Aluminum alloy / polyurethane bonded article, method of making and use thereof

Abstract

This invention belongs to the field of metal surface treatment and adhesive bonding technology, specifically relating to an aluminum alloy / polyurethane adhesive joint, its preparation method, and its application. The preparation method provided by this invention introduces hydration shaping, silane coupling activation, vacuum impregnation, and graded curing steps on top of anodizing, synergistically improving the wettability, mechanical interlocking, and chemical bonding ability of the aluminum alloy / polyurethane interface, reducing interfacial porosity and insufficiently wetted areas, thereby improving the mechanical strength, fracture energy dissipation, and environmental stability of the adhesive joint.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment and adhesive bonding technology, specifically relating to an aluminum alloy / polyurethane adhesive component, its preparation method, and its application. Background Technology

[0002] Aluminum alloys, due to their advantages such as low density, high specific strength, and good corrosion resistance, are widely used in the aerospace, automotive, shipbuilding, and equipment manufacturing industries. Polyurethane adhesives, with their advantages of good flexibility, impact resistance, high weather resistance, and strong interfacial stress buffering capacity, have broad application prospects in metal / polymer dissimilar joining and adhesive assembly of metal components.

[0003] However, untreated aluminum alloy surfaces typically have natural oxide films, oil stains, and low surface activity, resulting in poor interfacial wettability and insufficient mechanical interlocking between them and polyurethane. This makes the bonded joints prone to interfacial peeling and low-energy fracture.

[0004] Anodizing can construct micro- and nano-porous oxide layers on aluminum alloy surfaces, increasing the actual contact area and improving wettability. It is a low-cost and easily scalable surface treatment method. However, relying solely on the mechanical interlocking of porous oxide layers still suffers from insufficient interfacial chemical bonding, incomplete pore filling, and limited density of the cured structure.

[0005] In summary, in existing aluminum alloy / polyurethane bonding processes, under conventional application conditions, polyurethane adhesives are difficult to fully penetrate the oxide pores, and unwetted areas are easily left at the interface. At the same time, during the conventional curing process, solvent escape from the adhesive layer, exothermic reaction, and uneven release of interfacial stress can easily cause local under-curing or weak interfacial areas, which ultimately affect the joint strength and service stability. Summary of the Invention

[0006] The purpose of this invention is to provide an aluminum alloy / polyurethane adhesive joint, its preparation method, and its application. The preparation method provided by this invention can improve the mechanical strength, fracture energy dissipation, and environmental service stability of the adhesive joint, thereby obtaining an aluminum alloy / polyurethane adhesive joint with high interface strength, high fracture energy dissipation, and good hygrothermal stability.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing aluminum alloy / polyurethane adhesive parts, comprising the following steps: Anodizing is performed on the aluminum alloy substrate to form a micro-nano porous oxide layer on the surface of the aluminum alloy substrate, resulting in anodized aluminum alloy substrate. The anodized aluminum alloy substrate is subjected to a hydration and shaping treatment to obtain a hydration and shaping aluminum alloy substrate. The hydrated and shaped aluminum alloy substrate is contacted with a silane coupling agent solution to form a coupling activation layer on the surface of the hydrated and shaped aluminum alloy substrate, thereby obtaining a coupling activated aluminum alloy substrate. Polyurethane adhesive is applied to the surface of the coupled and activated aluminum alloy substrate, and then vacuum impregnation is performed to obtain the adhesive-coated aluminum alloy substrate. Two aluminum alloy substrates after adhesive application are overlapped to form an overlap joint. The overlap joint is then pre-cured and post-cured sequentially, with the post-curing temperature being higher than the pre-curing temperature, to obtain the aluminum alloy / polyurethane adhesive joint.

[0008] Preferably, the anodizing treatment uses a sulfuric acid electrolyte, wherein the concentration of H2SO4 in the sulfuric acid electrolyte is 0.2~1.5 mol / L; the conditions for the anodizing treatment include: anodizing current of 0.5~1.5 A and anodizing time of 5~45 min.

[0009] Preferably, the hydration and shaping treatment is carried out in hot water at a temperature of 70-100°C; and the hydration and shaping treatment takes 5-30 minutes.

[0010] Preferably, the silane coupling agent in the silane coupling agent solution includes one or two of aminosilane, epoxysilane, and isocyanate-based silane; the percentage content of the silane coupling agent in the silane coupling agent solution is 0.1~3 wt%; and the contact treatment time is 5~60 min.

[0011] Preferably, the aminosilane is 3-aminopropyltriethoxysilane; the epoxysilane is 3-glycidoxypropyltrimethoxysilane; and the isocyanate-based silane is 3-isocyanate-propyltriethoxysilane.

[0012] Preferably, the preparation method of the polyurethane adhesive includes the following steps: mixing polyethylene glycol, toluene diisocyanate and an organic solvent to react and obtain the polyurethane adhesive; wherein the number average molecular weight of the polyethylene glycol is 8000~12000, the organic solvent is toluene, the mass ratio of toluene diisocyanate to polyethylene glycol is 1:10~15, and the reaction temperature is 55~65 °C.

[0013] Preferably, the vacuum degree of the vacuum impregnation process is -0.02 to -0.09 MPa, and the processing time is 1 to 15 min.

[0014] Preferably, the overlap area of ​​the lap joint is 10×20 mm. 2 ~15×30 mm 2The pre-curing temperature is room temperature, and the time is 12~48 h; the post-curing temperature is 40~80 ℃, and the time is 1~8 h.

[0015] The present invention provides an aluminum alloy / polyurethane adhesive component prepared by the preparation method described in the above technical solution.

[0016] This invention provides the application of the aluminum alloy / polyurethane adhesive as described above in the adhesive bonding of engineering structures, including adhesive bonding of aerospace engineering structures, adhesive bonding of automotive engineering structures, or adhesive bonding of marine engineering structures.

[0017] This invention provides a method for preparing an aluminum alloy / polyurethane adhesive, comprising the following steps: anodizing an aluminum alloy substrate to form a micro-nano porous oxide layer on the surface of the aluminum alloy substrate, obtaining an anodized aluminum alloy substrate; hydrating and shaping the anodized aluminum alloy substrate to obtain a hydration-shaped aluminum alloy substrate; contacting the hydration-shaped aluminum alloy substrate with a silane coupling agent solution to form a coupling activation layer on the surface of the hydration-shaped aluminum alloy substrate, obtaining a coupling-activated aluminum alloy substrate; applying polyurethane adhesive to the surface of the coupling-activated aluminum alloy substrate, and then performing vacuum diffusion treatment to obtain an adhesive-coated aluminum alloy substrate; overlapping two adhesive-coated aluminum alloy substrates to form an overlap joint; and sequentially pre-curing and post-curing the overlap joint, wherein the post-curing temperature is higher than the pre-curing temperature, to obtain the aluminum alloy / polyurethane adhesive. The preparation method provided by this invention involves constructing a micro-nano porous oxide layer on the surface through anodic oxidation; subsequently, hydration and shaping treatment and silane coupling activation treatment are performed to obtain an interface layer with both pore structure and surface chemical activity; the coupled activated aluminum alloy substrate obtained by this invention has a micro-nano porous oxide layer and a coupling activation layer on its surface, and then a vacuum impregnation treatment is used to promote the penetration and filling of polyurethane adhesive into the oxide pores of the micro-nano porous oxide layer and form a composite interface with the coupling activation layer; finally, a graded curing method of pre-curing and post-curing is adopted to obtain an aluminum alloy / polyurethane adhesive with high interface strength, high fracture energy dissipation and good hygrothermal stability. Compared with the prior art, the present invention has the following beneficial effects: First, the anodic oxide layer provides a micro-nano porous structure and a high specific surface area, which is beneficial for the wetting and mechanical integration of polyurethane adhesive; Second, the silane coupling activation layer can establish a chemical bridge between the micro-nano porous oxide layer and the polyurethane adhesive layer, improving the interfacial bonding stability; Third, vacuum impregnation can reduce the proportion of residual gas and unwetted areas inside the pores, improving the integrity of pore filling; Fourth, staged curing is beneficial for relieving interfacial stress and improving curing uniformity, thereby improving adhesive strength and environmental service stability.

[0018] In summary, the preparation method provided by this invention introduces hydration shaping, silane coupling activation, vacuum impregnation and graded curing steps on the basis of anodic oxidation, which synergistically improves the wettability, mechanical interlocking and chemical bonding ability of the aluminum alloy / polyurethane interface, reduces interfacial porosity and insufficiently wetted areas, and thus improves the mechanical strength, fracture energy consumption and environmental stability of the adhesive joint. Detailed Implementation

[0019] This invention provides a method for preparing aluminum alloy / polyurethane adhesive parts, comprising the following steps: Anodizing is performed on the aluminum alloy substrate to form a micro-nano porous oxide layer on the surface of the aluminum alloy substrate, resulting in anodized aluminum alloy substrate. The anodized aluminum alloy substrate is subjected to a hydration and shaping treatment to obtain a hydration and shaping aluminum alloy substrate. The hydrated and shaped aluminum alloy substrate is contacted with a silane coupling agent solution to form a coupling activation layer on the surface of the hydrated and shaped aluminum alloy substrate, thereby obtaining a coupling activated aluminum alloy substrate. Polyurethane adhesive is applied to the surface of the coupled and activated aluminum alloy substrate, and then vacuum impregnation is performed to obtain the adhesive-coated aluminum alloy substrate. Two aluminum alloy substrates after adhesive application are overlapped to form an overlap joint. The overlap joint is then pre-cured and post-cured sequentially, with the post-curing temperature being higher than the pre-curing temperature, to obtain the aluminum alloy / polyurethane adhesive joint.

[0020] In this invention, unless otherwise specified, all raw materials / components used in preparation are commercially available products well-known to those skilled in the art. Unless otherwise specified, all percentages in this invention refer to mass percentages. Unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent; for example, sulfuric acid solution is an aqueous solution of sulfuric acid. Room temperature in this invention generally refers to a temperature between 15°C and 30°C, and is generally defined as 25°C.

[0021] The present invention performs anodizing treatment on an aluminum alloy substrate to form a micro-nano porous oxide layer on the surface of the aluminum alloy substrate, thereby obtaining anodized aluminum alloy substrate.

[0022] This invention does not have special requirements for the aluminum alloy substrate. In specific embodiments of this invention, the aluminum alloy substrate can be an Al2O24-T3 aluminum alloy sheet. In this invention, the thickness of the aluminum alloy substrate is preferably 0.1~1 mm, and in some embodiments it can be 0.5 mm.

[0023] In this invention, prior to the oxidation treatment, the aluminum alloy substrate is preferably pretreated. The pretreatment preferably includes sequentially performing degreasing, alkaline washing, a first water wash, acid pickling activation, and a second water wash on the aluminum alloy substrate. In this invention, the degreasing is performed using an organic solvent, such as ethanol. The degreasing time is preferably 5-10 minutes. The reagent used for the alkaline washing is preferably a NaOH solution. The percentage of NaOH in the NaOH solution is preferably 0.1-0.5 wt%, more preferably 0.2-0.4 wt%, and in the examples, it can be 0.2 wt% or 0.3 wt%. The alkaline washing time is preferably 1-5 minutes, and in the examples, it can be 2 minutes. The first water wash is preferably performed using deionized water. The reagent used for the acid pickling activation is preferably an HNO3 solution. The percentage of HNO3 in the HNO3 solution is preferably 0.5-2 wt%, more preferably 0.8-1.5 wt%, and in the examples, it can be 1.2 wt% or 1 wt%. The acid pickling activation time is preferably 0.5-2 minutes, and in the examples, it can be 1 minute. The second water wash is preferably performed using deionized water.

[0024] In this invention, the anodizing treatment is constant current anodizing, specifically sulfuric acid constant current anodizing in the embodiments. The anodizing treatment preferably uses a sulfuric acid electrolyte. The sulfuric acid electrolyte is a sulfuric acid solution. The concentration of H2SO4 in the sulfuric acid electrolyte is preferably 0.2~1.5 mol / L, more preferably 0.35~0.50 mol / L, and in the embodiments it can be 0.4144 mol / L or 0.50 mol / L. The anodizing conditions preferably include: an anodizing current preferably 0.5~1.5 A, more preferably 0.9~1.2 A, and in the embodiments it can be 1.0907 A or 1.20 A. The anodizing time is preferably 5~45 min, more preferably 4~8 min, and in the embodiments it can be 5.505 min or 8 min. After the anodizing treatment, the treated substrate is sequentially washed with water and dried to obtain the anodized aluminum alloy substrate. The washing is preferably done with deionized water. The drying is carried out at room temperature.

[0025] After obtaining the anodized aluminum alloy substrate, the present invention performs a hydration and shaping treatment on the anodized aluminum alloy substrate to obtain a hydration and shaping aluminum alloy substrate.

[0026] In this invention, the hydration and shaping treatment is preferably carried out in hot water. The temperature of the hot water is preferably 70~100℃, more preferably 80~95℃, and in the embodiments it can be 90℃ or 80℃. The hot water is deionized water. The time of the hydration and shaping treatment is preferably 5~30 min, more preferably 10~20 min, and in the embodiments it can be 5 min, 10 min, 20 min or 15 min.

[0027] After obtaining the hydrated and shaped aluminum alloy substrate, the present invention contacts the hydrated and shaped aluminum alloy substrate with a silane coupling agent solution to form a coupling activation layer on the surface of the hydrated and shaped aluminum alloy substrate, thereby obtaining a coupling activated aluminum alloy substrate.

[0028] In this invention, the silane coupling agent in the silane coupling agent solution preferably includes one or two of aminosilane, epoxysilane, and isocyanate-based silane. The aminosilane can be 3-aminopropyltriethoxysilane (APTES). The epoxysilane is 3-glycidoxypropyltrimethoxysilane. The isocyanate-based silane is preferably 3-isocyanate-propyltriethoxysilane. The percentage content of the silane coupling agent in the silane coupling agent solution is preferably 0.1~3 wt%, more preferably 0.5~2 wt%, and in the examples, it can be 0.1, 0.5, 1, 1.5, 2, 2.5, or 3 wt%. When the silane coupling agent is preferably any two of the above substances, the mass ratio of any two silane coupling agents can be 1:1. The solvent in the silane coupling agent solution is preferably a mixed solution of ethanol and water, and the volume content of ethanol in the mixed solution of ethanol and water is preferably 90~99%, and in the examples, it can be 95%. The contact treatment preferably involves immersing the hydrated and shaped aluminum alloy substrate in the silane coupling agent solution for silane coupling agent activation. The contact treatment time is preferably 5-60 min, more preferably 10-30 min, and in the embodiments, it can be 5, 10, 15, 20, 25, or 30 min. After the contact treatment, the obtained treated substrate is preferably dried to obtain the coupled and activated aluminum alloy substrate. The drying temperature is preferably 80-85 °C, and the drying time is preferably 5-10 min.

[0029] After obtaining the coupled and activated aluminum alloy substrate, the present invention applies polyurethane adhesive to the surface of the coupled and activated aluminum alloy substrate, and then performs vacuum impregnation treatment to obtain the adhesive-coated aluminum alloy substrate.

[0030] In this invention, the preparation method of the polyurethane adhesive preferably includes the following steps: mixing polyethylene glycol (PEG), toluene diisocyanate (TDI), and an organic solvent to react and obtain the polyurethane adhesive. In this invention, the mixing preferably includes: dissolving the polyethylene glycol in an organic solvent, then adding the toluene diisocyanate under heating and stirring conditions, and continuing stirring and mixing to obtain the polyurethane adhesive. The number average molecular weight of the polyethylene glycol is preferably 8000-12000. The organic solvent is preferably toluene. The mass ratio of the toluene diisocyanate to polyethylene glycol is preferably 1:10-15. This invention does not have special requirements for the amount of organic solvent used, as long as the reaction proceeds smoothly. The stirring can be magnetic stirring, and the heating temperature is preferably 55-65 °C, and in the examples, it can be 60 °C. The reaction is carried out under stirring conditions. The reaction temperature is preferably 55-65 °C, and in the examples, it can be 60 °C. The reaction is carried out under stirring conditions, and the stirring time is preferably 30-120 min, more preferably 45-90 min, and more preferably 60 min, in order to obtain a polyurethane adhesive that can be uniformly applied.

[0031] In this invention, the preferred application amount of the polyurethane adhesive is 0.02~0.03 g / cm³. 2 In the examples, the value can be 0.028 g / cm³. 2 The vacuum degree of the vacuum impregnation process is preferably -0.02 to -0.09 MPa, more preferably -0.03 to -0.06 MPa, and in the embodiment, it can be -0.04 MPa. The processing time of the vacuum impregnation process is preferably 1 to 15 min, more preferably 5 to 10 min.

[0032] In this invention, the surface of the aluminum alloy substrate after adhesive application has a micro-nano porous oxide layer and a coupling activation layer. The polyurethane adhesive fills the pores of the micro-nano porous oxide layer and forms a composite interface with the coupling activation layer.

[0033] After obtaining the coated aluminum alloy substrate, the present invention overlaps two coated aluminum alloy substrates to form an overlap joint. The overlap joint is then subjected to pre-curing and post-curing in sequence. The post-curing temperature is higher than the pre-curing temperature to obtain the aluminum alloy / polyurethane adhesive joint.

[0034] In this invention, the overlap area of ​​the lap joint is preferably 10 × 20 mm. 2 ~15×30 mm 2 In the embodiment, it can be 12.5 × 25 mm. 2The pre-curing temperature is preferably room temperature, and the curing time is preferably 12-48 hours, with 36 hours in the embodiment. The post-curing temperature is preferably ≤80℃, preferably 40-80℃, and more preferably 50-70℃. In the embodiment, it can be 50℃, 60℃, or 70℃. The post-curing time is preferably 1-8 hours, more preferably 2-6 hours, with 2 hours, 4 hours, or 1 hour in the embodiment.

[0035] In summary, this invention constructs a micro-nano porous oxide layer on the surface of an aluminum alloy substrate by constant current anodizing with sulfuric acid after ethanol degreasing, NaOH alkaline washing, and HNO3 activation. Subsequently, hot water hydration and silane coupling activation are performed to obtain an interface layer with both pore structure and surface chemical activity. Then, a polyurethane adhesive is prepared using a PEG / TDI system, and vacuum impregnation is used to promote the adhesive's penetration into the oxide pores. A staged curing method of room temperature pre-curing followed by low temperature post-curing is adopted to finally obtain an aluminum alloy / polyurethane bond with high interfacial strength, high fracture energy dissipation, and good hygrothermal stability.

[0036] This invention provides an aluminum alloy / polyurethane adhesive component prepared by the preparation method described above. In this invention, the aluminum alloy surface of the aluminum alloy / polyurethane adhesive component has a micro-nano porous oxide layer and a coupling activation layer, and the polyurethane adhesive fills the pores of the micro-nano porous oxide layer and forms a composite interface with the coupling activation layer.

[0037] This invention provides the application of the aluminum alloy / polyurethane adhesive components described above in adhesive bonding of engineering structures. The adhesive bonding of engineering structures can include aerospace engineering structure bonding, automotive engineering structure bonding, marine engineering structure bonding, or general engineering structure bonding.

[0038] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1 A 0.5 mm thick Al2024-T3 aluminum alloy sheet was used as the substrate and cut into 100 mm × 25 mm samples. The surface of the aluminum alloy sheet was first degreased with anhydrous ethanol for 5 min.

[0040] The aluminum alloy sheet was then placed in a 0.2 wt% NaOH solution for 2 min, rinsed with deionized water, activated in a 1 wt% HNO3 solution for 1 min, and then rinsed with deionized water again.

[0041] The treated aluminum alloy sheet was placed in a sulfuric acid electrolyte solution for constant current anodizing. The concentration of the sulfuric acid electrolyte solution was 0.4144 mol / L, the current was 1.0907 A, and the treatment time was 5.505 min. After treatment, it was thoroughly rinsed with deionized water and dried at room temperature.

[0042] The anodized aluminum alloy sheet was placed in deionized water at 90 °C for 10 min to hydrate and shape the oxide layer. Then, the sheet was immersed in a 1 wt% ethanol / water mixed solution of 3-aminopropyltriethoxysilane (95% ethanol) for 20 min, and then dried at 80 °C for 10 min to obtain the coupled activated aluminum alloy substrate.

[0043] The polyurethane adhesive was prepared as follows: Polyethylene glycol (PEG) (number average molecular weight 10000) was added to 10 mL of toluene and magnetically stirred at 60°C until completely dissolved; then toluene diisocyanate (TDI) was added, with a TDI to PEG mass ratio of 1:10, and the mixture was stirred continuously at 60°C for 60 min. A uniformly applied polyurethane adhesive was obtained.

[0044] The polyurethane adhesive obtained above was applied to the surfaces of two aluminum alloy plates activated by the silane coupling agent, with a coating amount of 0.028 g / cm³. 2 Vacuum impregnation was performed at -0.06 MPa for 5 min, resulting in an overlap area of ​​12.5 × 25 mm. 2 The lap joints were prepared. The assembled samples were pre-cured at room temperature for 24 h, then cured at 60°C for 2 h, and then naturally cooled to room temperature to obtain aluminum alloy / polyurethane adhesive joints.

[0045] Example 2 The preparation method is basically the same as that in Example 1, except that the concentration of sulfuric acid electrolyte in the constant current anodizing step is 0.50 mol / L, the anodizing current is 1.20 A, and the treatment time is 8 min.

[0046] The silane coupling agent was replaced with a 1 wt% epoxy silane solution (3-glycidyl etheroxypropyltrimethoxysilane solution), and the treatment time was 30 min; the vacuum degree of vacuum impregnation was -0.08 MPa, and the treatment time was 8 min; the assembled sample was first pre-cured at room temperature for 24 h, and then cured at 50℃ for 4 h to obtain aluminum alloy / polyurethane adhesive parts.

[0047] Example 3 The preparation method is basically the same as that in Example 1, except that: the hydration and setting temperature is 80℃ and the time is 20 min; the coupling activation uses a complex solution of aminosilane (3-aminopropyltriethoxysilane) and epoxysilane (3-glycidoxypropyltrimethoxysilane), wherein the content of 3-aminopropyltriethoxysilane is 0.5 wt% and the content of 3-glycidoxypropyltrimethoxysilane is 0.5 wt%, and the treatment time is 25 min.

[0048] The vacuum degree of the vacuum impregnation was -0.04 MPa, and the processing time was 10 min. The assembled sample was first pre-cured at room temperature for 36 h, and then cured at 70℃ for 1 h to obtain aluminum alloy / polyurethane adhesive parts.

[0049] Comparative Example 1 The preparation method is basically the same as in Example 1, except that: the anodized aluminum alloy sheet is placed in deionized water at 90 °C for 10 min to hydrate and set the oxide layer. The polyurethane adhesive is applied to the surfaces of the two aluminum alloy sheets after the oxide layer hydration and setting treatment, i.e., no coupling activation treatment is performed after anodizing, and the remaining steps are the same as in Example 1. In the resulting bonded parts, although the wetting of the porous oxide layer by the polyurethane adhesive is improved, the interface mainly relies on mechanical interlocking, and the chemical bridging effect is insufficient.

[0050] Comparative Example 2 The preparation method is basically the same as in Example 1, except that: the polyurethane adhesive is applied to the surfaces of two aluminum alloy plates activated by the silane coupling agent, without vacuum impregnation, and the plates are left to stand for 5 minutes under normal pressure after application. The remaining steps are the same as in Example 1. In the resulting bonded parts, the polyurethane fills the oxide pores to a lower degree than in Example 1, and there are often unwetted areas remaining at the interface.

[0051] Comparative Example 3 The preparation method is basically the same as that in Example 1, except that: the polyurethane adhesive is applied to the surface of two aluminum alloy plates after activation treatment with the silane coupling agent, and vacuum impregnation is performed for 5 minutes under -0.06 MPa conditions, thus forming an overlap area of ​​12.5 × 25 mm. 2 The lap joints were constructed. The assembled samples were not pre-cured at room temperature but directly placed in a 60°C oven for continuous curing for 2 hours, followed by natural cooling to room temperature. The remaining steps were the same as in Example 1. In the resulting adhesive joints, the adhesive layer cured rapidly, resulting in insufficient release of interfacial stress and a tendency for uneven curing or micro-defects to form in localized areas.

[0052] The strength of the bonded joint was evaluated using a single lap shear test with an lap area of ​​12.5 × 25 mm. 2The testing speed was 2 mm / min. Contact angle testing was used to evaluate changes in the wettability of the aluminum alloy surface, using 5 μL of deionized water as the test solution. A damp heat aging test was used to evaluate the environmental stability of the bonded parts, with aging conditions of 85℃ / 85%RH and an aging time of 168 h.

[0053] Table 1 Key process conditions for the examples and comparative examples

[0054] Table 2 Reference performance data and fracture modes

[0055] As shown in Table 2, the initial single lap shear strength of Examples 1 to 3 is significantly higher than that of the comparative examples. The initial single lap shear strength of Example 1 reaches 11.20 MPa, which is about 30.1%, 24.2% and 28.1% higher than that of Comparative Examples 1, 2 and 3, respectively.

[0056] The water contact angles of Examples 1-3 were significantly lower than those of the comparative examples, indicating that the present invention, through anodizing, hydration shaping and coupling activation treatment, can significantly improve the wettability of aluminum alloy surfaces, providing more favorable conditions for the spread and wetting of polyurethane adhesives at the interface.

[0057] Examples 1-3 all showed a strength retention rate of over 83% after damp heat aging, while the strength retention rate of each comparative example was less than 77%, indicating that the "micro-nano porous oxide layer + coupling activation layer + vacuum impregnation filling + graded curing dense interface" formed by the present invention has better environmental stability.

[0058] From the perspective of fracture morphology, Examples 1 and 2 mainly exhibit cohesive fracture or mixed fracture dominated by cohesive fracture, indicating that the interfacial bonding strength has approached or exceeded the strength of the polyurethane adhesive layer itself; while Comparative Example 1 mainly exhibits interfacial fracture or mixed fracture dominated by the interface, indicating that the interface is still a weak link when coupling activation is lacking.

[0059] In summary, the present invention, through a synergistic process of anodizing, coupling activation, vacuum impregnation, and graded curing, can significantly improve the wettability, interfacial bonding strength, and stability under humid and hot conditions of the aluminum alloy / polyurethane adhesive interface, and has good engineering application value.

[0060] As can be seen from the above embodiments, the preparation method of the aluminum alloy / polyurethane adhesive provided by the present invention is specifically an anodizing-coupling activation-vacuum impregnation preparation method for improving the interfacial strength of aluminum alloy / polyurethane adhesive. The preparation method provided by the present invention includes the following steps: degreasing, alkaline washing and acid washing activation of the aluminum alloy substrate; placing the pretreated aluminum alloy substrate in sulfuric acid electrolyte for constant current anodizing to construct a micro-nano porous oxide layer on the aluminum alloy surface; hot water hydration and silane coupling activation of the anodized aluminum alloy substrate; preparing a polyurethane adhesive using polyethylene glycol and toluene diisocyanate as raw materials; applying the polyurethane adhesive to the treated aluminum alloy surface, performing low negative pressure vacuum impregnation followed by overlapping assembly, and then pre-curing at room temperature and post-curing at low temperature to obtain the aluminum alloy / polyurethane adhesive. This invention significantly improves the wettability, mechanical interlocking, and chemical bonding ability of the aluminum alloy / polyurethane interface through the synergistic effect of micro-nano porous oxide layer construction, coupling activation, vacuum impregnation, and graded curing, thereby enhancing the interfacial strength, fracture energy dissipation, and service stability of the bonded joint.

[0061] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing an aluminum alloy / polyurethane adhesive component, characterized in that, Includes the following steps: Anodizing is performed on the aluminum alloy substrate to form a micro-nano porous oxide layer on the surface of the aluminum alloy substrate, resulting in anodized aluminum alloy substrate. The anodized aluminum alloy substrate is subjected to a hydration and shaping treatment to obtain a hydration and shaping aluminum alloy substrate. The hydrated and shaped aluminum alloy substrate is contacted with a silane coupling agent solution to form a coupling activation layer on the surface of the hydrated and shaped aluminum alloy substrate, thereby obtaining a coupling activated aluminum alloy substrate. Polyurethane adhesive is applied to the surface of the coupled and activated aluminum alloy substrate, and then vacuum impregnation is performed to obtain the adhesive-coated aluminum alloy substrate. Two aluminum alloy substrates after adhesive application are overlapped to form an overlap joint. The overlap joint is then pre-cured and post-cured sequentially, with the post-curing temperature being higher than the pre-curing temperature, to obtain the aluminum alloy / polyurethane adhesive joint.

2. The preparation method according to claim 1, characterized in that, The anodizing treatment uses a sulfuric acid electrolyte with a H2SO4 concentration of 0.2–1.5 mol / L. The anodizing conditions include an anodizing current of 0.5–1.5 A and anodizing time of 5–45 min.

3. The preparation method according to claim 1 or 2, characterized in that, The hydration and shaping treatment is carried out in hot water at a temperature of 70-100 ℃; the hydration and shaping treatment time is 5-30 min.

4. The preparation method according to claim 1, characterized in that, The silane coupling agent in the silane coupling agent solution includes one or two of aminosilane, epoxysilane, and isocyanate-based silane; the percentage content of the silane coupling agent in the silane coupling agent solution is 0.1~3 wt%; and the contact treatment time is 5~60 min.

5. The preparation method according to claim 4, characterized in that, The aminosilane is 3-aminopropyltriethoxysilane; the epoxysilane is 3-glycidoxypropyltrimethoxysilane; and the isocyanate-based silane is 3-isocyanate-propyltriethoxysilane.

6. The preparation method according to claim 1, characterized in that, The preparation method of the polyurethane adhesive includes the following steps: mixing polyethylene glycol, toluene diisocyanate and an organic solvent to react and obtain the polyurethane adhesive; the number average molecular weight of the polyethylene glycol is 8000~12000, the organic solvent is toluene, the mass ratio of toluene diisocyanate to polyethylene glycol is 1:10~15, and the reaction temperature is 55~65 ℃.

7. The preparation method according to claim 1 or 6, characterized in that, The vacuum degree of the vacuum impregnation process is -0.02 to -0.09 MPa, and the processing time is 1 to 15 min.

8. The preparation method according to claim 1, characterized in that, The overlap area of ​​the lap joint is 10×20mm. 2 ~15×30 mm 2 The pre-curing temperature is room temperature, and the time is 12~48 h; the post-curing temperature is 40~80℃, and the time is 1~8 h.

9. The aluminum alloy / polyurethane adhesive obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the aluminum alloy / polyurethane adhesive as described in claim 9 in adhesive bonding of engineering structures, wherein the adhesive bonding of engineering structures includes adhesive bonding of aerospace engineering structures, adhesive bonding of automotive engineering structures, or adhesive bonding of marine engineering structures.

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