DE1009884B - Process for the pretreatment of workpieces made of aluminum or aluminum alloys for the production of high-gloss, anodically oxidized surfaces - Google Patents

Description

GERMAN

Around the surface of workpieces made of aluminum or aluminum alloys have high corrosion resistance while maintaining their metallic appearance To impart, the application of anodically produced top layers of high transparency is sought. In the process usually used here, the metal surface is anodized before the Oxidation first mechanically polished, then degreased and - especially with workpieces made of aluminum high degree of purity - chemically or anodically smoothed after degreasing. By the latter In the treatment stage, a more or less strong attack on the metal structure and a certain Do not avoid etching the metal surface. In addition, errors occur in the surface, such as B. Oxide inclusions, Accumulation of metallides, more apparent than before. It goes without saying that this Procedure, especially if the degree of purity is insufficient of aluminum often leads to unsatisfactory results; in general it is for them Handling of castings inappropriately.

In the course of detailed investigations, the surprising finding has now been made that high-gloss, anodically oxidized surfaces on aluminum or its. Alloys - regardless of their degree of purity and structure - can be obtained, if the surface of the workpieces treated with a pickling solution after dry polishing and then - expediently with cooling - the polishing is done wet.

It has been found that when dry polishing a sparingly soluble, presumably from low-water aluminum oxyhydrates, z. B. Boehmite, ber standing layer that is still contaminated by aluminum abrasion. This layer is to be regarded as the cause of the clouding of the oxide layers applied without further pretreatment. According to the previously known pre-treatment process this layer cannot be removed with the usual degreasing agents, but it can be removed with the chemical or anodic smoothing process, why this in itself to be regarded as indispensable: it would be if it were not on the other hand through the already described Disadvantages would only have a limited applicability.

According to the method according to the invention, the layer resulting from dry polishing is removed using suitable pickling solutions, and the required layer is removed Smoothing of the surface through the subsequent wet polishing, which at the same time creates a matt finish possibly caused by the pickling solution are removed from the surface again, completed. In this way the will be anodic disadvantages resulting from chemical smoothing are avoided.

Process for pretreatment
of workpieces made of aluminum

or aluminum alloys
for the production of high-gloss,
anodically oxidized surfaces

Applicant:

United Aluminum Works

Corporation,
Bonn, at the north station

Dipl ^.: Ing. Werner Helling, Grevenbroich (Ndrh.),

and Heinrich Neunzig,
Gustorf near Grevenbroich (Ndrh.),
have been named as inventors

Laurels in particular have proven useful as pickling solutions, ζ. B. 10% sodium hydroxide solution, and for wet polishing Slurries, proven of magnesia or clay. The polishing fluid becomes appropriate cooled so that the temperature on the workpiece surface is a maximum of about 30 ° C.

The anodic oxidation of aluminum or aluminum alloys when the specified conditions are observed The layers produced are characterized by high reflectivity. In particular the suitability of the process for treating aluminum alloys should be emphasized.

The method according to the invention is on. Hand of the following example explained in more detail:

A commercially available sheet made of an aluminum-magnesium alloy, containing 0.01% copper, 0.011% zinc, 0.066% silicon, 0.033% iron, 0.002% manganese, 1.92% magnesium, remainder Aluminum, sample taken after deburring, was ground using commercially available pastes and prepolished, then pickled for 30 seconds in an approximately 10% sodium hydroxide solution at 50 to 60 ° C and then polished with a slurry of Viennese lime in water with the addition of soap. By cooling, the temperature of the solution and the workpiece was here to about 18 to Maintained 20 ° C.

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After the anodic oxidation carried out in the usual way in a 20% sulfuric acid at 18 ° C. for 10 minutes with a current density of 1.5 A / dm ² , the reflectivity of the workpiece was determined. The total reflection was 86.9% and the specular reflection 79.6%.

For comparison, further samples were taken from the same sheet metal and treated as follows:

A sample was ground and polished only with commercially available paste and then under the Anodically oxidized conditions given above. Determining the total reflection resulted 81%, that of the directional reflection 63%>.

Another sample was made in accordance with the state of the art (see Schenk, »Material Aluminum und seine anodische Oxydation ”, 1948, p. 754, example 2) ground with commercially available paste and polished, then pickled (20% sodium hydroxide solution - 20 ° C - 5 minutes) and then again anodically oxidized under the above conditions. the Reflection values resulted in 74.8% for the total reflection and 21.7% for the directed reflection.

Claims (3)

Patent claims: 1. A method for the pretreatment of workpieces ¹ made of aluminum or aluminum alloys for the production of high-gloss, anodically oxidized surfaces, characterized in that the workpieces are pickled and wet-polished after a pretreatment carried out in a known manner by dry polishing. 2. The method according to claim 1, characterized in that for pickling alkaline solutions, z. B. caustic soda can be used. 3. The method according to claim 1 and 2, characterized in that the serving for wet polishing Solution is cooled,. Considered publications:
Schenk, "Material aluminum and its anodic oxidation", 1948, p. 754. © 709 547/387 5.5?