Anodic oxidation of aluminium (anodising process)
Since the natural oxide layer of aluminium cannot withstand all corrosion loads, it may be necessary to reinforce it artificially by a multiple of between 50 to 5000. This is done by the electrochemical process of anodisation (also known as the anodising process). The oxide layers produced in this way offer high resistance to abrasion, wear and corrosion.
For anodic oxidation, the component to be treated is placed in an electrically conductive liquid (electrolyte), where it is connected as an anode to a DC voltage source. The cathode is usually made of stainless steel, lead or aluminium. In the resulting tension field, oxygen-containing anions containing oxygen migrate to the aluminium substrate.
Here, they react with the material, forming aluminium oxide. Its larger volume increases the thickness of the metal surface by up to a third, and it is firmly bonded to the aluminium. Hydrogen forms at the cathode and escapes in the form of gas.
Sulfuric acid and sulfuric acid-oxalic acid are the most widely used electrolytes for anodisation. The two most important processes for the production of oxide layers are named for these substances: the direct current sulfuric acid (GS) process and direct current sulfuric acid oxalic acid (GSX) process. Other processes exist that lead to the formation of a coloured oxide layer.
Types of oxide layers
The resulting oxide layer consists of an extremely thin barrier layer, which is almost non-porous, very strongly bonded and electrically insulating, and a much thicker, slightly porous and electrically conductive cover layer, which is the result of a chemical reaction of the barrier layer with the electrolyte forms.
Coloured oxide layers by immersion
In immersion dyeing, anodic oxide layers are formed by immersion with organic or inorganic dyes in aqueous solution. The dyes are embedded in the pores of the anodiaed layer.
Possible mechanical pretreatments:
Possible chemical pretreatments:
We also offer combined processes of chromating (yellow or colourless) and anodising to realise eg mass points or surfaces.