JPH01212796A - Formation of opaque gray film of aluminum alloy - Google Patents

Abstract

PURPOSE:To form the subject opaque gray film having excellent corrosion resistance in a short time with good productivity by forming stress strains on the surface of an extrusion-molded Al alloy member, aging the member, and then anodizing the member under specified conditions. CONSTITUTION:Stress strains are formed on the whole or a part of the surface of an extrusion-molded Al alloy member by a mechanical means such as sandblast. The member is aged at 130-250 deg.C for 1-30hr according to the conventional method, and anodized in an aq. soln. of sulfuric acid, chromic acid, phosphoric acid, etc., by applying an electric current with the member as an anode. After anodization, a voltage lower than that in the anodization is impressed to apply a current, and hence the colorless and transparent anodic oxide film is colored in grayish black. As a result, an opaque grayish-black anodic oxide film having excellent strength and resistance to corrosion and wear is formed. The anodic oxide film is sealed, as required, and baked to form a grayish-black composite film with excellent adhesion of a coating film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming an opaque achromatic film on an aluminum alloy. The present invention relates to a method of forming a colored film.

[Conventional technology]

In general, aluminum alloys have excellent workability and corrosion resistance, so they are widely used as building materials such as sash and curtain walls, and usually have a silver, bronze, or gold colored film formed on them. However, in recent years, due to the diversification of needs in the construction industry, there has been an increasing demand for aluminum shapes in opaque colors (pastel tones), especially opaque gray shades.

Conventionally known methods for forming an opaque gray colored film on the surface of an aluminum alloy include a pretreatment method, an electrolytic coloring method, a current recovery method, an alloy method, and a method involving aging treatment.

As a pretreatment method, for example, as described in Japanese Patent Publication No. 49-24330, an aluminum profile is treated with Cρ.
- A method is known in which the surface of an aluminum profile is roughened by corrosion in an ion-containing solution and then colored gray by anodizing. However, such corrosion methods have the drawback that uneven components remain on the upper part of the film after the anodizing treatment, which makes it look gray, resulting in a powdery appearance, and subsequent adhesion of the film becomes poor.

On the other hand, as an electrolytic coloring method, for example, JP-A-61-143
No. 593 discloses that after the anodic oxide film is formed, 1 salt and Zn
A method of performing secondary electrolytic coloring in salt to make it gray is described. However, this method uses Zn as a coloring substance, which has the drawbacks of extremely poor weather resistance and poor coverage.Furthermore, if this zinc gets into the etching bath, it can cause roughness. .

The current recovery method, as described in, for example, JP-A-50-148247, is a method in which, after an anodic oxide film is formed, a current recovery process is performed at a voltage lower than the applied voltage to develop a gray color. However, in the case of this method, in order to obtain a gray colored oxide film, the current recovery treatment must be performed for 30 minutes.
Therefore, there is a problem that the film performance deteriorates due to the long immersion time in the weakly acidic electrolyte, and it is also necessary to increase the electrolyte concentration, temperature, or control the waveform. If an attempt is made to shorten the color development time by this, there is a problem that the color becomes chromatic and it is difficult to obtain an achromatic gray-black color.

Further, as an alloy method, for example, JP-A-51-99610
In the publication, an aluminum alloy billet containing 1 to 5% Si and 0.3 to 0.9% Mg is homogenized at a temperature of 480 to 550°C, and then extruded by preheating at a temperature of 380 to 480°C. , followed by T-5 (tempering) treatment, followed by anodizing treatment to produce a pale gray colored film. However, in such a method, St
Due to the high content, the extrusion speed is slow and workability is poor, and in the case of complex-shaped shapes, the content of Si, which is a coloring substance, differs between the front and rear ends of the extruded material depending on the extrusion temperature and extrusion speed. Therefore, it is difficult to achieve uniform coloring.

Furthermore, as a method involving aging treatment, for example, Japanese Patent Publication No. 57-23759 discloses a method in which a 6063 series aluminum alloy is extruded, and after cooling, the Mg2Si precipitated phase is overaged and tempered to become a β' intermediate phase. A method is described in which a gray colored film is produced by anodic oxidation after pretreatment of caustic etching treatment and acid immersion treatment. After tempering an aluminum alloy to the point of over-aging, it is anodized in an electrolyte containing mainly sulfuric acid, and then treated at a voltage lower than the applied voltage, thereby producing a gray colored film. Are listed. However, in the case of such a method, since the aluminum alloy shape is over-aged, it is inferior in strength, increases thermal energy consumption, and has disadvantages in that productivity is also poor.

[Problem to be solved by the invention]

As described above, various methods are known for forming an opaque achromatic colored film on the surface of an aluminum alloy, but each method has advantages and disadvantages.

By the way, if you suddenly switch the voltage to a low voltage while anodizing an aluminum alloy, or first stop the current supply and lower the voltage to zero, then apply a voltage lower than the applied voltage for anodizing treatment. In the beginning, almost no current flows, but it gradually begins to flow and eventually reaches a steady state. This is called a current recovery phenomenon, and it is well known that by utilizing this phenomenon, an almost colorless and transparent anodic oxide film can be colored into a transparent achromatic color.

The above-mentioned Japanese Patent Application Publication No. 1982-148247, Japanese Patent Publication No. 1983
The method described in Japanese Patent No. 32815 is a method that utilizes this recovery phenomenon.

This method of forming a colored oxide film using the current recovery method has various advantages such as being able to perform the process using a single electrolytic solution used for anodizing, but as mentioned in the explanation of the prior art,
In order to obtain an achromatic, especially gray-black colored oxide film,
There is a basic problem in that current recovery processing requires a long time of 30 minutes or more. Therefore, the immersion time in the weakly acidic electrolyte becomes long, resulting in a disadvantage that the film performance deteriorates in terms of corrosion resistance and the like.

On the other hand, if an attempt is made to shorten the color development time by increasing the concentration or temperature of the electrolytic solution or controlling the waveform, there is a problem that the electrolyte becomes colored and it is difficult to obtain an achromatic colored film.

In order to solve the problem of the current recovery method, in the method described in Japanese Patent Publication No. 54-32615, an extruded aluminum alloy that has been tempered to avoid overaging is anodized and colored by current recovery. It is intended to apply processing. However, in this case, as mentioned above, it is undeniable that the strength is inferior due to the over-aging treatment, and new problems arise such as increased thermal energy consumption and poor productivity.

Therefore, an object of the present invention is to provide a method for solving these problems and forming an achromatic grayish-black colored oxide film in a short period of time with high productivity and excellent film performance such as strength, corrosion resistance, and abrasion resistance. It is about providing.

Another object of the present invention, in connection with the above object, is to provide a method for forming an achromatic gray-black composite film on the surface of an aluminum alloy, which has excellent paint film adhesion and film performance.

[Means to solve the problem]

According to the present invention, in order to achieve the first object, (A) mechanical operation is applied to the aluminum alloy surface after extrusion molding to cause stress strain, and (B) the aluminum alloy is then subjected to aging treatment. (C) Thereafter, the aluminum alloy is connected to an anode and subjected to DC electrolysis to form an anodized film, and (D) Subsequently, DC electrolysis is performed at a voltage lower than the applied voltage for the above anodization treatment. This causes a current recovery phenomenon,
Provided is a method for forming an opaque achromatic coating on an aluminum alloy, which is characterized by forming an achromatic colored oxide coating.

Furthermore, according to the present invention, in order to achieve the second object, after forming a colored oxide film by the above method, further (
E) A method for forming an opaque achromatic composite film of an aluminum alloy is provided, which comprises baking after electrodeposition coating.

[Operation and mode of the invention]

The method of the present invention achieves the above object by utilizing a combination of surface conditioning before aging treatment and current recovery phenomenon.

The effect will be explained in detail below.

General 1:6063 S alloys and other aluminum alloys containing Mg and St as main additive elements are subjected to aging treatment after extrusion processing to increase their strength. GP (
It is said that forming a precipitated phase in which II) and the β' intermediate phase coexist is the best way to increase the strength.

However, in the subsequent film coloring step using the current recovery method, when Mg25i coexists with GP (II) and β' intermediate phase, it takes a considerable amount of time for coloring to occur, as mentioned above. As the residence time in the weakly acidic liquid becomes longer, the performance of the colored oxide film deteriorates, and the finished appearance, coverage, etc. also deteriorate.

On the other hand, if the aging treatment time is increased or the aging temperature is increased to increase the β' intermediate phase, color can be developed in a short time, but since the GP(IF) phase disappears,
It has a weak strength and cannot be used as a building material. Moreover, it is a great waste of thermal energy.

In the method of the present invention, the above-mentioned 2.
This method satisfies two points at the same time, and the surface that has undergone stress strain due to the surface conditioning process has a Mg2
A difference is caused in the precipitation form (precipitation speed) of 81.

That is, in the method of the present invention, after extrusion processing and before aging treatment, stress strain is caused in the surface layer portion of the aluminum alloy shape in the surface conditioning step to create a dislocation state. Note that since the force that causes this stress strain is at most about 0.5 to 10 kg/c-, the stress strain is limited to only the surface layer of the shape material and does not reach deep inside the shape material. After that, by applying normal aging treatment, only the surface layer where dislocations occurred due to stress strain in the surface conditioning process, the Mg2Si precipitation form changes quickly due to temperature rise, and even in normal aging treatment, β'
The color changes to an intermediate phase, and as a result, the time required for color development in the subsequent film color development process using the current recovery method becomes considerably shorter. On the other hand, in the deep part of the shape where no stress strain has occurred, the stress strain has not applied, so the precipitation form of Mg2Si is naturally the same as usual. Therefore, even during aging treatment, the GP (n) + β It remains a precipitated phase with coexisting phases. As a result, the strength is equivalent to that of a material subjected to normal aging treatment, and there is no problem in using it as a building material.

As a result of this treatment, an achromatic grayish-black coloring is obtained, which is an extremely short coloring process compared to the coloring method using current recovery, has good spreadability, and is extremely superior in performance such as strength and chemical resistance. It became possible to obtain a film. In addition, the surface layer of the aluminum alloy has a large amount of β' intermediate phase with good conductivity, so electricity can easily pass through it, so there is less uneven coloring in the coloring process, and the coloring is less due to the coloring of the anodic oxide film itself. Since coloring is not caused by dissimilar metals such as secondary electrolytic coloring, there is no problem of abnormal corrosion. Furthermore, it is possible to perform etching treatment to impart uniform slipperiness to the surface of the coating, so that when electrodeposition is applied afterwards, the coating will have good uniformity, and the smooth unevenness of the coating surface will improve the adhesion of the coating. will also be excellent.

Furthermore, as is clear from the comparative example described later, if the surface is simply adjusted as described above and the color development process by current recovery is not performed, the surface will only become satin-like and an achromatic gray-black color. film cannot be obtained. On the other hand, even if both the surface conditioning step and the coloring step by current recovery are carried out, the effects of the present invention cannot be obtained if the surface conditioning is carried out after the aging treatment. That is, the above-mentioned effects of the method of the present invention are unique and can only be achieved by a combination of surface conditioning before aging treatment, aging treatment, and coloring treatment by current recovery.

Each step of the method of the present invention will be explained below.

(A) Surface conditioning treatment First, on an aluminum alloy extruded according to a conventional method,
Apply surface conditioning by mechanical operation.

This surface conditioning is performed before the post-extrusion aging treatment (T-5 treatment).
The purpose is to cause stress strain (dislocation, lattice strain) only in the surface layer by applying pressure, etc. to the surface of the shape partially or entirely, and therefore does not include chemical treatments such as etching.

Methods for this surface conditioning include a blasting method in which abrasive grains such as glass particles, sand, iron powder, or alumina particles are sprayed, a high-pressure injection method in which a liquid such as water is injected at high pressure, and a brush that scratches the aluminum alloy surface. There are various mechanical means such as a roller method using an embossing plate roll, and a press method using a die press.

This surface conditioning may be performed on an extruded shape at room temperature that has been cooled after extrusion, or may be performed on an extruded shape in a relatively high temperature state immediately after extrusion. For example, with the aim of improving workability, a large number of high-pressure injection grooves (holes) are installed in a mold or metal frame (jig) that has the same shape as the extrusion mold and has a certain gap of clearance in the aluminum alloy immediately after extrusion. The surface may be adjusted continuously by spraying water or an abrasive, or instead of the high-pressure spray described above, a metal or ceramic claw-shaped It is also possible to use a method in which a jig is installed and the surface of the profile is rubbed with a constant pressure.

For example, FIG. 2 shows the relationship between the abrasive grain projection pressure and the degree of color development when surface conditioning is performed by shot blasting (abrasive grains A120+). The higher the value, the lighter the color, and the lower the value, the darker the color. From the same figure, it can be seen that a projection pressure of 0.5 to 10.0) cg/cd is effective, and that a nearly constant degree of color development can be obtained preferably at a projection pressure of 2.0 to 5.0 kg/c; The strain caused by the stress is limited to only the upper layer of the shape, and even after the oxide film is formed, there is no noticeable deterioration in performance due to such strain or scratches.

(B) Aging treatment (T-5 treatment) The aluminum profile subjected to the above surface conditioning is then subjected to an aging treatment according to a conventional method. As a result, the precipitated Mg2Si phase becomes a β' intermediate phase at the location where stress strain has occurred during the surface adjustment. On the other hand, since the surface adjustment does not affect the deep part of the shape, normal GP (If) and β' intermediate phase coexist.

To explain the aging treatment, for example, in the case of aluminum alloy A-60633 material, the influence of age hardening temperature and time on the hardness of the alloy is as shown in FIG. That is, the hardness reaches its maximum value after a certain period of time at any temperature, and age hardening at this stage is defined as complete age hardening. Also in the present invention, it is preferable to carry out this aging treatment to the extent that complete age hardening is achieved.

As is clear from FIG. 1, the higher the treatment temperature, the shorter the treatment time until complete aging, and the lower the treatment temperature, the longer the treatment time. Also, depending on the material and processing temperature of the aluminum alloy, once the hardness reaches full aging, the hardness tends to decrease as the processing time increases. good.

Conditions for the aging treatment vary depending on the material of the aluminum alloy, but it is generally recommended to carry out the aging treatment at a temperature of 130 to 250° C. for 1 to 30 hours. If it is less than 130°C, it will take too long to reach the desired hardness, resulting in poor productivity, and if it exceeds 250°C, uniform age hardening will not be possible, which is undesirable. Moreover, if it is less than 1 hour, uniform age hardening cannot be achieved, whereas if it exceeds 30 hours, it will take too much time, resulting in poor productivity.

(C) Anodizing treatment The aluminum alloy that has gone through each of the above steps is subjected to treatments such as degreasing, washing with water, and removing smut as necessary by a conventional method, and then connecting the aluminum alloy to an anode according to a conventional method. An anodic oxide film is formed by direct current electrolysis.

That is, it contains well-known electrolytes of inorganic acids and/or organic acids, such as sulfuric acid, chromic acid, phosphoric acid, etc., or mixed acids thereof, oxalic acid, malonic acid, etc., or mixed acids of these or with inorganic acids. The aluminum alloy is anodized in an electrolyte using a direct current or similar current waveform. The applied voltage, application time, etc. for the anodizing treatment may be the same as usual and are sufficient, but it is usually carried out within the range of 5 to 100 V, depending on the type of treatment liquid. If it is less than 5V, it will take a long time to obtain the desired film thickness, resulting in poor productivity.On the other hand, if it exceeds 100V, there will be large variations in film thickness, and there will be a large waste of energy due to high voltage processing. Therefore, it is undesirable.

(D) Film coloring treatment using current recovery method After the above anodic oxidation treatment, at a voltage lower than the applied voltage,
DC current is applied to the aluminum alloy as an anode to restore the current. The conditions for this current recovery are 0.5 to 80% lower than the applied voltage for anodizing treatment, although it depends on the type of treatment liquid. O
V for 1 to 100 minutes, preferably 1.0 to 50. O
V range for 1 to 50 minutes. If it is less than 0.5V, it will take a long time for color development, resulting in poor productivity and film performance, which is undesirable.On the other hand, if it exceeds 80V, it will cause uneven color development, which is not preferred. Similarly, if it is less than 1 minute, uneven color development will occur, while if it exceeds 100 minutes, the color development time will be too long, which will deteriorate productivity and film performance, which is not preferable.

Note that the current recovery treatment liquid may be the same as or different from the anodization treatment liquid. If different, it is preferable to use oxalic acid, phosphoric acid, malonic acid, etc. as the current recovery treatment liquid, and depending on the conductivity of the liquid, a voltage higher than the anodizing treatment voltage may be applied. . When using the same treatment solution, the anodizing current density is slightly increased to generate an anodic oxide film in a short time, and part of the coloring treatment is performed in the treatment tank during the remaining time, and then the original film is formed. It is even better if the degree of color development is adjusted during the color development process. In addition, current recovery can be achieved by switching the applied voltage for anodizing treatment to a lower voltage, or
- Either stop the current supply and lower the voltage to zero before applying it, or
Either method can be adopted. In addition, the current recovery phenomenon may occur only once, but after reaching a steady state, the applied voltage is increased within a short time to a voltage higher than that applied voltage but lower than the applied voltage for anodizing treatment, and then the applied voltage is lowered again. It is also possible to perform the operation multiple times to increase the degree of coloring.

In film coloring treatment using this current recovery method, Mg2S
Since i is a β' intermediate phase, the time required for color development is significantly shorter than when no surface adjustment is performed, and as a result, various effects can be obtained. In addition, since the coverage becomes fairly uniform, it becomes much easier to control the degree of color development. In this color development process, a comparison of the degree of color development between areas where the surface has been conditioned and areas where the surface has not been conditioned using one profile is as shown in Figure 3, and it can be seen that the degree of color development is greatly improved by the surface conditioning treatment. I understand.

(E) Electrodeposition coating A colored oxide film is obtained through each of the steps described above, and thereafter, if necessary, treatments such as pore sealing and semi-sealing are performed, followed by electrodeposition coating and baking treatment according to well-known methods.

In the coloring method using current recovery, the structure of the barrier layer at the bottom of the porous film is made into a finely branched structure, which gives an achromatic grayish-black color due to the refraction of the light that hits it. By adding an electrodeposition coating to the material, the refraction of light becomes even more complex, resulting in an achromatic opaque gray-black color (pastel tone) with a strong solid feel that eliminates the transparency of aluminum. . Moreover, the adhesion of the coating film is improved due to the irregularities on the surface of the oxide film, resulting in a coating film with excellent performance such as corrosion resistance and weather resistance.

After the coloring step using the current recovery method, electrolytic coloring can be carried out in an electrolytic solution containing an inorganic metal salt if necessary, and in combination with this electrolytic coloring step, pastel-like opaque bronze or gold-like gray can be produced. It is possible to color it.

In addition, as for the material, pure aluminum is excluded in the method of the present invention, and aluminum alloys containing Mg5Si as a main additive element, such as JIS 6063S alloy, are preferably used, and alloy components are changed to increase the precipitation of Mg2Si. If the Si content is increased, an even greater effect can be obtained.

〔Effect of the invention〕

As described above, according to the method of the present invention, due to the interaction of surface conditioning by mechanical operation, aging treatment, and coloring treatment by current recovery method, the process can be completed in an extremely short time compared to the usual coloring method by current recovery method. It has good adhesion properties and can produce an achromatic grayish-black colored film. As a result, for example, the anodizing treatment and the coloring treatment can be carried out within the time required for the conventional anodizing treatment, and the part or the whole of the shape can be arbitrarily colored in an achromatic opaque gray color. Moreover,
Because the processing time is short, it has excellent corrosion resistance and chemical resistance, has little uneven color development, and has good strength, so it can be used as an exterior material as is. Other advantages include that processing is relatively simple and there is no need for vertical suspension, horizontal suspension, or regulation of shape shapes.

In addition, as described in claim 2, by performing electrodeposition coating after the coloring step, an achromatic opaque grayish-black electrodeposition coating with excellent adhesion and uniformity and a strong filling feeling with excellent film performance can be obtained. is obtained.

〔Example〕

The present invention will be specifically described below with reference to Examples.

Example 1 After hot extruding aluminum alloy 6063S using an extruder using a conventional method, shot blasting (
The entire surface was slightly roughened using abrasive grains (Ag 203.3 kg/cj).

After that, it was aged at 190°C for 4 hours as usual, and then anodized by applying electricity for 300 minutes at 16.7V DC (current density 1.3A/d) in dilute sulfuric acid (15w%) solution. An anodic oxide film of 11 μm was formed. Next, as a coloring step, the aluminum alloy was used as an anode in the same solution, and when the voltage was set to 6 V and direct current was applied for 15 minutes, an achromatic gray-black film was obtained.

After that, after sealing the hole with boiling water using a conventional method, the CAST corrosion resistance (J Is H-8681) was examined, and it was RNIO in 48 hours, and it also passed the sand drop abrasion test (J Is H-8681).
H-8682) was performed, and the speed was 80 seconds/μm, and there was no problem in terms of performance.

Further, in Example 1, the abrasive projection pressure was varied during shot blasting and its influence on the degree of color development was investigated. The results are shown in FIG.

Furthermore, in the color development process, the degree of color development was investigated in areas where the surface had been conditioned using one shape and in areas where it had not. The results are shown in FIG.

Example 2 The produced gray-black film was treated in exactly the same manner as in Example 1, except that it was semi-sealed at 72°C for 5 minutes instead of boiling water sealing, and then electrodeposited (paint product name: Elekron 370O).
N-Kansai Paint Co., Ltd.) was applied at 130V for 3 minutes, and then baked at 170°C for 40 minutes.

As a result, unlike in Example 1, an opaque, achromatic, grayish-black film was obtained that had a rather solid appearance. In addition, when this sample was tested for alkali resistance (0.5% NaOH) (Is H-8602), 72
The time was RN 10, and there were no performance problems.

Comparative Example 1 In Example 1, the same treatment as in Example 1 was performed except that no surface adjustment was performed, and no color development was observed in the anodic oxide film.

In addition, as a color development step, when electricity was applied for 500 minutes at 6 V DC using an aluminum alloy as an anode, an achromatic gray-black film similar to that of Example 1 was obtained, but when CAST corrosion resistance was examined after that, it was found that the film was energized for 48 hours. And RN9. It was also 55 seconds/μm in the sand drop abrasion test, and the performance was clearly inferior to that obtained in Example 1.

Comparative Example 2 In Example 2, the same treatment as in Example 2 was performed except that no surface adjustment was performed, and no color development was observed in the anodic oxide film.

In addition, in the coloring process, when electricity was applied for 500 minutes at 6 V DC using an aluminum alloy as an anode, an achromatic gray-black film similar to that of Example 2 was obtained, but in the subsequent alkali resistance test, after 72 hours. The RN was 9.0, and the performance was clearly inferior to that obtained in Example 2.

Comparative Example 3 In Example 1, the same treatment as in Example 1 was carried out except that the color development step was not performed. However, the surface only became satin-like, which was far from an achromatic gray-black color.

Comparative Example 4 When the same treatment as in Example 1 was carried out in Example 1 except that the surface conditioning step was carried out after the aging treatment, the surface only became satin-like, which was far from the plain grayish black color. there were.

[Brief explanation of the drawing]

Figure 1 is a graph showing the effect of aging treatment temperature and treatment time on the hardness of aluminum alloy (A-6063S), Figure 2 is a graph showing the relationship between abrasive blasting pressure of shot blasting method and degree of color development, Figure 3 is a graph showing the influence of surface conditioning on the degree of color development.

Claims (2)

[Claims] (1) (A) Apply mechanical manipulation to the aluminum alloy surface after extrusion molding to cause stress strain, (B) Next, apply an aging treatment to the aluminum alloy, (C) After that, the aluminum alloy (D) forming an anodized film by connecting to an anode and performing DC electrolysis, (D) causing a current recovery phenomenon by subsequently performing DC electrolysis at a voltage lower than the applied voltage of the above-mentioned anodizing treatment;
A method for forming an opaque achromatic film on an aluminum alloy, the method comprising forming an achromatic colored oxide film. (2) An aluminum alloy characterized by forming an achromatic colored oxide film by the method for forming an opaque achromatic film of an aluminum alloy according to claim 1, and further (E) baking after electrodeposition coating. A method for forming an opaque achromatic composite film.