Surface treatment method for improving bonding force of composite material-metal heterogeneous interface and connecting structure

Abstract

The invention relates to a surface treatment method for improving the bonding force of a composite material-metal heterogeneous interface and a connecting structure, and belongs to the technical field of preparation of composite materials, the surface treatment method comprises the following steps: step 1, sequentially carrying out mechanical polishing, chemical oil removal, anodic oxidation, corrosion-resistant coating coating, freeze drying and heat treatment on a metal material; 2, uniformly mixing the carbon nanotube dispersion liquid and the magnetic material dispersion liquid, purifying, filtering, and drying to obtain magnetic material coated carbon nanotube powder; step 3, dispersing the magnetic material coated carbon nanotube powder in absolute ethyl alcohol, and performing uniform ultrasonic dispersion to obtain a suspension; step 4, uniformly mixing the turbid liquid with an adhesive, and coating an interface of the composite material and the metal material with the mixture; and 5, magnets are placed on the upper surface and the lower surface of the composite material and metal material composite structural part, and the magnetic material coated carbon nanotubes are distributed in the heterogeneous interface in the vertical direction to achieve bonding.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material preparation, and in particular relates to a surface treatment method and a connection structure for improving the bonding strength of a composite material-metal heterogeneous interface. Background Art

[0002] Due to their high specific modulus and specific strength, carbon fiber composites are widely used in aerospace structures, transmission systems and other power fields. Compared with traditional metal materials such as aluminum, titanium, stainless steel, etc., carbon fiber composites have more ideal strength and modulus. At the same time, due to their designability, based on anisotropic materials, composite materials can be finely designed according to actual load requirements for composite material plies to form optimization plans, further improving the multi-field application of composite materials.

[0003] With the rapid development of fields such as aerospace and marine engineering, composite materials play an indispensable role in related fields. However, composite materials inevitably have to be structurally connected with metal materials during use. Under fatigue loads, the heterogeneous connection parts are very prone to damage, which affects the in-depth use of composite materials in related fields. At present, heterogeneous connection structures mostly use adhesive bonding, riveting or screwing methods to achieve the purpose of improving the bonding strength of heterogeneous interfaces. However, with the continuous improvement of indicators such as lightweight and low cost, the use of more efficient and stable heterogeneous connection structures and surface treatment methods for interface strength will become the future development direction of this technology field. Summary of the Invention

[0004] In order to improve the bonding strength of the composite material-metal heterostructure interface and enhance the coordinated deformation capability of the heterostructure interface, the present invention provides a surface treatment method and a connection structure for improving the bonding strength of the composite material-metal heterostructure interface.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A surface treatment method for improving the bonding strength of a composite material-metal heterogeneous interface comprises the following steps:

[0007] Step 1: mechanically polishing, chemically degreasing, and anodizing the metal material in sequence to obtain an anodized porous structure, coating the surface with a corrosion-resistant coating, and freeze-drying and heat-treating the metal material to remove surface moisture;

[0008] Step 2: Evenly mix the carbon nanotube dispersion and the magnetic material dispersion, purify, filter, and dry to obtain magnetic material-coated carbon nanotube powder;

[0009] Step 3: Dispersing the magnetic material-coated carbon nanotube powder in anhydrous ethanol, then adding a dispersant, and performing ultrasonic dispersion to obtain a suspension;

[0010] Step 4: Evenly mix the suspension and adhesive, remove bubbles and residual ethanol by vacuum, and then apply the adhesive to the interface between the composite material and the metal material;

[0011] Step 5: Place magnets on the upper and lower surfaces of the composite material and metal material composite structure so that the magnetic material-coated carbon nanotubes are vertically distributed in the heterogeneous interface to achieve bonding.

[0012] Furthermore, in step one, the mechanical polishing is a treatment method selected from lapping, polishing, tumbling, sandblasting or shot blasting to remove the nano-scale natural oxide layer on the metal surface; the degreasing agent used in the chemical degreasing is an acidic degreasing agent or an alkaline degreasing agent, the alkaline degreasing agent is composed of 30g / L sodium carbonate, 30g / L trisodium phosphate, 15g / L sodium silicate and deionized water, and the treatment temperature is 50°C; the acidic degreasing agent is composed of 100ml / L sulfuric acid with d=1.84, 25g / L OP emulsifier and deionized water, and the treatment temperature is room temperature; the anodic oxidation step is: using a metal material as an anode, an inert metal or graphite as a cathode, and an anodic oxidation liquid being a 10~20wt.% mixed acid aqueous solution, the mixed acid being sulfuric acid and oxalic acid, the mass ratio of sulfuric acid to oxalic acid being (1~1.5):1, the operating voltage being 10~30V, the temperature being 20~30°C, and the time being 1.5~2h. Anodic oxidation forms pores of 1-90 nm on the metal surface. The corrosion-resistant coating is a thermoplastic resin coating, wherein the thermoplastic resin is one of polystyrene and polyamide, and the coating is applied by spraying, with a coating thickness of 5-20 μm. The freeze-drying step is as follows: the coated metal material is placed in a cold storage or refrigerator at a temperature below 0°C for 3-5 hours, and then placed in a freeze dryer, under conditions of a vacuum degree below 10 Pa and a cold trap temperature of -50°C, and freeze-dried for 3-5 hours to remove moisture from the pores. The heat treatment process is as follows: under normal temperature conditions, the metal material is placed in a 2% H2 / N2 mixed atmosphere, the temperature is raised to 160°C at 15°C / min, the temperature is kept for 1-3 hours, then the temperature is raised to 300°C at 5°C / min, the temperature is kept for 1-3 hours, then the temperature is raised to 500°C at 20°C / min, the temperature is kept for 1-2 hours, and the temperature is cooled to room temperature by purging with a 2% H2 / N2 mixed atmosphere. The obtained metal surface contains electrochemically corroded macropores and chemically corroded mesopores, wherein the pore size of the macropores is in the range of 50-70nm, the pore depth of the macropores is 10-20nm, the pore size of the mesopores is in the range of 1-40nm, and the moisture content is less than 30mg / m 2The present invention increases the number of pores on the metal surface and effectively reduces the moisture content that is unavoidable during the pore formation process through freeze-drying and heat treatment. The metal material used in the present invention can be pure aluminum or aluminum alloys, and there are no special restrictions on the composition of the aluminum alloy, such as various aluminum alloys headed by VI and VII series alloys. The metal used in the present invention can also be Mg, Ti, stainless steel, and other metals, and there are no special restrictions on their shape.

[0013] Furthermore, in step 2, the carbon nanotube dispersion is prepared by adding CNTs powder to 400 ml of deionized water and stirring with an ultrasonic stirrer for 15 minutes to obtain a coarse CNTs dispersion; the magnetic material dispersion is prepared by adding a magnetic material to 400 ml of deionized water and stirring with an ultrasonic stirrer for 15 minutes to obtain a coarse magnetic material dispersion. The coarse magnetic material dispersion is then poured into the coarse CNTs dispersion and stirred with an ultrasonic stirrer for 30 minutes to obtain a coarse mixed dispersion. Preferably, the magnetic material is ferrosoferric oxide. The carbon nanotubes have a length range of 10-40 μm and a diameter range of 10-30 nm, and are normally distributed in size.

[0014] The purification and filtration steps are as follows: 30 ml of aqueous ammonia is added to a mixture of a carbon nanotube dispersion and a magnetic material dispersion. The mixture is mechanically stirred at 2000 rpm at 70°C for 3 hours. After uniform stirring, a magnet is used to gather the carbon nanotube and magnetic material composite (due to the weak magnetic properties of carbon nanotubes, they form a magnetic attraction with the magnetic material, causing the two to form a composite) at the bottom of a beaker. The mixture is then repeatedly cleaned and purified with deionized water until the pH of the purified water approaches 7. The cleaned solid particles are then filtered to obtain a powder. The dried mass is ground into a powder using a mortar and pestle and collected through a sieve. Finally, the magnetic material-coated carbon nanotube powder is placed in a vacuum oven and dried at 120°C for 12 hours.

[0015] The mass fraction of the ammonia water is 25%-30% to ensure the dispersion effect of the suspension.

[0016] Furthermore, the specific steps of step three are as follows: adding anhydrous ethanol to the magnetic material-coated carbon nanotube powder, stirring thoroughly to form a 100 mg / ml suspension, stirring the formed suspension using an ultrasonic stirrer for 15 minutes, and then adding sodium dodecylbenzenesulfonate (SDBS) in a ratio of magnetic material-coated carbon nanotube suspension: dispersant (1~2):1, stirring using an ultrasonic stirrer for 15 minutes to obtain a suspension.

[0017] Furthermore, in step 4, the ratio of the suspension to the adhesive is 5:2.

[0018] Preferably, the adhesive comprises epoxy resin and a curing agent.

[0019] A connection structure for improving the bonding strength of a composite-metal heterogeneous interface comprises a first and second rib on the surface of a composite structural member, and a first and second groove on the surface of a metal structural member; alternatively, a first and second groove are provided on the surface of a composite structural member, and a first and second rib are provided on the surface of a metal structural member. When the surfaces of the composite structural member and the metal structural member come into contact, the first rib fits within the first groove, and the second rib fits within the second groove. The composite structural member and the metal structural member are bonded together and fixedly connected by bolts. This connection structure can provide higher structural strength to resist vibration fatigue.

[0020] The heights of the first ribs and the second ribs are inconsistent, and the depths of the first grooves and the second grooves are inconsistent.

[0021] Preferably, the height of the second rib is half of the height of the first rib, and the depth of the second groove is half of the depth of the first groove.

[0022] Preferably, the first rib, the second rib, the first groove and the second groove are all annular, and the first rib is located inside the second rib, and the first groove is located inside the second groove.

[0023] Preferably, the first rib, the second rib, the first groove and the second groove are all annular, and the first rib is outside the second rib, and the first groove is outside the second groove.

[0024] The metal structural part is surface treated according to the above step 1. The composite structural part and the metal structural part are bonded according to steps 2 to 5.

[0025] The above-mentioned connection structure and metal surface treatment method can effectively enhance the bonding strength of the heterogeneous interface and achieve the purpose of resisting vibration fatigue.

[0026] Two positioning holes and a plurality of connection holes are provided on the metal structural part and the composite structural part. Bolts are passed through the positioning holes and the connection holes to position and connect the metal structural part and the composite structural part.

[0027] Position and assemble the two bolts according to the principle of opposite-side assembly to ensure that the first groove and the first rib, and the second groove and the second rib are fully engaged; then install the remaining bolts and tighten the metal structural parts and the composite structural parts; place the tightened structural parts on the heatable magnetic pole for curing, the curing system is: 120℃±5℃ / 3h, and complete the assembly work.

[0028] Furthermore, the composite material structural parts and the metal material structural parts need to be assembled within 1-3 hours.

[0029] Considering the material and process characteristics of composite materials, a double rib structure is designed at the bonding surface of composite structural parts. Its main purposes are threefold: (1) to increase the bonding area between the adhesive and the composite structural parts and improve the interface bonding strength; (2) to reduce the shear force in the heterogeneous interface through the mechanical meshing structure, improve the interface shear strength, and achieve self-locking connection; (3) to improve the formability through the lubricating effect of the adhesive, while avoiding contact corrosion between heterogeneous materials and increasing the sealing.

[0030] The grooves or ribs and evenly distributed connection holes on the bonding surface of metal structural parts are used for assembly with composite materials. This joining process combines the advantages of structural joining and bonding. It can be mass-produced using molds and presses, and features high precision, high efficiency, and high reliability. Furthermore, the process does not generate heat, has no impact on the properties of the connected tubes, and emits no harmful substances such as light, radiation, and exhaust gases. No filler materials are required, making the work environment friendly.

[0031] Surface treatment on the metal surface includes the following steps: mechanical polishing - chemical degreasing - anodizing - surface coating with corrosion-resistant coating - freeze drying - heat treatment. The surface treatment method has the following advantages: (1) Anodizing can produce 1-90nm pores on the surface of the metal material, increase the surface roughness of the metal and increase the interface shear strength; (2) The cooling and drying operation can effectively reduce the moisture content on the metal surface, reduce the hydrogen bond reaction between the adhesive and the water molecules on the metal surface, and improve the interface durability and weather resistance; (3) The heat treatment operation increases the pore content on the surface of the metal material, reduces the moisture content on the surface of the metal material, and further increases the heterogeneous interface bonding strength.

[0032] The treatment of the interface adhesive has the following advantages: (1) Due to the magnetic effect, the magnetic material-coated carbon nanotube particles are arranged in a vertical direction in the heterogeneous interface, which can effectively increase the interface shear strength; (2) Due to the presence of the magnetic material-coated carbon nanotube particles, a layered migration mechanism is formed around the particles when the crack propagates, which effectively inhibits the propagation of the crack; (3) The magnetic material-coated carbon nanotube particles can significantly improve the toughness of the heterogeneous interface and improve the deformation ability of the heterogeneous materials, thereby enhancing the interface strength.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention fully considers the characteristics of the heterogeneous interface between composite materials and metal materials. By structurally designing the ribs and grooves on the bonding surfaces of the composite materials and metal materials, mechanical engagement of the heterogeneous interface is achieved. This mechanical engagement provides high interface strength, improves the interface shear strength, and effectively avoids the drawback of surface-to-surface bonding and other connection methods that weaken the mechanical properties of the heterogeneous interface.

[0035] (2) The present invention fully considers the problem of contact corrosion easily generated when connecting heterogeneous metal materials. By coating the contact surface with a corrosion-resistant layer, direct contact between the two heterogeneous interfaces is avoided, which can effectively avoid the contact corrosion problem. At the same time, the sealing of the joint is increased, thereby achieving the effect of improving corrosion resistance, sealing and connection strength, and extending service life.

[0036] (3) The present invention fully considers the influence of the metal surface state on the mechanical properties of the interface. By anodizing the metal material to increase the surface porosity of the material and obtain uniformly distributed mesopores, the interface bonding strength can be effectively improved.

[0037] (4) The present invention fully considers the chemical properties of water molecules on the metal surface and the adhesive. Through freeze-drying and heat treatment operations, the moisture content on the surface of the metal material is effectively reduced, and macropores and mesopores are further formed on the metal surface, which effectively improves the interface shear strength, interface durability and weather resistance.

[0038] (5) The present invention fully considers the shear strength and deformation coordination ability of the heterogeneous interface. By using magnetic materials to coat carbon nanotube particles, the particles are arranged uniformly in the vertical direction, thereby improving the bonding ability of the interface adhesive; considering the interface crack propagation mechanism, the interface specific surface area is increased by increasing the magnetic material coating on the carbon nanotube particles, thereby effectively improving the interface strength.

[0039] (6) The present invention fully inhibits crack propagation and reduces interlayer damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram of the composite material-metal heterogeneous interface connection structure of the present invention;

[0041] Figure 2 This is a cross-sectional view of the composite material-metal heterogeneous interface connection structure of the present invention;

[0042] Figure 3 This is a schematic diagram of the assembly of the composite material-metal heterogeneous interface connection structure of the present invention;

[0043] Figure 4 This is a top view of the composite material-metal heterogeneous interface connection structure of the present invention;

[0044] In the figure, 1, first rib, 2, second rib, 3, first groove, 4, second groove, 5, metal material structural part, 6, composite material structural part, 7, bolt. DETAILED DESCRIPTION

[0045] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0046] Example 1:

[0047] A surface treatment method for improving the bonding strength of a composite material-metal heterogeneous interface comprises the following steps:

[0048] Step 1: mechanically polishing, chemically degreasing, and anodizing the metal material in sequence to obtain an anodized porous structure, coating the surface with a corrosion-resistant coating, and freeze-drying and heat-treating the metal material to remove surface moisture;

[0049] Step 2: Evenly mix the carbon nanotube dispersion and the magnetic material dispersion, purify, filter, and dry to obtain magnetic material-coated carbon nanotube powder;

[0050] Step 3: Dispersing the magnetic material-coated carbon nanotube powder in anhydrous ethanol, then adding a dispersant, and performing ultrasonic dispersion to obtain a suspension;

[0051] Step 4: Evenly mix the suspension and adhesive, remove bubbles and residual ethanol by vacuum, and then apply the adhesive to the interface between the composite material and the metal material;

[0052] Step 5: Place magnets on the upper and lower surfaces of the composite material and metal material composite structure so that the magnetic material-coated carbon nanotubes are vertically distributed in the heterogeneous interface to achieve bonding.

[0053] Furthermore, in step 1, the mechanical polishing is a polishing treatment to remove the nanoscale natural oxide layer on the metal surface. The degreasing agent used in the chemical degreasing is an acidic degreasing agent composed of 100 ml / L sulfuric acid with a d=1.84, 25 g / L OP emulsifier, and deionized water, and the treatment temperature is room temperature. The anodizing step is as follows: using a metal material as the anode and an inert metal or graphite as the cathode, the anodizing liquid is a 10 wt.% mixed acid aqueous solution, the mixed acid is sulfuric acid and oxalic acid, the mass ratio of sulfuric acid to oxalic acid is 1:1, the operating voltage is 10 V, the temperature is 20°C, and the time is 1.5 hours. Preferably, the metal material is an aluminum alloy, and anodization forms pores of 1-90 nm on the aluminum alloy surface. The corrosion-resistant coating is a thermoplastic resin coating, the thermoplastic resin is polystyrene, the coating method is spraying, and the coating thickness is 5 μm. The freeze-drying step is as follows: the coated metal material is placed in a cold storage with a temperature below 0°C for 3 hours, and then placed in a freeze dryer, and freeze-dried for 3 hours under the conditions of a vacuum degree below 10Pa and a cold trap temperature of -50°C to remove moisture in the pores. The heat treatment process is as follows: under normal temperature conditions, the metal material is placed in a mixed atmosphere with a volume fraction of 2% H2 / N2, and the temperature is raised to 160°C at 15°C / min, kept at this temperature for 1 hour, and then raised to 300°C at 5°C / min, kept at this temperature for 1 hour, and then raised to 500°C at 20°C / min, kept at this temperature for 1 hour, and then purged to room temperature with a 2% H2 / N2 mixed gas. The obtained metal surface contains electrochemically corroded macropores and chemically corroded mesopores, wherein the pore size range of the macropores is 50-70nm, the pore depth of the macropores is 10~20nm, the pore size range of the mesopores is 1-40nm, and the moisture content is less than 30mg / m 2 The present invention increases the number of pores on the metal surface and effectively reduces the moisture content that is unavoidable during the pore formation process through freeze drying and heat treatment.

[0054] Furthermore, in step 2, the carbon nanotube dispersion is prepared by adding CNT powder to 400 ml of deionized water and stirring for 15 minutes using an ultrasonic stirrer to obtain a coarse CNT dispersion. The magnetic material dispersion is prepared by adding the magnetic material Fe3O4 to 400 ml of deionized water and stirring for 15 minutes using an ultrasonic stirrer to obtain a coarse magnetic material dispersion. The coarse magnetic material dispersion is then poured into the coarse CNT dispersion and stirred for 30 minutes using an ultrasonic stirrer to obtain a coarse intermixed dispersion. The carbon nanotubes have a length range of 10-40 μm and a diameter range of 10-30 nm, and are normally distributed.

[0055] The purification and filtration steps are as follows: 30ml of ammonia water is added to a mixture of a carbon nanotube dispersion and a magnetic material dispersion. The mixture is mechanically stirred at 2000 rpm at 70°C for 3 hours. After uniform mixing, a magnet is used to aggregate the carbon nanotube and magnetic material composite at the bottom of a beaker. The composite is then repeatedly cleaned and purified with deionized water until the pH approaches 7. After filtration, the cleaned solid particles are obtained. The dried mass is ground into a powder using a mortar and pestle and collected through a sieve. Finally, the Fe3O4@CNT powder is placed in a vacuum oven and dried at 120°C for 12 hours.

[0056] The mass fraction of the ammonia water is 25%-30% to ensure the dispersion effect of the suspension.

[0057] Furthermore, the specific steps of step three are: adding anhydrous ethanol to the magnetic material-coated carbon nanotube powder, stirring thoroughly to form a 100 mg / ml suspension, stirring the formed suspension using an ultrasonic stirrer for 15 minutes, and then adding sodium dodecylbenzenesulfonate (SDBS) in a ratio of 1:1 of magnetic material-coated carbon nanotube suspension: dispersant, and stirring for 15 minutes using an ultrasonic stirrer to obtain a suspension.

[0058] Furthermore, in step 4, the ratio of the suspension to the adhesive is 5:2.

[0059] Preferably, the adhesive comprises epoxy resin and a curing agent.

[0060] Example 2:

[0061] A connection structure for improving the bonding strength of a composite material-metal heterogeneous interface, wherein a first rib 1 and a second rib 2 are provided on the surface of a composite material structural component 6, and a first groove 3 and a second groove 4 are provided on the surface of a metal material structural component 5; when the surface of the composite material structural component 6 contacts the surface of the metal material structural component 5, the first rib 1 is matched and arranged inside the first groove 3, and the second rib 2 is matched and arranged inside the second groove 4, and the composite material structural component 6 and the metal material structural component 5 are bonded together and fixedly connected by bolts 7.

[0062] The height of the second rib 2 is half of the height of the first rib 1 , and the depth of the second groove 4 is half of the depth of the first groove 3 .

[0063] The first rib 1 , the second rib 2 , the first groove 3 and the second groove 4 are all annular in shape, and the first rib 1 is located inside the second rib 2 , and the first groove 3 is located inside the second groove 4 .

[0064] The metal structural member 5 is surface treated according to step 1 of embodiment 1. The composite structural member 6 and the metal structural member 5 are bonded according to steps 2 to 5 of embodiment 1.

[0065] Example 3

[0066] A connection structure for improving the bonding strength of a composite material-metal heterogeneous interface, wherein a first groove 3 and a second groove 4 are provided on the surface of a composite material structural component 6, and a first rib 1 and a second rib 2 are provided on the surface of a metal material structural component 5; when the surface of the composite material structural component 6 contacts the surface of the metal material structural component 5, the first rib 1 is matched and arranged inside the first groove 3, and the second rib 2 is matched and arranged inside the second groove 4, and the composite material structural component 6 and the metal material structural component 5 are bonded together and fixedly connected by bolts 7.

[0067] The height of the second rib 2 is half of the height of the first rib 1 , and the depth of the second groove 4 is half of the depth of the first groove 3 .

[0068] The first rib 1 , the second rib 2 , the first groove 3 and the second groove 4 are all annular in shape, and the first rib 1 is located outside the second rib 2 , and the first groove 3 is located outside the second groove 4 .

[0069] The metal structural member 5 is surface treated according to step 1 of embodiment 1. The composite structural member 6 and the metal structural member 5 are bonded according to steps 2 to 5 of embodiment 1.

[0070] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0071] Example 4:

[0072] A surface treatment method for improving the bonding strength of a composite material-metal heterogeneous interface comprises the following steps:

[0073] Step 1: mechanically polishing, chemically degreasing, and anodizing the metal material in sequence to obtain an anodized porous structure, coating the surface with a corrosion-resistant coating, and freeze-drying and heat-treating the metal material to remove surface moisture;

[0074] Step 2: Evenly mix the carbon nanotube dispersion and the magnetic material dispersion, purify, filter, and dry to obtain magnetic material-coated carbon nanotube powder;

[0075] Step 3: Dispersing the magnetic material-coated carbon nanotube powder in anhydrous ethanol, then adding a dispersant, and performing ultrasonic dispersion to obtain a suspension;

[0076] Step 4: Evenly mix the suspension and adhesive, remove bubbles and residual ethanol by vacuum, and then apply the adhesive to the interface between the composite material and the metal material;

[0077] Step 5: Place magnets on the upper and lower surfaces of the composite material and metal material composite structure so that the magnetic material-coated carbon nanotubes are vertically distributed in the heterogeneous interface to achieve bonding.

[0078] Furthermore, in step 1, the mechanical polishing is a roller burnishing treatment that removes the nanoscale natural oxide layer on the metal surface. The degreasing agent used in the chemical degreasing is an acidic degreasing agent composed of 100 ml / L sulfuric acid with a d=1.84, 25 g / L OP emulsifier, and deionized water, and the treatment temperature is room temperature. The anodizing step comprises: using a metal material as the anode and an inert metal or graphite as the cathode, the anodizing liquid is a 10 wt.% mixed acid aqueous solution of sulfuric acid and oxalic acid, the mass ratio of sulfuric acid to oxalic acid being 1.5:1, the operating voltage is 20 V, the temperature is 30°C, and the time is 1.5 hours. Preferably, the metal material is an aluminum alloy, and the anodizing forms pores of 1-90 nm on the aluminum alloy surface. The corrosion-resistant coating is a thermoplastic resin coating, the thermoplastic resin is polystyrene, the coating method is spraying, and the coating thickness is 20 μm. The freeze-drying step is as follows: placing the coated metal material in a refrigerator at a temperature below 0°C for 4 hours, then placing it in a freeze dryer, freeze-drying it for 4 hours under the conditions of a vacuum degree below 10Pa and a cold trap temperature of -50°C to remove moisture in the pores. The heat treatment process is as follows: placing the metal material in a 2% H2 / N2 mixed atmosphere at room temperature, heating it to 160°C at 15°C / min, keeping it warm for 2 hours, then heating it to 300°C at 5°C / min, keeping it warm for 2 hours, then heating it to 500°C at 20°C / min, keeping it warm for 1 hour, and purging it to room temperature with a 2% H2 / N2 mixed gas. The obtained metal surface contains electrochemically corroded macropores and chemically corroded mesopores, wherein the pore size range of the macropores is 50-70nm, the pore depth of the macropores is 10~20nm, the pore size range of the mesopores is 1-40nm, and the moisture content is less than 30mg / m 2 The present invention increases the number of pores on the metal surface and effectively reduces the moisture content that is unavoidable during the pore formation process through freeze drying and heat treatment.

[0079] Furthermore, in step 2, the carbon nanotube dispersion is prepared by adding CNTs powder to 400 ml of deionized water and stirring with an ultrasonic stirrer for 15 minutes to obtain a coarse CNTs dispersion; the magnetic material dispersion is prepared by adding a magnetic material to 400 ml of deionized water and stirring with an ultrasonic stirrer for 15 minutes to obtain a coarse magnetic material dispersion. The coarse magnetic material dispersion is then poured into the coarse CNTs dispersion and stirred with an ultrasonic stirrer for 30 minutes to obtain a coarse mixed dispersion. Preferably, the magnetic material is ferrosoferric oxide. The carbon nanotubes have a length range of 10-40 μm and a diameter range of 10-30 nm, and are normally distributed in size.

[0080] The purification and filtration steps are as follows: 30ml of ammonia water is added to a mixture of a carbon nanotube dispersion and a magnetic material dispersion. The mixture is mechanically stirred at 2000 rpm at 70°C for 3 hours. After uniform mixing, a magnet is used to aggregate the carbon nanotube and magnetic material composite at the bottom of a beaker. The composite is then repeatedly cleaned and purified with deionized water until the pH approaches 7. After filtration, the cleaned solid particles are obtained. The dried mass is ground into a powder using a mortar and pestle and collected through a sieve. Finally, the Fe3O4@CNT powder is placed in a vacuum oven and dried at 120°C for 12 hours.

[0081] The mass fraction of the ammonia water is 25%-30% to ensure the dispersion effect of the suspension.

[0082] Furthermore, the specific steps of step three are: adding anhydrous ethanol to the magnetic material-coated carbon nanotube powder, stirring thoroughly to form a 100 mg / ml suspension, stirring the formed suspension using an ultrasonic stirrer for 15 minutes, and then adding sodium dodecylbenzenesulfonate (SDBS) in a ratio of 1.5:1 of magnetic material-coated carbon nanotube suspension: dispersant, and stirring for 15 minutes using an ultrasonic stirrer to obtain a suspension.

[0083] Furthermore, in step 4, the ratio of the suspension to the adhesive is 5:2.

[0084] Preferably, the adhesive comprises epoxy resin and a curing agent.

[0085] Example 5:

[0086] A surface treatment method for improving the bonding strength of a composite material-metal heterogeneous interface comprises the following steps:

[0087] Step 1: mechanically polishing, chemically degreasing, and anodizing the metal material in sequence to obtain an anodized porous structure, coating the surface with a corrosion-resistant coating, and freeze-drying and heat-treating the metal material to remove surface moisture;

[0088] Step 2: Evenly mix the carbon nanotube dispersion and the magnetic material dispersion, purify, filter, and dry to obtain magnetic material-coated carbon nanotube powder;

[0089] Step 3: Dispersing the magnetic material-coated carbon nanotube powder in anhydrous ethanol, then adding a dispersant, and performing ultrasonic dispersion to obtain a suspension;

[0090] Step 4: Evenly mix the suspension and adhesive, remove bubbles and residual ethanol by vacuum, and then apply the adhesive to the interface between the composite material and the metal material;

[0091] Step 5: Place magnets on the upper and lower surfaces of the composite material and metal material composite structure so that the magnetic material-coated carbon nanotubes are vertically distributed in the heterogeneous interface to achieve bonding.

[0092] Furthermore, in step 1, the mechanical polishing is performed by sandblasting to remove the nanoscale natural oxide layer on the metal surface. The degreasing agent used in the chemical degreasing is an alkaline degreasing agent composed of 30g / L sodium carbonate, 30g / L trisodium phosphate, 15g / L sodium silicate, and deionized water, and the treatment temperature is 50°C. The anodizing step comprises: using a metal material as the anode and an inert metal or graphite as the cathode, the anodizing liquid is a 10wt.% mixed acid aqueous solution of sulfuric acid and oxalic acid in a mass ratio of 1:1, the operating voltage is 30V, the temperature is 30°C, and the time is 2h. Preferably, the metal material is pure aluminum, and the anodizing forms pores of 1-90nm on the aluminum surface. The corrosion-resistant coating is a thermoplastic resin coating, the thermoplastic resin is polyamide, the coating method is spraying, and the coating thickness is 10μm. The freeze-drying step is as follows: placing the coated metal substrate in a cold storage at a temperature below 0°C for 5 hours, then placing it in a freeze dryer, freeze-drying it for 5 hours under the conditions of a vacuum degree below 10Pa and a cold trap temperature of -50°C to remove moisture in the pores. The heat treatment process is as follows: placing the metal material in a 2% H2 / N2 mixed atmosphere at room temperature, heating it to 160°C at 15°C / min, keeping it warm for 3 hours, then heating it to 300°C at 5°C / min, keeping it warm for 3 hours, then heating it to 500°C at 20°C / min, keeping it warm for 2 hours, and then purging it to room temperature with a 2% H2 / N2 mixed gas. The obtained metal surface contains electrochemically corroded macropores and chemically corroded mesopores, wherein the pore size range of the macropores is 50-70nm, the pore depth of the macropores is 10~20nm, the pore size range of the mesopores is 1-40nm, and the moisture content is less than 30mg / m 2 The present invention increases the number of pores on the metal surface and effectively reduces the moisture content that is unavoidable during the pore formation process through freeze drying and heat treatment.

[0093] Furthermore, in step 2, the carbon nanotube dispersion is prepared by adding CNTs powder to 400 ml of deionized water and stirring with an ultrasonic stirrer for 15 minutes to obtain a coarse CNTs dispersion; the magnetic material dispersion is prepared by adding a magnetic material to 400 ml of deionized water and stirring with an ultrasonic stirrer for 15 minutes to obtain a coarse magnetic material dispersion. The coarse magnetic material dispersion is then poured into the coarse CNTs dispersion and stirred with an ultrasonic stirrer for 30 minutes to obtain a coarse mixed dispersion. Preferably, the magnetic material is ferrosoferric oxide. The carbon nanotubes have a length range of 10-40 μm and a diameter range of 10-30 nm, and are normally distributed in size.

[0094] The purification and filtration steps are as follows: 30ml of ammonia water is added to a mixture of a carbon nanotube dispersion and a magnetic material dispersion. The mixture is mechanically stirred at 2000 rpm at 70°C for 3 hours. After uniform mixing, a magnet is used to aggregate the carbon nanotube and magnetic material composite at the bottom of a beaker. The composite is then repeatedly cleaned and purified with deionized water until the pH approaches 7. After filtration, the cleaned solid particles are obtained. The dried mass is ground into a powder using a mortar and pestle and collected through a sieve. Finally, the Fe3O4@CNT powder is placed in a vacuum oven and dried at 120°C for 12 hours.

[0095] The mass fraction of the ammonia water is 25%-30% to ensure the dispersion effect of the suspension.

[0096] Furthermore, the specific steps of step three are: adding anhydrous ethanol to the magnetic material-coated carbon nanotube powder, stirring thoroughly to form a 100 mg / ml suspension, stirring the formed suspension using an ultrasonic stirrer for 15 minutes, and then adding sodium dodecylbenzenesulfonate (SDBS) in a ratio of 2:1 of magnetic material-coated carbon nanotube suspension: dispersant, and stirring for 15 minutes using an ultrasonic stirrer to obtain a suspension.

[0097] Furthermore, in step 4, the ratio of the suspension to the adhesive is 5:2.

[0098] Preferably, the adhesive comprises epoxy resin and a curing agent.

[0099] Table 1 shows the performance test results of Examples 1 and 45.

[0100] Table 1 Performance test results

[0101] 180° peel strength (MPa) Example 1 12.4 Example 4 13.6 Example 5 15.7

Claims

1. A surface treatment method for improving the bonding strength of a composite material-metal heterogeneous interface, characterized in that: The following steps are involved: Step 1: mechanically polishing, chemically degreasing, and anodizing the metal material in sequence to obtain an anodized porous structure, coating the surface with a corrosion-resistant coating, and freeze-drying and heat-treating the metal material to remove surface moisture; Step 2: Evenly mix the carbon nanotube dispersion and the magnetic material dispersion, purify, filter, and dry to obtain magnetic material-coated carbon nanotube powder; Step 3: Dispersing the magnetic material-coated carbon nanotube powder in anhydrous ethanol, then adding a dispersant, and performing ultrasonic dispersion to obtain a suspension; Step 4: Evenly mix the suspension and adhesive, remove bubbles and residual ethanol by vacuum, and then apply the adhesive to the interface between the composite material and the metal material; Step 5: Place magnets on the upper and lower surfaces of the composite material and metal material composite structure so that the magnetic material-coated carbon nanotubes are vertically distributed in the heterogeneous interface to achieve bonding.

2. The surface treatment method according to claim 1, wherein: In step 1, the anodic oxidation step is as follows: using a metal material as an anode, an inert metal or graphite as a cathode, the anodic oxidation liquid is a 10-20 wt.% mixed acid aqueous solution, the mixed acid is sulfuric acid and oxalic acid, the mass ratio of sulfuric acid to oxalic acid is (1-1.5):1, the operating voltage is 10-30 V, the temperature is 20-30 ° C, and the time is 1.5-2 hours.

3. The surface treatment method according to claim 1, wherein: In step 1, the corrosion-resistant coating is one of polystyrene and polyamide.

4. The surface treatment method according to claim 1, wherein: In step 2, the purification and filtration steps are as follows: adding ammonia water to the mixed solution of the carbon nanotube dispersion and the magnetic material dispersion, stirring evenly, using a magnet to gather the complex of the carbon nanotubes and the magnetic material at the bottom of the beaker, and repeatedly washing and purifying with deionized water, and obtaining cleaned solid particles after filtration.

5. The surface treatment method according to claim 1, wherein: In step 3, the ratio of magnetic material coated carbon nanotube powder to anhydrous ethanol is 100 mg / ml, and the mass ratio of the mixed solution obtained by dispersing the magnetic material coated carbon nanotube powder in anhydrous ethanol to the dispersant is (1-2):

1.

6. The surface treatment method according to claim 1, wherein: In step 4, the ratio of the suspension to the adhesive is 5:

2.

7. A connection structure for improving the bonding strength of a composite material-metal heterogeneous interface, characterized by: A first rib (1) and a second rib (2) are provided on the surface of the composite material structural part, and a first groove (3) and a second groove (4) are provided on the surface of the metal material structural part; or, a first groove (3) and a second groove (4) are provided on the surface of the composite material structural part, and a first rib (1) and a second rib (2) are provided on the surface of the metal material structural part; when the surface of the composite material structural part contacts the surface of the metal material structural part, the first rib (1) is matched and arranged inside the first groove (3), and the second rib (2) is matched and arranged inside the second groove (4), and the composite material structural part and the metal material structural part are bonded together and fixedly connected by bolts (7).

8. The connection structure according to claim 7, characterized in that: The heights of the first rib (1) and the second rib (2) are inconsistent, and the depths of the first groove (3) and the second groove (4) are inconsistent.

9. The connection structure according to claim 7, characterized in that: The height of the second rib (2) is half the height of the first rib (1), and the depth of the second groove (4) is half the depth of the first groove (3).

10. The connection structure according to claim 7, characterized in that: The first rib (1), the second rib (2), the first groove (3) and the second groove (4) are all annular, and the first rib (1) is located inside the second rib (2), and the first groove (3) is located inside the second groove (4).

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