Aluminum material

Abstract

To provide an aluminum material that is inexpensive and excellent in a base corrosion resistance while maintaining a property of a raw material.SOLUTION: An aluminum material is composed of aluminum or an aluminum alloy. A chemical conversion coating with a corrosion resistance is formed on a surface of the aluminum material. The aluminum material has a corrosion resistance of 600 hours or more in a neutral salt spray testing method conforming to JIS H 8502. The chemical conversion coating may be electrically conductive. The chemical conversion coating may contain trivalent chromium.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an aluminum material. [Background technology]

[0002] Conventionally, various surface treatments for imparting corrosion resistance to aluminum materials made of aluminum or aluminum alloys have been known. For example, Patent Document 1 discloses that the surface of an aluminum alloy is anodized to form an anodized film to improve corrosion resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-25184 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when anodizing the surface of aluminum material, the process is complicated and the cost is high.On the other hand, when surface treatment such as plating or painting is performed, if a thick film is required to ensure sufficient corrosion resistance, the advantage of the material (aluminum), that is, its light weight, may be lost.

[0005] The present invention provides an aluminum material that is inexpensive and has excellent bare corrosion resistance while maintaining the material's characteristics. [Means for solving the problem]

[0006] The aluminum material according to one embodiment of the present invention is made of aluminum or an aluminum alloy. A corrosion-resistant chemical conversion coating is formed on the surface of the aluminum material. The aluminum material has a corrosion resistance of 600 hours or more in a salt spray test method conforming to JIS H 8502.

[0007] The aluminum material has corrosion resistance (rust prevention effect) of 600 hours or more in the salt spray test method due to the chemical conversion coating formed on the surface. Therefore, compared with the conventional method of forming an anodized coating by performing an anodizing treatment on the surface of the aluminum material, it is very inexpensive and can fully ensure excellent corrosion resistance.

[0008] As described above, the aluminum material can ensure excellent corrosion resistance only by the chemical conversion coating formed on the surface, and therefore has very good bare corrosion resistance while maintaining the advantage of light weight, which is a characteristic of the material (aluminum).

[0009] In the above aluminum material, the chemical conversion coating may have electrical conductivity. In this case, the electrical conductivity can be sufficiently ensured by the chemical conversion coating. For example, it is not necessary to ensure electrical conductivity by post-processing, as in the case of an anodized coating by anodizing.

[0010] The chemical conversion coating may contain trivalent chromium, in which case the chemical conversion coating can sufficiently ensure excellent corrosion resistance.

[0011] Furthermore, the chemical conversion coating does not have to contain hexavalent chromium. In this case, the absence of hexavalent chromium, which is a harmful substance, can reduce the effects on the human body and the environment.

[0012] The thickness of the chemical conversion coating may be 0.1 μm or less, which effectively exhibits the effect of providing excellent bare corrosion resistance while maintaining the advantage of light weight, which is a characteristic of the material (aluminum). [Brief description of the drawings]

[0013] [Figure 1] 1 is a photograph showing a test specimen of an aluminum material of an example after 600 hours of salt spray testing. [Diagram 2]1 is a photograph showing a test specimen of an aluminum material of a comparative example after 600 hours of salt spray testing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The aluminum material is made of aluminum or an aluminum alloy, that is, aluminum or an aluminum alloy is used as the raw material of the aluminum material.

[0015] As the aluminum, for example, pure aluminum (1000 series aluminum) can be used.

[0016] Examples of aluminum alloys that can be used include Al-Cu alloys (2000 series aluminum alloys), Al-Mn alloys (3000 series aluminum alloys), Al-Si alloys (4000 series aluminum alloys), A-Mg alloys (5000 series aluminum alloys), Al-Mg-Si alloys (6000 series aluminum alloys), Al-Zn-Mg and Al-Zn-Mg-Cu alloys (7000 series aluminum alloys), etc.

[0017] Other examples of the aluminum alloy that can be used include aluminum alloys for casting and aluminum alloys for die casting.

[0018] Examples of aluminum materials that can be used include sheet materials, extrusion materials, and cast materials such as wrought materials, casting materials, and die-cast materials, as well as various aluminum products processed from these materials for use in automobiles, home appliances, and the like.

[0019] A corrosion-resistant chemical conversion film is formed on the surface of the aluminum material, that is, the surface of the aluminum material is covered (coated) with a corrosion-resistant chemical conversion film.

[0020] A chemical conversion coating is a coating formed on the surface of an aluminum material by chemical conversion treatment, which is a process in which a coating is chemically deposited on the surface of an aluminum material using a chemical conversion treatment agent.

[0021] The chemical conversion treatment for forming a chemical conversion film is a simpler treatment process and less expensive than the conventional anodizing treatment for forming an anodic oxide film.

[0022] That is, anodizing involves many steps, each of which is cumbersome. Also, material and management costs are incurred for each step, which increases the cost. In addition, the anodized film is formed using electricity, and some steps require processing at high temperatures (close to 100°C), which increases the cost.

[0023] On the other hand, chemical conversion treatment requires fewer steps and each step is simple. In addition, electricity is not used to form the chemical conversion film, and high temperature treatment is not required (normal temperature to about 70°C). This helps to reduce costs.

[0024] Unlike anodized films formed by anodizing, chemical conversion films generally have electrical conductivity, and therefore do not need to be imparted with electrical conductivity through post-processing, as is the case with anodized films formed by anodizing.

[0025] The chemical conversion coating preferably contains trivalent chromium (Cr(III)), i.e., a trivalent chromium compound. The chemical conversion coating containing trivalent chromium can be formed, for example, by chemical conversion treatment using a chemical conversion treatment agent containing a trivalent chromium compound.

[0026] It is preferable that the chemical conversion coating contains trivalent chromium but does not contain hexavalent chromium (Cr(VI)), i.e., hexavalent chromium compounds. By not containing hexavalent chromium, which is a harmful substance, it is possible to reduce the impact on the human body and the environment.

[0027] The thickness of the chemical conversion coating is preferably 0.1 μm or less. Because the chemical conversion coating is thin, the advantage of the material (aluminum) being lightweight can be utilized without compromising this advantage.

[0028] The aluminum material has corrosion resistance for 600 hours or more in a salt spray test method conforming to JIS H 8502. Here, the salt spray test method is a test method for evaluating corrosion resistance in an atmosphere sprayed with a sodium chloride solution using a salt spray tester, etc. The aluminum material has excellent corrosion resistance (rust prevention effect) without the occurrence of corrosion such as white rust even after 600 hours in the salt spray test method.

[0029] Aluminum materials have excellent corrosion resistance only due to the chemical conversion coating formed on the surface. In other words, aluminum materials have excellent bare corrosion resistance. Here, bare corrosion resistance refers to corrosion resistance with only a single surface treatment in which the base material (aluminum) is covered (coated) with a material different from the base material. Therefore, the corrosion resistance of aluminum materials refers to corrosion resistance in a state in which a chemical conversion coating is formed on the surface by chemical conversion treatment (without other surface treatments).

[0030] Aluminum materials have excellent corrosion resistance solely due to the thin chemical coating (thickness 0.1 μm or less) formed on the surface, and therefore have extremely excellent bare corrosion resistance while making the most of the lightweight advantage of the material (aluminum) without compromising this advantage.

[0031] Examples of the aluminum material of the present invention will be described below in comparison with comparative examples. Here, test specimens of the aluminum materials of the examples and comparative examples were prepared and evaluated for corrosion resistance (rust prevention effect).

[0032] (Example) First, an aluminum material is prepared. The aluminum material is an aluminum product used for automobile parts. The material (raw material) of the aluminum material is an aluminum alloy for die casting (ADC12, an Al-Si-Cu aluminum alloy).

[0033] Next, the aluminum material is degreased (degreasing process). Specifically, a degreaser (Surf Cleaner, manufactured by Nippon Paint Surf Chemicals Co., Ltd., diluted at 3%) is sprayed onto the surface of the aluminum material at a temperature of 40°C for 3 minutes. This removes oil and dirt from the surface of the aluminum material. After that, the aluminum material is washed with water for 10 minutes (water washing process).

[0034] Next, the aluminum material is desmutted (desmutting step). Specifically, a smut remover (SurTec (registered trademark) 490P + sulfuric acid, manufactured by SurTec MMC Japan Co., Ltd., dilution rate: 2%) is sprayed onto the surface of the aluminum material at a temperature of 25°C for a time of 2 minutes. This removes smut remaining on the surface of the aluminum material. In the desmutting step, it is preferable to maintain room temperature in order to suppress excessive reaction. After that, the aluminum material is washed with water for a time of 10 minutes (water washing step).

[0035] Next, a chemical conversion treatment is performed on the aluminum material (chemical conversion treatment step). Specifically, a chemical conversion treatment agent (SurTec650V, manufactured by SurTec MMC Japan Co., Ltd., diluted at 10%) is used to chemically deposit a film (chemical conversion film) on the surface of the aluminum material.

[0036] Here, the chemical conversion treatment agent contains a trivalent chromium compound, an alkali metal salt of hexafluorozirconate, a zinc compound, etc. Specifically, the chemical conversion treatment agent contains chromium sulfate as the trivalent chromium compound, potassium hexafluorozirconate as the alkali metal salt of hexafluorozirconate (fluorine compound), and zinc sulfate as the zinc compound. Note that the chemical conversion treatment agent does not contain hexavalent chromium (hexavalent chromium compound).

[0037] The above-mentioned chemical conversion treatment agent is sprayed onto the surface of the aluminum material under conditions of a temperature of 35°C and a time of 2 minutes, and a film (chemical conversion film) is chemically deposited on the surface of the aluminum material. This forms a chemical conversion film on the surface of the aluminum material. The chemical conversion film is an inorganic chemical conversion film having corrosion resistance and heat resistance. The thickness of the chemical conversion film is 0.1 μm or less. In the chemical conversion treatment process, in order to form a good chemical conversion film, it is preferable to carry out the reaction while maintaining the temperature at 35 to 40°C.

[0038] Next, the aluminum material is washed with water for 10 minutes (washing process). After that, the aluminum material is dried at 80°C for 10 minutes (drying process). In the drying process, in order to prevent cracks from occurring after the chemical conversion coating is formed, it is preferable that the final drying oven temperature is not set to 80°C or higher and the material temperature is not set to 65°C or higher.

[0039] As described above, a test specimen of an aluminum material of the embodiment, that is, an aluminum material having a chemical conversion coating formed on its surface by chemical conversion treatment, was prepared.

[0040] (Comparative Example) First, an aluminum material is prepared. The aluminum material is the same as that in the example. Also, unlike the example, the surface of the aluminum material is not subjected to chemical conversion treatment. This was used as a test specimen of the aluminum material of the comparative example.

[0041] (Corrosion resistance evaluation by salt spray test) Next, a salt spray test in accordance with JIS H 8502 was carried out on the aluminum material specimens of the examples and comparative examples to evaluate the corrosion resistance (rust prevention effect).

[0042] Specifically, in a constant temperature room at 35°C, test solutions were sprayed onto the aluminum specimens of the examples and comparative examples using a salt spray tester (manufactured by Itabashi Rika Kogyo Co., Ltd., model: SQ-1200-ST-S). A neutral (pH 7.0) 5% sodium chloride solution was used as the test solution. The progress was observed every 100 hours, and the corrosion resistance (rust prevention effect) was evaluated based on the time it took for white rust to appear on the surface of the specimen.

[0043] The aluminum material of the embodiment did not show any significant change on the surface of the aluminum material after 600 hours had passed since the start of the salt spray test, and no white rust was observed. In other words, it was found to have corrosion resistance (rust prevention effect) for more than 600 hours. On the other hand, the aluminum material of the comparative example was significantly corroded on the surface of the aluminum material after 600 hours had passed since the start of the salt spray test, and white rust was observed.

[0044] From the above results, it was found that the aluminum material of the example had corrosion resistance (rust prevention effect) of 600 hours or more in the salt spray test method conforming to JIS H 8502. In addition, it was found that the aluminum material of the example had excellent bare corrosion resistance because it had excellent corrosion resistance only by the chemical conversion coating (by a single surface treatment).

[0045] In addition, in the aluminum material of the embodiment, the chemical conversion treatment for forming a chemical conversion film has fewer steps and each step is simpler than the conventional anodizing treatment for forming an anodic oxide film. In addition, electricity is not used to form the chemical conversion film, and the treatment is not performed at high temperatures. Therefore, the treatment process is simple and inexpensive. Therefore, an aluminum material with excellent corrosion resistance can be manufactured easily and at low cost.

[0046] The thickness of the chemical conversion coating is 0.1 μm or less. In other words, the aluminum material has excellent corrosion resistance only due to the thin chemical conversion coating (thickness 0.1 μm or less) formed on the surface. Therefore, the aluminum material has excellent bare corrosion resistance while making the most of the lightweight advantage of the material (aluminum) without compromising it.

[0047] Furthermore, unlike an anodized film formed by anodizing, a chemical conversion film has electrical conductivity, and therefore does not need to be imparted with electrical conductivity by post-processing, as is the case with an anodized film formed by anodizing.

[0048] In addition, while the chemical conversion coating contains trivalent chromium (trivalent chromium compounds), it does not contain hexavalent chromium (hexavalent chromium compounds). By not containing the harmful substance hexavalent chromium, it is possible to reduce the impact on the human body and the environment.

[0049] (Other embodiments) The present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be embodied in various forms without departing from the scope of the present invention.

[0050] For example, in the aluminum material of the embodiment, the surface of the aluminum material was sprayed with a chemical conversion treatment agent in the chemical conversion treatment, but a method of immersing the aluminum material in the chemical conversion treatment agent may also be used. Also, in the degreasing step and the desmutting step, an immersion method may be used instead of a spraying method.

[0051] In addition, the function of one component in the above embodiments may be distributed as multiple components, or the functions of multiple components may be integrated into one component. Also, a part of the configuration of the above embodiments may be omitted. Also, at least a part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. Note that all aspects included in the technical idea specified by the wording described in the claims are embodiments of the present invention.

Claims

1. An aluminum material made of aluminum or an aluminum alloy, A corrosion-resistant chemical conversion coating is formed on the surface of the aluminum material, In the salt spray test method conforming to JIS H 8502, it has corrosion resistance of 600 hours or more. Aluminum material.

2. The aluminum material according to claim 1 , wherein the chemical conversion coating has electrical conductivity.

3. The aluminum material according to claim 1 , wherein the chemical conversion coating contains trivalent chromium.

4. The aluminum material according to claim 3 , wherein the chemical conversion coating does not contain hexavalent chromium.

5. The aluminum material according to claim 1 , wherein the chemical conversion coating has a thickness of 0.1 μm or less.

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