JPH0625808A - Production of aluminum alloy sheet for anodic oxidation treatment - Google Patents

Abstract

PURPOSE:To produce an aluminum alloy sheet capable of forming an anodic oxidation film having uniform color tone and superior corrosion resistance. CONSTITUTION:An aluminum alloy having a composition which consists of, by weight, 0.05-0.5% Si, 0.15-0.9% Fe, 0.05-0.5% Cu, 0.01-0.05% Ti, <=0.05% each of inevitable impurities, and the balance Al (where Al content is regulated to >=199.00%) and in which, 0.30<=Si+Fe<=1.0%, >=<=Fe and 0.3 [si%]<=Mg<=1.0 [si%] are satisfied is heat-treated at 450-600 deg.C for 1-20hr. Hot rolling is started at 400-550 deg.C, and the rolling is finished at 200-300 deg.C. Successively, the resulting plate is subjected to cold rolling, to intermediate heat treatment at <=400 deg.C for >=30min, and to final cold rolling at >=30% reduction in thickness. By this method, the aluminum alloy sheet can be produced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the corrosion resistance of an anodized film,
Pure aluminum alloy plate used for various applications that require uniformity of color tone (stability) or uniformity of appearance when etched. The present invention relates to interior and exterior panel materials for construction, daily necessities, kitchen articles, lithographic printing plate supports, decorative members and the like.

[0002]

2. Description of the Related Art JIS-A1100, 1200 to 1050, 106 industrially used as a pure aluminum alloy.
In the alloys such as 0, 1070 and 1N00, 1N30, 1230, the corrosion resistance of the anodized film and the uniformity of the color tone are superior to those of other alloy type aluminum alloys other than pure aluminum type. However, as represented by acid rain,
The global environment has been remarkably deteriorated in recent years, and when it is used for exterior panels for buildings and the like, higher corrosion resistance than conventional pure aluminum alloys is required.

On the other hand, with respect to the uniformization of the color tone, nowadays, where a building or the like is seen as a part of fashion in a city, not as a simple building structure, there is a demand for a more uniform uniformity. Since these quality characteristics are controlled by Fe and Si as impurities contained in the alloy, they are generally dealt with by controlling the amounts of Fe and Si, that is, the purity of the pure aluminum alloy.

However, improving the corrosion resistance and the uniformity of the color tone of the anodized film by increasing the purity of aluminum raises the cost of the base metal and lowers the mechanical properties, especially hardness and strength. In order to improve the corrosion resistance, there is a method of increasing the film thickness of the anodized film, and a method of increasing the plate thickness to compensate for the decrease in strength due to the increase in aluminum purity, but both of these are not preferable because they increase costs. .
Although the film thickness is adjusted to make the color tone of the film uniform, it takes time to adjust the film thickness, resulting in an increase in cost.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides an aluminum alloy sheet which has an excellent corrosion resistance and has a sufficient mechanical strength without thickening the oxide film or increasing the plate thickness. The present invention is intended to provide a manufacturing method of.

[0006]

[Means for Solving the Problems] As a result of research on the mechanism of impairing the corrosion resistance of an anodized film, when Si contained in an aluminum alloy exists in the state of being precipitated as individual Si particles, such an aluminum alloy When the plate is anodized, Si particles remain in the film, and because the chemical properties of the particles are different from those of the surrounding film, they are selectively dissolved and dropped by a corrosive medium containing chlorine ions, resulting in film defects and corrosion. Became clear.

Further, the color tone of the film is distributed in the film 1.
It was found that the particle size distribution of fine Si particles having a size of μm or less and the difference in gloss due to uneven etching during caustic etching for removing scratches on the surface as a pretreatment for anodizing treatment are affected.

Therefore, a method for preventing the precipitation of the Si particles was examined, and an appropriate amount of Mg was added to the Mg ₂ Si layer.
It has been found that as a method for preventing uneven etching, it is possible to uniformly caustic-etch and add a uniform gloss to prevent uneven etching. The amount of Mg added is based on the solid solution of Si as a compound Mg.
An amount corresponding to the formation of ₂ Si is sufficient.

As a result of the above research, the constitution of the present invention is a method for producing an aluminum alloy plate capable of obtaining an anodized film having a uniform color tone and excellent corrosion resistance as described in the claims.

The above structure will be described below.

Since it is necessary to keep the mechanical properties and chemical properties within the range that can be handled as pure aluminum, which is generally known, the Al purity excluding the added components and unavoidable impurities must be 99.00% or more. I won't.

Fe is added to make the recrystallized grains finer. If it is less than 0.15%, the effect becomes small. 0.
Addition of Fe in excess of 9% forms coarse Al-Fe-based and Al-Fe-Si-based compounds, which lowers the formability of the sheet and causes local non-uniformity of chemical properties. Not preferred because of

The content of Si inevitably contained in the aluminum ingot is 0.05% or more, and if it is less than 0.05%, the ingot cost is increased. Si over 0.5% is Fe
This impairs the effect of refining recrystallized grains and reduces corrosion resistance.

The amount of {Si + Fe} is adjusted from the viewpoints of mechanical strength such as material strength, chemical properties, and ingot cost. If the amount is less than 0.30%, high-purity metal is used, resulting in higher cost and lower material strength.

When the amount of {Si + Fe} is 1.0% or more, Al is less than 99.00%, and the characteristics as pure aluminum are impaired. Actually, the following Cu, Ti, Mg
And the unavoidable impurities must be less than 1.0%.

When the amount of Si exceeds the amount of Fe, the effect of refining the recrystallized grains by Fe is impaired and the corrosion resistance is also lowered, so that {Fe%} ≧ {Si%} is required.

Cu is an element that affects caustic etching generally performed as a pretreatment for anodizing treatment. If the caustic etching becomes non-uniform, the gloss becomes uneven, which causes variations in color tone after anodizing. Cu is 0.0
When it is added in an amount of 5% or more and 0.5% or less, caustic etching is uniformly performed, and uneven gloss is eliminated. 0.05%
If less than, the effect cannot be obtained. If it exceeds 0.5%, the corrosion resistance of the base plate before anodizing is deteriorated, which is not preferable.

Ti is added mainly for refining the crystal grains of the ingot. If it is less than 0.01%, the effect is small.
If it exceeds 05%, a coarse Al-Ti compound is formed,
It may be distributed in a streaky pattern on the rolled plate and may cause defects in the anodized film.

Ti also has the effect of refining the recrystallized grains of the rolled plate.

There is also a method of adding Ti and B in combination, instead of Ti alone, for refining the crystal grains. Even in this case, it is preferable to adjust the Ti amount in the range of 0.01 to 0.05%. Although the amount of B is included as an impurity, the amount added is usually 30 ppm or less.

Mg is an additive component relating to the main points of the present invention. Si particles that impair the corrosion resistance of the anodized film are Al-Fe.
-Si that is not a Si compound but is solid-solved in Al (matrix) is precipitated alone. The Si particles remain in the film without being dissolved by the anodizing treatment. When Mg is added to form a compound of Mg ₂ Si, it dissolves together with aluminum in the anodizing process, and thus does not become a film defect. 0.05-0.5% S contained in this alloy
Part of i is combined with Fe and Al to form Al-Fe-S.
It is an i-based compound, and this bonded Si does not precipitate as Si particles.

That is, Si to be Mg ₂ Si is
It is the amount that does not become an Al-Fe-Si compound but is solid-solved in the Al matrix, and it is estimated from the analysis result by the X-ray microanalyzer, that amount is the amount of Si added, the amount of Fe contained at the same time, Although it varies depending on the heat treatment conditions and the like, it is considered to be about 20 to 60% of the total amount of Si added.

In consideration of the above matters, various examinations have been made on the amount of added Mg required to achieve the object of the present invention, and as a result,
M in the range of 3 × {Si%} ≦ Mg ≦ 1.0 × {Si%}
It has been found necessary to control the amount of g.

However, {Si%} is the Si content (%).

If Mg is small, solid solution Si remains and S
Precipitates as i particles.

Further, since excess Mg forms a solid solution in the Al matrix and does not remain in the anodized film, it does not affect the corrosion resistance or the color tone. The material strength is slightly increased or the chemical properties are changed, but the effect is slight.

Next, the manufacturing method will be described.

An aluminum alloy blended with a predetermined composition is formed into an ingot by a usual method, and if the surface segregation layer is harmful to the quality of the final product, it is cut and removed. Cutting and removal may be performed after the homogenizing heat treatment and before the hot rolling.

Next, the ingot is homogenized in the casting structure and F
e and Si are heat-treated to form an Al-Fe-Si-based compound. At a temperature lower than 450 ° C or higher than 600 ° C, formation of this compound is unlikely to occur. The heat treatment time is preferably longer, but it is within 20 hours from the viewpoint of productivity (economical efficiency). There is no problem in practical use in 3 to 10 hours.

After this heat treatment, the substrate is cooled to room temperature and reheated after removing the surface layer, or without cooling, 4
Hot rolling is started at 00 ° C. to 550 ° C., multi-pass rolling is performed, and rolling is finished so that the material temperature at the end is 200 to 300 ° C.

If the starting temperature is lower than 400 ° C., rolling is difficult, and if the starting temperature is higher than 550 ° C., the Al—Fe—Si compound may decompose, which is not preferable because the rolling plate surface is oxidized.

The end temperature is regulated for the refinement of the crystal structure. If the temperature is lower than 200 ° C., the rolling oil cannot be completely evaporated and remains on the plate surface, causing surface contamination and corrosion. When the temperature is higher than 300 ° C., the recrystallized grains grow coarsely and the final plate has uneven band tone (gloss) due to the band-like structure. Within these temperature ranges, the optimum temperature is determined so as to optimize the crystal structure of the final plate, the anisotropy of mechanical properties, and the like.

Performing hot rolling in such a temperature range is also important for forming Mg ₂ Si during rolling and during cooling after rolling.

After hot rolling, cold rolling and intermediate heat treatment are performed. By performing cold rolling before the intermediate heat treatment, the recrystallized grains in the intermediate heat treatment become fine, and streaky color tone (gloss) unevenness due to the crystal grains when the final plate is etched can be prevented. When the hot rolling finish temperature is lower than 250 ° C, the same effect as cold rolling is obtained. Performing the intermediate heat treatment at 400 ° C. or lower and for 30 minutes or longer is due to solid solution of Si and M.
This is because g is a compound of Mg ₂ Si. At a temperature higher than 400 ° C. or less than 30 minutes, this compound is hard to be produced. Usually, this intermediate heat treatment recrystallizes the work structure by cold rolling, so it is heated to 300 ° C. or higher, but if recrystallization is not necessary, it may be lower than 300 ° C.

The final cold rolling of 30% or more performed after the intermediate heat treatment is to adjust the mechanical properties of the final plate.
If the degree of processing is large, strength and hardness increase. The optimum value is selected based on the end plate application.

Depending on the application, it may be preferable to use an annealed material having a large elongation. For this purpose, heat treatment may be applied at 200 to 400 ° C. after the final cold rolling. 20
At temperatures lower than 0 ° C, changes in mechanical properties are slow. 400 ° C
At higher temperatures, the recrystallized grains become coarse. In addition, the formed Mg ₂ Si is decomposed and Mg and Si are redissolved, which is not preferable.

If the intermediate heat treatment is performed by rapid heating at an average temperature rising rate of 10 ° C./sec, the recrystallized grains become finer, and the moldability and appearance when etched are improved.
To recrystallize, it is necessary to heat to 400 ° C. or higher for 5 seconds or longer. If this heat treatment temperature is higher than 500 ° C. or if the holding time is too long, the decomposition and re-solid solution of Mg ₂ Si formed during the latter half of hot rolling and during cooling after the end of hot rolling will occur. It is practically harmless if it is within the specified conditions.

The final plate thus obtained is used by, for example, etching it with an aqueous solution of caustic soda, neutralizing it, and then anodizing it in an aqueous solution of sulfuric acid to impart aesthetics and corrosion resistance.

[0039]

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

Example 1 An aluminum alloy having the chemical composition shown in Table 1 was melt cast to obtain an ingot. After cutting and removing the surface segregation layer, 500
After heat treatment at ℃ × 8 hours, directly subjected to hot rolling,
Rolling was performed so that the end temperature was 245 ± 15 ° C. After making the hot rolled plate thickness 6 mm to 3.5 mm by cold rolling,
An intermediate heat treatment of 360 ± 10 ° C. × 2 hours was performed, and then cold rolling was performed to obtain a plate having a thickness of 2.0 mm. The plate thickness reduction rate of the final cold rolling is 43%. This is designated as H14 material.

Further, a cold-rolled sheet having a thickness of 0.70 mm (sheet thickness reduction rate of 80%) is designated as H18 material.

Further, this H18 material was heated at 250 ° C. for 2 hours to be semi-annealed. (H24 material) Further, a product that was completely annealed by heating at 360 ° C. for 2 hours was manufactured. (O material) The corrosion resistance of the anodic oxide film of each of these materials was evaluated as follows.

First, a 10% aqueous sodium hydroxide solution (40 ° C.)
Etched in 2 minutes. After washing with water and neutralization, anodization is performed for 10 minutes at a current density of 1 A / dm ^{2 in} a 15% sulfuric acid bath (25 ° C.). The thickness of the film formed is approximately 2.5 μm. Next, 3% saline solution (25
(10 ° C.), the coating is corroded by performing alternate dipping for 10 minutes for dipping and 50 minutes for drying for 10 cycles. Next, electricity is applied for 2 V × 3 minutes in a saturated copper sulfate solution (25 ° C.). As a result, if the anodic oxide film has defects such as micropores,
Copper is reduced and deposited there by energization.

[0044]

[Table 1]

When the plate thus treated is magnified and observed under an optical microscope, spotted copper can be observed. Evaluation of the corrosion resistance of the coating is shown in Table 1, No. 4, 8, 1
The density of copper precipitation points (film defects) generated in the films of Nos. 2 and 16 (comparative material) was ranked as rank 5, the state without any defects was ranked as rank 0, and the spaces between them were classified into ranks 4, 3, 2, 1. .

Therefore, the evaluation is a relative evaluation. In addition, the evaluation of the corrosion resistance of the original plate before anodizing is performed according to JIS Z237.
1 Based on the salt spray test method, 10% of 5% saline at 35 ° C was used.
It was sprayed for 0 hour, and the results were compared relatively and expressed by the following three-stage evaluation.

Equivalent to JIS A 1050: ○ Slightly inferior to JIS A 1050: △ Inferior to JIS A 1050: × In addition, there was no great difference in the corrosion resistance of the base plate due to the tempering of the H14, H18, H24 and O materials. The results of H14 material are shown.

The evaluation results are shown in Table 2. As compared with the comparative material having a low Mg content, the corrosion resistance of the film was improved in the invention material containing Mg, and it can be seen that when the content of Cu exceeds the composition range of the present invention, the corrosion resistance of the base plate is poor.

[0049]

[Table 2]

Further, the color tone stability of the anodized film was evaluated as follows.

Among the alloys shown in Table 1, No. 13, 1
About H18 material of 7, 18, 19 150-450 ℃
After annealing for 8 hours each, etching in 6% caustic soda aqueous solution (70 ° C) for 3 minutes to neutralize
1.5 A / dm ² × 40 mi in a 5% sulfuric acid bath (20 ° C.)
Anodizing treatment of n (coating thickness 15 μm) was performed, and sealing treatment was performed in normal pressure boiling water, and the color tone of the coating was measured.

The results are shown in Table 3. In the alloy containing Mg and Cu (No. 13, 17), it can be seen that the color tone of the anodized film hardly changes depending on the annealing temperature in the range of 200 to 400 ° C. This means that even if conditions such as hot rolling temperature and heat treatment change in the manufacturing process of the rolled plate, the film color tone of the final plate hardly changes, and stable color tone is obtained between multiple lots or within one coil. Is shown.

[0053]

[Table 3]

(Note) The film color tone display conforms to JIS Z8729-1980.

L * is bright (large) ← → dark (small) a * is red (+) ← → green (-) b * is yellow (+) ← → blue (-).

Example 2 Alloys Nos. 20 and 21 shown in Table 4 were agglomerated, and after removing the surface segregation layer, they were heated at 540 ° C. for 4 hours and then 480
Cool to ℃ and start hot rolling. End temperature is 275 ± 15
It was hot-rolled to a temperature of 5 mm and a thickness of 5 mm, and then cold-rolled to a thickness of 2 mm. Here, after the intermediate heat treatment conditions were variously changed, the plate was cold-rolled at a plate thickness reduction rate of 50% to obtain a plate (H14 material) having a thickness of 1 mm. The temperature rising rate in the intermediate heat treatment was 30 ° C / sec. Further 360
A plate (0 material) that had been subjected to a final heat treatment of ° C x 2 hours was prepared, and the corrosion resistance thereof after the anodizing treatment was evaluated in the same manner as in Example 1. In addition, the appearance of the anodized plate surface was visually inspected, and the degree of streaky color tone (gloss) unevenness caused by crystal grains was evaluated as the appearance quality. The evaluation value is a relative evaluation within the same alloy material. The results are shown in Table 5. When the temperature of the intermediate heat treatment is low and the time is short, sufficient recrystallization does not occur, and the coarse crystal grains generated by hot rolling are rolled as they are. Will be noticeable. Intermediate heat treatment temperature 500
If the temperature is higher than 0 ° C, recrystallization will occur sufficiently, but it will become a little coarser and present streaky unevenness, and the corrosion resistance of the film will decrease.

The lower the intermediate heat treatment temperature was, the better the corrosion resistance of the anodized film was.

In the final 0 material, the sufficiently cold-rolled sheet was recrystallized and the streak unevenness was smaller than that of the H14 material.
The effect was still recognized in the unsuitable intermediate heat treatment.

[0059]

[Table 4]

[0060]

[Table 5]

Note) Description of appearance quality ◯: good, Δ: streak-like gloss unevenness is recognized but slight,
X: Partial uneven streaks are observed, XX: Uneven streaks are observed on the entire surface.

Example 3 Alloy No. 22 shown in Table 6 was ingoted, cut into small pieces, and subjected to homogenizing heat treatment, hot rolling, cold rolling, intermediate heat treatment and cold rolling to prepare a material for H14. The corrosion resistance of the anodized film and the color tone of the film were evaluated in the same manner as in Example 1.

The results are shown in Table 7. The corrosion resistance of the anodized film was not good in the intermediate heat treatment for a long time at a high temperature of over 400 ° C. or the homogenization treatment at a low temperature of less than 450 ° C.

[0064]

[Table 6]

[0065]

[Table 7]

[0066]

[Table 8]

[0067]

As described above, in the past, in order to improve the corrosion resistance and color stability of the anodic oxide film, which was dealt with by increasing the purity of the base metal, the alloy with a high purity was obtained by adding a small amount of Mg and Cu. Since the same effect can be obtained, it is possible to avoid an increase in the cost of bullion, and the economic effect is large. Same purity (Si, F
When the amount e of metal is used, the corrosion resistance is improved and the product life is extended.

Further, by positively adding and adjusting Mg, which has been treated as an impurity, whose amount has not been conventionally controlled, the variation in corrosion resistance, which fluctuates depending on the metal used, is eliminated, and quality stabilization is achieved. To be done.

Claims (3)

[Claims] 1. Si based on weight; 0.05-0.5%,
Fe; 0.15-0.9%, Si + Fe; 0.30% or more, less than 1.0%, Si% ≦ Fe%, and further C
u: 0.05 to 0.5%, Ti: 0.01 to 0.05
%, Mg; including {Si%} × {0.3 to 1.0}%,
An aluminum alloy in which the balance between these components and 0.05% or less of each inevitable impurities is Al (however, 99.00% or more) is cast by semi-continuous casting, and then, if necessary, a surface segregation layer. Cutting and removing, 450 ℃ or more 600
Heat treatment at temperatures below 400C for 1 to 20 hours
The hot rolling was started below and the material temperature was 200 ° C or higher 3
It is characterized in that the rolling is finished so that the temperature becomes 00 ° C. or less, then the cold rolling and the intermediate heat treatment at 400 ° C. or less for 30 minutes or more are performed to perform the final cold rolling at a sheet thickness reduction rate of 30% or more. A method for producing an aluminum alloy plate, which can obtain an anodized film having a uniform color tone and excellent corrosion resistance. 2. The intermediate heat treatment according to claim 1 is 400 ° C.
The condition when performing at a higher temperature is changed so that the average temperature rising temperature is 10 ° C./sec or more and the temperature is heated to more than 400 ° C. and 500 ° C. or less and held for 5 seconds or more and 30 seconds or less. 1. A method for producing an aluminum alloy plate, which can obtain an anodized film having a uniform color tone according to 1 and excellent corrosion resistance. 3. After the final cold rolling, 200 to 400 ° C.
The method for producing an aluminum alloy plate according to claim 1 or 2, wherein the anodized film having a uniform color tone and excellent corrosion resistance is obtained.