DE2353842C2 - Process for the production of aluminum sheet - Google Patents

Description

The invention relates to the use of a Process for the production of aluminum sheet, which at the color anodisatlon in an anodizing electrolyte an oxide layer colored from light gold to black made possible on aluminum-magnesium alloys.

It is already known per se (US-PS 33 79 580), products made of aluminum and aluminum alloys, such as Sheets, extruded articles, cast rods and the like, for architectural and other anodic purposes Subject to oxidation to produce integrated color coatings, giving them a very attractive appearance obtain.

The electrolyte consists of an aqueous solution of sulfosallcylic acid with small amounts of sulfuric acid and / or sulfates. Later it was found that numerous compounds, both organic as well as inorganic, ml: small amounts of sulfuric acid and / or metal sulfates in aqueous solutions can be used to anodic. To produce integrated colored oxidative coatings. As examples Such compounds are to be cited sulfophthalic acid, sulforesorcln, lgnosulfonic acid, oxalic acid, maleic acid, Succinic acid and combinations thereof, furthermore chromates, molybdates, tungstates and vanadates. It Many other connections could be cited.

s The term "color anodizing" or "color anodizing" used in the past is intended to refer to the anodizing process which produces a colored anodic oxide coating that is deposited by an In considerable degree of increasing resistance ίο and characterized by a color 1st, which is the first Line is a function of the bath voltage applied during anodizing.

In technical color anodizing processes, the desired color is usually achieved through a variation achieved the electrical program sequence that is used during anodizing, such as. B. the Current density, voltage and the like. The electrical programs used so far existed of

(1) a two-stage program in which the initial stage works with a constant current density until a predetermined peak voltage has been reached, and in which the second stage works with constant voltage at that peak voltage until the desired color and coating thickness is achieved , and from
(2) a one-step program in which the current density is kept at a constant value range until the desired color and oxide thickness is achieved. The current density at the constant current density stage can be between about 1.1 and 5.4 Amp./dm ² and the voltage between 30 and 75 volts at the constant voltage stage. Occasionally the bath temperature is increased or decreased from a normal 3ä operating temperature of 25 ° C to 15 ° C or 35 ° C for darker or lighter colorations.

Already in the initial phase of the development of the color anodizing process it was clearly recognized that, in spite of the fact, that the process applied a wide range of stains on numerous aluminum alloys, which are actually used for color anodizing on an industrial scale suitable alloys would be quite limited. This was due to the fact that many aluminum alloys provide speckled or streaked anodized oxide coatings, and that many alloys could not be anodically oxidized with the formation of a wide range of colors, without the parameters of anodic oxidation, such as bath composition, Bath temperature, current density, voltage and the like, modify quite considerably. The changes in the composition of the bath and However, changes in the bath temperatures are inexpedient and costly measures. Further is it has previously been extremely difficult to apply anodic oxide coatings In a thickness range that is technically useful for exterior architectural purposes, in particular cladding, namely a range from about 0.01 to about 0.04 mm, in a wide range of colors by appropriate Variation of voltage and current density and moderate changes in bath temperature of, for example, up to 10 "C. With regard to the maximum thickness of the anodized While there is a limitation on oxide coatings, there is it is clear from an economic point of view that the higher the oxide layer thickness, the higher the costs, which would have to be used to produce the coating.

It was established early on that various Lots of the same alloy and batch delivered oxide coatings despite the same anodizing program, which did not match in color, d. H. not that showed the same appearance when viewed side by side. True, the color developed may be the same be, d. H. gold-colored, amber-colored, statue-bronze-colored or black, but there can be certain differences be present in the tone or the nuance of the coloring, so that the color anodized material is a visual can have a different appearance and is therefore technically unusable.

Now it had been desired for a long time, two or more Having three separate alloys available to produce the full range of colors on the sheet metal products to be able to. The modified alloy 5005 from AA was used to create shades from gold to to produce dark brown or statue bronze colors. To obtain a black anodic oxide coating, had to use a different alloy, e.g. B. 5086 of the AA can be used.

The invention is based on the object of an aluminum alloy or to create such an aluminum sheet that can be color-anodized in a much improved manner is, with shades of light gold to black within a technically useful Thickness range from 0.0127 to 0.0381 mm, solely by changing the parameters of the color anodization.

The object is achieved by using a method for producing aluminum sheet, wherein The ingot is poured, in a temperature range of 538 to 607 ° C, avoiding temperature fluctuations of more than ± 16.5 ° C for related Batches homogenize., And are hot-rolled to sheet thickness, on an aluminum alloy

0.05 to 0.20% silicon,

0.15 to 0.40 * iron,

0.15 to 0.30% copper,

0.10 to 0.30% manganese,

0.6 to 1.0% magnesium and

0.04 to 0.12% chromium

and aluminum as the remainder with permissible additions.

The alloy is composed of preferential cores

0.08 to 0.14% silicon,

0.15 to 0.25% Elsen,

0.16 to 0.25% copper,

0.16 to 0.25% manganese,

0.70 to 0.90% magnesium,

0.04 to 0.08% chromium

and aluminum as the remainder with permissible additions.

The sum of the copper and manganese contents should not exceed 0.45%.

The content of permissible admixtures should be 0.05%, in particular 0.03%, and their total amount Do not exceed 0.15%, preferably 0.10%. Unless otherwise noted, all mean in this description of the invention indicated percentages% by weight.

Albeit many of the legends the coloring of the resulting oxide coating. Chromium is special in the present alloy of decisive importance with regard to the reproducibility of the color, i. H. on the match Im Hue. Without the presence of chromium in the amounts indicated, it will cause small variations in the

50

55

60

65 Manganese content, especially in the lower part of the quantity range, large fluctuations in color tone when the workpiece is color-modified.

In the method according to the invention, the aluminum alloy is of the composition given above Poured into ingots, usually using the chill casting process. Then it is homogenized annealing and finally hot rolled. If desired, the sheet can also be cold-rolled. To the Achieving a uniform color reproduction band the homogenization annealing should be carried out for 4 to 24 hours at a temperature between 538 ° C and 607 ° C will. The maximum variation in the temperature of the diffusion annealing or homogenization annealing from batch to batch The range should be ± 16.5 ° C concerned to ensure the production of a uniform color. A relatively slow one Heating rate of less than 38 degrees / h, in particular of 24 degrees / h, is the case with homogeneous solution annealing particularly advantageous.

After homogenization, the bars are allowed to cool to room temperature, preferably with a Speed of less than 38 degrees / h; they are then descaled. After descaling, the Ingots back to rolling temperature, e.g. B. 400 to 454 ° C and then hot rolled. A modified one The working method after casting consists of descaling, homogenizing and cooling a to the hot rolling temperature and hot rolling. If desired, the sheet can be cold rolled at a temperature below 121 ° C.

The following examples are intended to facilitate the practical implementation illustrate the invention and its advantages.

40

Example I.

An ingot was obtained from a co-current heated melting furnace of the following alloy composition poured:

Elsen 0.21%

Copper 0.18%

Manganese 0.16%

Chromium 0.06%

Silicon 0.13%

Magnesium 0.73% and as

Remainder aluminum with the normal impurities.

The bar was homogenized for 6 hours at 538 ° C., with a heating and cooling rate of 15.5 ° C per hour was maintained, was then descaled (scalped) and hot-rolled at an initial temperature of 440 ° C and a final temperature of 343 ° C and was then cooled to room temperature. The samples were cleaned in an inhibited alkaline cleaner. In a 50% nitric acid solution deoxidized, pickled for 10 minutes in a 5% solution of a caustic alkali at 57 "C, and it was The matting is removed (desmutted) in a 50% nitric acid solution. Four samples of this sheet material were in an aqueous electrolyte, the 65 g / lter Suifosalicylic acid. 5.8 g / liter of sulfuric acid and 1.7 g / liter of dissolved aluminum contained, with 4 different electrical programs anodically oxidized. The colors of the resulting anodic oxide coatings were gold-colored, amber-colored, statue-bronze-colored or black, and the various parameters of the anodic oxidation treatment that was used,

to produce these colorations are summarized below. It should be noted that the statue bronze coloration and the black coloration were obtained in 20 and 40 minutes, respectively, using a total amount of current of 1.08 and 1.3 ampere-hours per dm ² , respectively.

Table I.

Parameters of anodic oxidation treatment

Color current peak total total current thickness of bath

of the coating tight tension duration of the amount of oxide layer temperature

anodic ampere-oxidation hours amp./dm ² volts per dm ² mm ° C

gold 1.3 40 55

amber 2.15 51 30

Statue bronze 3.23 65 20

black 3.23 65 40

0.97
1.08
1.08
1.3

0.0203
0.0203
0.0203
0.0229

25th
25th
25th
15th

Example 2

There are three separate alloys, de "en compositions are given in Table II below prepared, and it was poured three bars of each alloy. An ingot of each alloy composition at temperatures of 538 ° C, 579 ° C and 607 ⁰ C. The heating rate and the cooling rate were in each case 15.5 ° C. per hour. The bars were then descaled at room temperature, reheated to a temperature of 440 ° C. and rolled to a thickness of 3.556 mm Sheet metal products were then prepared for anodic oxidation by cleaning in an inhibited alkaline cleaner, deoxidizing in a 50% nitric acid solution, pickling for 10 minutes in a 5% solution of caustic alkali at 57 ° C, desmutting in a 50% The samples were then anodically oxidized in an aqueous electrolyte, &-> .r 65 g / liter sulfosallcylic acid acid, 5.8 g / liter sulfuric acid and 1.7 g / liter dissolved aluminum. The temperature of the electrolyte was maintained at 25 ° C ± 1 ° C. The anodizing program used was a two-stage program in which a constant current density of 3.23 amps / dm ^{2 was} passed through in the first stage, a peak voltage of 65 volts was reached, and a constant voltage period of 65 volts was maintained in the second stage until a total of 1.08 ampere-hours per dm ^{2 had} passed. The coloring of all samples corresponded to a statue bronze color and generally showed a good tone-on-tone impression. The photometric color determinations are summarized in Table III below. The instrumental evaluation of the coloration was carried out with a reflection strength measuring device "Photovolt Model 610" with a "Model T-Head". The reflectivity values were measured against a porcelain enamel standard calibrated against MgO used at 100%. The "yellowness factor" is determined from the relationship

Y = 100 (A-B) / G,

where A is the reflectance value for the amber color, B the Reflexion value for blue and G is the reflection value for green.

Table II
composition

tion
No.

Si

Fe

Mg Cu

Mn

Cr

Al

³⁰ 3

0.13
0.10
0.12

0.21
0.20
0.22

0.73
0.75
0.84

0.18
0.16
0.25

0.16
0.24
0.19

0.06 remainder
0.05 remainder
0.06 remainder

Table III
Instrumental evaluation

alloy Homogenization Reflection “Yellowness No. tempera worth for factor" tur ⁰ C green 1 538 4.2 i6 1 580 5.2 21 1 607 6.1 26th 2 538 4.0 10 2 580 4.5 16 2 607 5.8 24 3 538 3.8 13th 3 580 4.7 20th 3 607 5.7 25th

The reflectance value for green is usually indicative for the lightness or darkness of the sample in the sense that the lower the reflectance value, the darker the color. the "yellowness! ts" factor bezv, ic: inet In general the degree of yellowness of the Pattern; the higher the factor, the more yellow it is Appearance of the coating. A variation of the value for the green reflection by less than 4, preferably by less than 3, for lighter colors and by less than 2.0, preferably by less than 1, for the darker shades is for architectural applications in general As mentioned above, those are justifiable Sheet metal products produced using the method according to the invention are distinguished by the fact that that they form an integrated colored anodic oxide coating, which, if certain anodization conditions are observed has a coloration that reflects green owns by less than 4 units, for habitual

llrh by less than 3 lighter colors, with the lighter colors and less than 2 units, usually less than 1 unit, for the darker colors fluctuates with another sample of the sheet material mentioned, which anodically oxidizes in the same catfish has been.

Claims (3)

Patent claims: 1. Application of a method for the production of aluminum sheet with a structure that in the Color anodization by varying the working conditions enables the formation of a 0.0127 to 0.0381 mm thick, light gold to black colored oxide layer, the ingots being cast, homogenized and hot rolled to sheet thickness on an aluminum alloy the end 0.05 to 0.20 «silicon,
0.15 to 0.40 * Elsen,
0.15 to 0.30 »copper,
0.10 to 0.30 »manganese,
0.6 to 1.096 magnesium,
0.04 to 0.12 "chromium and aluminum as the remainder with permissible additions with the proviso that in a temperature range of 538 to 607 ° C while avoiding temperature fluctuations Homogenization annealed of more than ± 16.5 ° C for related batches will. 2. Application of the method according to claim 1 to an aluminum alloy made of: 0.08 to 0.14% silicon,
0.15 to 0.25% Elsen,
0.16 to 0.25% copper,
0.16 to 0.25% manganese,
0.70 to 0.90% magnesium,
0.04 to 0.08% chromium Lid aluminum as the rest with permissible additions. 3. Application of the method according to claim 1 or 2 to an aluminum alloy, in which the The sum of copper and manganese does not exceed 0.45%.