JP6960672B2 - Aluminum alloy material with high strength and high corrosion resistance, its manufacturing method, and surface treatment method for aluminum alloy material - Google Patents

Description

The present invention relates to an aluminum alloy material having improved corrosion resistance and a method for producing the same. More specifically, the present invention relates to an aluminum alloy material having a film having a high anticorrosion effect and at the same time having an improved strength of an aluminum alloy as a base material. Then, the present invention relates to the manufacturing method of such an aluminum alloy material.

Aluminum alloys containing aluminum as a main component are lighter than steel materials, have higher rigidity than organic materials such as resins, and have many advantages such as 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.

The environment in which these aluminum alloys are used is high for aluminum alloys having a relatively low melting point, and there is concern about corrosion due to surface oxidation. Further, when aluminum is left in the air, a natural oxide film is formed and becomes passivated, but since the oxide film is very thin at several nanometers, it is easily corroded in an extreme humidity, acid or alkaline environment. Therefore, a surface treatment method for improving the corrosion resistance of an aluminum alloy has been studied for a long time. Currently, chemical conversion treatments such as alumite treatment, chromate treatment, boehmite treatment, and plating treatment are known depending on the usage environment. In these various chemical conversion treatments _{, an aluminum alloy to be treated is contacted and immersed in a treatment liquid containing an acid such as H 2} SO ₄ or a heavy metal ion such as an alkali or Cr to form an anticorrosion film on the alloy surface.

Japanese Unexamined Patent Publication No. 6-192888 Japanese Unexamined Patent Publication No. 5-005185 Japanese Unexamined Patent Publication No. 6-128753

Conventionally known methods for imparting corrosion resistance such as chemical conversion treatment may be disadvantageous in terms of raw material cost for adjusting the treatment liquid, waste liquid treatment, and efficiency. In addition, chemical conversion treatment that handles acids / alkalis and heavy metals has a high burden on the environment, which makes it difficult to comply with the strict environmental standards.

Further, the conventionally known corrosion resistance imparting treatment mainly for forming a film has the meaning of treating an aluminum alloy material at the final stage from the viewpoint of protecting the formed film. Therefore, after the film forming treatment, it is difficult to perform additional treatment such as processing / deformation treatment and heat treatment. In this regard, when further expanding the scope of application of aluminum alloys, it is desired to improve the characteristics of the alloy base material, especially the strength, but there is a treatment method that can improve the corrosion resistance and modify the alloy base material. Until now unknown.

The present invention has been made based on the above background, and provides a treatment method capable of improving the corrosion resistance of an aluminum alloy while being simple and low cost, and at the same time improving the strength of an alloy base material. At the same time, the purpose is to clarify the composition of the aluminum alloy having a novel composition found by this method.

The present inventor has conducted diligent studies to solve the above problems, and found that the corrosion resistance can be improved by treating the aluminum alloy with steam whose treatment conditions, particularly temperature conditions are strictly controlled. The details of this steam treatment will be described later, but as a result of further studies on the composition of the aluminum alloy material after this treatment, the present inventors have formed a film having an unprecedented structure on the aluminum alloy base material. We have found an aluminum alloy base material according to the present invention as being capable of forming.

That is, in the present invention, in an aluminum alloy material composed of a base material made of an aluminum alloy and a film formed on at least one surface of the base material, the aluminum alloy used as a base material is an element other than aluminum. The film contains at least one solute element, and the film is composed of a monohydrated aluminum oxide (AlO (OH)) and an Al-based layered double hydroxide represented by the following formula, and X-rays formed on the film. Regarding the diffraction peak of diffraction, the ratio (Y) of the peak intensity (X) of 200 reflection of monohydrated aluminum oxide (AlO (OH)) and the peak intensity (Y) of 003 reflection of Al-based layered double hydroxide. / X) is an aluminum alloy material characterized by being 0.1 to 0.5.

The aluminum alloy material according to the present invention has a film based on monohydrated aluminum oxide (AlO (OH)) on the surface of the alloy base material. The monohydrated aluminum oxide is also called boehmite, and as can be seen from the above-mentioned prior art, it is a general component as a component of a corrosion-resistant film formed of an aluminum alloy material. In the present invention, an Al-based layered double hydroxide (hereinafter, may be referred to as LDH in some cases) is used as a component that further improves the corrosion resistance of the film while being based on monohydrated aluminum oxide. Is added.

Here, the layered double hydroxide is a compound formed by forming a laminated structure of a double hydroxide in which ions of Al, which is a trivalent metal, are solid-dissolved in a hydroxide of a divalent metal (M). be. The general formula of this layered double hydroxide is shown in the above formula 1, but [M ²⁺ _1-x Al ³⁺ _x (OH) ₂ ] in the formula may be referred to as a double hydroxide basic layer. ^{Further, [An-} _{x / n} · yH ₂ O] in the formula of Chemical formula 1 may be referred to as an intermediate layer. In the layered double hydroxide laminated structure, since the basic double hydroxide layer has a positive charge, the structure in which the intermediate layer, which is a negatively charged anion, is sandwiched between the layers is maintained.

Layered double hydroxides exchange guest substances with anions in the intermediate layer while maintaining the structure of the basic layer of double hydroxides (host layer) when other anions or molecules (guest substances) are in close proximity. However, it is said that guest substances can be taken in between the layers of the host. This action is referred to as the ability to exchange anions by the host-guest reaction. In the present invention, the above-mentioned anion exchange ability can be mentioned as a factor that the layered double hydroxide improves the corrosion resistance of the film. This is because when the film is exposed to a corrosive environment such as salt water, it is considered that erosion of the film can be suppressed by taking in anions in the environment.

The aluminum alloy material according to the present invention forms a film on the surface of which a monohydrated aluminum oxide (AlO (OH)) and an Al-based layered double hydroxide (LDH) are suitably composited. As a result, it has more suitable corrosion resistance than a film composed of only monohydrated aluminum oxide. Hereinafter, the structure of the aluminum alloy material according to the present invention will be described in detail.

The aluminum alloy as the base material is an alloy containing aluminum as a main component and an additive element (hereinafter, it may be referred to as a solute element (solute atom), but it is synonymous). As the additive element, at least one or more elements such as zinc (Zn), magnesium (Mg), silicon (Si), copper (Cu), manganese (Mn), lithium (Li), and iron (Fe) were added. Aluminum alloy is the base material. The additive element may contain any one of the above-mentioned various elements, but since it forms a layered double hydroxide together with Al, it is a metal element (Zn, Mg, Cu, Fe) capable of generating divalent metal ions. , Ni, etc.) is preferably contained at least one kind. Further, in an aluminum alloy containing two or more kinds of metal elements, an Al-based layered double hydroxide containing each metal element is formed in the film. For example, when Zn and Mg are contained, a Zn—Al-based layered double hydroxide and an Mg-Al-based layered double hydroxide are simultaneously formed in the film. The total amount of these additive elements added is preferably 0.01% by mass or more and less than 50% by mass.

Specific examples of the aluminum alloy include aluminum alloys specified by the international aluminum alloy name. For example, 2000 series Al-Cu based alloys (duralmin, super duralmin), 6000 series Al-Mg-Si based alloys, Al-Mg-Si-Cu based alloys, 7000 series Al-Zn-Mg based alloys, Al. Various aluminum alloys such as −Zn−Mg—Cu based alloy (ultra-ultramin) can be applied. However, the present invention is not limited to standardized alloy systems such as these, and alloy systems having a wide range of compositions can be applied.

As described above, the anticorrosion film of the aluminum alloy material according to the present invention is composed of monohydrated aluminum oxide (AlO (OH)) and Al-based layered double hydroxide (LDH). Both are formed by a predetermined steam treatment on an aluminum alloy base material. Aluminum monohydrate oxide is the main component of the film, but aluminum monohydrate oxide is chemically stable and inherently useful as an anticorrosion film.

The feature of the film in the present invention is that it contains an Al-based layered double hydroxide, which is expected to have a further anticorrosion effect. The Al-based layered double hydroxide is represented by the general formula shown in Chemical formula 1 above. The constituent elements of the Al-based layered double hydroxide are supplied from the aluminum alloy base material and water vapor. ^{Al ions (Al 3+} ) and metal ions (M ²⁺ ) in the Al-based layered double hydroxide are supplied from the aluminum alloy base material. In particular, the metal ion (M ²⁺ ) is derived from a solute element (additional element) contained in the aluminum alloy. Also, ^{A n-it} is an anion, hydroxide ion (OH ^-), carbonate ions _(CO ^{3 2-),} nitrate ion (NO ₃ ^-), sulfate ion _(SO ^{4 2-),} fluorine ion (F ^- ), At least one of chlorine ions (Cl ⁻ ), but these anions are supplied from the steam of the film forming treatment. For example, when water vapor is generated from pure water and the film formation treatment is performed with this water vapor, carbon dioxide in the air is contained in the water vapor, so carbonic acid ions (CO ₃ ^2- ) are mainly supplied as anions. Will be done.

In the aluminum alloy material found by the present inventors, it is considered that the content of the Al-based layered double hydroxide in the film is within a predetermined range. In the present invention, the content of the Al-based layered double hydroxide is defined based on the diffraction peak of the X-ray diffraction performed on the film surface. Specifically, the ratio (Y) of the peak intensity (X) of 200 reflection of the monohydrated aluminum oxide (AlO (OH)) and the peak intensity (Y) of 003 reflection of the Al-based layered double hydroxide. / X) is an aluminum alloy material characterized by being 0.1 to 0.5. The Al-based layered double hydroxide protects the film by the above-mentioned anion exchange ability and improves the corrosion resistance of the aluminum alloy material, but when the peak intensity ratio Y / X is less than 0.1, the amount is too small. Therefore, the film is not effectively protected and may be eroded. On the other hand, the upper limit of the peak intensity ratio Y / X is set to 0.5 because the amount of Al-based layered double hydroxide having a lower density than that of monohydrated aluminum oxide (AlO (OH)) is large. This is because the average density of the film is reduced, and as a result, the corrosion resistance of the film is impaired. A more preferable range of this peak intensity ratio Y / X is 0.15 to 0.40.

In the present invention, the content of the Al-based layered double hydroxide is defined by the peak intensity ratio in X-ray diffraction because it is a fine compound and it is difficult to directly observe it with a microscope or the like. This is because X-ray diffraction is a relatively simple analytical means, and there is a certain degree of reliability in the quantification of a trace substance called an Al-based layered double hydroxide. Here, the peak of 200 reflections of monohydrated aluminum oxide (AlO (OH)) shows the maximum peak intensity and is an independent peak, which is optimal as a reference for calculating the peak intensity ratio. The peak of 200 reflections of the reference monohydrated aluminum oxide (AlO (OH)) is observed in the vicinity of 2θ = 48 to 49 °. On the other hand, the diffraction peak of 003 reflection is applied as the diffraction peak of the Al-based layered double hydroxide because it shows the maximum peak intensity as the peak of the Al-based layered double hydroxide. The position of the diffraction peak of the Al-based layered double hydroxide differs depending on the included metal ion and anion, but is observed in the vicinity of 2θ = 9 to 12 °.

Regarding the present invention, the film composed of the monohydrated aluminum oxide and the Al-based layered double hydroxide preferably has a thickness of 1 to 100 μm. If it is less than 1 μm, if a minute scratch is generated, erosion of the base material will occur from the scratch. On the other hand, if it exceeds 100 μm, the film may be cracked or peeled due to stress or thermal shock, and the corrosion resistance may be inferior.

By the way, according to the study by the present inventors, the aluminum alloy material subjected to the steam treatment by the present inventors is a material provided with the anticorrosion film described above, but at the same time, the strength of the aluminum alloy base material is increased. It has been confirmed that it has occurred. When the factors for strengthening the material were examined, it was found that the solute atoms (atoms of the additive elements) of the aluminum alloy were moved by the heat generated by the steam treatment, and precipitates were formed. Then, it was considered that this precipitate functions as dispersed particles and reinforces the aluminum alloy base material. However, the present inventors considered that there is a suitable range for both size (particle size) and dispersibility (formation density) in order for the precipitate to appropriately contribute to material strengthening.

According to the present inventors, in the aluminum alloy material according to the present invention, the size of the precipitates in the base material has an average diameter of 2 nm or more and 7 nm or less. Precipitates smaller than this size do not exert any strengthening effect. Coarse precipitates also reduce the degree of strengthening action. Aggregates of atoms of a size within this range have the greatest dispersion-enhancing effect. It is not required that all the precipitates have the same size, but it is preferable that the sizes of the precipitates are the same. Regarding the measurement of the size of the precipitate, any precipitate that can be observed with an electron microscope or the like may be directly measured. Further, the equivalent diameter of the precipitate may be calculated from the number of atoms of the solute atom constituting the precipitate and the atomic radius of the element.

In order for the precipitate to act as a reinforcing factor for the aluminum alloy base material, its dispersibility is also required. Specifically, it is preferable that the number density of precipitates formed is 2 × 10 ²³ / nm ³ or more and 15 × 10 ²³ / nm ³ or less. The region in which the above precipitates are preferably distributed may be expressed in the entire base material, but the precipitates may be distributed only in a part of the base material (near the surface or the like).

As described above, the aluminum alloy material according to the present invention is excellent in corrosion resistance because it has an effective anticorrosion film, and the microstructure of the aluminum alloy base material is also improved and strengthened. The shape of the aluminum alloy material according to the present invention is not limited, and any shape such as a plate shape and a tubular shape can be applied. In addition, there are no restrictions on the dimensions. This is because, as will be described later, in the surface treatment method performed in the method for producing an aluminum alloy material according to the present invention, a film can be formed without any shape limitation or dimensional limitation. Further, the formation of the film may be partial and may be either single-sided or double-sided.

Next, a method for producing an aluminum alloy material according to the present invention will be described. As described above, the present invention is a material in which a film composed of a monohydrated aluminum oxide and an Al-based layered double hydroxide is formed on an aluminum alloy material. As a result of examining suitable film forming means, the present inventors have found steam treatment in which a strict temperature range is set. That is, the method for producing an aluminum alloy material according to the present invention is a method including a step of bringing a base material made of an aluminum alloy into contact with water vapor of 150 ° C. or higher and lower than 200 ° C. to form a film on the surface of the base material. be.

In the film forming treatment on the aluminum alloy base material in the present invention, strict control of the temperature and pressure of water vapor is an essential configuration. According to the study by the present inventor, in the steam treatment at less than 150 ° C., the formation of Al-based layered double hydroxide is not observed, and sufficient corrosion resistance cannot be imparted to the film. On the other hand, the Al-based layered double hydroxide cannot be effectively present even in the steam treatment at 200 ° C. or higher.

Further, the steam treatment of the present invention changes the microstructure of the base material in addition to forming an anticorrosion film on the aluminum alloy. The heat of water vapor promotes the movement of solute atoms in the alloy to form precipitates. The strength of the aluminum alloy base material can be improved by the suitable distribution state of the precipitate. That is, the steam treatment of the present invention has two material property improving effects, that is, the effect of improving the corrosion resistance by forming the film and the effect of improving the strength of the aluminum alloy, and at the same time, these effects can be exhibited.

Then, as described above, the precipitate has a suitable size and formation number density. The temperature of the steam treatment is preferably 150 ° C. or higher and lower than 200 ° C. in order to make the distribution state of the precipitates suitable. This is because at 150 ° C. or lower, small-sized precipitates (aggregates of solute atoms) that are difficult to contribute to the strength improving effect are preferentially generated instead of the precipitates having a strengthening effect. On the other hand, at 200 ° C. or higher, the precipitate becomes too coarse and the strength is lowered. A more preferable temperature is 170 or more and 190 ° C. or less.

For steam treatment, the above temperature range must be specified, and other conditions can be adjusted arbitrarily. The pressure of water vapor is preferably in the range of 0.1 to 10 MPa. The pressure is more preferably 0.2 to 5 MPa, still more preferably 0.5 to 2 MPa. This is because the pressurization brings about a two-phase equilibrium state of saturated steam and sub-critical water, and it is possible to promote the reactivity to the formation of the corrosion-resistant film. By keeping the pressure constant, a uniform film can be formed.

Water vapor is generated by heating and vaporizing water, but water used as a water vapor source is pure water or an aqueous solution as appropriate. The pure water is preferably ion-exchanged water, distilled water, or ultrapure water having an electric conductivity of 1 mS / m or less. Further, as the aqueous solution, the vapor of an aqueous solution of an anion-containing carbonate, nitrate, sulfate, or fluoride salt can be used.

The method of contact between the water vapor and the aluminum alloy base material is not particularly limited. The steam treatment may be performed by exposing an aluminum alloy as a treatment material to steam in a closed space such as a predetermined reactor or container. As a specific method, the treatment is possible by arranging the base material together with water in a container and exposing the base material to the water vapor atmosphere generated by controlling the temperature and pressure. Further, the treatment may be performed by directly injecting water vapor onto the treatment material.

The treatment atmosphere may be the air or the treatment may be carried out in a container purged with an inert gas. When the Al-based layered double hydroxide of the film is formed, anions are taken in from the treatment atmosphere. When steaming in the atmosphere, carbonic acid ions are taken in from the atmosphere to form an Al-based layered double hydroxide.

The treatment time of the treatment liquid with water vapor is not particularly limited, but the treatment of 0.5 hours or more is preferable from the viewpoint of forming a film having a suitable film thickness. In addition, the steam treatment improves the strength of the base material at the same time as forming the film. When strengthening the entire base material, the processing time can be adjusted according to the size of the base material.

For the aluminum alloy material that has been subjected to the above treatment, post-treatment such as cleaning may or may not be appropriately performed. This is because the salt concentration in the treatment liquid is low, so that the amount of impurities adsorbed on the surface of the aluminum alloy material after the treatment is reduced. Further, the treated aluminum alloy material may be painted.

The steam treatment in the present invention is also useful as a surface treatment method for an existing aluminum alloy member without a film. For example, by performing the above steam treatment using an untreated building material, structural material, or the like as a base material, a suitable film can be formed to improve corrosion resistance and the strength of the base material can be improved. Although this surface treatment method requires temperature control, it can only be carried out by bringing water vapor into contact with the base material. Therefore, there are no shape or dimensional restrictions on the material to be treated, and it can be said that its usefulness is high. ..

As described above, the aluminum alloy material according to the present invention has a film in which a monohydrated aluminum oxide and an Al-based layered double hydroxide are composited, and the film has more suitable corrosion resistance. In addition, at the same time as the film is formed, a peculiar change occurs in the microstructure of the base material, which also improves the strength.

The method for producing and treating an aluminum alloy material according to the present invention is a method for applying water vapor in which the temperature and pressure are strictly controlled. This steam treatment is different from the conventional chemical conversion treatment using chemical solutions such as acids, alkalis, and heavy metals, and can be carried out at low cost and has a low environmental load. Then, this steam treatment can simultaneously improve the material properties having different properties of forming an effective anticorrosion film and strengthening the aluminum alloy base material. The present invention is simple but highly effective, and can be applied to large members and structures, so that it can be expected to be widely used.

The figure which outlines the structure of the steam treatment apparatus used in this embodiment. SEM photograph of the surface of aluminum alloy material steam-treated at each temperature. XRD analysis results of aluminum alloy material steam-treated at each temperature. Polarization curve of aluminum alloy material steam-treated at each temperature.

Hereinafter, preferred embodiments of the present invention will be described.
First Embodiment : In the present embodiment, as the aluminum alloy base material, an Al-Zn-Mg-Cu alloy (composition: 5.6 mass% Zn, 2.6 mass% Mg, 1.) Which is an aluminum alloy in the 7000 series. 8 mass% Cu, the balance Al) was prepared, and this base material was subjected to steam treatment. A commercially available material having the above composition cut out to a size of 20 × 20 mm and a thickness of 1.5 mm was used as a test piece.

The above test piece was surface-treated for film formation using a steam treatment device. The steam treatment apparatus of FIG. 1 is a horizontal autoclave, and pure water (electrical conductivity of 0.1 mS / m or less) as a steam source is injected into the lower part. In addition, a plurality of test pieces can be hung from the upper part of the device. For the steam treatment, the temperatures were set to 100 ° C., 170 ° C., 180 ° C., and 240 ° C., the pressure was 1 MPa at each temperature, the treatment time was 0.5 hours, and the surface treatment was performed while maintaining the temperature and pressure.

Then, the surface film of the aluminum alloy test piece after the surface treatment was observed (FE-SEM), and then the XRD analysis was performed on the surface of the test piece. XRD was measured as an X-ray source Cu-Kα at a voltage of 50 kV and a current of 300 mA. Then, the corrosion resistance was evaluated in order to confirm the effect of the steam treatment. As an evaluation of corrosion resistance, the polarization curve was measured. As for the polarization curve, the electrolytic solution was a 5 mass% NaCl solution. Before the measurement, the solution was bubbled with nitrogen and then the polarization was measured.

Furthermore, in order to confirm the effect of the steam treatment performed in this embodiment on the aluminum alloy base material, the distribution state of solute atoms inside the base material was analyzed. As this analysis, three-dimensional atom probe analysis (3DAP: manufactured by CAMECA, product name Oxford NanoScience Three-Dimensional Atom Probe) was performed. In three-dimensional atom probe analysis, strong electrolysis is applied to a needle-shaped sample, thereby ionizing and desorbing atoms on the sample surface (electrolytic evaporation), and the ions are analyzed one by one with a two-dimensional detector to form an atomic arrangement. This is a method of obtaining a three-dimensional atomic distribution of a sample by specifying.

In the present embodiment, for each sample, a needle-shaped sample having a tip radius of curvature of 30 to 80 nm is prepared, and under the conditions of a temperature of 30 K and a pulse fraction of 20%, 3 under an ultra-high vacuum of ^{10-8 Pa or less.} Dimensional atom probe analysis was performed to analyze the three-dimensional distribution of solute atoms Mg and Si. Then, from the obtained profile, the diameter of the precipitate and the density of formed numbers were calculated. For the number density of precipitates, the number of precipitates present in ^{the analysis region (nm 3) was counted.} Further, the precipitate diameter was determined by counting the solute atoms constituting the captured individual precipitates. In this embodiment, 100 or more precipitates were captured for each sample, and the individual diameters were measured by the above method to obtain an average value thereof.

Further, in the present embodiment, in order to confirm the strength of the aluminum alloy base material after the steam treatment, the hardness of the base material surface was measured. The hardness was measured using a Micro Vickers hardness tester (HM-103, manufactured by Mitutoyo Co., Ltd.) on the sample surface from which the film was mechanically polished and removed before the measurement. The measurement conditions were a test load of 2.94 N and a load time of 15 s.

The evaluation results of the aluminum alloy material steam-treated at each temperature will be described below. First, FIG. 2 shows the morphological observation results of the sample surface (film). The formation of acicular crystals is observed in the samples treated at 170 ° C and 180 ° C. The acicular crystals are considered to be monohydrated aluminum oxide (AlO (OH)). On the other hand, in the sample treated at 100 ° C., the presence of the film itself covering the surface of the base material can be confirmed, but the formation of needle-like crystals is not observed. A thick film was also formed on the sample treated at 240 ° C., but the acicular crystals disappeared.

FIG. 3 shows the XRD analysis results of the aluminum alloy material steam-treated at each temperature. In the samples treated at 170 ° C. and 180 ° C., peaks derived from monohydrated aluminum oxide (AlO (OH)) were observed, and particularly clearly appeared near 2θ = 14 ° and 48 °. In addition to this, a peak derived from layered double hydroxide (ZnAl-LDH) is observed (2θ = around 10.5 °, around 19.5 °). On the other hand, at the treatment temperatures of 100 ° C. and 240 ° C., neither the peak of AlO (OH) nor the peak of LDH was observed.

From the XRD profile of the samples treated at 170 ° C and 180 ° C, the peak intensity (X) of 200 reflections of monohydrated aluminum oxide (AlO (OH)) and the peak of 003 reflections of Al-based layered double hydroxides. The ratio (Y / X) to the intensity (Y) was calculated. As a result, Y / X = 0.17 at 170 ° C. and Y / X = 0.37 at 180 ° C. In particular, the peak of LDH can be clearly observed by the treatment at 180 ° C., and it is considered that the growth of LDH is remarkable at this temperature.

Then, FIG. 4 shows the polarization curves of the aluminum alloy material steam-treated at each temperature obtained by using Potence / Galvanostat (VersaSTAT3, manufactured by Princeton Applied Research). FIG. 4 also shows the polarization curve of the aluminum alloy without steam treatment. From FIG. 4, it is considered that the steam treatment at 100 ° C. is almost the same as that of the untreated sample, and the steam treatment at this temperature has almost no anticorrosion effect. The corrosion current density of the samples treated at 170 ° C, 180 ° C, and 240 ° C decreased, but the sample treated at 240 ° C observed a rapid increase in current density due to pitting corrosion at around -0.3V. Has been done. It can be seen that the treatment at 240 ° C. does not provide a sufficient anticorrosion effect even if a film is formed. The decrease in corrosion current density was confirmed in the sample treated at 180 ° C, which showed a significant decrease in corrosion current density and expansion of the non-active region, and an effective anticorrosion effect without a rapid increase in current density due to pitting corrosion. can. Although the decrease in corrosion current density is smaller than 180 ° C even in the treatment at 170 ° C, the anticorrosion effect is recognized. The above difference in corrosion resistance in each sample is consistent with the XRD results for the coating. That is, it can be seen that the anticorrosion effect of the film is greatly increased by the formation of AlO (OH) and LDH.

Next, the analysis / evaluation results of the aluminum alloy base material will be described. Table 1 shows the results of precipitate measurement based on three-dimensional atom probe analysis performed on the base material of the aluminum alloy material steam-treated at each temperature. Table 2 shows the results of hardness measurement of each sample.

Regarding the steam treatment performed in the present embodiment, a large number of precipitates are formed in the treatment at 100 ° C., but the average diameter thereof is very small and the strengthening action is poor. This is because the temperature is low and the movement of solute atoms has not yet occurred actively. On the contrary, in the treatment at 240 ° C., the movement of solute atoms is promoted and bonds between the precipitates are formed, so that it can be said that coarse precipitates are generated at a low density. On the other hand, in the treatments at 170 ° C. and 180 ° C., the solute atoms move appropriately, and it is considered that precipitates having a suitable size and capable of maximizing the strengthening action are produced at high density. ..

Then, from the results of hardness measurement of each sample, it was confirmed that the sample having the treatment temperature of 170 ° C. and 180 ° C. increased by 20 Hv or more with respect to the untreated material. In particular, the hardness when treated at 180 ° C. shows a hardness of 150% or more (35 Hv increase) of the untreated material. In the steam treatment at 240 ° C., the hardness of the untreated material is increased, but the width is small.

Second Embodiment : In the present embodiment, as the aluminum alloy base material, an Al—Cu alloy (composition: 3.94% by mass Cu, balance Al) which is an aluminum alloy in the 2000s and Al which is an aluminum alloy in the 6000s. -Mg-Si (composition: 0.96% by mass Mg, 0.59% by mass Si, balance Al) and Al-Mg-Si-Cu alloy (composition: 0.74% by mass Mg, 0.65% by mass) Si, 0.85 mass% Cu, and the balance Al) were prepared, and a piece cut out to a size of 20 × 20 mm and a thickness of 1.5 mm was used as a test piece. Then, this base material was subjected to the same steam treatment as in the first embodiment.

For steam treatment, the same steam treatment apparatus as in the first embodiment is used, the temperatures are set to 100 ° C., 170 ° C., 180 ° C., and 240 ° C., the pressure is 1 MPa at each temperature, the treatment time is 0.5 hours, and the temperature and pressure are set. Retained and surface treated.

Then, XRD analysis, corrosion resistance evaluation (polarization curve measurement), three-dimensional atom probe analysis, and hardness measurement were performed on each aluminum alloy test piece after the steam treatment. The conditions in these analyzes and tests were the same as in the first embodiment.

The evaluation results of the two aluminum alloy materials treated with steam in the second embodiment will be described below. First, regarding the XRD analysis, the analysis results of the three aluminum alloy materials all showed the same tendency as the aluminum alloy materials of the first embodiment. That is, in the samples treated at 170 ° C. and 180 ° C., peaks derived from each of monohydrated aluminum oxide (AlO (OH)) and layered double hydroxide (LDH) were observed. On the other hand, at the treatment temperatures of 100 ° C. and 240 ° C., neither the peak of AlO (OH) nor the peak of LDH was observed. The peak intensity (X) of 200 reflection of monohydrated aluminum oxide (AlO (OH)) and the peak intensity (Y) of 003 reflection of Al-based layered double hydroxide in two aluminum alloy samples treated at 180 ° C. The results of calculating the ratio (Y / X) with and to are shown in Table 3.

Explaining the result of the corrosion resistance evaluation, also in this evaluation item, the aluminum alloy material of the second embodiment shows a decrease in corrosion current density in the sample treated at 170 ° C. and 180 ° C., and has an effective anticorrosion effect. Was confirmed. On the other hand, no anticorrosion effect was observed in the sample treated with steam at 100 ° C.

Table 4 shows the results of precipitate measurement based on the three-dimensional atom probe analysis of each aluminum alloy base material. Table 5 shows the results of hardness measurement.

From these tables, the effects of steam treatment of the aluminum alloys (Al-Cu alloy, Al-Mg-Si alloy, Al-Mg-Si-Cu alloy) used in the second embodiment are shown in the aluminum alloy of the first embodiment. It can be seen that the same tendency can be seen. That is, from the result of hardness measurement, in the sample in which the treatment temperature is 170 ° C. and 180 ° C., there is a clear effect of improving the strength as compared with the untreated material. In particular, the sample treated at 180 ° C. was a preferable result. The steam treatment at 240 ° C. shows an increase in hardness with respect to the untreated material, but is equivalent to the treatment result at 100 ° C. and the effect is small. And the state of the precipitate ascertained from the three-dimensional atom probe analysis supports the result regarding this hardness. In the treatment at 100 ° C., the precipitates are minute, and in the treatment at 240 ° C., the precipitates become coarse and the density becomes low. On the other hand, it can be confirmed that in the treatments at 170 ° C. and 180 ° C., precipitates capable of effectively exerting the strengthening action are produced at a high density by appropriate movement and aggregation of solute atoms.

In this embodiment, in addition to the above three aluminum alloys, Mg is 0.59 to 0.96% by mass and Si is 0.59 to 0. With respect to Al-Mg-Si, which is an aluminum alloy in the 6000 series. The alloys in the range of 96% by mass were subjected to steam treatment, and the corrosion resistance, hardness, and precipitates were examined. It has been confirmed that the same effect as described above was obtained in this composition range as well.

As described above, the aluminum alloy material according to the present invention exhibits suitable corrosion resistance due to an anticorrosion film in which an Al-based layered double hydroxide is compounded with a monohydrated aluminum oxide. At the same time, the strength of the base material is also improved. Since the steam treatment for producing this aluminum alloy material is a treatment with water, it is a treatment method with low cost and low environmental load. Further, this steam treatment can cause the aluminum alloy base material to be strengthened at the same time as forming the anticorrosion film. The present invention is a technique that can be applied to various uses of aluminum alloys as well as constituent materials of transportation equipment such as automobiles and aircraft.

Claims (6)

In an aluminum alloy material composed of a base material made of an aluminum alloy and a film formed on the surface of at least one of the base materials.
The aluminum alloy as the base material is at least 1 Tane含no solute element is an element other than aluminum, 2000 series according to the provisions of international aluminum alloy name, 6000 series, becomes more or 7000 series aluminum alloy,
The film is composed of monohydrated aluminum oxide (AlO (OH)) and Al-based layered double hydroxide shown in Chemical formula 1 below.
Regarding the diffraction peak of X-ray diffraction performed on the film, the ratio of the peak intensity (X) of 200 reflection of the monohydrated aluminum oxide and the peak intensity (Y) of 003 reflection of the Al-based layered double hydroxide. An aluminum alloy material having (Y / X) of 0.1 to 0.5.

In the aluminum alloy as the base material, precipitates formed by the aggregation of solute element atoms are dispersed.
The precipitate is 2 nm or more and 7 nm.
The aluminum alloy material according to claim 1, wherein the number density of the precipitates formed is 2 × 10 ²³ / nm ³ or more and 15 × 10 ²³ / nm ^{3 or less.} The aluminum alloy material according to claim 1 or 2, wherein the solute element is at least one of zinc, magnesium, silicon, copper, manganese, lithium, and iron. The aluminum alloy material according to any one of claims 1 to 3, wherein the thickness of the film is 1 to 100 μm. The method for producing an aluminum alloy material according to any one of claims 1 to 4, wherein a base material made of an aluminum alloy and water vapor at 170 ° C. or higher and 190 ° C. or lower are brought into contact with each other for 0.5 hours or longer. A method for producing an aluminum alloy material, which comprises a step of forming a film on the surface of a base material. In a surface treatment method for forming a film on the surface of an aluminum alloy material composed of aluminum alloys in the 2000s, 6000s, and 7000s according to the regulations of the international aluminum alloy name, which contains at least one solute element which is an element other than aluminum.
A method for surface-treating an aluminum alloy material, which comprises a step of forming the film by contacting the aluminum alloy material with water vapor of 170 ° C. or higher and 190 ° C. or lower for 0.5 hours or longer.

Images