DE3331857A1 - METHOD FOR ELECTROLYTIC YELLOW TO ORANGE COLORING OF ALUMINUM OR ALUMINUM ALLOYS - Google Patents

Description

- γ - description

The invention relates to a method for electrolytic

Coloring of aluminum and its alloys. 5

Electrolytic coloring processes are numerous known which are applicable to previously anodized aluminum and its alloys, and with which a variety can be obtained from colors including such as bronze, gold, yellow, orange and red.

For example, a method is known in which aluminum or an aluminum alloy is coated beforehand with a layer of porous oxide by anodic oxidation (i.e. by anodizing) in phosphoric acid with Treated direct or alternating current and then, for example, with a nickel or tin containing Electrolyte is colored electrolytically, depending on the duration of the electrolytic coloring. ^ tations from yellow to gold and orange to red can be obtained.

Such a method is known, for example, from US Pat. No. 4,251,330, the colors formed so-called ^ th optical interference effects can be attributed.

The aforementioned older method has problems with the final color obtained because of the color after electrolytic dyeing and before final "^ fixation, as is customary in such processes is carried out, can fade.

The fading of the color is attributed to that the electrolytically deposited deposited pigment ~ ^ by acidic electrolyte residues, - which in the pores of the

anodic oxide layer is left behind, is dissolved again. US Pat. No. 4,251,330 cites a known method for Avoiding the fading of the color, in particular those processes in which a stabilizing

Treatment by dipping the electrolytically colored 5

Workpiece is made in a chromate bath, and proposes in turn a new process in which at the same time two metals are electrodeposited, which form acid-resistant alloys. Through this procedure

the fading of the colors after the 10th

Avoided coloring, but it is associated with disadvantages insofar as there are major technical difficulties and causes higher material consumption.

Furthermore, in US Pat. No. 3,382,160, the electrolytic 15

Deposition of selenium on anodized aluminum is described to give the aluminum a yellow-gold or red-gold color to rent. In the process described, the electrodeposition process must last for about 10 minutes

a voltage of 13 to 20 volts. Under 20

these conditions remain relatively large amounts of acid electrolytes in the pores of the aluminum oxide layer back and accordingly are in the course of the subsequent Fixing larger amounts of residue released. As a result, the method of U.S. Patent 3,382,160 corrodes

produced electrolytically colored aluminum with selenium faster and does not pass the corrosion tests required for certain architectural applications.

The object of the present invention is to provide a method

for electrolytic yellow or orange coloring of aluminum or an aluminum alloy that avoids the disadvantages of conventional methods described will.

To solve this problem, a method for electrolytic yellow or orange coloring of aluminum or

Proposed aluminum alloys with improved color stability, which is characterized in that one anodized aluminum or an anodized aluminum alloy of an electrolytic pretreatment in one Subjects the bath, which contains phosphoric acid in concentrations of 150 to 300 g / l and is traversed by alternating current is, and then the thus treated aluminum or the aluminum alloy in a selenium electrolyte containing bath electrolytically colors, one -IQ an alternating voltage of 8 to 2 0 volts for a period of time of less than 10 minutes to the bath and the electrolytically colored aluminum or the Aluminum alloy directly and permanently fixed without intermediate color stabilization.

The colors obtained by the new process are stable and are not subject to change by, for example Influence of light. There is none before final fixation stabilizing treatment necessary. The end products have a high level of corrosion resistance

It has surprisingly been found that with the inventive Process aluminum and its alloys in different shades from yellow to orange “J- can be colored, the colors in particular are stable against changes caused by solution processes caused by the acidic electrolyte as well as by light and weather influences, i.e. corrosion in general.

The new process uses pre-anodized aluminum

or its alloys are used on which a porous layer of anodic aluminum oxide, usually with a layer thickness of at least 3 μm, has been deposited. The ^ ₁ - aluminum and its alloys are based on conventional

Way, generally in a sulfuric acid bath, anodized, by passing direct current through it, the voltage and duration of the sulfuric acid concentration and the temperature of the bath. Usually will be

Concentrations from 100 to 200 g / l and tensions from 10 5

to 20 volts at room temperature applied over a period of 20 to 50 minutes.

The anodized aluminum or its alloy is then subjected to an electrolytic pretreatment, which serves to optimize the subsequent electroytic pigment deposition. It is believed that Such a pretreatment modifies the size and geometry of the pores in the anodic oxide layer.

In this stage of the process, an acid bath, in particular

Phosphoric acid or a mixture thereof with an organic or inorganic acid such as sulfuric acid, Oxalic acid or tartaric acid used. The phosphoric acid concentration is a critical factor in the context of the 20th

method according to the invention and it is in the range from 150 to 300 g / l. If other acids are added to the phosphoric acid, the latter should be in amounts greater than 5 0% of the acid mixture should be present in the bath.

During the pre-treatment stage, alternating current is used a voltage of 9 to 15 volts is usually passed through the treatment bath for 1 to 5 minutes. The treatment is at a temperature of 10 to 35 C and normally

carried out at room temperature.
30th

In the method according to the invention, the pretreatment stage follows during which the pores of the anodic oxide layer are presumably expanded, the stage of

actual electrolytic coloring in a one 35

Bath containing selenium electrolytes. Usually will be

either selenium dioxide or an alkaline selenite is used in concentrations of 1 to 30 g / l. In addition to the selenium compound, the electrolytic coloring bath should contain an acid, preferably H ₃ SO ₄ in concentrations of 1 to 30 g / l. Electrolytic coloring is carried out with alternating current at 8 to 20 volts for a period of up to 10 minutes. The temperature should be in the range of 10 ■
temperature.

in the range from 10 to 35 C and preferably at room

According to the method according to the invention, the pretreatment and the electrolytic coloring is carried out in two separate stages in two different baths. While the pretreatment for pore modification is preferred

_{1 (} - as H-.PO. Used in concentrations of 200 to 300 g / l. The subsequent electrolytic coloring in the bath containing a selenium electrolyte is preferably carried out at a voltage of 8 to 16 volts for 3 to 4 minutes.

With the method according to the invention is after the electrolytic Staining obtained a stable color, which during the interval between the end of the electrolytic The coloring stage and the final fixation of the color, as required in this type of process, are not affected will. Accordingly, there is no preparatory work for stabilizing the color, such as, for example, before the fixing requires immersion in a chromate bath or co-deposition of two metals, as is the case with the conventional method is the case.

Following the electrolytic coloring step, an ordinary fixing process is accordingly carried out, such as boiling in deionized water with an additive such as a nickel salt added

can be.

The aluminum or its alloy, which is electrolytically colored with selenium, has a yellow to orange color Color that changes depending on the duration of the pre-treatment in phosphoric acid. The colors obtained are light- and weather-resistant, so that aluminum articles colored with the method according to the invention in particular are suitable for use in the construction sector and in other areas of application where high demands are made be placed on the corrosion resistance.

The invention is illustrated below with the aid of examples.

. _ Example 1

D.

One in an H ₉ SO. Bath with a concentration of 180 g / 1

2
Aluminum sample oxidized at 15 volts and 1.5 A / dm with direct current for 30 minutes was treated with alternating current (10 volts, 1 minute) in an H-PO. Solution at a concentration of 250 g / l at room temperature. After rinsing with deionized water, the electrolytic coloring was carried out in a bath containing SeO ₃ (10 g / l) and H ₂ SO. (20 g / L) was carried out at 12 volts over a period of 3 minutes. A pink-yellow color was obtained. The sample showed no changes after fixing in a solution of nickel salts at 95 ° C.

Example 2

One in a H ^ O ^ bath with a concentration of 180 g / l

at 15 volts and 1.5 A / dm "with direct current for 30 minutes oxidized aluminum sample was in a solution of Η-, ΡΟ, a concentration of 250 g / l and sulfuric acid niner Konzoril rat: ion of "> () q / 1 bo j clears pinperat ur nüt:

Alternating current (10 volts, 1.5 minutes) treated. After rinsing with deionized water, the electrolytic coloring in a solution of SeO ₉ (10 g / l) and H ₉ SO. (20 g / l) at 12 volts over a period of 3 minutes. A gold-yellow color was obtained. On subsequent fixation in a solution of nickel salts at 95 ° C., the sample showed no change in color.

Example 3

One in an H-SO. Bath with a concentration of 180 g / l Aluminum sample oxidized at 15 volts and 1.5 A / dm with direct current for 30 minutes was then placed in a H ^ PO, solution (300 g / l) treated at room temperature with alternating current at a voltage of 10 volts for 2.5 minutes. To 5

Rinsing with deionized water, electrolytic coloring was carried out in a solution of SeO ₉ (10 g / l) and H ₉ SO ₄ (20 g / l) at 12 volts for a period of 3 minutes using a stainless steel counter electrode.

An orange color was obtained. After fixing in a nickel salt!
Color change.

a nickel salt solution at 95 C, the sample showed none

Table 1 below reproduces some color examples as they depend on the method according to the invention from the duration of the pore changing pretreatment.

Tabel

Thickness of the oxide layer formed
by anodizing
with direct current in
H ₇ SO ₄ in to

Pretreatment time nrt g / l "H ₃ PO ₄ and alternating current (minutes) alternating current

electrolytic

Color with 10 g / l

SeO "and

g / l -H-SO,

Color fixation with nickel salt at 95 ° C and 3 minutes // around oxide '

Yl

12th
12th
18th
18th
18th
20th
20th
20th

1.0

1.5 2.5

1.0 2.0 3.0 1.5 2.5 3.5 pink-yellow

gold-yellow

orange

pink-yellow

gold-yellow

orange

pink-yellow

gold-yellow

orange

No color change observed

as above as just as above as above as above as above as above as above

- 12 -

Example 4

The electrolytic process according to the invention Colored aluminum articles were tested according to standard UNI 4529 (Xeno test) with regard to their light resistance examined.

The results are given below:

Oixdschicht-
thickness colour Determined lightfast
speed 12 to pink-yellow
gold-yellow
orange 8th
8th
6-7 12 to pink-yellow
gold-yellow
orange 8th
8th
6-7

The above results relate to aluminum articles having an anodic oxide layer 12 or 18 µm thick; it is found that in the electrolytic dyeing according to the invention with selenium, colors are obtained which have maximum or almost maximum light resistance. In the Xeno test, the value 8 gives maximum light resistance at.

The method of the invention is particularly effective in the treatment of aluminum alloys such as aluminum-magnesium-silicon and aluminum-magnesium-silicon-manganese alloys. Information on Al-Mg-Si and Al-Mg-Si-Mn alloys can be found in UNI-.3571 and UNI-3 56 9 data can be taken.

Claims (8)

Claims /l.i Process for electrolytic yellow to orange coloring of aluminum or aluminum alloys, characterized in that anodized aluminum or subjects an anodized aluminum alloy to an electrolytic pretreatment in a bath, which Contains phosphoric acid in concentrations of 150 to 300 g / l and is traversed by alternating current and then the aluminum or the aluminum alloy treated in this way in a selenium electrolyte containing bath electrolytically colors, using an alternating voltage of 8 to 2 0 volts for a period of time of less than 10 minutes to the bath and the electrolytically colored aluminum or the Aluminum alloy directly and permanently fixed without intermediate color stabilization. 2. The method according to claim 1, characterized in that the pretreatment is carried out in a bath, which as an electrolyte phosphoric acid or a mixture thereof with an organic or inorganic Contains acid, the mixture containing more than 50% by weight of phosphoric acid. 3. The method according to claim 2, characterized in that a mixture is used, which in addition to which phosphoric acid contains oxalic acid, tartaric acid and / or sulfuric acid. 4. The method according to claims 1 to 3, characterized in that that the pretreatment is carried out in a bath which H-.PO. in concentrations of 200 to 300 g / l, and a voltage of 9 to volts for 1 to 5 minutes to the bath. 5. Process according to claims 1 to 4, characterized in that the electrolytic ^ coloring is used a voltage of 8 to 16 volts and for a period of no more than 3 to 4 minutes. 6. Process according to Claims 1 to 5, characterized in that the selenium electrolyte used is SeO ₂ or an alkaline selenite. 7. Process according to Claims 1 to 6, characterized in that a bath is used for electrolytic dyeing used, which contains the selenium electrolyte in concentrations of 1 to 30 g / 1 and sulfuric acid in concentrations contains from 1 to 30 g / l. 8. The method according to claims 1 to 7, characterized in that the final fixation of the electrolytic colored aluminum or aluminum alloy in boiling deionized water, which optionally contains a nickel salt.