer and deionized water are mixed as raw materials, and ammonium persulfate is added as an initiator. After the reaction is completed, the reaction solution is collected and cooled to room temperature for later use.

[0008] Step 2: Select or prepare a silane coupling treatment solution;

[0009] Step 3: Perform surface treatment on the metal sheet, and then spray the silane coupling treatment liquid onto the surface of the metal sheet until the silane treatment liquid is cured on the surface of the metal sheet.

[0010] Step 4: Spray the reaction liquid of the chemically reinforced layer obtained in Step 1 evenly onto the surface of the CFRP board, and then dry it to solidify the reaction liquid on the surface of the CFRP board to form a chemically reinforced layer.

[0011] Step 5: Place the metal sheet on the CFRP sheet, with the surface of the metal sheet containing the silane coupling treatment solution facing the chemical strengthening layer, and then clamp the metal sheet and the CFRP sheet together.

[0012] Step 6: Turn on the welding equipment, set the process parameters, and weld the metal sheet and CFRP sheet together.

[0013] Step 7: After welding, place the workpiece at room temperature to cool and solidify, forming a joint based on the interface chemical reinforcement layer.

[0014] As a preferred option, in step 1, the reaction temperature is controlled at 60-90℃ and the reaction time is controlled at 4-10 hours.

[0015] As a more preferred embodiment, in step 1, the proportions of vinylpyrrolidone monomer (2-15 parts), acrylic acid monomer (2-15 parts), deionized water (70-95 parts), and ammonium persulfate (1-5 parts) are determined by mass ratio.

[0016] Further, the surface treatment steps for the metal sheet are as follows: The surface of the metal sheet is sequentially polished with 800#, 1500#, and 3000# sandpaper to remove the oxide film. Then, the metal sheet is ultrasonically cleaned in an acetone solution to remove surface oil. Next, the surface of the metal sheet is polished with diamond polishing compound, followed by surface hydroxylation treatment. For materials such as titanium alloys and stainless steel, they can be immersed in a carboxylic acid solution for 3-5 seconds; for aluminum alloy sheets, they can be immersed in a 5%-150% sodium hydroxide solution to hydroxylate the surface.

[0017] As a preferred option, the drying temperature in step 4 is 60-160℃, and the drying time is 4-8 hours.

[0018] As a preferred option, friction stir welding is preferably used for welding in step 6. The process parameters for friction stir welding are: tool head rotation speed of 500 rpm to 2000 rpm, tool head feed speed of 500 mm / min to 4000 mm / min, and tool head shoulder deflection of 0.2 mm to 0.5 mm. Alternatively, thermocompression welding, resistance welding, laser welding, ultrasonic welding, or induction welding can also be used for welding in step 6.

[0019] As a preferred option, when using a tool head with a stirring pin, the lower end of the stirring pin is always located inside the metal plate and above the position of the silane coupling layer; when using a tool head without a stirring pin, the action is directly applied to the upper surface of the metal plate through the shoulder of the tool head.

[0020] As a preferred option, the metal sheet may be made of aluminum alloy, magnesium alloy or titanium alloy.

[0021] Beneficial effects: The solution of this invention can achieve effective connection between metal materials and CFRP in the interface temperature range of 110-280℃, significantly expanding the original interface temperature range (240-280℃) to 110-280℃, significantly reducing the implementation difficulty and making it more conducive to industrial application; This invention uses an amphiphilic polymer as an intermediate layer (chemical reinforcement layer), which significantly improves the connection strength and stability between metal materials and CFRP materials (compared to conventional connection of dissimilar materials between metal and CFRP); During implementation, the chemical reinforcement layer can be formed and cured on the surface of the CFRP board by solution spraying and drying, which is convenient, fast, efficient, and environmentally friendly. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the friction stir welding state of metal and CFRP in the embodiment. In the figure: 1—aluminum alloy plate, 2—silane coupling layer, 3—chemical strengthening layer, 4—CFRP plate, 5—tool head of friction stir welding equipment. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] Combination Figure 1As shown, this embodiment provides a friction stir welding method for connecting a metal (3mm thick aluminum alloy plate 1) and a CFRP plate 4 (3mm thick 30% carbon fiber reinforced PA66 plate (CF-PA66)) based on an interface chemical strengthening layer. The steps include:

[0026] Step 1: Preparation of the reaction solution for chemically reinforced layer 3. 5g vinylpyrrolidone monomer, 5g acrylic acid monomer and 90g deionized water are used as raw materials. The mixture is stirred thoroughly at 70℃ for 20 minutes to ensure uniform mixing. Then, 1g ammonium persulfate is added as an initiator and the reaction continues at 70℃ for 6 hours. After the reaction is completed, the reaction solution is collected and cooled to room temperature for later use.

[0027] Step 2: Prepare the silane coupling treatment solution. Mix 90g ethanol, 6g KH550 and 4g deionized water thoroughly at room temperature. Adjust the pH of the silane treatment solution to acidic using acetic acid solution. Stir at room temperature for 5 minutes to activate the treatment solution and obtain the silane coupling treatment solution.

[0028] Step 3, surface treatment of the metal sheet: Use 800#, 1500#, and 3000# sandpaper sequentially to polish the surface of the metal sheet to remove the oxide film. Then, place the metal sheet in an acetone solution for ultrasonic cleaning for 120 seconds to remove surface oil. Next, polish the surface of the metal sheet with diamond polishing paste. Finally, immerse the polished metal sheet in a 10% sodium hydroxide solution (immersion time 20 seconds) to hydroxylate the surface of the metal sheet.

[0029] Then, the silane coupling treatment solution was sprayed onto the surface of the metal plate and then placed in a 120°C oven until the silane treatment solution cured on the surface of the metal plate to form silane coupling layer 2.

[0030] Step 4: The reaction liquid of the chemically reinforced layer 3 obtained in step 3 is evenly sprayed onto the surface of the CFRP board 4, and then placed in a constant temperature environment of 70℃ to dry so that the reaction liquid is cured on the surface of the CFRP board 4 to form the chemically reinforced layer 3.

[0031] Step 5: Place the metal sheet on the CFRP sheet 4, with the surface of the metal sheet containing the silane coupling treatment solution facing / attaching to the chemical strengthening layer 3. Then clamp the metal sheet and the CFRP sheet 4 (use a clamp to fix the CF-PA66 sheet 4 and the aluminum alloy sheet 1 on the welding worktable).

[0032] Step 6: Turn on the friction stir welding equipment and set the welding process parameters (tool head 5 rotation speed 600 rpm, tool head 5 travel speed 3000 mm / min, tool head 5 shoulder downward pressure 0.4 mm). Weld the metal sheet and CFRP sheet 4 together. In this embodiment, a tool head 5 without stirring pins is used, and welding is performed directly on the upper surface of the metal sheet through the shoulder of the tool head 5. During the friction stir welding process, the interface temperature between the aluminum alloy and the CFRP sheet located directly below the tool head 5 was monitored to be 130℃.

[0033] Step 7: After welding, place the workpiece at room temperature to cool and solidify, forming a joint based on the interface chemical reinforcement layer 3.

[0034] Example 2

[0035] A friction stir welding method based on an interface chemically reinforced layer to connect a metal (3mm thick aluminum alloy sheet) and a CFRP (3mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) is disclosed. The steps are the same as in Example 1, but the main difference between the two methods is that the welding process parameters are as follows: the rotation speed of the tool head 5 is 1300 rpm, the travel speed of the tool head 5 is 2500 mm / min, and the shoulder depressor of the tool head 5 is 0.3 mm. During the friction stir welding process, the interface temperature between the aluminum alloy and the CFRP was monitored to be 220℃.

[0036] Example 3

[0037] This embodiment provides a friction stir welding method for connecting a metal (3mm thick aluminum alloy sheet) and a CFRP (3mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) based on an interface chemical reinforcement layer. The steps include:

[0038] Step 1: Preparation of the reaction solution for the chemically reinforced layer. 5g of vinylpyrrolidone monomer, 5g of acrylic acid monomer and 90g of deionized water are used as raw materials. The mixture is stirred thoroughly at 70℃ for 20 minutes to ensure uniform mixing. Then, 1g of ammonium persulfate is added as an initiator and the reaction is continued at 70℃ for 6 hours. After the reaction is completed, the reaction solution is collected and cooled to room temperature for later use.

[0039] Step 2: Prepare the silane coupling treatment solution. Mix 90g ethanol, 6g KH550 and 4g deionized water thoroughly at room temperature. Adjust the pH of the silane treatment solution to acidic using acetic acid solution. Stir at room temperature for 8 minutes to activate the treatment solution and obtain the silane coupling treatment solution.

[0040] Step 3, surface treatment of the metal sheet: Use 800#, 1500#, and 3000# sandpaper sequentially to polish the surface of the metal sheet to remove the oxide film. Then, place the metal sheet in an acetone solution for ultrasonic cleaning for 150 seconds to remove surface oil. Next, use diamond polishing paste to polish the surface of the metal sheet. Finally, immerse the polished metal sheet in a 10% sodium hydroxide solution (immersion time 2 minutes) to hydroxylate the surface of the metal sheet.

[0041] Then, the silane coupling treatment solution is sprayed onto the surface of the metal sheet and then placed in a 120°C oven until the silane treatment solution is cured on the surface of the metal sheet.

[0042] Step 4: Spray the reaction liquid of the chemically reinforced layer obtained in Step 3 evenly onto the surface of the CFRP board, and then place it in a constant temperature environment of 70℃ to dry it so that the reaction liquid is cured on the surface of the CFRP board to form a chemically reinforced layer.

[0043] Step 5: Place the metal sheet on the CFRP sheet, with the surface of the metal sheet containing the silane coupling treatment solution facing / attaching to the chemical strengthening layer. Then clamp the metal sheet and the CFRP sheet together (use a clamp to fix the CF-PA66 sheet and the aluminum alloy sheet on the welding worktable).

[0044] Step 6: Turn on the friction stir welding equipment, set the welding process parameters (tool head rotation speed of 2000 rpm, tool head travel speed of 2000 mm / min, tool head shoulder depressor of 0.2 mm), and weld the metal sheet and CFRP sheet together; in this embodiment, a tool head with a stirring pin is used, the lower end of which is always located inside the metal sheet and 1 mm higher than the location of the silane coupling layer; during the friction stir welding process, the interface temperature between the aluminum alloy and CFRP was monitored to be 341℃;

[0045] Step 7: After welding, place the workpiece at room temperature to cool and solidify, forming a joint based on the interface chemical reinforcement layer.

[0046] Comparative Example 1

[0047] A friction stir welding method for bonding metal (3mm thick aluminum alloy sheet 1) and CFRP sheet 4 (3mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) based on an interface chemical reinforcement layer, comprising the following steps:

[0048] Step 11: Prepare the silane coupling treatment solution. Mix 90g ethanol, 6g KH550 and 4g deionized water thoroughly at room temperature. Adjust the pH of the silane treatment solution to acidic using acetic acid solution. Stir at room temperature for 5 minutes to activate the treatment solution and obtain the silane coupling treatment solution.

[0049] Step 12, surface treatment of the metal sheet: Grind the surface of the metal sheet sequentially with 800#, 1500#, and 3000# sandpaper to remove the oxide film. Then, ultrasonically clean the metal sheet in acetone solution for 120 seconds to remove surface oil. Next, polish the surface of the metal sheet with diamond polishing paste. Finally, immerse the polished metal sheet in a 10% sodium hydroxide solution (immersion time 20 seconds) to hydroxylate the surface of the metal sheet.

[0050] Then the silane coupling treatment solution was sprayed onto the surface of the metal plate and then placed in a 120°C oven until the silane treatment solution cured on the surface of the metal plate to form silane coupling layer 2;

[0051] Step 13: Place the metal sheet on the CFRP sheet 4, with the surface of the metal sheet containing the silane coupling treatment liquid facing the CFRP sheet 4. Then clamp the metal sheet and the CFRP sheet 4 (use a clamp to fix the CF-PA66 sheet 4 and the aluminum alloy sheet 1 on the welding worktable).

[0052] Step 14: Turn on the friction stir welding equipment, set the welding process parameters (tool head 5 rotation speed is 600 rpm, tool head 5 travel speed is 3000 mm / min, tool head 5 shoulder downward pressure is 0.4 mm), and weld the metal sheet and CFRP sheet 4 together; in this embodiment, a tool head 5 without stirring pin is used, and welding is performed directly on the upper surface of the metal sheet through the shoulder of the tool head 5; during the friction stir welding process, the temperature at the interface between the aluminum alloy and CFRP was monitored to be 132℃;

[0053] Step 15: After welding, place the workpiece at room temperature to cool and solidify, forming a joint.

[0054] Comparative Example 2

[0055] A friction stir welding method for bonding metal (3mm thick aluminum alloy sheet 1) and CFRP sheet 4 (3mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) based on an interface chemical strengthening layer, comprising the following steps:

[0056] Step 21: Prepare the silane coupling treatment solution. Mix 90g ethanol, 6g KH550 and 4g deionized water thoroughly at room temperature. Adjust the pH of the silane treatment solution to acidic using acetic acid solution. Stir at room temperature for 5 minutes to activate the treatment solution and obtain the silane coupling treatment solution.

[0057] Step 22, surface treatment of the metal sheet: Grind the surface of the metal sheet sequentially with 800#, 1500#, and 3000# sandpaper to remove the oxide film on the surface of the metal sheet. Then, place the metal sheet in an acetone solution for ultrasonic cleaning for 120 seconds to remove surface oil. Next, polish the surface of the metal sheet with diamond polishing paste. Then, immerse the polished metal sheet in a 10% sodium hydroxide solution (immersion time 1 minute) to hydroxylate the surface of the metal sheet.

[0058] Then the silane coupling treatment solution was sprayed onto the surface of the metal plate and then placed in a 70°C oven until the silane treatment solution cured on the surface of the metal plate to form silane coupling layer 2;

[0059] Step 23: Place the metal sheet on the CFRP sheet 4, with the surface of the metal sheet containing the silane coupling treatment liquid facing the CFRP sheet 4. Then clamp the metal sheet and the CFRP sheet 4 (use a clamp to fix the CF-PA66 sheet 4 and the aluminum alloy sheet 1 on the welding worktable).

[0060] Step 24: Turn on the friction stir welding equipment, set the welding process parameters (tool head rotation speed of 1300 rpm, tool head travel speed of 2500 mm / min, tool head shoulder depressor of 0.2 mm), and weld the metal sheet and CFRP sheet together. In this embodiment, a tool head with a stirring pin is used, and the lower end of the stirring pin is always located inside the metal sheet and is 1 mm higher than the location of the silane coupling layer. During the friction stir welding process, the interface temperature between the aluminum alloy and the CFRP sheet located directly below the tool head is monitored to be 221°C.

[0061] Step 25: After welding, place the workpiece at room temperature to cool and solidify, forming a joint.

[0062] Mechanical property tests were conducted on samples of the connection structures prepared in Examples 1-3 and Comparative Examples 1-2. The results showed that the tensile strength of the joint in Example 1 was 23.5 MPa, the tensile strength of the joint in Example 2 was 19.3 MPa, the tensile strength of the joint in Example 3 was 16.2 MPa, the tensile strength of the joint in Comparative Example 1 was 6.9 MPa, and the tensile strength of the joint in Comparative Example 2 was 11.8 MPa.

[0063] Examples 4-6

[0064] A friction stir welding method based on an interface chemical reinforcement layer to connect a metal (3mm thick aluminum alloy sheet) and a CFRP (3mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) is described in Example 1. The key parameters that differ from those in Example 1 are shown in Table 1.

[0065] Table 1 Key parameters in Examples 4-6

[0066] Vinylpyrrolidone 3g 5g 7g 1g acrylic acid 7g 5g 3g 9g Deionized water 90g 90g 90g 90g ammonium persulfate 0.1g 0.1g 0.1g 0.1g reaction temperature 70℃ 70℃ 70℃ 70℃ Connection strength at joints 20.9MPa 23.5MPa 21.2MPa 19.0MPa

[0067] The solution of this invention enables effective bonding between metal materials and CFRP within an interface temperature range of 110-280℃, significantly expanding the original interface temperature range (240-280℃) to 110-280℃, thereby significantly reducing implementation difficulty and facilitating industrial applications. This invention uses an amphiphilic polymer as an intermediate layer (chemical reinforcement layer), significantly improving the bonding strength and stability between the metal and CFRP materials (compared to conventional bonding of dissimilar materials like metal and CFRP). During implementation, the chemical reinforcement layer can be formed and cured on the surface of the CFRP sheet through solution spraying and drying, which is convenient, fast, efficient, and environmentally friendly.

[0068] Example 7

[0069] A method for joining (thermopressive welding) a metal (5mm thick aluminum alloy sheet 1) and a CFRP sheet 4 (5mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) based on an interface chemical reinforcement layer includes the following steps:

[0070] Step 1: Preparation of the reaction solution for the chemically reinforced layer. 7g vinylpyrrolidone monomer, 7g acrylic acid monomer and 80g deionized water are used as raw materials. The mixture is stirred thoroughly at 70℃ for 20 minutes to ensure uniform mixing. Then, 1g ammonium persulfate is added as an initiator and the reaction continues at 70℃ for 6 hours. After the reaction is completed, the reaction solution is collected and cooled to room temperature for later use.

[0071] Step 2: Prepare the silane coupling treatment solution. Mix 90g ethanol, 6g KH550 and 4g deionized water thoroughly at room temperature. Adjust the pH of the silane treatment solution to acidic using acetic acid solution. Stir at room temperature for 8 minutes to activate the treatment solution and obtain the silane coupling treatment solution.

[0072] Step 3, surface treatment of the metal sheet: Use 800#, 1500#, and 3000# sandpaper sequentially to polish the surface of the metal sheet to remove the oxide film. Then, place the metal sheet in an acetone solution for ultrasonic cleaning for 150 seconds to remove surface oil. Next, use diamond polishing compound to polish the surface of the metal sheet. Finally, immerse the polished metal sheet in a 10% sodium hydroxide solution (immersion time 3 minutes) to hydroxylate the surface of the metal sheet.

[0073] Then, the silane coupling treatment solution is sprayed onto the surface of the metal sheet and then placed in a 120°C oven until the silane treatment solution is cured on the surface of the metal sheet.

[0074] Step 4: Spray the reaction liquid of the chemically reinforced layer obtained in Step 3 evenly onto the surface of the CFRP board, and then place it in a constant temperature environment of 70℃ to dry it so that the reaction liquid is cured on the surface of the CFRP board to form a chemically reinforced layer.

[0075] Step 5: Place the metal sheet on the CFRP sheet, with the surface of the metal sheet containing the silane coupling treatment solution facing / attaching to the chemical strengthening layer. Then clamp the metal sheet and the CFRP sheet together (use a clamp to fix the CF-PA66 sheet and the aluminum alloy sheet on the welding worktable).

[0076] Step 6: Turn on the hot press welding equipment, set the process parameters (pressure 0.3MPa, pressure head temperature 120℃, holding time 30min), and connect the metal sheet and CFRP sheet together through the hot press equipment; In this embodiment, the heat generated by the hot press is transferred to the interface through the heat conduction of the aluminum sheet and CFRP sheet. During the welding process, the interface temperature between the aluminum alloy and CFRP was monitored to be 115℃.

[0077] Step 7: After welding, the workpiece is placed at room temperature to cool and solidify, forming a joint based on the interface chemical reinforcement layer. The tensile strength of the resulting joint is 20.5 MPa.

[0078] Example 8

[0079] A method for joining (resistance welding) a metal (3mm thick aluminum alloy sheet 1) and a CFRP sheet 4 (3mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) based on an interface chemical strengthening layer, comprising the following steps:

[0080] Step 1: Preparation of the reaction solution for the chemically reinforced layer. 9g of vinylpyrrolidone monomer, 6g of acrylic acid monomer and 85g of deionized water were used as raw materials. The mixture was stirred thoroughly at 70℃ for 20 minutes to ensure uniform mixing. Then, 0.5g of ammonium persulfate was added as an initiator and the reaction was continued at 70℃ for 7 hours. After the reaction was completed, the reaction solution was collected and cooled to room temperature for later use.

[0081] Step 2: Prepare the silane coupling treatment solution. Mix 86g ethanol, 8g KH550 and 6g deionized water thoroughly at room temperature. Adjust the pH of the silane treatment solution to acidic using acetic acid solution. Stir at room temperature for 8 minutes to activate the treatment solution and obtain the silane coupling treatment solution.

[0082] Step 3, surface treatment of the metal sheet: Use 800#, 1500#, and 3000# sandpaper sequentially to polish the surface of the metal sheet to remove the oxide film. Then, place the metal sheet in an acetone solution for ultrasonic cleaning for 150 seconds to remove surface oil. Next, use diamond polishing paste to polish the surface of the metal sheet. Finally, immerse the polished metal sheet in a 10% sodium hydroxide solution (immersion time 2 minutes) to hydroxylate the surface of the metal sheet.

[0083] Then, the silane coupling treatment solution is sprayed onto the surface of the metal sheet and then placed in a 120°C oven until the silane treatment solution is cured on the surface of the metal sheet.

[0084] Step 4: Spray the reaction liquid of the chemically reinforced layer obtained in Step 3 evenly onto the surface of the CFRP board, and then place it in a constant temperature environment of 70℃ to dry it so that the reaction liquid is cured on the surface of the CFRP board to form a chemically reinforced layer.

[0085] Step 5: Place the metal sheet on the CFRP sheet, with the surface of the metal sheet containing the silane coupling treatment solution facing / attaching to the chemical strengthening layer. Then clamp the metal sheet and the CFRP sheet together (use a clamp to fix the CF-PA66 sheet and the aluminum alloy sheet on the welding worktable).

[0086] Step 6: Turn on the single-sided resistance spot welding equipment, set the process parameters (pre-pressure time 800ms, welding current 10kA, welding time 300ms, welding pressure 7kN, holding time 300ms, post-weld pressure holding time 1000ms), and connect the metal sheet and CFRP sheet together using the single-sided resistance spot welding equipment; in this embodiment, the single-sided resistance welding current passes through the interface between the aluminum plate and the CFRP sheet and generates welding heat;

[0087] Step 7: After welding, the workpiece is placed at room temperature to cool and solidify, forming a joint based on the interface chemical reinforcement layer. The tensile strength of the resulting joint is 19.1 MPa.

[0088] Example 9

[0089] An ultrasonic welding method for joining a metal (3mm thick aluminum alloy sheet 1) and a CFRP sheet 4 (3mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) based on an interface chemical strengthening layer, comprising the following steps:

[0090] Step 1: Preparation of the reaction solution for the chemically reinforced layer. 6g of vinylpyrrolidone monomer, 6g of acrylic acid monomer and 88g of deionized water were used as raw materials. The mixture was stirred thoroughly at 70℃ for 15 minutes to ensure uniform mixing. Then, 1g of ammonium persulfate was added as an initiator and the reaction was continued at 70℃ for 6 hours. After the reaction was completed, the reaction solution was collected and cooled to room temperature for later use.

[0091] Step 2: Prepare the silane coupling treatment solution. At room temperature, mix 84g ethanol, 7g KH550 and 9g deionized water thoroughly. Adjust the pH of the silane treatment solution to acidic using acetic acid solution. Stir at room temperature for 8 minutes to activate the treatment solution and obtain the silane coupling treatment solution.

[0092] Step 3, surface treatment of the metal sheet: Use 800#, 1500#, and 3000# sandpaper sequentially to polish the surface of the metal sheet to remove the oxide film. Then, place the metal sheet in an acetone solution for ultrasonic cleaning for 150 seconds to remove surface oil. Next, use diamond polishing paste to polish the surface of the metal sheet. Finally, immerse the polished metal sheet in a 10% sodium hydroxide solution (immersion time 2 minutes) to hydroxylate the surface of the metal sheet.

[0093] Then, the silane coupling treatment solution is sprayed onto the surface of the metal sheet and then placed in a 120°C oven until the silane treatment solution is cured on the surface of the metal sheet.

[0094] Step 4: Spray the reaction liquid of the chemically reinforced layer obtained in Step 3 evenly onto the surface of the CFRP board, and then place it in a constant temperature environment of 70℃ to dry it so that the reaction liquid is cured on the surface of the CFRP board to form a chemically reinforced layer.

[0095] Step 5: Place the metal sheet on the CFRP sheet, with the surface of the metal sheet containing the silane coupling treatment solution facing / attaching to the chemical strengthening layer. Then clamp the metal sheet and the CFRP sheet together (use a clamp to fix the CF-PA66 sheet and the aluminum alloy sheet on the welding worktable).

[0096] Step 6: Turn on the ultrasonic welding equipment and set the process parameters (frequency: 20kHz, welding pressure: 0.3MPa, welding time: 2.0s, amplitude: 35μm, holding time: 3s). Connect the metal sheet and CFRP sheet together using the ultrasonic welding equipment. In this embodiment, the interface between the aluminum sheet and the CFRP sheet generates welding heat through friction and viscoelastic deformation under the high-frequency vibration of the ultrasonic waves.

[0097] Step 7: After welding, the workpiece is placed at room temperature to cool and solidify, forming a joint based on the interface chemical reinforcement layer. The tensile strength of the resulting joint is 18.5 MPa.

[0098] Example 10

[0099] A method for joining a metal (5mm thick aluminum alloy sheet 1) and a CFRP sheet 4 (5mm thick 30% carbon fiber reinforced PA66 sheet (CF-PA66)) based on an interface chemical strengthening layer (induction welding connection) includes the following steps:

[0100] Step 1: Preparation of the reaction solution for the chemically reinforced layer. 10g of vinylpyrrolidone monomer, 5g of acrylic acid monomer and 85g of deionized water were used as raw materials. The mixture was stirred thoroughly at 70℃ for 30 minutes to ensure uniform mixing. Then, 0.8g of ammonium persulfate was added as an initiator and the reaction was continued at 70℃ for 6 hours. After the reaction was completed, the reaction solution was collected and cooled to room temperature for later use.

[0101] Step 2: Prepare the silane coupling treatment solution. Mix 90g ethanol, 6g KH550 and 4g deionized water thoroughly at room temperature. Adjust the pH of the silane treatment solution to acidic using acetic acid solution. Stir at room temperature for 8 minutes to activate the treatment solution and obtain the silane coupling treatment solution.

[0102] Step 3, surface treatment of the metal sheet: Use 800#, 1500#, and 3000# sandpaper sequentially to polish the surface of the metal sheet to remove the oxide film. Then, place the metal sheet in an acetone solution for ultrasonic cleaning for 150 seconds to remove surface oil. Next, use diamond polishing paste to polish the surface of the metal sheet. Finally, immerse the polished metal sheet in a 10% sodium hydroxide solution (immersion time 2 minutes) to hydroxylate the surface of the metal sheet.

[0103] Then, the silane coupling treatment solution is sprayed onto the surface of the metal sheet and then placed in a 120°C oven until the silane treatment solution is cured on the surface of the metal sheet.

[0104] Step 4: Spray the reaction liquid of the chemically reinforced layer obtained in Step 3 evenly onto the surface of the CFRP board, and then place it in a constant temperature environment of 70℃ to dry it so that the reaction liquid is cured on the surface of the CFRP board to form a chemically reinforced layer.

[0105] Step 5: Place the metal sheet on the CFRP sheet, with the surface of the metal sheet containing the silane coupling treatment solution facing / attaching to the chemical strengthening layer. Then clamp the metal sheet and the CFRP sheet together (use a clamp to fix the CF-PA66 sheet and the aluminum alloy sheet on the welding worktable).

[0106] Step 6: Turn on the induction welding equipment, set the process parameters (heating current 800A, heating time 10s, holding current 300A, pressure 0.3MPa), and connect the metal plate and CFRP plate together using the ultrasonic welding equipment; In this embodiment, the interface between the aluminum plate and the CFRP plate generates welding heat under the action of the induction magnetic field, thereby connecting the aluminum plate and CFRP together.

[0107] Step 7: After welding, the workpiece is placed at room temperature to cool and solidify, forming a joint based on the interface chemical reinforcement layer. The tensile strength of the resulting joint is 22.3 MPa.

Claims

1. A method for joining metals and CFRP based on an interface chemical reinforcement layer, characterized by the following steps: include: Step 1: Preparation of the reaction solution for the chemically reinforced layer. Vinylpyrrolidone monomer, acrylic acid monomer and deionized water are mixed as raw materials, and ammonium persulfate is added as an initiator. After the reaction is completed, the reaction solution is collected and cooled to room temperature for later use. Step 2: Prepare the silane coupling treatment solution; Step 3: Perform surface treatment on the metal sheet, and then spray the silane coupling treatment liquid onto the surface of the metal sheet until the silane treatment liquid is cured on the surface of the metal sheet. Step 4: Spray the reaction liquid of the chemically reinforced layer obtained in Step 1 evenly onto the surface of the CFRP board, and then dry it to solidify the reaction liquid on the surface of the CFRP board to form a chemically reinforced layer. Step 5: Place the metal sheet on the CFRP sheet, with the surface of the metal sheet containing the silane coupling treatment solution facing the chemical strengthening layer, and then clamp the metal sheet and the CFRP sheet together. Step 6: Turn on the welding equipment, set the welding process parameters, and weld the metal sheet and CFRP sheet together. Step 7: After welding, place the workpiece at room temperature to cool and solidify, forming a joint based on the interface chemical reinforcement layer.

2. The connection method according to claim 1, characterized in that: In step 1, the reaction temperature is controlled at 60-90℃ and the reaction time is controlled at 4-10 hours.

3. The connection method according to claim 1, characterized in that, In step 1, by mass ratio, the proportions of vinylpyrrolidone monomer are 2-15 parts, acrylic acid monomer are 2-15 parts, deionized water is 70-95 parts, and ammonium persulfate is 1-5 parts.

4. The connection method according to claim 1, characterized in that, The steps for surface treatment of metal sheets are as follows: First, use 800#, 1500#, and 3000# sandpaper to grind the surface of the metal sheet in sequence to remove the oxide film. Then, place the metal sheet in an acetone solution for ultrasonic cleaning to remove surface oil. Next, use diamond polishing paste to polish the surface of the metal sheet. Finally, treat the metal sheet to hydroxylate the surface. For titanium alloys and stainless steel, immerse them in a carboxylic acid solution for 3-5 seconds. For aluminum alloy sheets, immerse them in a 5%-15% sodium hydroxide solution to hydroxylate the surface.

5. The connection method according to claim 1, characterized in that, The drying temperature in step 4 is 60-160℃, and the drying time is 4-8 hours.

6. The connection method according to any one of claims 1-5, characterized in that, In step 6, friction stir welding is used for welding connection. The welding process parameters are: tool head rotation speed of 500rpm~2000rpm, tool head travel speed of 500mm / min~4000mm / min, and tool head shoulder depressurization of 0.2mm~0.5mm.

7. The connection method according to claim 6, characterized in that: When using a tool head with a stirring pin, the lower end of the stirring pin is always located inside the metal sheet and above the position of the silane coupling layer; when using a tool head without a stirring pin, the action is directly applied to the upper surface of the metal sheet through the shoulder of the tool head.

8. The connection method according to claim 7, characterized in that: The metal sheet material is made of aluminum alloy, magnesium alloy or titanium alloy.

9. The connection method according to any one of claims 1-5, characterized in that: In step 6, hot-press welding, resistance welding, laser welding, ultrasonic welding, or induction welding are used for welding connections.

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