JPH11323577A - Alloy surface treatment method and alloy with excellent surface aging resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-soluble compound which does not impair a poorly soluble compound layer useful for protecting the inside of a material and which causes a problem with time-deterioration of the surface such as hygroscopicity. Provided are a surface treatment method for producing a material having a more stable and high-functional surface by selectively eluting and removing only the material, and an alloy material produced by the method and having excellent resistance to aging. SOLUTION: An alloy containing a metal element forming a water-soluble compound as a component is mixed with an alkaline degreasing agent to form an alloy of 5 to 5%.
After the removal of 0 mg / m ² , the alloy is immersed in water having a pH of 5 to 8 and a total concentration of impurity elements of 100 ppm or less, or the water is sprayed on the alloy so that the surface of the alloy is sprayed. Only the formed water-soluble compound is selectively eluted / removed, and the atomic fraction of the metal element contained in the water-soluble compound existing in a depth region up to 5 nm from the surface of the alloy is reduced to the same depth region. The present invention provides an alloy having excellent surface aging resistance of 10 at.% Or less with respect to all elements except H present in the alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates mainly to the field of metal industry, particularly to the fields of automobiles, building materials, cans, and the like, in the production process of these alloy materials and in the use environment after production. By selectively removing water-soluble compounds that are formed on the surface and significantly affect the material properties, a method of treating the alloy surface to form an alloy surface with excellent surface aging resistance, and excellent surface aging resistance It is about alloys.

[0002]

2. Description of the Related Art Conventionally, as a method of removing a surface layer such as an oxide layer formed on the surface of an alloy, a mechanical method such as grinding, cleaning by ion sputtering or arc discharge (for example, R.F. Welding Journal September Issue (1976) PP.1750
−59) (RF Ashton et al .: Welding Journal, Sep.
t. (1976), pp. 1750-1759.), an acid (Japanese Patent Publication No. 7-116629) and an alkaline solution (Japanese Patent Application Laid-Open No.
4835) immersion chemistry has been used.

As a method for evaluating the surface of a material obtained in this manner, the relationship between the atomic composition of the surface and the surface performance has mainly been considered by elemental analysis such as chemical analysis. The relationship between the abundance ratio of the elements present in each chemical state, such as the valence number, and the surface performance did not matter. Therefore, for example, even when it is known that the alloy surface has deteriorated with time due to the presence of the surface oxide film, it has been clarified what compounds in the surface oxide film cause the time deterioration. As a result, no effective measures were taken.

[0004]

A conventional method for removing a surface layer centered on an oxide layer formed on the surface of an alloy is as follows.
Like the method of immersing the alloy in acid, etc., the surface layer extends from the outermost surface to a certain depth, regardless of its composition or chemical state,
It is a method of removing uniformly. However, as a result of a detailed study of the relationship between the composition and the chemical state of various compounds present in the surface layer of these alloys and the surface performance, the inventors found that the cause of surface aging is that Among the compounds, they were found to be particularly water-soluble compounds. That is, the water-soluble compound has a strong hygroscopic property, and such a hygroscopic part is
It was found to be highly reactive and to easily form harmful corrosion products by combining with Cl and F contained in water and CO _{2 in} the air and the like, and the material surface was easily deteriorated with time.

However, the conventional method of removing the surface layer by immersion in an acid or alkali removes the compounds in the surface layer indiscriminately, so that a useful surface function such as protection of the material surface is provided. It was also clarified that the hardly soluble compound layer was removed at the same time, and the active metal layer was exposed on the surface, which rather deteriorated the surface performance. The present invention is directed to a method of absorbing moisture in a material production process or a use environment after production without impairing a hardly soluble compound having a useful surface function such as protection of a material surface among various compounds in a material surface layer. And selectively elute and remove only water-soluble compounds that react with harmful elements on the surface with time degradation such as Cl and F existing in those atmospheres, and are more chemically stable, and It is an object of the present invention to provide a surface treatment method for producing a material having a highly functional surface, and an alloy material having a surface which has been treated by the treatment method and has excellent resistance to deterioration with time.

[0006]

SUMMARY OF THE INVENTION The present invention removes a water-soluble compound formed on the surface of an alloy in the process of preparing an alloy containing a metal element forming a water-soluble compound or in a use environment after the preparation. After removing 5 to 50 mg / m ² of the surface layer of the alloy using an alkaline degreasing agent,
Is 5 to 8 and the total content concentration of impurity elements is 1
A treatment of an alloy surface characterized by immersing in water of not more than 00 ppm or spraying the water on the alloy to selectively elute and remove only water-soluble compounds formed on the alloy surface. It provides a method.

In particular, the alloy containing the metal element forming the water-soluble compound is an alloy containing Mg, and the water-soluble compound formed on the surface of the alloy is a water-soluble magnesium compound. An alloy surface treatment method is provided. Further, among them, M
Another object of the present invention is to provide an alloy surface treatment method, wherein the alloy containing g is an alloy containing Al as a main component.

An alloy containing a metal element forming a water-soluble compound, wherein the atomic fraction of the metal element contained in the water-soluble compound existing in a depth region up to 5 nm from the surface of the alloy Provides an alloy having excellent surface aging resistance, characterized in that the content is 10 at.% Or less with respect to all elements except H present in the depth region. Among them, particularly, the alloy containing the metal element forming the water-soluble compound is an alloy containing Mg, and the water-soluble compound formed on the surface of the alloy is a water-soluble magnesium compound. The present invention provides an alloy containing Mg and having excellent surface aging resistance.

Further, among them, the present invention provides an alloy excellent in surface aging resistance, characterized in that the alloy containing Mg is an alloy containing Al as a main component. An alloy containing a metal element forming a water-soluble compound is coated with an alkaline degreasing agent to form a surface layer of 5 to 50 mg / m 2.
^{2 After the} removal, immerse in water having a pH of 5 to 8 and a total content of impurity elements of 100 ppm or less, or spray the water on the alloy so that 5 nm
Elute and remove water-soluble compounds present in the depth range up to
The atomic fraction of the metal element contained in the water-soluble compound present in the depth region is 10 at.
% Or less, which provides an alloy having excellent surface aging resistance.

In particular, the alloy containing a metal element forming a water-soluble compound is an alloy containing Mg, and the water-soluble compound formed on the surface of the alloy is a water-soluble magnesium compound. The present invention provides an alloy having excellent surface aging resistance. In particular, the present invention provides an alloy excellent in surface aging resistance, characterized in that the alloy containing Mg is an alloy containing Al as a main component.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the surface of an alloy that deteriorates with time under the use environment is considered to be a cause of the deterioration with time in the material manufacturing process such as rolling at a high temperature and annealing at the time of manufacturing the alloy. A water-soluble compound is produced. Such an alloy contains a metal element that forms a water-soluble compound on the surface of the alloy, and examples of such a metal element include Li, Mg, Ca, and Ba. Alloys containing these metal elements as components include Al-Mg, Al-Li, Cu-Mg, Fe
-Mg alloy and the like. Among the water-soluble compounds formed on the surface of these alloys, compounds that presently pose an industrial problem include Li ₂ O, MgO, CaO, BaO and the like.

By the way, on the outermost surface of such an alloy material, a grease component used as a lubricating oil or a rolling oil in a material manufacturing process such as rolling or annealing at a high temperature is often attached. . Since such a fat component is a hardly soluble compound, it is difficult to remove the alloy material by treating it under the same conditions as those for removing the water-soluble compound. Furthermore, since such fats and oils components are often non-uniformly adhered to the outermost surface of the alloy, the same conditions as those for removing the water-soluble compounds without any pretreatment to remove the fats and oils components are used. When the treatment is carried out, the portion where the oil component is adhered will be water-repellent and thus will not be removed, and only the water-soluble compound in the portion where the oil component is not adhered will be dissolved. It may be uneven and may cause unfavorable phenomena such as uneven color tone for surface performance. Thus, in the case of an alloy material in which the fat and oil component is non-uniformly adhered to the outermost surface layer as described above, as a pretreatment, the hardly soluble fat and oil component in the non-uniform outermost surface layer was removed using an alkaline degreasing agent. Thereafter (hereinafter referred to as pretreatment), the alloy plate is immersed in a treatment water bath having a pH of 5 to 8 and the total content of impurity elements is 100 ppm or less, or the treated water is sprayed on the alloy surface. In this case (hereinafter, referred to as the present treatment), it was found that the water-soluble compound in the surface layer could be uniformly removed, and that a phenomenon unfavorable for surface performance such as uneven color tone did not occur. Experimental results have shown that the removal amount of the outermost surface layer by the alkaline degreasing agent in such a pretreatment step is preferably about 5 to 50 mg / m ² . In the case of the pre-treatment and the present treatment, when the alloy is a cut plate such as a thick plate, the alloy plate is placed on a transport roll and transported for processing or the like during processing. It is most effective to provide a nozzle for spraying the treated water. In the case of a coil-like material such as a thin plate, it is preferable to provide an immersion water tank and let the coil pass therethrough.

In general, as the alkaline degreasing agent, any of commercially available caustic soda, sodium phosphate and sodium silicate degreasing agents may be used. However, since the surface oxidized layer of the Al alloy containing Mg elutes in both alkali and acid, a degreasing agent having a high elution rate with respect to the surface oxidized layer, such as a caustic soda-based or sodium phosphate-based degreaser, must be used. If it is used, the entire surface oxide layer is eluted and removed in a short time, the removal amount of the surface layer is controlled to 5 to 50 mg / m ^2, and only the fat component in the outermost surface layer can be removed. Technically difficult. Therefore, when performing alkali degreasing treatment on an Mg-containing Al alloy using these degreasing agents having a high elution rate, the pH of the degreasing solution must be lowered and the treatment temperature must be lowered, so that the removal amount is precisely controlled. Difficult to control. On the other hand, the sodium silicate degreasing agent has a low elution rate of the surface oxide layer of the Mg-containing Al alloy and hardly etches hardly soluble compounds such as Al ₂ O _3. it is relatively easy to manage to 50 mg / m ^2,
It is most suitable as an alkaline degreasing agent for removing the fat component of the outermost surface layer of the surface oxide layer of the Mg-containing Al alloy.

By the way, the removal amount by such an alkali degreasing treatment can be easily obtained by measuring the weight difference before and after the treatment. The determination of color tone unevenness can be sufficiently made by visual inspection, but can be performed more accurately by using an optical microscope, particularly a polarizing microscope. The immersion water or spray water used for the treatment after the alkali degreasing is not required to be distilled water as long as the pH is 5 to 8, and even ordinary tap water containing various ions and organic substances as impurities is sufficient. It is possible to increase the effect. However, it is necessary to use water having a total impurity concentration of 100 ppm or less.

When the pH of the treated water is less than 5 or more than 8 and is in an acid or alkali region, not only water-soluble compounds but also poorly soluble compounds which are protective layers on the surface are eluted, which is not preferable. In addition, the kind of impurities contained in the treated water has little effect on the elution rate of the water-soluble compound if it is a trace amount, but if the total concentration of the contained impurities exceeds 100 ppm, on the other hand, these impurities are contaminated on the surface. And the elution rate of the water-soluble compound is reduced, and the effect is lost. Conventionally, industrial water that has been used to remove contaminants and the like physically attached to the material surface includes:
Since it contains a large amount of impurities such as Si, P, Ca, Mg, SO ₄ , Cl, and F, the impurity element contained in water adheres to the alloy surface before the water-soluble compound elutes. Such industrial water is not suitable as the treated water of the present invention.

The temperature of the immersion water or the spray water is not particularly limited, but the reaction rate varies depending on the temperature coefficient of solubility.
It is preferable to use the above warm water. In the case of immersion instead of spraying, it is desirable to use water at 90 ° C. or lower, which is stable as water. By the way, among the compound layers on the material surface, a problem which is particularly problematic in relation to deterioration with time is the outermost layer portion of the material which directly contacts and reacts with the environment. Therefore, when examining the correlation between the chemical state of the elements present in the outermost layer and the deterioration with time, among the elements that may form a water-soluble compound, the outermost layer of the atoms in a specific chemical state is also considered. It has been found that the abundance affects the aging phenomenon. That is, the abundance of the elements contained in the water-soluble compound present in a depth region up to 5 nm from the surface of the alloy is 10 a in terms of the atomic fraction with respect to all the elements except H present in the depth region.
It was found that when the content was less than t.%, excellent aging resistance was exhibited.

With respect to several alloys which have been subjected to the surface treatment method of the present invention and whose deterioration with time has not progressed by a time-dependent deterioration test, the atomic composition and chemical state of a region at a depth of about 5 nm from the alloy surface are determined by X-ray photoelectron Analysis by spectroscopy revealed that the content of metal elements contained in the water-soluble compound present in the same depth region and causing deterioration with time was not more than 10 at.% In atomic fraction with respect to all elements except H. Had become. (A method of analyzing the atomic composition and chemical state of the alloy surface by X-ray photoelectron spectroscopy will be described later.)
Also, the outermost layer of the same material having a thickness of about 5 nm is removed by sputtering with argon ions, and the depth from the surface is 5 nm.
When a region of about 10 nm to about 10 nm was analyzed by the same method as that for the outermost surface layer, the amount of the metal element contained in the water-soluble compound in the same layer was 10
Some were more than at.%. In other words, 5 nm from the alloy surface
Up to 10 at.% Of the metal element contained in the water-soluble compound present in the layers up to 10 at.
% Or less, the water-soluble compound is 10 at.
This indicates that even with the above-described presence, deterioration with time such as moisture absorption and surface reaction does not progress. This is because, even when the water-soluble compound of the outermost surface layer is removed by the surface treatment method of the present invention, the hardly soluble compound present on the outermost surface remaining without being removed becomes a protective layer, and further moisture absorption and This is because deterioration with time such as a surface reaction does not progress. Further, for comparison, the same analysis was performed on an untreated material having low aging resistance, and the depth from the surface was 5 to 1%.
In a region of about 0 nm, the alloy is not so different from an alloy excellent in aging resistance, but the amount of metal contained in the water-soluble compound existing at a depth of 5 nm from the surface is determined by the atomic fraction of all elements except H. Rate exceeded 10 at.%.

From the above, the amount of the metal element contained in the water-soluble compound existing in the depth region up to 5 nm from the surface of the alloy is determined by the atomic amount relative to all the elements except H existing in the same depth region. It can be seen that alloys having a fraction of 10 at.% Or less are alloys having excellent resistance to deterioration over time. Whether the compound formed on the surface of such an alloy is water-soluble or poorly soluble depends not only on the type of element contained in the compound but also on its compounding state. For example, in the case of Mg, it is water-soluble and harmful to the surface properties is Mg.
Among compounds containing MgO, MgCl ₂ , Mg
MgAl ₂ O ₄ which is only CO ₃ and other oxide
(Spinel) and MgFe ₂ O ₄ (magnesium ferrite) do not have such properties.

Among such water-soluble compounds, particularly, A
It is known that a water-soluble magnesium compound mainly composed of MgO formed on the surface of a Mg-containing alloy such as a 1-Mg, Fe-Mg, Cu-Mg alloy has a high hygroscopicity and reactivity. Such an alloy-based material is dipped in a solution at a temperature of 70 ° C. with a sodium silicate-based degreasing agent to obtain 5 to 50 mg / m 2.
^{2 After} removal, washing with water, immersion for 15 seconds in ion-exchanged water having a treated water temperature of 50 to 90 ° C. and a total impurity concentration of 50 to 100 ppm, by X-ray photoelectron spectroscopy,
As a result of measuring the atomic composition and chemical state of Mg in the outermost surface layer of about 5 nm, Mg contained in MgO, which is a water-soluble magnesium compound formed on the surface, was found in all alloy materials.
It was 10 at.% Or less, and only Al ₂ O ₃ , Fe ₂ O ₃ , and CuO were present on the surface of each alloy except MgO. When a time-dependent deterioration test was performed on these surface-treated alloys, the time-dependent deterioration phenomena such as moisture absorption and surface reaction did not progress. That is, all the compounds present on the surface after the treatment are poorly soluble compounds, and only the water-soluble magnesium compound causing various aging deterioration is eluted.
It is considered that, because of the removal, the occurrence of the temporal deterioration phenomenon was suppressed.

Further, among the alloys containing Mg, in particular, an alloy containing Al as a main component (Al—Mg—X, where X = Si, Cu, Zn;
Described as Mg alloy. ) Is widely used industrially as a structural material such as a car body, a can material, and the like, and all of the surfaces are covered with a surface layer mainly composed of Mg. MgO in such a surface layer has an adhesive property,
It has been found that it becomes a cause of inhibiting important surface functions such as weldability and chemical conversion. In the case of alloys containing Al as a main component, various methods have been devised and used as a method of removing such a Mg oxide layer, but in any case, the entire oxide layer is indiscriminately used. Since the protective layer is damaged and removed, an important protective layer (for example, Al ₂ O ₃ ) is also removed together, and the deterioration resistance with time is rather lowered for the following reason. That is, in the Al-Mg alloy system, usually, in a manufacturing process such as heat treatment, a layer in which the atomic composition of metallic magnesium is higher than the bulk alloy composition is present at the interface between the surface oxide layer and the bulk alloy layer. Many. If the oxide layer is indiscriminately removed by pickling or the like, such an interface layer in which metallic magnesium is concentrated is exposed on the surface. The concentration of such metallic magnesium differs depending on the alloy preparation conditions and atmosphere, but may reach the same level as the maximum of magnesium in the surface oxide layer. Since such metallic magnesium is extremely active, the metallic magnesium immediately oxidizes even at room temperature if the pickled alloy is left in the air immediately after pickling, forming magnesium oxide. This again causes deterioration with time of the surface. Therefore, the conventional surface treatment method that also impairs the poorly soluble protective layer will impair the deterioration resistance over time, but the method of the present invention removes water-soluble magnesium without impairing the protective layer. Therefore, it is possible to manufacture an Al—Mg alloy having excellent resistance to deterioration over time.

As described above, the abundance of an element in a specific chemical state existing in the outermost layer affects the aging resistance, but the chemical state of the element in the outermost layer region in the alloy is determined. And the abundance ratio can be easily determined by X-ray photoelectron spectroscopy, Auger electron spectroscopy, or the like.
In particular, in X-ray photoelectron spectroscopy, if the same element has a different chemical state, for example, whether it is metallic or forms a compound, etc., the binding energy of electrons is different. When the substance is mixed in the surface layer, the binding energy spectrum is divided into several peaks. Therefore, if the peak position and peak shape (symmetric or asymmetric, etc.) of the target chemical state are known in advance from the measurement of the reference material or the literature, the atomic fraction of the target compound can be obtained. .

In the following, taking the Mg compound formed on the surface of the Al—Mg alloy as an example, the spectrum of the core electron level unique to Mg measured by X-ray photoelectron spectroscopy shows that Mg
A quantitative method for determining the atomic fraction of each compound containing an element will be specifically described. FIG. 1 is a schematic diagram of a spectrum in a Mg2p state on the surface of an Al-Mg alloy by X-ray photoelectron spectroscopy. First, a background 2 is subtracted from an actually measured spectrum 1 as shown in FIG. 1 by an appropriate method such as an integration method, and then, using an appropriate fitting curve 4, a least square method is used. The subtracted spectrum is converted to spectrum 3 of several single chemical states.
Decomposes into a to 3c.

Next, according to the literature and the measurement of the standard substance,
A determination is made as to which binding energy of the decomposed spectrum is closest to that of any of the compounds known so far, and the spectrum is identified. For example, if 3a is a spectrum of MgO, the atomic fraction of MgO to the whole Mg in the analysis region can be easily obtained as (area 1 at peak of 3a) / (area 1 of whole spectrum of Mg).

Further, in order to determine the atomic fraction with other elements, an apparatus function, a sensitivity coefficient, and the like are required. In any case, in the X-ray photoelectron spectroscopy, the surface atomic composition other than H is already used. A widely used method can be easily applied as a method for determining the amount of glycerol. The surface oxide film thickness remaining on the material surface treated by the method of the present invention is determined by glow discharge emission spectroscopy.
(Glow Discharge Optical Emission Spectroscopy: G
It can be confirmed relatively easily by measuring a depth profile by D-OES (hereinafter abbreviated as GD-OES).

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 1 mm thick Mg-containing Al alloy sheet (4.5 watts)
In order to remove the water-soluble oxide formed on the surface of the t.%-Mg-containing alloy (5182 (JIS standard)), the alloy thin plate was treated as a pretreatment with a sodium silicate-based degreasing agent (FC).
-315 (manufactured by Nippon Parker)) is immersed in a solution at a temperature of 70 ° C. at 2% to remove 5 to 50 mg / m ² , and then washed with water. After immersing in 50 to 120 ppm of ion exchange water for 15 seconds, it was dried to obtain a test piece. The measurement of the removal amount in the alkaline degreasing was obtained from the weight difference before and after the treatment. Further, the surface oxide film thickness of each test piece was determined from the result of the depth profile by GD-OES. (The film thickness determined by GD-OES is the average value of the surface area having a diameter of about several millimeters.) Mg from the surface of the material before and after the treatment to a depth of 5 nm
The change in the atomic composition for each chemical state was measured by X-ray photoelectron spectroscopy (hereinafter abbreviated as XPS), and the further processed samples were subjected to an exposure test under the conditions shown in Table 1. Table 2 shows the results. In addition, spraying was performed under the same conditions, but almost the same results were obtained.

For each sample, the peak separation of the spectrum data of the Mg2p level from the surface of the material measured by XPS to a depth of 5 nm was performed. In each sample, only the peak of metallic Mg or MgO was observed. Was done. Since the oil and fat component on the surface of the material treated by the treatment method of the present invention has been completely removed by the pretreatment, color tone unevenness does not occur, and the water-soluble compound on the material surface is selected by this treatment. The sample treated with the method of the present invention has a lower surface M than the untreated material.
It was found from the XPS analysis that the Mg concentration in gO was significantly reduced. From the above results, it is clear that all of the elements exhibit good aging resistance when the atomic fraction of Mg forming MgO on the surface is 10 at.% Or less of all elements except H in the same area. It is.

Next, a description will be given as a comparative example of a material processed under conditions deviating from the conditions of the present invention. As a pre-treatment, a material whose removal amount by alkali degreasing was 50 mg / m ² or more (Comparative Example 1) was not subjected to coloration unevenness even if treated in the subsequent main treatment under the conditions of the present invention. It can be seen that the degree of deterioration with time is not good. This means that the oxide film thickness is 1
As can be easily understood from the fact that it is as thin as nm,
Most of the oxide film was eluted in the pretreatment stage, and a layer of concentrated magnesium on the surface of the alloy (total Mg: 20 a)
%) was exposed, and after the treatment, the metallic magnesium was oxidized to become almost MgO (20 at.%) again from the XPS results.

Pretreatment is appropriate (removal amount: 36 mg /
m ² ), the treated water of this treatment is pH 4 (Comparative Example 2), pH 9
It can be seen that, similarly to Comparative Example 1, in the case of (Comparative Example 3) and the processing plate out of the conditions of the present invention, color tone unevenness does not occur, but the degree of deterioration with time is not good. This is because the oxide film thickness is 1 nm
As can be easily understood from the fact that the oil and fat components were appropriately removed in the pretreatment, all the remaining oxide films in the pretreatment were indiscriminately in the main treatment. It is considered that the alloy layer was eluted and removed, and as in Comparative Example 1, the portion where the alloy layer was exposed on the surface increased, and Mg in the alloy layer rapidly formed magnesium oxide again after the treatment.

In the case where the amount of removal by alkali degreasing in the pretreatment was 5 mg / m ² or less (Comparative Example 4), the color tone unevenness was observed even after the proper treatment under the conditions of the present invention. Occurs, and the deterioration resistance with time is poor. This is because, as can be seen from the relatively thick oxide film having a thickness of 10 nm, the grease was not sufficiently removed in the pre-treatment, so that even in this main treatment, the MgO in the portion where the grease remained adhered was also used. Is considered to be because water cannot be sufficiently removed due to water repellency, and 16 at.% Of Mg contained in MgO remains.

Further, as shown in Comparative Example 5, the same pretreatment as in Comparative Example 4 (amount removed by alkaline degreasing: 5 mg / m ²⁾
The following treatment is performed, and even when the conditions of this treatment are pH4 and out of the conditions of the present invention, color tone unevenness may not occur. As can be seen from the fact that the oxide film thickness is 1 nm, although the fat and oil components were not sufficiently removed by the pretreatment, the conditions of the subsequent main treatment were similar to those of the pickling, and the water-soluble M
This is because not only gO but also all oxide film components including fats and oils components that could not be sufficiently removed by the pretreatment were removed. However, under such conditions, the alloy layer is exposed as in the case of Comparative Examples 1 to 3, and it can be seen that the deterioration resistance with time is inferior.

Further, as shown in Comparative Example 6, even if the pretreatment is carried out under appropriate conditions, if the total amount of impurities contained in the treated water of this treatment exceeds 100 ppm, the oil and fat components on the surface are removed. Although no color tone unevenness occurs, in the subsequent treatment, impurities rapidly adhere to the surface and the elution of the water-soluble compound hardly proceeds, so that the oxide film thickness is large (6n).
m), and Mg contained in MgO on the surface is also 11 at.%.
, Is out of the range of the present invention, so that the aging resistance is inferior.

Further, as shown in Comparative Example 7, if the amount of impurities contained in the treated water is less than 100 ppm even in the pretreatment, and if the total amount of impurities contained in the treated water exceeds 100 ppm, the pretreatment also removes oil and fat components. However, even in this treatment, MgO cannot be sufficiently removed, so that color tone unevenness occurs and the deterioration resistance with time deteriorates. Further, as shown in Comparative Example 8, the untreated material is inferior in aging deterioration resistance because Mg constituting MgO on the surface is present at 20 at.%, But there is no unevenness in color tone. There is something. This is a phenomenon that occurs because the unevenness of the adhesion of the fat component differs depending on the material, and is not directly related to the method of the present invention.

[0033]

According to the present invention, among various compounds present in the surface layer formed on the surface of the material, without impairing the poorly water-soluble compound layer useful for surface protection and the like,
It is possible to easily and inexpensively produce a material having a more stable and high-functional surface by selectively removing only a water-soluble compound having properties such as hygroscopicity and causing a problem with the surface aging of the material. It is possible. Further, the alloy produced by the method of the present invention has excellent resistance to deterioration over time.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a spectrum in the Mg2p state of the surface of an Al alloy containing Mg by X-ray photoelectron spectroscopy.

[Explanation of symbols]

1 ... measured photoelectron spectrum 2 ... background (inelastically scattered photoelectron component, etc.) 3 ... spectrum 3a ... MgO components separated for each occurrence state by peak separation fitting (water-soluble compound component) 3b ... MgAl ₂ O ₄ ( Spinel) component (poorly soluble compound component) 3c ... Metallic Mg (alloy component) (poorly soluble compound component) 4 ... fitting curve corresponding to each component of 3

[Table 1]

[Table 2]

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuo Takagi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Yoshimi Kada 20-1 Shintomi, Futtsu-shi, Chiba New Japan Steel Technology Co., Ltd.

Claims (9)

[Claims] 1. In a manufacturing process of an alloy containing a metal element forming a water-soluble compound, or in a use environment after the manufacturing,
A method for removing a water-soluble compound formed on an alloy surface, wherein the surface layer of the alloy is removed using an alkaline degreasing agent.
After the removal of 50 mg / m ² , the alloy is immersed in water having a pH of 5 to 8 and a total concentration of impurity elements of 100 ppm or less, or the water is sprayed on the alloy to form on the alloy surface A method for treating the surface of an alloy, comprising selectively eluting and removing only the water-soluble compound thus obtained. 2. An alloy containing a metal element forming a water-soluble compound is an alloy containing Mg, and the water-soluble compound formed on the surface of the alloy is a water-soluble magnesium compound. The method for treating an alloy surface according to claim 1. 3. The method according to claim 2, wherein the alloy containing Mg is an alloy containing Al as a main component. 4. An alloy containing a metal element forming a water-soluble compound, wherein the atomic fraction of the metal element contained in the water-soluble compound existing in a depth region up to 5 nm from the surface of the alloy. Is not more than 10 at.% With respect to all elements except H present in the depth region, and the alloy has excellent surface aging resistance. 5. An alloy containing a metal element forming a water-soluble compound is an alloy containing Mg, and the water-soluble compound formed on the surface of the alloy is a water-soluble magnesium compound. 5. The alloy according to claim 4, wherein the alloy has excellent surface aging resistance. 6. The alloy according to claim 5, wherein the alloy containing Mg is an alloy containing Al as a main component. 7. An alloy containing a metal element forming a water-soluble compound is coated with an alkaline degreasing agent to form a surface layer of 5 to 5%.
After removing 0 mg / m ² , the alloy is immersed in water having a pH of 5 to 8 and the total content of impurity elements is 100 ppm or less, or the water is sprayed on the alloy to form a surface of the alloy. Elutes and removes water-soluble compounds present in a depth region from 5 to 5 nm, and the atomic fraction of the metal element contained in the water-soluble compounds present in the depth region is An alloy having excellent surface aging resistance, characterized in that the content is not more than 10 at. 8. An alloy containing a metal element forming a water-soluble compound is an alloy containing Mg, and the water-soluble compound formed on the surface of the alloy is a water-soluble magnesium compound. 8. The alloy according to claim 7, which is excellent in surface aging resistance. 9. The alloy according to claim 8, wherein the alloy containing Mg is an alloy containing Al as a main component.