DE1906225A1 - Process and electrolyte for the production of colored oxide layers of aluminum or aluminum alloys by anodic oxidation - Google Patents

Description

Process and electrolyte for making colored

Oxide layers of aluminum or aluminum alloys

by-anodic oxidation

The invention relates to a method and an electrolyte for self-coloring anodic oxidation of aluminum and its alloys, as well as the objects obtained by this process *

It is known to have a coating made of naturally colored Aluminum oxide without the use of dye on objects from aluminum or aluminum alloys using a process known as self-coloring anodic oxidation could be designated; In this process, the objects are anodically oxidized in an electrolyte, from an aqueous solution of a mixture of organic acids from the group of aromatic sulfonic acids, the optionally sulfonated aliphatic acids and optionally sulfuric acid.

9850/1281

OSfGlNAL

-Z-

■ It -..- were, already = with success. various. Electrolyte \ compositions used; so ζ . ~ B »> a« what fresh solution _iV! of Chromofcropsäure, - (Nat rl ums al ζ der - !, J-DiliydroicynaphthaMii-3, o-disulphonic acid) =, and-SuIfsuccinäure ader. an aqueous solution of 2; -Naphtho.l-3,6-disulphonic acid., = sulphoinaleinic acid and sulphuric acid. .-: .. ^; ; ^ - : · ^; -; - - ";'■' - '■■ / ^: ΐ, - ■

JMe electrolytes, the aromatic sulfonic acid, - ent- ^; _: r ^ r hold> siirid but relatively, expensive * -It was mm> established, t-, r that "even without these acids · good results can be achieved: ·.:. if the aliphatic sulfonic acid is carefully selected.

The present invention is therefore directed to. lyten, the one aliphatic sulfonic acid. contains-. and; with ^1! -.- * which on aluminum and its alloys: create a layer of self-colored aluminum oxide; 'lets that- = parton he ■ ■ has from hot! bronze to ever darker bronze .and -. v:; ■ · brown tones up to black; , the: .Invention re.iff.tf furthermore the method · in which this electrolyte r ·; .J is used, as well as ¹ the objects deleted according to this process,

The according to the invention / electrolyte is an aqueous " ¹ solution of SuI formale in the mud - · -" ..: ■■ · .- "* '- .-: -.-. ·· - ^: - ^: '■' ■ ' -''"- ^: .. ^;

.SDoH:

(KOOG- CH-- G

the sulfuric acid is added.

According to a preferred embodiment. is the, ", -. ·; -. ,, - .; electrolyte _; one, Lösting, .a_us- 10, r- 30 ° · gA» ~ in particular ... ._ ,,,, 50 -. 2QO ₁ g / l. SuIf onaleic acid and / Oj-l ^ g / l.,.; Insbes, onclere ^ ~ _r , 0.5-8 g / l-, sulfuric acid, in e

909850 / 126T '"'''''''" ^

_BA D

- 3 - IA-35

Before the anodic oxidation, the surface of the objects can be pretreated in various ways in order to obtain a matt or shiny appearance. Matt surfaces are achieved by chemical or electrochemical stripping, for example by immersing for 10 min in a ^{solution kept at 50 0} C, which contains 50 g / l soda, then rinsing with running water, dipping in nitric acid 36 ⁰ Be and rinsing again with water . The glossy surface is achieved by mechanical polishing or by chemical or electrolytic means.

The self-coloring anodic oxidation in the inventive Electrolytes are supplied with direct current, with alternating current or with pulsating direct current, which is itself E.g. from a superposition of direct current and alternating current, performed. Direct current is preferred worked, the clamping voltage of the cell in which the anodic oxidation takes place, adjusted so that

2 2

the current density is 0.5-10 A / dm, preferably 1- k A / dm of the anodically oxidized surface.

The temperature of the electrolyte during the anodic oxidation at -10 to +50 ⁰ C, preferably at 15 - 30 ⁰ C maintained. After a current passage time of about half an hour to 1 hour, an aluminum oxide layer with a thickness of generally 10-50 λχ , which is more or less dark bronze tones or even black, is obtained, which after rinsing with water and sealing is extraordinarily hard and remarkably durable against the destructive or discolouring effects of light or weather conditions . The aluminum oxide layer is sealed by immersion for 30 minutes in boiling distilled water, which preferably contains salts such as nickel acetate in a concentration of 0.5-2 g / l.

9098S0 / 1261

For an electrolyte of a given composition and a given alloy, the hue of the oxide layer can be determined in a certain range by determining the two main parameters, ie the current density and the electrolyte temperature. The color becomes lighter, the weaker the current density and the higher the temperature. . . . ': ■ -'- ■.-.- "" .- ■

Become objects with originally shiny appearance treated, different working methods can be used to achieve this appearance even after the anodic ■ To preserve oxidation; this is how, for example, anodic oxidation

at a low current density (^ 1 A / dm) for about 10 minutes

»Started in the electrolyte according to the invention and then with one higher current density, preferably> 1.5 A / dm to the end. .. '-

The composition of the aluminum or aluminum alloy has a noticeable influence on the color tone; the obtained aluminum oxide layer. Should e.g. the appearance of dark shades is favored _s an alloy containing manganese is used. It is noteworthy, however, that with the electrolyte according to the invention, with appropriate selection of the aforementioned parameters (temperature, current density), the appearance of dark shades, e.g. brown or black shades, can be favored, u if matt or shiny objects made of aluminum alloys that do not contain manganese It is interesting to note that no comparable property has been observed in other known organic electrolytes of a similar formula, for example in sulfinic acid.

The invention will now be illustrated by the following examples explained in more detail.

909850/1261

Example 1 ■

A. Profile piece made of the alloy A-GS, which contains 0.5 wt. % Si, 0.5 wt. % Mg, remainder Al, degree of purity 99.5 % , was anodically oxidized in an aqueous solution containing 100 g / l SuIf © contained maleic acid and 5 g / l sulfuric acid. It xvurde 40 long 2O ⁰ G with direct current and at a current density of 1.5 A / dm oxidized at bath temperature min. The 18 M thick aluminum oxide layer obtained showed a uniform, light bronze and UV-resistant coloration after sealing.

Example 2

A profile piece made of the same alloy as in the example 1 was in an aqueous solution containing 150 g / l sulfomaleic acid and 2 g / l sulfuric acid with direct current Oxidized for 30 minutes, bath temperature 20 ° C., current density

ρ
2.5 A / dm. The aluminum oxide layer obtained was 20 / U thick and, after sealing, was uniformly dark bronze in color and resistant to UV light.

Example 3

A sheet made of an alloy A-GO, 6 containing 0.6 wt. % Mg, the remainder Al purity 99.7 % was anodically oxidized for 40 minutes in an aqueous solution containing 80 g / l sulfomaleic acid and 6 g / l silicic acid, bath temperature 21 ⁰ C, current density 1.5 A / dm .The obtained 18 / U strong aluminum oxide layer was bright bronze color after sealing, uniformly colored and UV light resistant.

Example k ''

A profile of the alloy A-SGM containing 1 part by weight Ji 'Si, 1 wt -.% Mg, 1 wt -.% Mn, balance aluminum of purity 99.5% was for 60 minutes in an aqueous

9 0 9 8 5 0/1261

Solution containing 120 g / l sulfomaleic acid and k g / l sulfuric acid at bath temperature 20 ⁰ C with a stream

density of 2.5 A / dm anodically oxidized. The received 30 / U thick aluminum oxide layer was uniformly black colored and UV light resistant. ·

Example 5 .

A polished profile piece made of the alloy.A-GS with ^; the same composition as the alloy used in Example 1 was contained in an aqueous solution of 150 g / l Sulfomaleinsaure and 2 g / l sulfuric acid at a bath temperature of 2O ⁰ G anodically using DC

oxidized. During the first 10 minutes, a current ditch was

te of 0.5 A / dm observed; during the following 30 min

the current density was increased to 3.0 A / dm. After sealing, the aluminum oxide layer obtained was shiny and showed a uniform dark bronze and UV lightfast Colour" .

Claims

909 8 50/126 1

Claims (8)

Patent claims Process for the production of colored oxide layers on aluminum or aluminum alloys by anodic Oxidation in an aqueous sulfuric acid electrolyte, characterized in that the anodic Oxidation in an electrolyte containing about 10 to 300 g / l sulfmaleic acid and about 0.5 to 15 g / l sulfuric acid performs. 2. The method according to claim 1, characterized in that the anodic oxidation is carried out at a bath temperature of -10 to +50 ⁰ C and with a current density of 0.5 to 10 A / dm ² . 3. The method according to claim 1 or 2, characterized geke η η ze I η et that with an electrolyte containing 50-2oO g / l sulforaaleinic acid and 0.5 to 8 g / l sulfuric acid at a bath temperature of 15 to 30 ⁰ g and works with a current density of 1 to 4 A / dm. 4. The method according to claim 1 to 3t, characterized in that 'that one is the aluminum or the aluminum alloys subjected to a chemical, electrochemical or mechanical surface pretreatment. 5. The method according to claim 1 to 4, characterized in that · to maintain the glossy surface anodic oxidation with low amperage - 2 - 909850/1261 8th ^1A -35 744 <1 A / dm for about 10 minutes and then with higher Current density, preferably} 1.5 A / dm leads to an end. 6. The method according to claim 1 to 5 »characterized in that the aluminum oxide layers by immersion for 30 minutes in boiling water, which preferably contains salts such as kickel acetate in a concentration of 0.2 to 2 g / l, an aftertreatment subject. . 7. Application of the method according to claim 1 to 6 to achieve light bronze to very dark brown or black shades on manganese-free aluminum alloys. 727909850/1261