Pickling of aluminium

1. Characteristics and properties

In order to galvanize aluminium, prior pickling is essential. For decorative aspects it is also possible to pickle aluminium. Both to chromate it later and to give it a different degree of gloss. Immediately after pickling, pickled aluminium has a very bright and almost white appearance similar to platinum. After a short time, however, it is coated again with an oxide layer. This causes the surface to darken only very slightly.

From an electrochemical point of view, aluminium is very base, it immediately coats itself in the ambient air with an oxide film several atoms thick, which effectively protects it from further surface attacks. It is very resistant to most acids. Only strong alkaline media can attack and dissolve the aluminium. The pickling itself takes place in a highly alkaline solution in which the oxide film is completely dissolved. Only the alloying elements on the surface remain unaffected. To remove these and protect the surface from further attack by the pickling solution, the workpiece is pickled in an oxidizing acid solution after a rinsing step. The surface created by this process can then be chromated or electroplated.

2. Benefits and areas of application

Typical areas of application are decorative articles of any kind, heat sinks or conductive elements.

3. Basic material

All aluminium alloys and aluminium from all manufacturing processes are suitable for pickling aluminium.

4. Required delivery condition

The goods provided must be largely metallically bright. Residual oils or residual impurities must be removable with standard aqueous alkaline degreasers. Oils containing silicone, alkali/alkaline earth and high-pressure additives must be avoided at all costs.

5. Pre-treatment

Before pickling, the workpieces must be thoroughly degreased and cleaned. There must be no oil or grease on the surface, as this would not allow the pickling of the oil-wetted areas and thus would not achieve a uniform surface structure.