JP7137869B2 - Aluminum alloy material excellent in corrosion resistance and strength and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum alloy material improved in both corrosion resistance and strength, and a method for producing the same. More specifically, the present invention relates to an aluminum alloy material having a dense coating with a high anticorrosion effect and improved strength of the aluminum alloy used as the base material.

Aluminum alloys containing aluminum as a main component have many advantages such as being lighter than steel materials, having higher rigidity than organic materials such as resins, and being recyclable. Therefore, in recent years, it has been widely used as a constituent material for transportation equipment such as automobiles and aircraft in order to replace steel materials.

For an aluminum alloy with a relatively low melting point, the usage environment for the above applications can be said to be a high-temperature environment. Therefore, there is concern about corrosion due to surface oxidation of the aluminum alloy material. When aluminum is left in the air, a natural oxide film is formed and becomes passivated. Since the thickness of this natural oxide film is several nanometers, it is easily corroded in extreme humidity, acid or alkali environments. Therefore, conventionally, surface treatment methods for improving the corrosion resistance of aluminum alloys have been studied. At present, in addition to alumite treatment, boehmite treatment and plating treatment, chemical conversion treatments such as phosphate chromate treatment, chromate chromate treatment, zinc phosphate treatment and non-chromate treatment are known depending on the usage environment. In these various chemical conversion treatments, an aluminum alloy to be treated is brought into contact with and immersed in a treatment solution containing acid or alkali such as H ₂ SO ₄ and heavy metal ions such as Cr to form an anticorrosion film on the alloy surface.

In surface treatment techniques such as chemical conversion treatment as described above, there have been problems of increased costs for procurement of a unique treatment solution and treatment of waste solution, and problems of burdens on the environment. Therefore, as a surface treatment method that is more efficient than the chemical conversion treatment and has less environmental load, a surface treatment technique using water vapor is attracting attention (Patent Document 1). The inventors of the present invention have also disclosed a surface treatment method in which the alloy surface is brought into contact with water vapor within a predetermined temperature range in order to improve the corrosion resistance of the aluminum alloy material. In the steam treatment of such an aluminum alloy material, a film containing aluminum hydroxide oxide (AlO(OH)) as a main component is formed on the surface, and the anticorrosion action of this film improves the corrosion resistance.

Further, it has been confirmed that the steam treatment of an aluminum alloy material by the present inventors in Patent Document 2 can improve the strength of the aluminum alloy serving as the base material, in addition to improving the corrosion resistance by forming a film. This steam treatment optimizes the temperature and pressure of the steam that contacts the base material, thereby adjusting the distribution of the particle size and other properties of precipitates composed of solute elements contained in the aluminum alloy base material. improve the strength of

JP 2011-121306 A International Publication No. 2017/135363 pamphlet

Steam treatment can impart corrosion resistance to aluminum alloy substrates relatively easily, and is also safe and environmentally friendly from the viewpoint of waste liquid treatment. Moreover, the steam treatment of Patent Document 2 also has the advantage of being able to simultaneously achieve the formation of an anticorrosion coating and the enhancement of the strength of the base material in one step. However, considering the expansion of the range of application of aluminum alloy materials as described above, there is a demand for more excellent corrosion resistance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and it is an object of the present invention to provide an aluminum alloy material to be coated with a film by steam treatment, which is more excellent in corrosion resistance than conventional ones. For this purpose, the present invention provides an aluminum alloy material and a method for producing the same, which can also achieve strength improvement and is improved in both corrosion resistance and strength.

The inventor of the present invention conducted intensive studies while considering the above-described prior art, and focused on adjusting the structure of the aluminum alloy substrate, which is the source of the film, as a direction for improving the corrosion resistance of aluminum alloy materials by steam treatment. did. In the steam treatment, a film containing aluminum hydroxide oxide (AlO(OH)) as a main component is formed, but as long as steam is used, it is difficult to greatly change the composition itself. The inventors of the present invention believe that as a means of improving the anti-corrosion effect of the coating, it is possible to improve structural factors such as the density and adhesion of the coating, and the uniformity of the AlO(OH) crystals, rather than the composition of the coating. I considered that there is

The inventors of the present invention have found that optimizing the material structure of the aluminum alloy substrate before the steam treatment, that is, before the film is formed, produces a more effective anticorrosion effect.

However, regarding the relationship between the material structure of the base material and the anticorrosion action, patent document 2 discusses structure adjustment during steam treatment. However, according to the study of the present inventors, it is considered that the adjustment of the material structure by steam treatment is not necessarily sufficient in improving corrosion resistance and strength. In order to further improve the corrosion resistance of the aluminum alloy substrate, the inventors of the present invention believed that it was preferable to optimally control the material structure of the substrate before the film was formed. In addition, the inventors have also found that the aluminum alloy material having this controlled and optimized material structure can exert a stronger effect than ever before. The inventors of the present invention arrived at the present invention as a result of investigations to identify the structure of aluminum alloy materials that are excellent in such corrosion resistance and strength.

That is, the present invention provides an aluminum alloy material comprising a substrate made of an aluminum alloy containing at least one solute element and a coating formed on at least one surface of the substrate, wherein the coating is , containing aluminum hydroxide oxide (AlO (OH)), and in the profile of the aluminum alloy material when X-ray diffraction is performed from above the film, at least one compound containing the solute element has n diffraction peaks. , one diffraction peak of aluminum hydroxide oxide appearing in the range of 2θ=14° to 15° is observed, and the peak intensities of the n diffraction peaks of the compound are respectively Xn (n=1, 2, 3 ), and the peak intensity of the diffraction peak of the aluminum hydroxide oxide appearing in the range of 2θ=14° to 15° is S, the diffraction peak of the compound satisfying Xn/S≧1.4 is An aluminum alloy material characterized by observing at least one.

As described above, the aluminum alloy material according to the present invention comprises a base material made of an aluminum alloy and a coating mainly composed of aluminum hydroxide oxide (AlO(OH)) on the surface of the base material. In this substrate, as a result of controlling the material structure, a compound derived from the solute element of the aluminum alloy that is the substrate is precipitated. In the present invention, in order to specify the composition of the material structure of this base material, diffraction peaks of compounds that appear when an aluminum alloy material is subjected to X-ray diffraction analysis (XRD) are used. Hereinafter, in order to describe the details of the aluminum alloy material according to the present invention, each configuration and features in X-ray diffraction will be described.

I. Aluminum Alloy Substrate The aluminum alloy serving as the substrate of the present invention is an alloy containing aluminum as a main component and at least one solute element added thereto. The solute elements include zinc (Zn), magnesium (Mg), silicon (Si), copper (Cu), manganese (Mn), lithium (Li), iron (Fe), nickel (Ni), silver (Ag), The base material is an aluminum alloy to which at least one element of zirconium (Zr) and chromium (Cr) is added. The substrate of the present invention is preferably an aluminum alloy containing 0.1% by mass or more and less than 50% by mass of these solute elements in total.

Specific aluminum alloys include various aluminum alloys defined by international aluminum alloy names. For example, 2000 series Al-Cu alloys (duralumin, super duralumin), 6000 series Al-Mg-Si alloys, No. 7000 Al-Zn-Mg alloys, Al-Zn-Mg-Cu alloys Various aluminum alloys such as (extra super duralumin) can be applied. However, it is not limited to these standardized alloy systems, and alloy systems with a wide range of compositions can be applied.

II. Coating In the aluminum alloy material according to the present invention, the coating formed on the substrate surface is an important component for ensuring the corrosion resistance of the alloy material. This film is a film mainly containing aluminum hydroxide oxide (AlO(OH)). Aluminum hydroxide oxide, also called boehmite, has chemical stability and high anticorrosion effect. The composition of this coating essentially includes aluminum hydroxide oxide, and may be composed only of it. However, the film may contain substances other than aluminum hydroxide oxide. For example, it may contain a trace amount of a solute element of the aluminum alloy that is the base material or a compound thereof (intermetallic compound, oxide, hydroxide, etc.). It may also contain compounds (oxides, hydroxides, hydrates, salts) derived from components in water vapor that contact the substrate for film formation. The film of the present invention may contain 10% by mass or more of aluminum hydroxide oxide while allowing the inclusion of LDH, which will be described later.

In the prior art, in addition to aluminum hydroxide oxide, Al-based layered double hydroxide (hereinafter sometimes referred to as LDH) is included as a component of the film formed by steam treatment. is stated. LDH is a hydroxide of a divalent metal (M) derived from the solute element of an aluminum alloy, and a double hydroxide in which ions of Al, which is a trivalent metal, are substituted at divalent metal sites to form a laminated structure. It is a compound represented by the chemical formula “[M ²⁺ _1−x Al ³⁺ _x (OH) ₂ ][A ⁿ⁻ _x/n ·yH ₂ O]”. In this chemical formula, A ^n- is an anion, hydroxide ion (OH ^- ), carbonate ion (CO ₃ ^2- ), nitrate ion (NO ₃ ^- ), sulfate ion (SO ₄ ^2- ), fluoride ion (F ⁻ ), chlorine ions (Cl ⁻ ) and the like are often formed.

The film of the present invention may contain the LDH, but it is not an essential component. In the prior art described above, it is stated that LDH has the effect of improving the corrosion resistance of the film based on its unique behavior (anion exchange ability due to host-guest reaction). Although the inventors do not deny the efficacy of LDH, it has been confirmed that LDH is not always generated in the coating of the present invention. In addition, the present inventors consider that the effect of improving corrosion resistance in the present invention does not require the presence of LDH in the film, and that it can be exhibited only by the formation of aluminum hydroxide oxide. . Therefore, LDH is not an essential component in the coating of the present invention. However, the presence of LDH in the film is unavoidable.

The film of the present invention preferably has a thickness of 0.05 to 100 μm. If the film has a thickness of less than 0.05 μm, if a minute scratch occurs, the substrate will be eroded from the scratch. If the thickness exceeds 100 μm, the coating may crack or peel off due to stress or thermal shock, and the corrosion resistance may rather deteriorate.

III. Peak intensity ratio in X-ray diffraction analysis In the aluminum alloy material according to the present invention, the material structure related to the dispersion state of the compound of the solute element in the base material is controlled. , the strength of the substrate is also improved. In the present invention, in order to specify the state of the material structure of this base material, the peak intensity of the compound based on the profile obtained by X-ray diffraction analysis of the alloy material is used.

Here, the material structure of the aluminum alloy base material presents a structure in which a compound containing a solute element is precipitated and dispersed in an aluminum parent phase serving as a matrix. This compound is a compound composed of the solute elements of the aluminum alloy. The specific composition of the compound is based on the composition of the aluminum alloy that serves as the base material. As described above, zinc, magnesium, silicon, copper, manganese, lithium, iron, nickel, silver, zirconium, chromium, and the like are often added as solute elements in aluminum alloy substrates. In this case, the compound dispersed in the aluminum alloy substrate consists of at least one of these metal elements. Specifically, Mg—Si compounds (Mg ₂ Si, etc.), Mg—Zn compounds (MgZn ₂ , etc.), Al—Mg—Zn compounds (Mg ₃ Zn ₃ Al ₂ , etc.), Cu—Mg compounds (CuMg ₂ etc.), Al-Fe compounds (AlFe ₂ etc.), Al-Fe-Si compounds (Al ₁₂ Fe ₃ Si etc.), Al-Cu compounds (CuAl ₂ etc.), Al-Cu-Mg systems Compounds (AlCuMg, Al ₂ CuMg, etc.), Al—Mn compounds (Al ₆ Mn, etc.), Al—Mn—Fe compounds (Al ₆ MnFe, etc.), Al—Mn—Si compounds, Al—Fe—Mn— A compound such as a Si-based compound is dispersed.

When the aluminum alloy according to the present invention is subjected to X-ray diffraction analysis, a peak of at least one of the compounds of the solute elements described above is observed. Diffraction peaks of compounds are often observed for a plurality of types of compounds, and even for the same compound, a plurality of peaks are observed depending on the diffraction plane.

On the other hand, when the aluminum alloy according to the present invention is subjected to X-ray diffraction analysis, the peak of aluminum hydroxide oxide (AlO(OH)) constituting the film is clearly observed. In particular, the peak of aluminum oxide hydroxide appears clearly in the range of 2θ=14° to 15°. In the present invention, the peak intensity ratio of each compound is measured based on the intensity of the aluminum hydroxide oxide peak appearing at 2θ=14° to 15°, and the aluminum alloy according to the present invention is determined. do.

That is, in the present invention, when n compound peaks are observed by X-ray diffraction analysis, the peak intensity of each diffraction peak is defined as Xn (n=1, 2, 3 . . . ) (n is positive). integer). Also, let S be the peak intensity of the diffraction peak of aluminum hydroxide oxide appearing in the range of 2θ=14° to 15°. Then, the ratio (Xn/S ((n=1, 2, 3...)) of the peak intensity of each compound and the peak intensity of aluminum hydroxide oxide is measured.

In the present invention, the peak intensity ratio (Xn/S) calculated as described above must be 1.4 or more (Xn/S≧1.4). In the present invention, it is required that the material texture control of the base material has progressed sufficiently. The degree of growth of the compound serves as a measure of the progress of this structure control. When the ratio (Xn/S) of the peak intensity of the compound to the peak intensity of aluminum hydroxide oxide is less than 1.4 , it is determined that the growth of the compound is insufficient and the structure control is not completed. And since the film formed on such an insufficiently controlled base material lacks anticorrosion effect, such a standard is set. The measurement/calculation of the ratio (Xn/S) to the peak intensity may be performed for all peaks of the compound. However, extract about one or two peaks with high intensity from the observed multiple peaks, calculate the peak intensity ratio (Xn / S), and if the result is 1.4 or more, the present invention It may be determined that it is within the range.

The upper limit of the ratio (Xn/S) of the peak intensity of the compound to the peak intensity of aluminum hydroxide oxide is preferably 100. This is because it is assumed that there is a limit to the growth of the compound, and it is considered difficult to develop an intensity ratio exceeding 100 in reality. In addition, it is assumed that excessive growth of the compound is not preferable in terms of the balance between corrosion resistance and strength. The composition of the compound is not limited such that the ratio to the peak intensity of aluminum hydroxide oxide is 1.4 or more. It may vary depending on the composition of the substrate. Moreover, although at least one such peak should be observed, a plurality of such peaks may be observed. A plurality of peaks derived from one type of compound may be observed, or individual peaks derived from a plurality of types of compounds may be observed.

As described above, the aluminum alloy substrate of the present invention includes 2000 series alloys (Al--Cu alloys), 6000 series alloys (Al--Mg--Si alloys), and 7000 series alloys ( Al--Zn--Mg system alloys, Al--Zn--Mg--Cu system alloys, etc. can be applied. As a specific example, when these aluminum alloys are applied to the present invention, the structure of compounds that may be observed by X-ray diffraction and the peak intensity (S) of aluminum hydroxide oxide suitable for contrasting The composition (peak position) of the compound is shown below.

The aluminum alloy film according to the present invention essentially contains aluminum hydroxide oxide (AlO(OH)). Then, in order to confirm the presence of aluminum hydroxide oxide, in the X-ray diffraction pattern, the peak intensity (S) of the diffraction peak of aluminum hydroxide oxide appearing at 2θ = 14 ° to 15 ° is the diffraction peak of the aluminum alloy material. The peak intensity ratio (S/A) to the peak intensity (A) of the peak (2θ=38° to 39°) is preferably 0.01 or more. The upper limit of this peak intensity ratio (S/A) is preferably 0.5 or less.

The X-ray diffraction profile described above can be analyzed from the film of the aluminum alloy material. The detection depth in X-ray diffraction analysis varies slightly depending on the type of tube target used, the incident angle, etc., but under general conditions the detection depth is several nanometers to several tens of micrometers. . Therefore, even if the aluminum alloy material on which the film is formed is analyzed as it is, both the aluminum hydroxide oxide in the film and the compound in the material on the substrate surface can be detected. X-ray diffraction analysis can be carried out under known conditions, but preferably, Cukα rays are used as the X-ray source and the measurement is carried out in the range of 2θ=5 to 90°. Moreover, it is preferable to calculate the peak intensity in a state where the influence of the background is eliminated.

As described above, the aluminum alloy material according to the present invention is excellent in both corrosion resistance and strength due to the optimally textured aluminum alloy base material and the coating formed thereon. The shape of the aluminum alloy material according to the present invention is not limited, and any shape such as a plate shape or a tubular shape can be applied. Also, there are no restrictions on the dimensions. This is because the steam treatment applied in the manufacturing process of the aluminum alloy material according to the present invention can form a film without imposing restrictions on shape and size. Furthermore, the coating may be formed partially, either on one side or on both sides.

IV. Method for Producing Aluminum Alloy Material According to the Present Invention As described above, in the production of the aluminum alloy material according to the present invention, a film is formed by steam treatment. A feature of the present invention is that the material structure of the aluminum alloy substrate is controlled before the coating is formed. In this step of controlling the structure of the base material, the base material is heated to a high temperature to form a solution, and then heated at a predetermined temperature to adjust the dispersed state of the compound.

That is, in the method for producing an aluminum alloy material according to the present invention, a substrate made of an aluminum alloy containing at least one solute element is heated to 450° C. to 570° C. and cooled to be solutionized, and then the solutioned. A structure control treatment is performed by heating the base material at 50 ° C. to 300 ° C. for 0.1 hour to 168 hours, and the base material after the structure control treatment is brought into contact with water vapor at a temperature of 100 ° C. to 350 ° C., and on the base material It includes a step of forming a film.

(i) Substrate structure control step Controlling the material structure of the aluminum alloy substrate is an essential step of the present invention. This structure control step is a step for forming a film excellent in anticorrosion effect by making the material structure of the base material before film formation into a state in which compounds of a suitable size are uniformly dispersed. In addition, by optimizing the dispersed state of the compound, it has the effect of improving the strength of the substrate. The reason why the anti-corrosion effect of the film is improved by the structure control treatment of the base material is not necessarily clear. The inventors of the present invention believe that a change in the state of dispersion of the compound in the base material causes a change in the surface condition around the compound, and a favorable change in the adhesion or morphology of the film formed on the surface of the base material. We speculate that this is a factor in the improvement.

The texture control treatment of the base material is performed on the base material after solution treatment. In general aluminum alloy materials for manufactured and commercial products, the material structure has the potential to make film formation uneven and irregular, such as the dispersion of irregular compounds, the dispersion of coarse compounds, and the lack of compounds. It is expected that Therefore, an alloy material with stable properties is obtained by homogenizing the structure of the base material by solution treatment and then controlling the structure. Solution treatment involves heating the substrate to 450° C. to 570° C. and then cooling. The heating time is preferably 0.1 to 48 hours. Cooling is preferably water cooling, and more preferably water cooling at 5°C or less.

The base material homogenized by solution treatment is subjected to texture control treatment. The texture control treatment heats the substrate at 50° C. to 300° C. for 0.1 hour to 168 hours. This heat treatment promotes formation/precipitation of compounds by solute elements, and reorganization/refining of the dispersed state of compounds due to re-dissolution/re-precipitation of solute elements in the aluminum matrix. As a result, the material structure of the base material is controlled in a suitable state. The heat treatment temperature is set to 50.degree. C. to 300.degree. If the temperature is less than 50° C., the diffusion of the solute elements is difficult to occur, and the progress of the structure control is extremely retarded. On the other hand, if the temperature exceeds 300° C., excessive coarsening of the compound may occur, and recrystallization may change the mechanical properties of the base material. Also, the heating time is 0.1 to 168 hours. If the heat treatment is less than 0.1 hour, the diffusion of the solute elements is insufficient, and the change in the material structure is poor. A preferable condition for this structure control treatment is heating at 100° C. to 250° C. for 0.5 hour to 24 hours.

(ii) Steam Treatment Step Then, the aluminum alloy material according to the present invention is obtained by contact-treating the base material that has undergone the above-described structure adjustment treatment step with steam to form a coating. In the steam treatment process for film formation, the temperature of steam is 100.degree. C. to 350.degree. In the steam treatment at less than 100° C., sufficient formation of aluminum oxide hydroxide cannot be observed, and corrosion resistance cannot be imparted to the film. On the other hand, if the temperature exceeds 350° C., coarsening of the aluminum hydroxide oxide will progress, causing problems such as the film becoming porous. The temperature of steam is more preferably 140 to 280°C.

The water vapor to be brought into contact with the substrate is generated by heating and vaporizing water, and as the water used as the water vapor source, industrial water or tap water can be used, and pure water is preferably used. Aqueous solutions containing appropriate salts can also be used. When using pure water, it is preferable to use ion-exchanged water, distilled water, or ultrapure water having an electric conductivity of 1 mS/m or less. As the aqueous solution containing salts, vapors of aqueous solutions of carbonates, nitrates, sulfates, and fluoride salts can be used. These salts include alkali metal (lithium, sodium, potassium, etc.) salts (sodium carbonate, sodium nitrate, etc.) and alkaline earth metal (calcium, strontium, barium, etc.) salts (calcium carbonate, calcium nitrate, etc.). , noble metal salts, common metal salts and the like can be applied. An aqueous solution in which one or more of these salts are combined can be used.

The steam pressure is preferably in the range of 0.1 to 10 MPa. The pressure is more preferably 0.2-5 MPa. When pressurized steam is applied, a two-phase equilibrium state of saturated steam and subcritical water is established, and reactivity to film formation can be promoted. A uniform film can be formed by keeping the steam pressure constant during the treatment.

There are no particular restrictions on the method of bringing the water vapor into contact with the aluminum alloy substrate. The steam treatment may be carried out by exposing the aluminum alloy as the treatment material to steam in a closed space such as a predetermined reactor or vessel. As a specific method, the treatment can be performed by placing the base material together with water in a container and exposing the base material to a water vapor atmosphere generated by controlling the temperature and pressure. Alternatively, the treatment may be performed by directly injecting steam onto the treatment material.

In addition, the condition of the steam treatment for simultaneously progressing film formation and structure control, which is a conventional technology (Patent Document 2) by the present inventors, is that the steam temperature is 150 ° C. or higher and lower than 200 ° C. (preferably 170 ° C. or higher and 190 ° C. below). Therefore, the steam treatment conditions of the present invention can be applied in a wider range than this prior art. In the present invention, the material texture is controlled to a better state than the prior art prior to steam treatment. Therefore, a wide range of well-known conditions can be applied for steam treatment. However, the steam treatment under the conditions described in Patent Document 2 is, of course, permitted.

As described above, the aluminum alloy material according to the present invention provides a coating having an excellent anticorrosive effect as compared with conventional techniques by controlling the material structure of the base material to an optimum state. In addition, the control of the structure of the base material also contributes to the strength improvement, resulting in an alloy material with higher strength than the conventional technology. INDUSTRIAL APPLICABILITY The present invention is simple, yet highly effective, and can be applied to large-sized members and structures, so it can be expected to be widely used.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which outlines the structure of the steam treatment apparatus used by this embodiment. 4 is a SEM photograph of the surfaces (coatings) of the aluminum alloy materials of the first embodiment and Comparative Example 1. FIG. 4 shows XRD profiles of the aluminum alloy materials of the first embodiment and comparative example 1. FIG. 4 shows polarization curves of the aluminum alloy materials of the first embodiment and comparative example 1. FIG. 8 is a SEM photograph of the surfaces (coatings) of the aluminum alloy materials of the second embodiment and comparative example 2; XRD analysis results of the aluminum alloy materials of the second embodiment and Comparative Example 2. 4 shows polarization curves of the aluminum alloy materials of the second embodiment and comparative example 2. FIG.

First Embodiment : A preferred embodiment of the present invention will be described below. In the present embodiment, an Al-5.6% by mass Zn-2.6% by mass Mg—Cu alloy (7075 alloy), which is a 7000 series aluminum alloy, is used as the aluminum alloy base material, which is subjected to a structure control treatment and steam. Aluminum alloy materials treated to provide a coating were produced and evaluated.

In the present embodiment, a commercially available material having the above composition was prepared and cut into a size of 20×20 mm and a thickness of 1.5 mm to obtain a test piece. First, this test piece was subjected to a texture control treatment. After heating the test piece at 470° C. for 2 hours, it was cooled with water and subjected to solution treatment. Then, the test piece was heated in an oil bath (silicone oil) at 120° C. for 24 hours for texture control treatment.

The test piece subjected to the texture control treatment was subjected to steam treatment to form a film. In the steam treatment, the steam curing apparatus shown in FIG. 1 was used. The steam curing apparatus in FIG. 1 is a horizontal autoclave, and pure water (20 ml) serving as a steam source is injected into the lower part. A plurality of test pieces can be suspended from the top of the device. Film formation was carried out at a temperature of 180° C. and a pressure of 1.0 MPa for 1 hour while maintaining the temperature and pressure.

Comparative Example 1 : As a comparative example for an aluminum alloy material that had undergone a structure control treatment prior to film formation, the base material was directly subjected to steam treatment to form a film to produce an aluminum alloy material. The conditions for the steam treatment at this time were the same as in the present embodiment.

The steam treatment conditions (temperature: 180° C., pressure: 1.0 MPa) of this embodiment and Comparative Example 1 are within the range of the steam treatment conditions described in Patent Document 2. Therefore, in Comparative Example 1, it is predicted that structure control (precipitation of compounds) progresses to some extent during steam treatment.

The surface morphology of the film was observed by SEM observation for the aluminum alloy materials of the present embodiment and the comparative example manufactured by the above steps. FIG. 2 is a SEM photograph showing the surface morphology of each aluminum alloy material. From FIG. 2, in both the aluminum alloy materials of the present embodiment and the comparative example, crystals presumed to be AlO(OH) are densely formed. Although the aluminum alloy material according to the present embodiment, in which the microstructure was controlled before film formation, the size of the crystal grains can be seen to be finer, it can be judged that there is not much difference in appearance between the two.

Next, X-ray diffraction analysis (XRD) was performed on the aluminum alloy materials of this embodiment and the comparative example. XRD was measured using Cu-Kα as an X-ray source at a voltage of 50 kV and a current of 300 mA. XRD was performed on test pieces of the aluminum alloy materials of the present embodiment and the comparative example on which a film was formed and the aluminum alloy materials on which no film was formed.

FIG. 3 is an XRD profile of each aluminum alloy material. A diffraction peak derived from AlO(OH) is clearly observed near 2θ=14° in both the aluminum alloy materials of the present embodiment and the comparative example when compared with the profile of the substrate without film formation.

In the aluminum alloy material of the present embodiment, among Mg, Zn, and Cu, which are the main solute elements of the base material, strong diffraction originating from the Mg—Zn compound (MgZn ₂ ), which is a compound of Mg and Zn. A peak is observed around 2θ=19.5°. Further, the aluminum alloy material of the present embodiment includes, as compounds other than the Mg--Zn-based compound, a Cu--Mg-based compound ( _CuMg.sub.2 ), an Al--Fe-based compound ( _AlFe.sub.2 ), an Al--Cu--Mg-based compound ( AlCuMg, Al ₂ CuMg) and the like are observed.

Regarding the aluminum alloy material of the present embodiment, among the multiple diffraction peaks of the compound, the intensity of the peak of the Mg—Zn compound observed near 2θ = 19.7° is X, and 2θ = 14.5. The intensity of the AlO(OH) peak near ° was defined as S, and their ratio X/S was calculated. The calculation result of this peak intensity ratio X/S was 4.0. In the present embodiment, the peak intensity (S) of the diffraction peak of aluminum hydroxide oxide is the peak intensity ratio of the peak intensity (A) of the diffraction peak (2θ = 38° to 39°) of the aluminum alloy material. S/A was 0.1.

On the other hand, even in the aluminum alloy material of Comparative Example 1, which was not subjected to the structure control treatment before steam treatment, a diffraction peak derived from the Mg—Zn compound (MgZn ₂ ) was observed. Therefore, as in the present embodiment, the ratio of the peak intensity of the Mg—Zn-based compound observed near 2θ=19.5° to the peak intensity of AlO(OH) near 2θ=14° was calculated. . The peak intensity ratio X/S of the compound of Comparative Example 1 was 1.3, which was clearly lower than the value (4.0) of this embodiment. This is presumed to be due to the precipitation and fine dispersion of compounds (such as Mg--Zn compounds) as a result of subjecting the base material to appropriate structure control treatment prior to film formation by steam treatment. As for the peak intensity (S) of the diffraction peak of the aluminum hydroxide oxide of Comparative Example 1, the peak intensity ratio S/A was 0.08.

Then, an evaluation test regarding corrosion resistance and strength was performed on the aluminum alloy materials of the present embodiment and the comparative example. As the corrosion resistance evaluation, the polarization curve was measured for the alloy material. A 5% by mass NaCl solution was used as the electrolytic solution for the measurement of the polarization curve. Polarization curves were measured using a potentio/galvanostat (VersaSTAT4, Princeton Applied Research) after nitrogen was bubbled through the solution prior to measurement. The strength evaluation was performed by measuring the hardness of the base material surface. The hardness was measured on the surface of the sample from which the film was removed by mechanical polishing before measurement. The hardness was measured using a micro Vickers hardness tester (HM-103, manufactured by Mitutoyo Co., Ltd.) under the conditions of a test load of 2.94 N and a load time of 15 s.

FIG. 4 shows polarization curves of the aluminum alloy materials of the present embodiment and comparative examples. Also shown in FIG. 4 is the polarization curve for an aluminum alloy substrate without film formation. Based on these polarization curves, the corrosion current density and corrosion potential of each sample were read.

Table 2 shows the corrosion current densities and corrosion potentials read from the polarization curves of the aluminum alloy materials of the present embodiment and the comparative example, and the Vickers hardness values measured for the base material of each alloy material.

From Table 2, it can be seen that the aluminum alloy materials of the present embodiment and Comparative Example 1, on which a film was formed by steam treatment, had a significant decrease in corrosion current density compared to the base material without a film, and the effect of improving corrosion resistance by the film was observed. It is confirmed. Comparing the present embodiment with Comparative Example 1, the aluminum alloy material subjected to the structure control of the present embodiment has a further lower corrosion current density and a nobler corrosion potential than Comparative Example 1. I know you do. From this result, it can be seen that the aluminum alloy material subjected to the structure control treatment before the steam treatment has improved corrosion resistance as compared with the conventional technology.

In addition, regarding the strength (hardness) of the base material, it can be seen that the aluminum alloy material of the present embodiment has higher hardness than the aluminum alloy material of Comparative Example 1. In Comparative Example 1 as well, structure adjustment in the process of steam treatment and hardness increase due to the adjustment are observed, but the effect of hardness increase is greater in this embodiment. From the above, it was confirmed that the aluminum alloy material in which the dispersed state of the compound was optimized by the structure control treatment before the steam treatment of the present invention is excellent in both corrosion resistance and strength.

Second Embodiment : In this embodiment, a 6000 series aluminum alloy, Al-0.6 mass % Mg-1.0 mass % Si alloy (6022 alloy) is used as the aluminum alloy base material, and the first embodiment In the same manner as in , the structure control treatment and steam treatment were performed to produce an aluminum alloy material, and the characteristics were evaluated.

In this embodiment, a commercially available aluminum alloy plate material was processed into a test piece in the same manner as in the first embodiment, and subjected to a structure control treatment. In the texture control treatment, the test piece was subjected to solution treatment by heating at 560° C. for 30 minutes and then heated at 180° C. for 6 hours to perform texture control treatment. Then, steam treatment was performed under the same conditions as in the first embodiment (temperature 180° C., pressure 1.0 MPa) to form a film. In addition, as a comparative example for the second embodiment, a sample subjected to only steam treatment was also prepared (Comparative Example 2).

Then, the aluminum alloys of the second embodiment and the second comparative example were subjected to surface morphology observation (SEM), XRD, polarization curve, and hardness measurement of the coating. These analysis/test conditions are the same as in the first embodiment.

FIG. 5 is a SEM photograph of the surface of the aluminum alloy material of this embodiment. As in the first embodiment, crystals presumed to be AlO(OH) are densely formed. Also in this embodiment, no significant difference in appearance was observed in comparison with the comparative example.

FIG. 6 shows the XRD profile of the aluminum alloy material of this embodiment. Also in the aluminum alloy material of the present embodiment, based on the solute elements (Mg, Si) of the base material, in addition to Mg—Si compounds (for example, Mg ₂ Si), Cu—Mg compounds and the like are observed.

Regarding the aluminum alloy material of the present embodiment, X is the intensity of the peak of the Mg—Si compound observed near 2θ=35.7° among the diffraction peaks of the multiple compounds, where 2θ=14. The intensity of the AlO(OH) peak near .2° was defined as S, and their ratio X/S was calculated. The calculation result of this peak intensity ratio X/S was 1.7. On the other hand, in the aluminum alloy material of Comparative Example 2 as well, when the peak intensity ratio X/S of the compound was calculated based on the peak of the same compound, it was 0.6. In the present embodiment, the peak intensity (S) of the diffraction peak of aluminum hydroxide oxide is the peak intensity ratio of the peak intensity (A) of the diffraction peak (2θ = 38° to 39°) of the aluminum alloy material. S/A was 0.07. Moreover, the peak intensity ratio S/A of Comparative Example 2 was 0.03.

Also, FIG. 7 shows polarization curves for the aluminum alloy materials of the second embodiment and the second comparative example. Furthermore, Table 3 shows the values of corrosion current density, corrosion potential, and Vickers hardness of the aluminum alloy materials and substrates of the second embodiment and comparative example 2.

From Table 2, it can be seen that the aluminum alloy material of the second embodiment also has a lower corrosion current density and a nobler corrosion potential compared to Comparative Example 2. Further, the hardness of the base material of the second embodiment is higher. Therefore, from the results of this embodiment as well, it was confirmed that the aluminum alloy material in which the dispersed state of the compound is optimized by the structure control treatment before the steam treatment is excellent in both corrosion resistance and strength.

As described above, in the aluminum alloy material according to the present invention, a film having a high anticorrosion effect is formed by controlling the material structure of the base material to an optimum state before forming the film by steam treatment. there is In addition, the base material with the optimized material structure also has improved strength, so that the alloy material has higher strength than that of the conventional technology. INDUSTRIAL APPLICABILITY The present invention is a technique that can be applied to aluminum alloys for various uses, in addition to the constituent materials of transportation equipment such as automobiles and aircraft.

Claims (4)

An aluminum alloy material comprising a substrate made of an aluminum alloy containing at least one solute element and a coating formed on at least one surface of the substrate,
The film contains aluminum hydroxide oxide (AlO (OH)),
Aluminum hydroxide oxide having n diffraction peaks of at least one compound containing the solute element and appearing in the range of 2θ = 14° to 15° in the profile of the aluminum alloy material when X-ray diffraction is performed from above the coating. One diffraction peak of is observed,
Let the peak intensities of n diffraction peaks of the compound be Xn (n = 1, 2, 3...), and the peak intensity of the diffraction peak of the aluminum hydroxide oxide appearing in the range of 2θ = 14° to 15°. An aluminum alloy material characterized in that at least one diffraction peak of a compound satisfying 1.4≦Xn/S is observed, where S is the aluminum alloy material. Solute elements are zinc (Zn), magnesium (Mg), silicon (Si), copper (Cu), manganese (Mn), lithium (Li), iron (Fe), nickel (Ni), silver (Ag), and zirconium. 2. The aluminum alloy material according to claim 1, which is at least one of (Zr) and chromium (Cr). 3. The aluminum alloy material according to claim 1, wherein the coating has a thickness of 0.05 to 100 μm. A method for producing an aluminum alloy material according to any one of claims 1 to 3,
After heating a substrate made of an aluminum alloy containing at least one solute element to 450° C. to 570° C. and cooling it to a solution,
A structure control treatment is performed by heating the solution-treated base material at 50 ° C. to 300 ° C. for 0.1 hour to 168 hours,
A method for producing an aluminum alloy material, comprising the step of contacting the substrate after the structure control treatment with water vapor at a temperature of 100° C. to 350° C. to form a coating on the substrate.

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