JPH03100144A - Method for controlling color tone after anodic oxidation treatment of rolled aluminum alloy plate for building material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for producing rolled aluminum alloy sheets that are anodized and used in construction materials such as building curtain walls and interior materials, and in particular, The present invention relates to a method of adjusting the color tone after anodizing treatment to three levels, from achromatic dark gray to light gray to milky white, using an alloy having the same composition.

BACKGROUND OF THE INVENTION Generally, aluminum alloy rolled sheets used for applications such as curtain walls and interior decoration materials are often subjected to anodization treatment from the viewpoint of corrosion resistance. Aluminum alloys for anodizing treatment for these purposes are often light gray to silver in color, and such alloys generally include JI81-050 alloy, 1100 alloy, and 500500 alloy.
5 alloy, and the gray one is Al-
1-4% Si alloys are common. On the other hand, from the viewpoints of economy and corrosion resistance, sulfuric acid bath anodization is usually used for anodizing, especially for large building materials.

By the way, in the above-mentioned applications, the surface after anodizing treatment is often required to have a desired color tone for aesthetic reasons. Methods of giving the desired color tone to anodized plates include painting, dyeing, secondary electrolytic coloring, alloy coloring,
Although coloring can be achieved by using an anodizing solution, from the viewpoints of economy and corrosion resistance, it is desirable to develop color as is after being anodized, especially as it is anodized using a sulfuric acid bath.

On the other hand, for building curtain walls, interior materials, etc., due to design requirements, anodized boards in several different colors are used, especially achromatic anodized boards in different colors ranging from dark gray to milky white. May be used in combination.

In such cases, conventional approaches have been to combine alloys with different compositions, or to use alloys with the same composition but with different anodizing conditions and secondary electrolysis conditions, or to vary the color tone by dyeing. method has been applied.

Problems to be Solved by the Invention As mentioned above, when using a combination of several types of anodized plates with different colors, combining alloys with different component compositions has the following problems. Ta. That is, in this case, the anodizing treatment conditions differ for each alloy, and the pretreatment conditions such as desmutting also differ for each alloy, resulting in a significant increase in cost compared to the case where the same alloy is treated. In addition, in this case, since alloys with different compositions are combined, separate management of scrap is required.
In addition, consideration must be given to problems such as electrolytic corrosion and welding.
There are restrictions on the type of alloy used.

On the other hand, combining sheets with different color tones by using alloys with the same composition but with different anodizing treatment conditions and secondary electrolysis conditions has the problem of significantly increasing costs, and However, under anodic oxidation treatment conditions and secondary electrolysis conditions, it is extremely difficult to reliably vary the color tone from dark gray to milky white, especially in achromatic colors with little color.

Furthermore, when using the dyeing method, corrosion resistance is significantly inferior, so
If used in building materials such as curtain walls of buildings, the color tone would fade, so it could not be practically applied to building materials.

Therefore, it is necessary to develop a method that uses alloys with the same composition to change the color tone without changing the anodizing treatment conditions, and in particular, a method that adjusts achromatic colors from dark gray to light gray to milky white. Although this is desired, it has been thought that such a method would be difficult to put into practical use.

This invention was made against the background of the above circumstances, and in manufacturing aluminum alloy rolled sheets for building materials, alloys with the same composition are used as raw materials, and the anodizing treatment conditions are also the same, so that the color tone after the anodizing treatment is darkened. The object is to provide a method for adjusting the color to three levels: gray to light gray to milky white.

Means for Solving the Problems In order to solve the above-mentioned problems, the inventors of the present invention have carried out extensive experiments and studies, and have determined that the composition of the alloy has been appropriately set and the manufacturing conditions, particularly the ingot heating conditions, have been adjusted accordingly. By changing the intermetallic compounds and controlling the intermetallic compounds, the color tone after anodizing treatment can be changed to three levels from dark gray to light gray to milky white, using alloys with the same composition and without changing the anodizing treatment conditions. They discovered that it can be adjusted and came up with this invention.

Specifically, the invention of claim 1 provides for manufacturing aluminum alloy rolled sheets for building materials using aluminum alloys having the same composition as raw materials, and changing the color tone of the rolled sheets after anodization treatment from dark gray to light gray. In the method of adjusting to three levels of gray and milky white, Fe is used as a material in a range of 0.8 to 2.
Using an aluminum alloy containing Ovj% and controlling Si to Q, 21% or less, with the remainder consisting of Al and other unavoidable impurities, the molten metal of the alloy was heated to 35 to 150%.
Casting by DC casting method at a casting speed within the range of / -,
Depending on the color tone to be obtained after anodizing the rolled plate for the obtained ingot, A. To obtain a dark gray tone: 350°C or more and less than 500°C. B. To obtain a light gray color tone: 500°C or more. Less than 550°C To obtain a milky white color: Select any temperature condition from A, B, or C of 550°C or higher and 630°C or higher for 0.5 to 24 hours at a temperature within that temperature range. After heating, hot rolling and further cold rolling are performed to obtain the final thickness, so that more than 90% of the intermetallic compounds are 5ii
ra or less and the total amount of intermetallic compounds is 2
．． Within the range of 5 to 7 vt%, and intermetallic compound A
Depending on the color tone to be obtained after anodizing treatment, the ratio between the amount of 16 Fe and the amount of Al3Fe is: a In the case of a dark gray tone: AJ6Fe/(Al3Fe+A76Fe)≧0.7b
In the case of light gray tone: 0.7>AJs Fe/ (AJ3 Fe+Als F
e) > 0.1C When obtaining a milky white color tone: Obtaining a rolled plate in which 0.1≧A76Fe/(A13Fe+AA'6Fe) or more is within the range of a, b, or c. It is something.

Further, the invention of claim 2 provides that, in manufacturing an aluminum alloy rolled plate for building materials using an aluminum alloy having the same composition as described above, the color tone of the rolled plate after anodizing treatment is changed to dark gray or light gray. , in the method of adjusting the milky white color to three levels, Fe is used as a material in the range of 0.8 to 2.
．． Contains 0wt% and MnO,O5~0.
2v1%, Mg 0.05-1.5v1%, CrO,
Using an aluminum alloy containing any one or two of 0.05 to O, lvj%, with Si regulated to 9.21% or less, and the remainder consisting of Al and other unavoidable impurities, the claim The intermetallic compound is adjusted in the same manner as described above by processing in the same manner as in the invention of No. 1.

First, the reason for limiting the composition of the aluminum alloy material will be explained.

Function Fe: Fe is an important element that generates an Al-Fe-based intermetallic compound and determines the color tone after anodizing treatment. In other words, if the intermetallic compound AJ6Fe increases in combination with the ingot heating conditions (homogenization treatment conditions), the color tone after anodizing becomes dark gray, and if AJ3Fe increases, the color tone after anodizing becomes milky white. Become. The amount of Fe is 2. Ovj
%, coarse compounds increase and the color tone after anodizing becomes yellowish, while if the Fe amount exceeds 0.8v+
If it is less than %, the absolute number of AJ-Fe intermetallic compounds will be small, the overall color will be shallow, and the range of change in color tone after anodizing treatment depending on the ingot heating conditions will also be small. Therefore, the amount of Fe is 0.8 to 2. It was set within the range of Qvj%.

Si: Si tends to generate an abnormal structure called fir wood frame in the ingot. If fir wood edges occur in the ingot, band-like patterns called streaks will appear on the surface when the rolled plate is anodized, impairing its appearance. In order to prevent the occurrence of this fir wood border, it is necessary to regulate the amount of Si to 0.21% or less.

In addition to the above Fe and Si, basically AJ and other unavoidable impurities can be used, but if necessary, Mn,
One or more of Mg and Cr may be added. The reason for these additions and the reason for limiting the amount added are as follows.

Mn: Mn is an element that stabilizes Al6Fe in the ingot and makes it difficult to generate fir wood edges, especially when the amount of Si is 0.1 = 0
．． When the amount of Mn is relatively high, about 2 wt%, the effect of preventing the formation of fir wood edges by adding Mn is large.

If the amount of Mn is less than 0.05W1%, the above-mentioned effect will be insufficient, while if it exceeds 0.2V1%, the color tone after anodizing will be reddish and will deviate from the achromatic color system aimed at in this invention. Put it away. Therefore, when adding Mn, the amount of Mn added was 0.05 to G, 2v1%.

Mg: Mg is sometimes added to improve strength.

If the Mg amount is less than 0.05v1%, a sufficient strength improvement effect cannot be obtained, while if it exceeds 1.5vt%, fir wood edges are likely to occur in the ingot. Therefore, when Mg is added, the amount of Mg added is within the range of 0.05 to 1.5% (v)%.

Cr: Cr may also be added to improve strength.

If the Cr content is less than 0.05vt%, the strength improvement effect cannot be sufficiently obtained; If it exceeds lvj%, the color tone after the anodizing treatment becomes yellowish and deviates from the achromatic color system. Therefore, when adding Cr, the amount of Cr added is 0.
It was set within the range of 0.05 to 0.1v+%.

Furthermore, in general aluminum alloys, trace amounts of Ti or Ti and B are sometimes added to refine the crystal grains of the ingot, but in the case of the present invention, even if trace amounts of Ti or Ti and B are added, In addition, the effect of grain refinement by these additions is effective in preventing texture and streaks in the rolled plate. In that case, Ti is 0.
Below 0G3vj%, the above effects cannot be obtained; on the other hand, Ti
If Ti exceeds 0.15v1%, there is a risk that a coarse intermetallic compound of TiAl3 will be formed.
~G, preferably within the range of 15v1%. In addition, B exhibits a crystal grain refining effect when coexisting with Ti, but this effect cannot be obtained when B is less than ippm;
If B exceeds pp, linear defects will occur due to coarse Ti82 particles, so B is desirably within the range of 1 to 1100 pp.

Next, manufacturing conditions will be explained.

First, a molten aluminum alloy within the above-mentioned composition range is melted according to a conventional method, and the casting speed is 35 to 150.
DC casting (semi-continuous casting) is performed at mm/min. Here, the casting speed affects the generation of fir wood structure in the ingot, and if the casting speed is too fast, fir wood structure is likely to occur. If the casting speed is less than 35 m/m, the productivity is too low to be economical, while if it exceeds 150 m/mh, fir wood structure will occur and streaks will occur in the rolled plate, spoiling the appearance. Therefore, the casting speed was set within the range of 35 to 150 m5/m.

Next, the ingot is subjected to heat treatment for 0.5 to 24 hours. This ingot heating is not only necessary for homogenizing the ingot structure, but also has a great effect on the color tone after anodizing. That is, if the ingot heating temperature is high, the intermetallic compound Al6Fe in the ingot transforms into Al3Fe, and the color tone of the rolled plate after anodizing changes from dark gray to light gray and then to milky white. Therefore, by controlling the ingot heating temperature, the color tone of the rolled plate after the anodizing treatment can be adjusted. Specifically, the ingot heating temperature conditions are divided into the following three types, A, B, and C, depending on the color tone to be obtained after anodizing treatment.

A: 350°C or higher, lower than 500°C In this case, Al6Fe hardly transforms into A73Fe, and 70% or more of the intermetallic compound becomes Ar1Fe phase.
A dark gray tone is obtained after anodizing.

B: 500°C or higher, lower than 550°C In this case, A76Fe transforms to AA'3Fe to some extent, resulting in a structure in which Al3Fe and Al3Fe are mixed, that is, AA'3Fe accounts for 30 to 90%, and the color becomes light gray after anodizing. The color tone is obtained.

C: 55 G° C. or higher and 630° C. or lower In this case, almost all of the A76Fe is transformed into A73Fe, and 90% or more of the intermetallic compound becomes the A73Fe phase, resulting in a milky white color tone after the anodizing treatment.

If the ingot heating temperature is less than 350°C, the texture of the structure after hot rolling will become rough, and a pattern will appear on the surface, impairing the appearance. On the other hand, if the temperature exceeds 630° C., crystal grains become coarse, streaks occur, and local melting occurs in some cases.

Furthermore, if the ingot heating time is less than 0.5 hours, the above-mentioned effects cannot be obtained sufficiently, while if it exceeds 24 hours, the effects are saturated.
Since this would only increase the cost, the time was limited to 0.5 to 24 hours.

After heating the ingot as described above, hot rolling and cold rolling are performed to obtain the final thickness. Here, hot rolling may be carried out according to a conventional method, but it is generally carried out at a temperature below the heating temperature of the ingot. Intermediate annealing may be performed immediately after hot rolling or during cold rolling. Intermediate annealing is 2
Generally, the heating is carried out at 50 to 450°C for 0.5 to 12 hours.

In order to adjust the color tone after the anodizing treatment to dark gray to light gray to milky white in the rolled plate of the final thickness obtained in this way, the amount, size and Type matters.

Firstly, the amount of intermetallic compound is important in order to enable a change in color tone after anodizing. The amount of intermetallic compounds is 2.
If it is less than 5vj%, the color becomes shallow and neither dark gray nor milky white is achieved. In other words, even if the heating conditions of the ingot are changed, the variation in color tone is small and only light gray can be obtained. On the other hand, if the amount of the intermetallic compound exceeds 7.0 wt%, it becomes difficult to obtain a milky white color tone. That is, even under the above-mentioned ingot heating condition C, the ingot becomes more yellowish and deviates from the milky white color. Therefore, the total amount of intermetallic compounds is 2.5~
? , 0wt%.

Additionally, if the proportion of large-diameter intermetallic compounds with more than 5 lines exceeds 10% of the intermetallic compounds, the color tone after anodizing becomes shallow and it is difficult to vary the color from dark gray to milky white. Become. Therefore, intermetallic compounds with a diameter of 5 μm or less must account for 90% or more.

Furthermore, the ratio of the intermetallic phases Al6Fe and Al3Fe determines the color tone after anodization.

That is, the weight ratio is AA'6 Fe/(Al3 Fe
+Al6 Fe), a: A16 Fe/(AJ3 Fe+Al6 Fe)≧
Dark gray tone at 0.7, b: 0.7>A16 F e/ (Al!3 F
e+Al6 Fe e)≧0.1 and light gray tone c:0.1≧Al6 Fe/ (AlF3 Fe+AA
'6 Fe) gives a milky white tone. The phase ratio of such intermetallic compounds can be adjusted by controlling the ingot heating conditions, as described above.

As described above, by regulating the intermetallic compounds in the rolled sheet of the final thickness within a predetermined condition range, the color tone of the subsequently anodized sheet can be controlled to be dark gray, light gray, or milky white. I can do it.

Although the anodizing treatment may be carried out according to a conventional method, it is advantageous to use a sulfuric acid electrolytic bath in terms of economy and corrosion resistance.
As described above, a dark gray to light gray to milky white color tone can be obtained by anodizing using a sulfuric acid electrolytic bath.

Before anodizing, degreasing and etching are generally performed to remove surface stains and surface defects in advance. Etching is usually performed using caustic soda-based alkaline etching. In the anodizing process itself, the H2SO4 concentration is 10 to 25 vol.
% sulfuric acid bath, bath temperature 15-30°C, current density 0.
5AlM or more1. Conducted at less than OAl-, film thickness lθ~2
It is desirable to form a five-sided anodic oxide film.

Here, if the concentration of 1 (2804) in the sulfuric acid bath is less than 10vol%, the color tone after anodizing treatment will become yellowish,
In addition, the porosity of the film decreases and the bath voltage becomes high.
If the 2so4 concentration exceeds 25vol%, the surface will become rough and the anodic oxide film will become soft. Further, if the bath temperature is less than 15°C, the color tone after the anodizing treatment will have a strong yellowish tinge and will deviate from an achromatic color, while if it exceeds 30°C, the corrosion resistance after the anodizing treatment will decrease. Furthermore, the current density is 1. O
At Aldli or higher, the color tone after anodizing becomes yellowish and deviates from an achromatic color, while at 0.5 Aldl1
If it is less than that, it takes a considerable amount of time to form an anodic oxide film of the required thickness, which impedes productivity and also reduces corrosion resistance. Furthermore, if the thickness of the anodic oxide film formed is less than 10 mm, sufficient corrosion resistance cannot be obtained;
It is not economical to increase the thickness beyond zero, and furthermore, the color tone after anodizing becomes yellowish and deviates from an achromatic color.

Note that the color tone after the anodizing treatment can be evaluated by the values of the brightness index and the chromaticness index a and b according to Hunter's color difference formula (see 1!!l 28730). That is, the higher the L value of the lightness index, the whiter it is, while the Romanticness index is about the degree of coloration, and the higher the a value, the stronger the redness, and the higher the b value, the stronger the yellowness. Here, achromatic colors such as dark gray, light gray, and milky white can be determined as follows.

Dark gray: L value < 60, -3 x a value, 3-3 x b value
3 Light gray = 60 ≦ L value < 75, -3 × a value × 3-3 × b
3 Milky white=75≦L value, -3kuavalueku3-3<bvalueku
3. Example First, the effects of casting speed and alloy composition on the structure of the ingot and the streaks of the rolled plate were investigated as follows.

The molten metals of Alloy Fish 1 to Fish 8 shown in Table 1 were melted according to a conventional method, and the casting speed shown in Table 2 (mainly 65 μ/l) was melted.
l111 part is 175mm/z) semi-continuous casting method (DC
An ingot with a cross-sectional dimension of 100×300M was cast by the casting method. A part of it was sliced and the structure of the ingot was examined. The resulting ingot was heated at 600°C for 6 hours, then hot-rolled at 400°C to obtain a hot-rolled plate with a thickness of 6 nm, and then cold-rolled to a plate thickness of 4 nm. At this stage, intermediate annealing was carried out at 350°C for 5 hours, followed by cold rolling to obtain a rolled plate with a thickness of 2.5 mm, which was then anodized in a sulfuric acid electrolytic bath according to a conventional method to obtain streaks. We investigated whether or not this occurred.

Table 2 shows the results of examining the ingot structure and the presence or absence of streaks.

As shown in Table 2, Table 1, and Table 2, the casting speed was set to 175 nn/min.
In the comparative method and alloy Nα6 with a high St content, a fir-like structure occurs in the ingot, and in the alloy Na8 with a high Mg content, the structure of the ingot becomes coarse and uneven, and in both cases streaks appear on the rolled plate. occurred, and it was determined that the appearance was poor.

Next, the following process was carried out as an example of the method of the present invention and a comparative example.

Among the alloys with the respective component compositions shown in Table 1, the alloys (Nal~5°Nα7) in which streaks did not occur in Table 2 were cast by the DC casting method at a casting speed of 65 min/mn, and the cross-sectional dimensions were determined. A 100X 300aa ingot was obtained.

Next, each ingot was heated under various conditions as shown in Table 3, and then hot rolled in the same manner as above.
Cold rolling, intermediate annealing, and cold rolling to obtain a plate thickness of 2.5m.
It was made into a rolled plate. Thereafter, each rolled plate was anodized using a sulfuric acid electrolytic bath with a sulfuric acid concentration of 15 vol% at a bath temperature of 20° C. and a current density of 1.5 AldIi.

The surface color tone of the anodic oxide film of each board was examined using Colormeter 5M-3-MCl manufactured by Suga Test Instruments. The color tone was evaluated using the brightness index and chromaticness index a and b according to Hunter's color difference formula. The result is the third
Shown in the table. Note that the achromatic dark gray to light gray to milky white color is the a value.

All b values are -3 to 3. L value is less than 60, dark gray, 6
If it is 0 or more and less than 75, it can be judged as light gray, and if it is 75 or more, it can be judged as milky white.

On the other hand, for each plate, the total amount of intermetallic compounds, 5/1
The proportion of the number of intermetallic compounds below m, and AJ6 Fe
/ (Al3Fe+A76Fe) ratio was investigated. The results are also shown in Table 3.

Note that the amount of intermetallic compounds was measured as follows. That is, first, about 0.5 to 1 g of a sample was taken and heated at 170 to 180°C in 100 ml of phenol solution.
After dissolving for 30 minutes, 50 ml of benzyl alcohol was added at 140°C to prevent coagulation of the phenol solution, filtered, and the residue was washed with alcohol, and the residue was analyzed by weight.

The phase of the intermetallic compound was identified as follows. That is, first, about 0.5 to 1 g of a sample was taken, and it was heated in 100 ml of phenol solution at 170 to 180°C for 30 minutes.
After dissolving for 0 minutes and adding 50 ml of benzyl alcohol at 140° C. to prevent coagulation of the phenol solution, the mixture was filtered, the residue was washed with alcohol, and the residue was identified by X-ray diffraction.

Furthermore, the size of the intermetallic compound was determined by polishing the sample and then measuring the distribution of the maximum length of the intermetallic compound by image analysis. However, fine intermetallic compounds less than 0.5 m were ignored.

As shown in Table 3, when the process of this invention is applied to alloys within the composition range of this invention (numbers 1 to Na4), the color tone after anodizing treatment ranges from achromatic dark gray to It is clear that the color can be reliably adjusted to a light gray to milky white color and that no appearance defects such as streaks occur.

Effects of the Invention According to the method of the present invention, when manufacturing aluminum alloy rolled sheets for building materials that are anodized, the anodizing process can be carried out using materials with the same composition and without changing the anodizing treatment conditions. The color tone after processing can be reliably adjusted to three levels of achromatic color: dark gray, light gray, and milky white.

Therefore, by applying the method of this invention, it is possible to significantly reduce the cost of obtaining building materials that combine different achromatic color tones, and it is also possible to significantly reduce the cost of building materials that combine different achromatic color tones. Because it is possible to obtain different color tones even after the anodization treatment, building materials with good corrosion resistance can be obtained.

Claims (1)

[Claims] (1) When manufacturing aluminum alloy rolled sheets for building materials using aluminum alloys having the same composition, the color tone of the rolled sheets after anodizing treatment is dark gray, dark gray,
In the method of adjusting to three levels of light gray and milky white, the material contains 0.8 to 2.0 wt% of Fe and S.
Using an aluminum alloy in which i is regulated to 0.2 wt% or less and the remainder consists of Al and other unavoidable impurities,
The molten metal of the alloy is cast by the DC casting method at a casting speed within the range of 35 to 150 mm/min, and the resulting ingot is cast into a dark gray color depending on the color tone to be obtained after anodizing the rolled plate. To obtain a color tone of: 350°C or higher and lower than 500°C B. To obtain a pale gray color tone: 500°C or higher and lower than 550°C. To obtain a milky white color tone: Among A, B, and C of 550°C or higher and 630°C or higher. After selecting one of the temperature conditions and applying heating at a temperature within the temperature condition range for 0.5 to 24 hours, hot rolling and further cold rolling are performed to obtain the final plate thickness. More than 90% of interlayer compounds are 5μm
The size is below and the total amount of intermetallic compounds is 2.5
~7 wt%, and intermetallic compound Al_
Depending on the color tone to be obtained after the anodizing treatment, the ratio between the amount of 6Fe and the amount of Al_3Fe is as follows: a For dark gray tone: Al_6Fe/(Al_3Fe+Al_6Fe)≧0.
7 b For light gray tone: 0.7>Al_6Fe/(Al_3Fe+Al_6Fe
)>0.1 c To obtain a milky white tone: 0.1≧Al_6Fe/(Al_3Fe+Al_6Fe
) A method for adjusting the color tone of an aluminum alloy rolled sheet for building materials after anodizing treatment, characterized by obtaining a rolled sheet falling within the ranges a, b, and c above. (2) When manufacturing aluminum alloy rolled sheets for building materials using aluminum alloys having the same composition, the color tone of the rolled sheets after anodizing treatment is dark gray, dark gray,
In the method of adjusting to three levels of light gray and milky white, the material contains 0.8 to 2.0 wt% of Fe, 0.05 to 0.21% of Mn, and 0.05 to 1.0 wt% of Mg.
5wt%, any one or two or more of Cr0.05 to 0.1wt%, and Si is 0.2wt%.
% or less, and the remainder consists of Al and other unavoidable impurities.
Depending on the color tone to be obtained after anodizing the rolled plate for the ingot obtained by casting using the C casting method, A. When obtaining a dark gray tone: 350°C or higher but below 500°C B. A pale gray color tone. To obtain: 500°C or higher and lower than 550°C C. To obtain a milky white color: Select one of the temperature conditions A, B, or C of 550°C or higher and 630°C or higher and at a temperature within that temperature condition range. After heating for 0.5 to 24 hours, hot rolling and further cold rolling are performed to obtain a final plate thickness, whereby more than 90% of the intermetallic compounds are 5 μm thick.
The size is below and the total amount of intermetallic compounds is 2.5
~7 wt%, and intermetallic compound Al_
Depending on the color tone to be obtained after the anodizing treatment, the ratio between the amount of 6Fe and the amount of Al_3Fe is as follows: a For dark gray tone: Al_6Fe/(Al_3Fe+Al_6Fe)≧0.
7 b For light gray tone: 0.7>Al_6Fe/(Al_3Fe+Al_6Fe
)>0.1 c To obtain a milky white tone: 0.1≧Al_6Fe/(Al_3Fe+Al_6Fe
) A method for adjusting the color tone of an aluminum alloy rolled sheet for building materials after anodizing treatment, characterized by obtaining a rolled sheet falling within any one of the above ranges a, b, and c.