DE2106388A1 - - Google Patents

Description

DIPL. ING. G. PULS SCHWeigerstrasse S.

DH.E.T.PECHMANN tblbfoh 28 06 31 DH. ING. D. BElIHENS PATENT LAWYERS

1Δ-39 028

Description of the patent application

CEGEDUE. GP

66, Avenue Marceau, Paris 8, France

concerning:

" Process for producing colored oxide layers with a blue base tone on aluminum alloys (I)"

The invention relates to a method for producing colored oxide layers with a blue base tone on aluminum alloys and workpieces made therefrom.

In the French patent 880 095 a method is described in which pigments on the basis deposited by metal compounds in the pores of an aluminum oxide layer previously produced on aluminum workpieces will. This deposition or deposition takes place by electrolysis with alternating current in an acidic solution a copper, nickel or silver salt. This well-known Process allows the production of pink, bronze, red or black hues. With the help of modifications that ■ **

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To improve this process, other shades will be like Yellow, brick red, chestnut brown, chocolate brown and much more.

For example, in French patent specification no. 447 823, the method for producing a blue hue is used. For this purpose, a foil made of aluminum with a degree of purity of 99 to 99 »9 % is first anodically oxidized with direct current in an aqueous bath containing 80 g / l chromic acid, and then by means of electrolysis with alternating current in a bath containing 25 g / l boric acid, 20 g / l nickel sulphate and 15 g / l ammonium sulphate ^ colored blue.

In another example, an aluminum foil, purity 99 to 99/9%, is contained with direct current in a bath 80 g / l sulfuric acid and 15 g / l oxalic acid, anodically oxidized and then electrolytically colored pale blue in a bath containing 25 g / l nickel sulfate and 15 g / l ammonium sulfate.

In practice, however, it has been shown that these results cannot be reproduced. Also be from the same Author of U.S. Patent 3,382,160 using the same type of metal and bath compositions and achieved bronze shades under the same conditions in terms of treatment time, temperature and current intensity. This latter result is consistent with practical experience.

There is thus still the need for a reliably working method with which "in Produce reproducible colored oxide layers with a blue base tone on aluminum and / or aluminum alloys permit.

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The method according to the invention meets this need. It allows generation in a reproducible manner of color tones on aluminum and / or aluminum alloys, ranging from a simple purple tinge to a vivid one Blue to a dark blue range.

It has surprisingly been found that this is done simultaneously three conditions must be met, and that these are the quality of the metal to be colored, the quality the porous alumina layer and the conditions when the coloring particles are deposited in the pores.

In the method according to the invention, an aluminum alloy is used to produce the workpieces to be colored, which, in addition to the usual accompanying substances of aluminum, contains one or more elements from the group magnesium, cobalt and nickel and, if necessary, manganese, silicon or a mixture of both. An alloy to be used according to the invention contains, for example, either 0.5 to 6 % magnesium or 0.5 to 2 ^c / o cobalt or 1 to 6 % nickel or a mixture of these two elements. Silicon, preferably in an amount of 0.3 to 1%, and manganese, preferably in an amount of 0.1 to 1%, can also be added to these alloys.

In order for a blue color layer to be achieved, the porous aluminum oxide layer must be anodic oxidation in one Electrolytes have been generated which simultaneously contains hexavalent and trivalent chromium ions. An easy Means to produce such an electrolyte is that in aqueous solution 10 to 200 g / l of chromic acid can react with oxalic acid, the chromic acid is partially reduced. According to a preferred embodiment of the method according to the invention, a mixture of

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60 g / l chromic acid and 20 g / l oxalic acid are used. the

Duration of the anodic oxidation is 50 min at 50 V at 50 ⁰ O, wherein a layer thickness of 5 "to 6 to be achieved.

Other layer thicknesses from 1 to 20 μm, the

2 *

with current densities of 0.1 to 5 A / dm or voltages of 10 to 100 V.

In the method according to the invention, the blue coloration or coloration with a blue base tone appears in the course of the Deposition carried out according to the procedure of the aforementioned French patent 880 095. It was Surprisingly to find that if the alloy contains magnesium, cobalt or nickel and the porous aluminum oxide layer is produced by anodic oxidation in a partially reduced chromic acid bath, the blue color in The presence of numerous metal compounds appears, the nature of which seems to be of minor importance. Among other things, the blue shades can be removed by electrolysis with alternating current in copper, nickel or cobalt salt solutions achieve. In order for a deposition to take place, the electrolysis must be carried out in an acidic bath and the one to be set pH depends on the metal under consideration and its position in the electrochemical series away. The concentration of metal salt, for example copper salt, cobalt salt or nickel salt, is generally 5 to 100 g / l. The workpiece forms one electrode; the other electrode or counter electrode is either inert and preferably made of stainless steel or soluble and made of copper, nickel or cobalt, depending on the metal salt used. During the electrolysis, which lasts from 30 seconds to 15 minutes, the temperature of the electrolyte is kept at 18 to 22 ° C. This electrolysis is carried out with a constant current density of 0.1 up to 5 effective A / dm or at a constant AC voltage of 10 to 50 eff. V carried out. According to preferred Embodiments are the following electrolytes A, B and

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O used. Cobalt sulfate 20th s / i Electrolyte A Boric acid 25th s / i Ammonium sulfate 15th s / i Nickel sulfate 100 s / i Electrolyte B Boric acid 25th s / i Ammonium sulfate 30th s / i Copper sulfate 15th s / i electrolysis sulfuric acid '5 s / i

The "blue color" appears in the course of the electrolysis Alternating current and is initially expressed in a shimmer or shine that plays into violet after a period of time, the depends on the type of metal and the process conditions and generally a deposition of a few 10 coules / dm * is equivalent to. The darker shades of blue are after a

Deposition achieved in the order of 100 coul./dm.

The colored oxide layer obtained in this way is porous and therefore not corrosion-resistant. It must therefore be sealed or be redensified. It has been shown that the customary recompaction in boiling water with optional additive of a nickel salt often changes the hue achieved according to the invention; on the other hand, good results are achieved when the workpiece is immersed in a boiling aqueous sodium silicate solution containing 0.1 to 1 for 1 to 45 minutes g / l sodium silicate, is immersed.

The invention is illustrated in more detail by means of the following examples.

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Examples

In all examples, the workpieces were subjected to the following operations:

1) Degreasing, i.e. only stripping if the finished Workpiece should have a dull appearance or be followed by mechanical polishing or pickling chemical or electrolytic gloss treatment, if the finished workpiece should look glossy;

2) anodic oxidation in a bath containing chromic acid and oxalic acid;

acidic

3) Alternating current electrolysis in a bath containing

a metal salt.

In a first series of tests, an aluminum alloy was used that contained the following alloy additives:

Mg 0.47 % Si 0.45 % Fe 0.24 % Gu 0.01 % Mn 0.05 %

The anodic oxidation was carried out in chromic acid baths increasing content of oxalic acid made; electrolyte A was used in the subsequent electrolysis. The results are summarized in Table 3 below, f

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TABEL

at
game Bath for anodic
oxidation
Chromic acid / oxalic acid
g / l electrolysis
(Electrolyte A) duration
min End
span
tion
V. Color
volume 60/0 current
density
A / dm ² 2 25th 1 60/5 0.6 2 30th Brown 2 60/10 0.6 2 30th brown with
blue shim
mer 3 60/20 0.6 2 32 bluish 4- 100/50 0.6 2 31 bright
blue 5 0.6 blue

Example 1 is not according to the invention. The comparison shows that the addition of oxalic acid, through which the hexavalent Chromium ions are partially reduced to trivalent chromium ions, is essential to achieve a blue sheen.

In a further series of tests, the alloy samples only differed in the magnesium content, which other conditions remained constant as far as possible, namely:

Content of accompanying substances or alloy components,

anodic oxidation in a bath containing 60 g / l chromic acid and 20 g / l oxalic acid,

Electrolytic deposition: electrolyte A, current density 0.4 Duration 2 and 4 minutes, final voltage approx. 30 V eff. The results are summarized in Table 2 below.

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1Λ-39Ο2Β 210,638 «

TABLE 2

Alloy additives separating color

game manure

Fe Si Cu Mg Mn _{Coule / dm} 2

7th 0.46 0.11 8th 0.46 0.11 9 0.52 0.13 10 0.52 0.13 11 0.45 0.12 12th 0.45 0.12

0.59 0.15 0.040 0.05 <0.04 96 gray

0.025 0.56 <0.04 48 playing into the violet

0.025 0.56 <D, 04 96 dark purple

0.050 1.40 <0.04 48 playing into the violet

0.059 1.40 <0.04 96 purple

0.025 5.54 <0.04 48 bright blue

0.025 5.54 <0.04 96 "

15 0.59 0.14 0.050 5.21 <D, 04 96 "

Example 6 is not according to the invention but merely serves as comparison. Examples 7 "to 15 according to the invention show that a magnesium content within the specified limits is necessary for the blue base tone (dominant) appears. The smolder is below 0.6% magnesium.

Another series of experiments shows the influence of the other Alloy components and / or accompanying substances such as silicon, manganese, nickel, cobalt, zinc and copper. The single ones Alloy samples were treated under the same general conditions as in Table 2; the individual deviating Conditions are summarized in Table 5 below.

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TABEL

at
game Cu Alloy
additive composition
Fe Si 0.20 the
Cu rehearse
Mg Mn other
elements 9
5 Farewell
manure
Coul / dm ² hue I. A-39 028 * ro O 14th Mn 0.58 6.7 0.13 0.005 1.20 108 Gray I. —A
O CO
CD 15th Mg Si 0.42 0.5 0.08 0.05 0.3 240 Gray 6388 CO
co 16 Si Mg 0.3 0.06
0.07 4th 0.6 - _ _ 48 Gray / 1683 17th
18th Si Co 0.12
0.11 0.06 0.03
0.02 0.01
0.01 0.03
0.02 Co 0,
Ni 4, 61 72
144 dark blue
Light Blue blue-purple 19th Mn 0.31 1.18 0.01 0.99 0.74 - - 108. ^ Ütun'kelblau ti 20th Mg Mn 0.44 0.39 0.01 0.92 0.46 108 11 21st 1
O
1 Mg Cu 0.19 0.06 0.23 0.47 <0.01 _ _ 48 22nd Zn 0.08 0.1 1.31 <0.005 Zn 4, 48

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Examples 14, 15 and 16 are not according to the invention. In the presence of silicon alone, therefore, no blue hue can be achieved. On the other hand, the presence of silicon in an alloy containing magnesium does not change the hue (example 5) and even lowers the lower limit for the magnesium content: an addition of 0.56 % magnesium alone (example 7) results in a hue that is violet; on the other hand, with the simultaneous addition of 0.45 % silicon and 0.47 % magnesium (Example 5), a bright blue color is achieved. Manganese also has a reinforcing effect, as a comparison of Examples 19 and 9 shows, and its presence does not affect the blue hue. . "''.

A high copper content (Example 16) prevents the appearance of a blue hue; However, copper can be used in an amount up to 0.2-0.3. $ be contained in the alloy, as Example 21 shows. Zinc in an amount up to 4.6 % does not prevent the blue coloration (Example 22); In other tests it has been shown that the zinc content of the alloy can be up to 6 % ; however, in the presence of this element, as with copper, there is a tendency towards a shade of violet.

A fourth series of tests shows that the deposition of the particles of a metal compound in the pores of the aluminum oxide layer can be made in very different ways and that especially the metal of the deposited Metal compound has little or no influence on the color shade achieved. In Table 4 are the conditions and the results of this series of experiments are summarized. All alloy samples were in a bath containing 60 g / l Chromic acid and 20 g / l oxalic acid up to a layer thickness of 8 / µm anodically oxidized. Example 20 is not according to the invention: Under the special conditions of this example

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(Alloy composition, conditions for creating the porous oxide layer, electrolyte for deposition)

36 coul./dm ρ were not enough to produce a blue hue to appear.

Examples 21 to 27 according to the invention show that the blue hue with cobalt, nickel and copper and with very different amounts of Strotö. is achieved; however, the darker hues correspond to the higher ones. Electricity: amounts per dm ²

Alloy to
sentences Si Mn CHART 4 Coua.y hue at
game Mg
C. 1.18 0.46 As of marriage
conditions 36 0.92 It ti Electrolyte counter
electrode 72 yellowish 23 Il It dd A go 90 Light Blue 24 ti ύ It ti «ι 108 blue 25th It Il ti ti η 180 dark blue 26th It It dd ti η 90 Il 27 It 0.45 0.05 Il tt 480 Il 28 0.56 It ti B Hi 96 blue 29 C Cu bright
blue 30th Cobalt stainless
sulfate steel
50 g / l Boric acid
35 g / l ■ ammonium
sulfate
20 g / l

PATENT CLAIM:

72 / XXIV

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109838 / 1G83

Claims (1)

Claim. Process for the production of colored OxiüschielrteE r? A ~ ^u blue basic tone on aluminum alloys by, anodic oxidation and subsequent electrolysis with alternating current in a bath, containing an aqueous-acidic solution of a heavy metal salt and densification of the colored oxide layer, characterized in that one contains an aluminum alloy 0.45 to 6 $> magnesium 0.5 to 2 io cobalt and / or 1 to 6 fo Mckel and, if necessary, up to 6 $> zinc, up to 0.3 i ° copper and up to 1 ^ silicon and up to to 1 ^ manganese and the anodic oxidation is carried out in a chromic acid bath containing chromium (III) ions. 7232 109838 / 1G83