Surface-treated aluminum material and joined body

Abstract

Provided are: a surface-treated aluminum material that is suitably used for adhesive bonding and can further improve adhesion durability with respect to other members or the like; and a joined body containing the surface-treated aluminum material. The surface-treated aluminum material has a silane film provided on at least a portion of the surface of an aluminum base material, wherein, when an element distribution is measured by glow discharge emission spectroscopy with respect to a region R1 on the outermost surface and a region R2 at a depth of 10 nm from the region R1 in the region where the silane film is provided, the atomic concentration of silicon in the region R1 is 3.0-30.0 at%. In addition, a reduction rate M of the silicon concentration is 45% or greater, as calculated by equation (1) on the basis of an atomic concentration A1 of silicon in the region R1 and an atomic concentration A2 of silicon in the region R2. (1): M=((A1-A2) / A1)×(100)

Description

Surface-treated aluminum material and joined body

[0001] The present invention relates to a surface-treated aluminum material and a joined body including the surface-treated aluminum material.

[0002] In the field of transportation equipment such as automobiles, ships, and aircraft, from the viewpoint of weight reduction, adhesive bonding is used as a joining technique between different materials such as steel materials and lightweight materials (aluminum alloys, titanium alloys, carbon fibers, etc.). Also, in response to on-site issues such as a shortage of successors to welding workers, technology transfer, and improvement of the working environment, adhesive bonding has attracted attention as an alternative to welding from the viewpoint of improving productivity and workability.

[0003] On the other hand, adhesive bonding has problems with strength reliability during long-term use. In an environment where stresses such as high temperature, high humidity, fatigue, or creep act in combination, it is known that strength reduction is likely to occur compared to welding or bolt tightening. In adhesive bonding, the adhesion between the adhesive and the adherent metal is important. If the adhesion between the metal material surface and the adhesive is insufficient, water penetrates into the interface between the metal and the resin. As a result, corrosion of the metal surface progresses, peeling occurs from the interface between the two, and the adhesive strength is significantly reduced. Therefore, it is necessary to prevent water from penetrating into the adhesive interface by enhancing the adhesion between the metal and the adhesive resin, and to modify the surface of the metal material so that the metal surface does not easily change its state even if water penetrates, and to adjust it to a surface state suitable for adhesion.

[0004] To solve the above problems, various surface treatment technologies have been proposed conventionally. For example, Patent Document 1 discloses an aqueous composition containing a tetraalkyl silicate or its monomeric or oligomeric hydrolysis product and a hydrated oxide sol such as silica sol. By treating metal materials such as aluminum materials, steel materials, and titanium materials with the above aqueous composition, the initial adhesion and long-term stability of adhesion of a coating film such as an adhesive formed thereon can be improved.

[0005] Japanese Patent Publication No. 10-510307

[0006] However, even when using the surface treatment technology described in Patent Document 1, long-term wet degradation tests result in a significant decrease in adhesive strength with resins such as adhesives. Therefore, the required adhesive durability cannot be obtained at the adhesive joint.

[0007] The present invention has been made in view of the above problems, and aims to provide a surface-treated aluminum material that has excellent adhesive strength with resins such as adhesives, and can further improve the adhesive durability with resins, and a joint including this surface-treated aluminum material.

[0008] The above objective of the present invention is achieved by the following configuration [1] relating to the surface-treated aluminum material.

[0009] [1] A surface-treated aluminum material having a silane film provided on at least a portion of the surface of an aluminum substrate, wherein, when the elemental distribution is measured by glow discharge emission spectroscopy in the outermost region R1 and region R2 at a depth of 10 nm from region R1, the atomic concentration of silicon in region R1 is 3.0 atomic% or more and 30.0 atomic% or less, and the rate of decrease M of silicon concentration, calculated by the following formula (1) based on the atomic concentration of silicon in region R1 A1 and the atomic concentration of silicon in region R2 A2, is 45% or more.

[0010] Furthermore, a preferred embodiment of the present invention relating to surface-treated aluminum material is described in [2] below.

[0011] [2] The surface-treated aluminum material according to [1], having an adhesive resin layer on the surface of the silane film.

[0012] The above objective of the present invention is achieved by the configuration of the joint described in [3] below.

[0013] [3] A joint comprising the surface-treated aluminum material described in [1] or [2], wherein a first member and a second member are joined via an adhesive resin layer, at least one of the first member and the second member is the surface-treated aluminum material, and the silane film of the surface-treated aluminum material and the adhesive resin layer are bonded together.

[0014] According to the present invention, it is possible to provide a surface-treated aluminum material that has excellent adhesive strength with resins such as adhesives, and can further improve the adhesive durability with resins, as well as a joined body containing this surface-treated aluminum material.

[0015] Figure 1 is a graph showing the silicon concentration distribution for Invention Examples No. 1-2 and Comparative Examples No. 1-3, with the vertical axis representing the atomic concentration of silicon and the horizontal axis representing the measurement depth. Figure 2 is a graph showing the silicon concentration distribution for Invention Example No. 3 and Comparative Examples No. 4-5, with the vertical axis representing the atomic concentration of silicon and the horizontal axis representing the measurement depth. Figure 3A is a side view showing the shape of the bonded test specimen. Figure 3B is a top view showing the shape of the bonded test specimen.

[0016] The inventors of the present invention have diligently researched aluminum materials that can improve adhesive strength and durability with resins. As a result, they have found that the above problems can be solved by appropriately controlling the proportion of silicon on the surface of an aluminum material having a silane film on the surface of the aluminum substrate. The surface-treated aluminum material according to an embodiment of the present invention will be described in detail below.

[0017] [Surface-treated aluminum material] The surface-treated aluminum material according to this embodiment has a silane film formed on at least a portion of the surface of the substrate. The substrate and the silane film will be described in more detail below.

[0018] <Base Material> An aluminum base material is used as the base material. In this specification, the term "aluminum base material" includes base materials made of pure aluminum and base materials made of aluminum alloys. As aluminum alloys, known alloys such as Al-Mg alloys, Al-Mg-Si alloys, Al-Zn-Mg alloys, Al-Si alloys, and Al-Cu alloys can be used. In this specification, both cases in which a base material made of pure aluminum is used and cases in which a base material made of aluminum alloy is used are referred to as surface-treated aluminum materials.

[0019] <Silane coating> The silane coating is provided on at least a portion of the surface of the above-mentioned substrate, and specifically, it is a surface treatment coating containing an organic silane compound. The silane coating containing the silane compound has excellent bonding properties with adhesives and excellent corrosion resistance, so the presence of the silane coating allows for excellent adhesive strength to be maintained when bonding with other components.

[0020] A silane film can be formed, for example, by applying an aqueous solution containing silicon oxide to the surface of a substrate. Silicon oxide is activated by aqueous solution and can self-polymerize through a sol-gel reaction. Furthermore, aluminum substrates have a naturally occurring oxide film. Therefore, by applying an aqueous silicon oxide solution to the oxide film on the substrate surface, the aluminum oxide film and silicon oxide react, and silicon oxide also polymerizes with each other. As a result, a silane film with excellent bonding strength to the substrate can be formed in a desired area on the substrate surface.

[0021] Furthermore, the silane coating exhibits high mutual solubility with machine oils such as machining oils and press oils, as well as organic compounds such as adhesives, resulting in excellent bonding properties with adhesives. In addition, the silane coating can mitigate the effects of machine oils such as machining oils and press oils, thus preventing a decrease in adhesive durability due to oiling and achieving excellent corrosion resistance.

[0022] In this embodiment, the silicon concentration on the surface is defined as an indicator of whether a silane film capable of fully exhibiting the above-mentioned effects has been formed. That is, the elemental composition of any region R1 on the outermost surface of the region where the silane film is provided must contain a certain amount of silicon and oxygen atoms.

[0023] (Atomic concentration of silicon in region R1: 3.0 atomic% or more and 30.0 atomic% or less) Here, region R1 is entirely covered with a silane film, and this silane film is entirely SiO ２ In this case, the composition of region R1 is SiO ２ Therefore, theoretically, the maximum atomic concentration of silicon in the elements constituting region R1 is the number of Si atoms / (number of Si atoms + number of O atoms) = 1 / (1 + 2) = 0.33. For example, if the concentration of silane compounds in the metal treatment solution becomes high, the silane compounds will react with each other, and the atomic concentration of silicon A1 in region R1 will be higher than the theoretical maximum value mentioned above. However, even if the atomic concentration of silicon A1 becomes higher than this, it does not contribute to adhesive durability, so in this embodiment, the upper limit of the atomic concentration of silicon A1 is set based on the above maximum value. However, since the above maximum value is a theoretical value, in reality, the film also contains some base metal elements. Therefore, considering the influence of the base metal, the upper limit of the atomic concentration of silicon in region R1 will be less than 33 atomic percent. Thus, in this embodiment, the atomic concentration of silicon in region R1 is preferably 30.0 atomic percent or less, preferably 25.0 atomic percent or less, and more preferably 20.0 atomic percent or less.

[0024] On the other hand, the minimum silicon concentration required to improve adhesive durability is, for example, about 1 / 10 of the above upper limit. Specifically, if the atomic concentration of silicon in the outermost surface region R1 is less than 3.0 atomic%, the desired silane film may not be formed, and sufficient adhesive durability cannot be obtained. Therefore, the atomic concentration of silicon in region R1 should be 3.0 atomic% or more, preferably 8.0 atomic% or more, and more preferably 10.0 atomic% or more.

[0025] In this embodiment, the atomic concentration of silicon is a value obtained by measuring the elemental distribution using glow discharge optical emission spectroscopy (GD-OES). GD-OES allows for the measurement of elemental distribution in the depth direction over a predetermined region. The elements to be measured are based on the elements that make up aluminum and aluminum alloys, and include silicon and oxygen, which are the main components of the film, aluminum, which is the main component of the substrate, and iron, copper, manganese, magnesium, chromium, zinc, titanium, nickel, etc., which are alloy components. Hydrogen, carbon, nitrogen, etc., which are included as organic contaminants, are not included in the calculation as denominators for calculating the atomic concentration of silicon.

[0026] (Decrease in silicon atomic concentration: 45% or more) In elemental analysis in the depth direction by GD-OES, the decrease in silicon in the depth direction indicates that the silicon concentration on the surface is higher than that of the base material, meaning that a silane film is formed in the outermost surface region R1. If the thickness of the silane film is too thin, the effect of improving adhesive durability cannot be obtained, but if the thickness of the silane film is too thick, the film becomes brittle, leading to a decrease in adhesive strength. Therefore, in this embodiment, the thickness of the silane film is defined by the atomic concentration of silicon in the depth direction.

[0027] If a silane film is formed in favorable conditions on the outermost surface region R1, the silicon content will be highest at the outermost surface and will decrease as the measurement depth increases. If the silane film is too thick, the silicon content will not decrease even at deeper measurement depths, resulting in a high value.

[0028] Typically, the thickness of the oxide film on a metal is about 5 nm, and a silane film is formed on top of it. Therefore, when analyzing the elemental distribution in the depth direction, it is desirable to measure the atomic concentration of silicon at a depth that is the thickness of the oxide film plus the thickness of the silane film that is formed (5 nm). However, if the thickness of the silane film is too thick, the thickness will be unevenly distributed, and accurate depth information will not be reflected. For this reason, the atomic concentration of silicon A2 is measured at a depth of about twice the thickness of the oxide film (10 nm) from the outermost surface, and the determination is made based on the rate of decrease from the atomic concentration of silicon A1 at the outermost surface.

[0029] In a surface-treated aluminum material, if the atomic concentration of silicon in the outermost region R1, where a silane film is formed, is denoted as A1, and the atomic concentration of silicon in region R2, located 10 nm deep from region R1, is denoted as A2, then the rate of decrease in silicon concentration M can be calculated using the following formula (1): M = ((A1 - A2) / A1) × 100 ... (1)

[0030] If the silicon concentration reduction rate M calculated by the above formula (1) is less than 45%, it can be determined that the silane coating is too thick and a brittle coating has been formed. Therefore, the silicon concentration reduction rate M should be 45% or more, and preferably 50% or more.

[0031] As described above, the surface-treated aluminum material according to this embodiment has a silane film provided on at least a portion of the surface of the aluminum substrate, which defines the atomic concentration of silicon in the surface region and the rate of decrease in the atomic concentration of silicon at a predetermined depth. Therefore, it has a silane film with excellent bonding properties and durability with adhesives, and can improve adhesive bonding with similar surface-treated aluminum materials and other components.

[0032] (Adhesive Resin Layer) The surface-treated aluminum material according to this embodiment may further have an adhesive resin layer on the surface of the silane film. As described above, by having an adhesive resin layer on the surface of the silane film, which has excellent bonding properties and durability with adhesives, the process of bonding the surface-treated aluminum material according to this embodiment to a similar surface-treated aluminum material or other components can be simplified.

[0033] The method for forming an adhesive resin layer on at least a portion of the surface of the silane film is not particularly limited, but for example, an adhesive sheet made in advance from an adhesive resin material may be attached to the surface of the silane film, or the adhesive resin material may be sprayed or coated onto the surface of the silane film.

[0034] In the present invention, the resin constituting the adhesive resin layer is not particularly limited, and adhesive resins that have been conventionally used when joining aluminum materials, such as epoxy resins, urethane resins, nitrile resins, nylon resins, and acrylic resins, can be used. Furthermore, the thickness of the adhesive resin layer is not particularly limited, but from the viewpoint of improving adhesive strength, it is preferably 10 to 500 μm, and more preferably 50 to 400 μm.

[0035] [Method for Manufacturing Surface-Treated Aluminum Material] The surface-treated aluminum material according to the above embodiment can be manufactured, for example, as follows. First, before applying the metal treatment solution to the surface of the substrate, the surface of the substrate is pre-treated by known methods such as etching or blasting. Etching methods include treatment with an acidic solution (acid pickling) and treatment with an alkaline solution (alkaline cleaning, alkaline degreasing).

[0036] Pretreatment such as etching or blasting cleans the surface of the substrate from contamination, making it easier for a silane film to form. Examples of blasting treatments include wet blasting and dry blasting, but the method of blasting is not particularly limited in this invention. However, when wet blasting is used, the rate of decrease M of silicon concentration tends to be higher. This is thought to be because, compared to wet blasting, dry blasting allows blast particles to penetrate the substrate surface more easily, and the metal treatment solution penetrates more easily between the embedded blast particles and the substrate surface. As a result, when dry blasting is used, it is thought that the silicon derived from the metal treatment solution influences the detection of a higher atomic concentration A2 of silicon in region R2. Therefore, from the viewpoint of adhesive durability, it is more preferable to apply wet blasting to the surface of the substrate as a pretreatment.

[0037] Next, a metal treatment solution is applied to the area of ​​the substrate where the silane film is to be formed. As the metal treatment solution, an aqueous solution containing a silane compound can be used. The method of applying the metal treatment solution to the substrate is not particularly limited; it is sufficient to apply it so that the main component, which is mainly a silane compound, is present on the surface of the substrate. Examples include spraying, showering, roll coating, brushing, and immersion treatment.

[0038] Subsequently, the solvent is evaporated from the metal treatment solution applied to the surface of the substrate to dry the substrate surface and promote the reaction between the silane compound and the oxide film, as well as the polymerization of the silane compounds. By blowing away excess liquid with air during drying, the thickness of the silane film can be controlled so that the silicon concentration reduction rate M falls within an optimal range. The drying temperature is not particularly limited, but for example, 50 to 100°C is preferable as it provides a good balance between productivity and energy consumption. In order to improve the integrity of the silane film and maximize the adhesion effect between the substrate and the silane film, the steps of applying the metal treatment solution to the surface of the substrate and drying the surface of the substrate may be repeated two to three times.

[0039] (Solution for metal treatment) Any solution containing a silane compound can be used as the solution for metal treatment. For example, a solvent containing 50 to 99.99% by mass of water and 0 to 50% by mass of an organic solvent can be used. It is more preferable that the mass of water relative to the total mass of the solution be 50 to 99.95% by mass. Furthermore, from the viewpoint of reducing volatile organic compounds (VOCs) and lowering the risk of explosion, it is preferable that the main component of the solvent be water.

[0040] When using organic solvents, various water-soluble solvents can be used, such as various alcohols and polyethers, including methanol, ethanol, propyl alcohol, and butanol (including isomers), glycol-based solvents, and their ethers.

[0041] Specifically, the metal treatment solution can be one containing 0.005% to 0.3% by mass of an alkyl silicate or its oligomer and 0.005% to 0.3% by mass of an organic silane compound, with a pH of 2 to 7. When the above metal treatment solution is applied to at least a portion of the surface of the substrate, the alkyl silicate or its oligomer is introduced to the surface of the substrate, forming a composite oxide film of aluminum and silicon. In the subsequent drying process, the organic silane compound and the composite oxide film are chemically bonded, forming a silane film made of the organic silane compound. The surface-treated aluminum material obtained in this way has excellent bonding properties with adhesives, excellent corrosion resistance, and its adhesive strength does not easily decrease even when exposed to high-temperature and humid environments, resulting in excellent adhesive durability. Furthermore, by using the above metal treatment solution, surface treatment with alkyl silicate or its oligomer and surface treatment with the organic silane compound can be performed in a single step, making it possible to manufacture a surface-treated metal material with excellent adhesive durability in a simplified process, thereby reducing equipment investment costs and manufacturing costs.

[0042] The pH of the metal treatment solution is preferably 2 or more and 7 or less. If the pH of the metal treatment solution is higher than 7, alkyl silicate or its oligomer is likely to polymerize excessively, and the storage stability of the solution may decrease, which is not preferable. Further, when the polymerization of alkyl silicate or its oligomer proceeds, the formed film becomes thick, and when stress is applied, breakage occurs inside the silane film, and high adhesive strength cannot be obtained. On the other hand, if the pH of the metal treatment solution is lower than 2, the dissolution of the surface of the base material becomes intense, and the film becomes non-uniform, so it becomes difficult to exhibit stable adhesive performance. Therefore, the pH of the metal treatment solution is preferably in the range of 2 or more and 7 or less. Considering the reactivity with the metal oxide film, the pH of the metal treatment solution is preferably 3 or more. Also, from the viewpoint of the stability of alkyl silicate, the pH of the metal treatment solution is preferably 6 or less. The pH of the metal treatment solution can be appropriately adjusted by adding an acid such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, or the like.

[0043] The concentration of alkyl silicate or its oligomer in the metal treatment solution is preferably 0.005% by mass or more and 0.3% by mass or less. If the concentration of alkyl silicate or its oligomer in the metal treatment solution exceeds 0.3% by mass, the formed film may become thick and the strength may decrease. On the other hand, if the concentration of alkyl silicate or its oligomer in the metal treatment solution is less than 0.005% by mass, the concentration of alkyl silicate or its oligomer is too low, so that a composite oxide film of aluminum and silicon cannot be sufficiently formed, and sufficient adhesive durability may not be obtained. The concentration of alkyl silicate or its oligomer in the metal treatment solution is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more. Also, the concentration of alkyl silicate or its oligomer in the metal treatment solution is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.15% by mass or less.

[0044] Furthermore, the concentration of the organic silane compound in the metal treatment solution is preferably 0.005% by mass or more and 0.3% by mass or less. If the concentration of the organic silane compound in the metal treatment solution exceeds 0.3% by mass, the resulting surface treatment film may become thicker, potentially reducing its strength. This is also undesirable because it reduces the stability of the solution. On the other hand, if the concentration of the organic silane compound in the metal treatment solution is less than 0.005% by mass, the concentration of the organic silane compound is too low, making it impossible to sufficiently form a surface treatment film containing the organic silane compound, and thus insufficient adhesive durability cannot be obtained. The concentration of the organic silane compound in the metal treatment solution is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more. Furthermore, the concentration of the organic silane compound in the metal treatment solution is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.15% by mass or less.

[0045] Furthermore, the Si atom concentration A1 in region R1, the Si atom concentration A2 in region R2, and the rate of decrease in Si concentration M are affected not only by the type and amount of silane compound contained in the metal treatment solution, but also by the presence or absence of pretreatment, the type of blast treatment, and the drying method of the metal treatment solution. Therefore, by performing appropriate pretreatment, controlling the concentration of the silane compound, and appropriately selecting the film formation method, it is possible to control the Si atom concentration A1, Si atom concentration A2, and the rate of decrease in Si concentration M, thereby obtaining excellent adhesive durability.

[0046] The type of alkyl silicate or its oligomer contained in the metal treatment solution is not particularly limited, but a tetraalkyl silicate or its oligomer that does not produce by-products that cause film corrosion or deterioration of the adhesive resin after the reaction is preferred. From this perspective, tetraalkyl silicates such as tetramethyl orthosilicate, tetraethyl orthosilicate (TEOS), tetraisopropyl orthosilicate, or their oligomers are preferred. Among them, from the perspectives of economy and safety, tetraethyl orthosilicate (TEOS) or its oligomer is preferred. Note that the polymer includes oligomers and the like. Here, as the alkyl silicate or its oligomer, only one type may be used alone, or two or more types may be used in combination.

[0047] The type of organic silane compound contained in the metal treatment solution is not particularly limited, but the organic silane compound may include a silane compound having a plurality of hydrolyzable trialkoxyl groups in the molecule, its hydrolyzate, or its polymer. The silane compound having a plurality of hydrolyzable trialkoxyl groups in the molecule not only forms a dense siloxane bond by self-polymerization but also has high reactivity with metal oxides and forms a chemically stable bond, so the durability of the silane film can be further enhanced. In addition, the silane film has high mutual solubility with organic compounds such as machine oils such as processing oil and press oil and adhesives, and even if machine oils such as processing oil and press oil adhere to the film, its influence can be mitigated, so it also plays a role in preventing the decrease in adhesive durability due to oil coating. The type of the above silane compound is not particularly limited, but from the perspective of economy, a silane compound (bissilane compound) having two hydrolyzable trialkoxysilyl groups in the molecule is preferred. For example, bistrialkoxysilyl ethane, bistrialkoxysilyl benzene, bistrialkoxysilyl hexane, bistrialkoxysilyl propylamine, bistrialkoxysilyl propyl tetrasulfide, etc. can be used. In particular, from the perspectives of versatility and economy, bistriethoxysilyl ethane (BTSE) is preferred. Here, as the organic silane compound, only one type may be used alone, or two or more types may be used in combination.

[0048] Furthermore, the organosilane compound may include a silane coupling agent having a reactive functional group capable of chemically bonding with an organic resin component, its hydrolysate, or its polymer. For example, by using a silane coupling agent having a reactive functional group such as an amino group, epoxy group, methacrylic group, vinyl group, or mercapto group alone, or in combination with a silane compound, a chemical bond can be formed between the film and the resin, further enhancing adhesive durability. The functional groups of the silane coupling agent are not limited to those mentioned above, and silane coupling agents having various functional groups can be appropriately selected and used depending on the adhesive resin used. Suitable specific examples of silane coupling agents include, for example, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(N-aminoethyl)-aminopropyltrimethoxysilane, 3-(N-aminoethyl)-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-methacryloxypropyltriethoxysilane. Here, the silane coupling agent may be used alone or in combination of two or more types.

[0049] In this embodiment, if the metal treatment solution contains particulate inorganic compounds with a diameter of 10 nm or more (hereinafter also simply referred to as "particulate inorganic compounds"), the resulting film may become thicker, potentially reducing adhesive strength and durability. Therefore, it is preferable that the metal treatment solution substantially does not contain particulate inorganic compounds. It should be noted that "substantially free of particulate inorganic compounds" does not mean completely free of particulate inorganic compounds; the presence of particulate inorganic compounds at an impurity level is permissible. Specifically, it is permissible for particulate inorganic compounds to be present up to 0.05% by mass or less of the total amount of the metal treatment solution. Examples of particulate inorganic compounds include sols of inorganic oxides such as silica and alumina. The diameter of the particulate inorganic compounds is determined by observation of the solid content after drying the treatment solution using a transmission electron microscope (TEM) or by measurement of the diluted treatment solution using a liquid particle counter.

[0050] Furthermore, in addition to the alkyl silicate or its oligomer and the organosilane compound mentioned above, the metal treatment solution may optionally contain one or more stabilizers, auxiliary agents, etc. For example, the stabilizer may include organic compounds such as carboxylic acids having 1 to 4 carbon atoms, such as formic acid and acetic acid, or alcohols having 1 to 4 carbon atoms, such as methanol and ethanol.

[0051] The following is one example of a method for preparing a metal treatment solution, but it is not limited to this method. First, an organic silane compound and a small amount of acetic acid as a catalyst are added to a mixture of alcohol such as ethanol and water, and the organic silane compound is thoroughly hydrolyzed to obtain an aqueous solution of the organic silane compound. Next, an aqueous solution of alkyl silicate or its oligomer is prepared by the same method, and the two solutions are mixed and diluted with water to a predetermined concentration to prepare a metal treatment solution. Furthermore, since alkyl silicate or its oligomer is basic and easily polymerizes, when using a basic compound as the organic silane compound, it is preferable to neutralize the organic silane solution with acetic acid or the like beforehand to avoid excessive polymerization of the alkyl silicate or its oligomer when the solutions are mixed, before preparing the solution.

[0052] The concentration of the silane compound in the metal treatment solution is preferably adjusted based on the amount of solution to be applied to the surface of the substrate and the desired silicon concentration on the surface of the surface-treated aluminum material as defined in this invention. Specifically, the concentration of the silane compound relative to the total mass of the metal treatment solution is preferably 0.01% by mass or more and 0.5% by mass or less. The above-mentioned organic solvent may be included in order to lower the surface tension of the metal treatment solution, thereby improving wettability and coating properties, and to improve the drying speed.

[0053] [Jointed Body] The jointed body according to this embodiment includes the surface-treated aluminum material described above. Specifically, the jointed body comprises a first member and a second member joined together via an adhesive resin layer. At least one of the first member and the second member is the surface-treated aluminum material described above, and the silane film of the surface-treated aluminum material is bonded to the adhesive resin layer.

[0054] The joint according to this embodiment, configured as described above, is less prone to a decrease in adhesive strength even when exposed to a high-temperature, humid environment, and exhibits excellent adhesive durability. As described above, either one of the first member or the second member may be the surface-treated aluminum material according to the present invention, or both may be the surface-treated aluminum material according to the present invention. When only one of the members (the first member) is the surface-treated aluminum material, the other member (the second member) may be a surface-treated metal material with another metal material as the base material, an untreated metal material, an untreated resin molded body, etc. As the surface-treated metal material with another metal material as the base material, titanium or titanium alloy material, stainless steel material, and various other metal materials can be used as the base material. As the untreated metal material, titanium or titanium alloy material, aluminum or aluminum alloy material, stainless steel material, and various other metal materials can be used.

[0055] Furthermore, as the resin molded body, fiber-reinforced plastic molded bodies formed from various fiber-reinforced plastics such as glass fiber reinforced plastic (GFRP), carbon fiber reinforced plastic (CFRP), boron fiber reinforced plastic (BFRP), aramid fiber reinforced plastic (AFRP, KFRP), polyethylene fiber reinforced plastic (DFRP), and Zylon fiber reinforced plastic (ZFRP) can be used. By using these fiber-reinforced plastic molded bodies, it is possible to reduce the weight of the joint while maintaining a certain level of strength.

[0056] In addition to the fiber-reinforced plastics mentioned above, non-fiber-reinforced engineering plastics such as polypropylene (PP), acrylic-butadiene-styrene copolymer (ABS) resin, polyurethane (PU), polyethylene (PE), polyvinyl chloride (PVC), nylon 6, nylon 6,6, polystyrene (PS), polyethylene terephthalate (PET), polyamide (PA), polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), and polyphthalamide (PPA) can also be used for the resin molded articles.

[0057] [Method for Manufacturing the Joint] The joint according to this embodiment can be manufactured by conventionally known methods. For example, an adhesive resin layer can be formed in the region where the silane film is formed by a known method, and other members can be joined so as to be in contact with this adhesive resin layer. The method for forming the adhesive resin layer is not particularly limited, but as described above, an adhesive sheet made of adhesive resin material may be used, or a method of spraying or coating the adhesive resin material onto the surface of the silane film may be used.

[0058] In the embodiments described above, an example of a surface-treated metal material having an adhesive resin layer formed for manufacturing a joint was shown. However, the present invention is not limited to the above example, and may also be a surface-treated metal in which a coating film of paint is formed on at least a part of the silane film. In a surface-treated metal material with a coating film formed thereon, the adhesion between the aluminum substrate and the silane film is excellent, as is the bonding between the silane film and the paint, so the effect of preventing paint peeling can be obtained.

[0059] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples, and modifications can be made to the extent that they are in line with the spirit of the present invention, and all such modifications are included within the technical scope of the present invention. Furthermore, the following various manufacturing conditions are merely examples, and this embodiment is not limited to these conditions.

[0060] [Manufacturing of Aluminum Test Specimens] <Preparation of Base Materials> First, two base materials were prepared for each test condition by cutting aluminum alloy plates, as shown below, to a length of 100 mm in the longitudinal direction and a width of 25 mm. The alloy numbers and plate thicknesses of each plate are shown below. ・Aluminum alloy (JIS standard A7075): Plate thickness 3.8 mm ・Aluminum alloy (JIS standard A5052): Plate thickness 2 mm

[0061] Next, the evaluation range for the substrate was set to 10 mm from the longitudinal end and 25 mm in the width direction, and the substrates of Invention Examples No. 1 and 6, and Comparative Example No. 3 were treated with dry blasting. The substrates of Invention Examples No. 2 to 5, and Comparative Examples No. 1, 2 and 4 were treated with wet blasting in the above evaluation range, and then rinsed with water for 1 minute. The treatment conditions for dry blasting and wet blasting were as follows.

[0062] (Dry blasting conditions) ・Dry blasting equipment: Nissanki Co., Ltd. shot blasting equipment (NAB-3K) ・Abrasive material: Showa Denko K.K. abrasive grains white molandum: WA #150, Uji Denki Kagaku Kogyo Co., Ltd. TOSA EMERY EXTRA #60 ・Blasting pressure: 0.7 (MPa)

[0063] (Wet blasting conditions) • Wet blasting equipment: BABY Blast II (Model: MBBII-25) manufactured by Makoh Co., Ltd. • Abrasive material: Showa Denko Corporation abrasive grains White Morundum: WA#150, WA#320, WA#180 • Air pressure: 0.12 MPa • Gun travel speed: 10 mm / sec

[0064] <Formation of Silane Film> Subsequently, the substrates of Invention Examples No. 1 to 6 and Comparative Examples No. 1 to 4 were immersed for 10 seconds at room temperature in a metal treatment solution containing silane compound 1 and silane compound 2 at various concentrations, as shown below, and then removed. A silane film was then prepared by drying in a forced-air drying oven at a temperature of 100°C for 60 seconds, and aluminum test materials (surface-treated aluminum materials) were obtained.

[0065] (Metal treatment solution) • Silane compound 1 (organosilane compound): Bistriethoxysilylethane (BTSE) • Silane compound 2 (alkyl silicate): Tetraethyl orthosilicate (TEOS) • Ethanol 2.0 g • Acetic acid 0.001 g • Water 97.8 g

[0066] In the above metal treatment solution, the concentrations of silane compound 1 and silane compound 2 were changed while keeping the ratio of ethanol, acetic acid, and water the same. The type of pretreatment, the type and concentration of silane compounds in the metal treatment solution, and the presence or absence of a silane coating are shown in Table 1 below.

[0067] [Measurement of Elemental Distribution in Aluminum Test Material] Within the evaluation range of the obtained aluminum test material, the elemental distribution of oxygen, aluminum, silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, and nickel was measured using a high-frequency glow discharge emission spectrometer (Horiba Jobin Yvon JY-5000RF) in an arbitrary region R1 at the outermost surface and a region R2 at a depth of 10 nm from region R1. The atomic concentration of silicon in region R1 (A1) and region R2 (A2) was then calculated. Furthermore, based on the above atomic concentrations A1 and A2, the rate of decrease in silicon concentration M was calculated using the following formula (1): M = ((A1 - A2) / A1) × 100 ... (1)

[0068] Furthermore, the silicon concentration distribution with respect to measurement depth was observed for Invention Examples No. 1 to 3 and Comparative Examples No. 1 to 4. Figure 1 is a graph showing the silicon concentration distribution for Invention Examples No. 1 and 2 and Comparative Examples No. 1 and 3, with the vertical axis representing the atomic concentration of silicon and the horizontal axis representing the measurement depth. Figure 2 is a graph showing the silicon concentration distribution for Invention Example No. 3 and Comparative Examples No. 2 and 4, with the vertical axis representing the atomic concentration of silicon and the horizontal axis representing the measurement depth. As shown in Figures 1 and 2, Invention Examples No. 1 to 3 show a high silicon atomic concentration A1 of approximately 12 to 15 atomic percent in the outermost region R1 because a silane film is formed on the surface of the substrate. Furthermore, the silicon atomic concentration decreases as the measurement depth increases, and in region R2, which is 10 nm deep, the silicon atomic concentration A2 is approximately 6 to 7 atomic percent. As shown by the arrows in Figures 1 and 2, the rate of decrease M in silicon concentration, calculated based on atomic concentrations A1 and A2, was approximately 45-55%.

[0069] On the other hand, in Comparative Examples No. 1 and 2, the atomic concentration of silicon in the outermost region R1 was higher than that of Invention Examples No. 1 to 3. In Comparative Example No. 3, the rate of decrease M of silicon concentration, calculated based on atomic concentrations A1 and A2, was less than 45%. In Comparative Example No. 4, the atomic concentration of silicon in the outermost region R1 was less than 3.0 atomic percent.

[0070] As shown in Figures 1 and 2, for Comparative Examples No. 1 and 2, the silicon atomic concentration is 4% to 7% in the region where the measurement depth is greater than 20 nm. This is because Comparative Examples No. 1 and 2 have a high concentration of silane compounds in the metal treatment solution, which is thought to allow Si to be detected even in regions that are somewhat deep from the substrate surface. Furthermore, the silicon atomic concentration in the region where the measurement depth is greater than 20 nm may also change depending on the blast treatment conditions. However, in the region where the measurement depth is greater than, for example, 2 μm, the silicon atomic concentrations of all the inventive examples and comparative examples are approximately the same.

[0071] [Manufacturing of Joined Test Specimens] Subsequently, two aluminum test materials were joined together with an adhesive to obtain a joined test specimen (joint). Figure 3A is a side view showing the shape of the joined test specimen, and Figure 3B is a plan view thereof. As shown in Figures 3A and 3B, an adhesive resin layer 35 was formed on the surface of the test material 31b (second member) in the evaluation area, and a test material 31a (first member) having the same configuration as the test material 31b was placed on top of this adhesive resin layer 35. The overlap length was set to 10 mm, and the test materials 31a and 31b were positioned so that only the area from the edge of each test material 31a and 31b overlapped by 10 mm.

[0072] For Invention Examples No. 1 to 6 and Comparative Examples No. 1 to 4, since a silane film was formed in the evaluation range described above, the 10 mm × 25 mm regions where the silane film was formed were placed facing each other via an adhesive resin layer 35. A structural thermosetting epoxy resin adhesive was used as the material for the adhesive resin layer. Furthermore, a small amount of glass beads (particle size 250 μm) was added to the adhesive resin material to adjust the thickness of the adhesive resin layer 35 to 250 μm. After placing the materials in the overlapping arrangement as described above, they were dried at room temperature for 30 minutes, and then heated at 180°C for 30 minutes to perform a thermosetting treatment. After that, they were left to stand at room temperature for 24 hours to prepare a bond test specimen (jointed body).

[0073] [Evaluation of Joint Test Specimens] <Degradation Test> A degradation test was conducted on some of the obtained joint test specimens to evaluate their adhesive durability. The degradation test involved immersing the joint test specimens in a 5% NaCl solution at 40°C for the period shown in Table 1 below.

[0074] <Tensile Test> To evaluate the adhesive durability of the obtained bonded specimens, a tensile test was conducted. Under the tensile conditions, both ends of the bonded specimen were pulled in the tensile direction indicated by the arrows in Figure 3A at a tensile speed of 50 mm / min until fractured. Subsequently, the fracture surfaces of specimen 31a (first member) and specimen 31b (second member) were observed, and the area of ​​the region where interfacial delamination occurred between the first member and the adhesive resin layer (interfacial delamination area of ​​the first member) and the area of ​​the contact surface between the first member and the adhesive resin layer (adhesion area of ​​the first member) were measured. Similarly, the area of ​​the region where interfacial delamination occurred between the second member and the adhesive resin layer (interfacial delamination area of ​​the second member) and the area of ​​the contact surface between the second member and the adhesive resin layer (adhesion area of ​​the second member) were measured. The cohesive failure rate was then calculated using the following formula (2).

[0075] Cohesive failure rate (%) = 100 - {(Interface delamination area of ​​the first member / Adhesion area of ​​the first member) × 100 + (Interface delamination area of ​​the second member / Adhesion area of ​​the second member) × 100} ... (2)

[0076] Table 2 below shows the calculation results of the silicon atomic concentration and the silicon concentration reduction rate M for each example of invention and comparative example, as well as the degradation test conditions and the calculation results of the cohesive failure rate.

[0077]

[0078]

[0079] As shown in Figure 1 and Table 2 above, in Invention Examples No. 1 to 6, the atomic concentration of silicon A1 and the rate of decrease in silicon concentration M in the outermost surface region R1 were within the range defined in this invention. Therefore, even after degradation testing, the cohesive failure rate was 85% or higher, and excellent adhesive durability was obtained.

[0080] In Comparative Example No. 1, the atomic concentration A1 of silicon in the outermost region R1 exceeded the upper limit defined in the present invention, and the rate of decrease M of silicon concentration was less than the lower limit defined in the present invention. For Comparative Example No. 1, the atomic concentration A1 of silicon in the outermost region R1 was 35.5%, and region R1 was entirely composed of SiO ２The Si content is greater than the theoretical maximum value when coated with a silane film consisting of the above. This is thought to be because the total concentration (1.0%) of silane compounds in the metal treatment solution of Comparative Example No. 1 was high. Specifically, it is thought that after the silane compounds TEOS and BTSE were hydrolyzed, the hydrolyzed silane compounds reacted with each other, such as through condensation polymerization, resulting in a Si content greater than the theoretical maximum value mentioned above, and that silane products that do not contribute to adhesive durability were generated in the outermost surface region R1.

[0081] In Comparative Example No. 2, the rate of decrease M of silicon concentration was within the range defined in the present invention, but the atomic concentration A1 of silicon in the outermost surface region R1 exceeded the upper limit defined in the present invention. Thus, in Comparative Examples No. 1 and 2, the concentration of the silane compound in the metal treatment solution was significantly higher compared to Invention Examples No. 1 to 6, which is considered to be why the atomic concentration A1 and the rate of decrease M of silicon concentration fell outside the range defined in the present invention. Consequently, the cohesive failure rate was low in all cases.

[0082] In Comparative Example No. 3, the atomic concentration A1 of silicon in the outermost surface region R1 was within the range defined in the present invention, but the rate of decrease M of silicon concentration was below the lower limit defined in the present invention, resulting in a low cohesive failure rate. It is believed that for Comparative Example No. 3, for example, the atomic concentration A1, atomic concentration A2, and the rate of decrease M of silicon concentration can be controlled to be within the range defined in the present invention by adjusting the conditions during blasting or the concentration of the silane compound.

[0083] In Comparative Example No. 4, the rate of decrease M of silicon concentration was within the range defined in the present invention, but the atomic concentration A1 of silicon in the outermost surface region R1 was below the lower limit defined in the present invention. This is thought to be because the concentration of the silane compound in the metal treatment solution was lower compared to Invention Examples No. 1 to 6. Consequently, the cohesive failure rate was low. Thus, the bonded test specimens of these comparative examples had low adhesive durability.

[0084] Although various embodiments have been described above, it goes without saying that the present invention is not limited to these examples. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. Furthermore, the components in the above embodiments may be combined in any way without departing from the spirit of the invention.

[0085] This application is based on a Japanese patent application (Patent Application No. 2024-198419) filed on November 13, 2024, the contents of which are incorporated by reference within this application.

[0086] 31a Test material (first component) 31b Test material (second component) 35 Adhesive resin layer

Claims

1. A surface-treated aluminum material having a silane film provided on at least a portion of the surface of an aluminum substrate, wherein, when the elemental distribution is measured by glow discharge emission spectroscopy in the outermost region R1 and region R2 at a depth of 10 nm from region R1, the atomic concentration of silicon in region R1 is 3.0 atomic% or more and 30.0 atomic% or less, and the rate of decrease in silicon concentration M, calculated by the following formula (1) based on the atomic concentration of silicon A1 in region R1 and the atomic concentration of silicon A2 in region R2, is 45% or more.

2. The surface-treated aluminum material according to claim 1, further comprising an adhesive resin layer on the surface of the silane film.

3. A joint comprising a surface-treated aluminum material according to claim 1 or 2, wherein a first member and a second member are joined via an adhesive resin layer, at least one of the first member and the second member is the surface-treated aluminum material, and the silane film of the surface-treated aluminum material and the adhesive resin layer are bonded together.

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