Anodisation

Innovative anodising process for aluminium surface finishing

Anodising (Eloxal): Processes and advantages

Eloxal stands for the electrolytic oxidation of aluminium, which is a process used for treating the surfaces of light metals. Anodisation converts the surface of the basic metal into a dense oxide layer, giving light metal components (made of aluminium) a tough, corrosion-resistant protective layer. Depending on the desired finish, either protective anodisation (protects from corrosion) or other anodising processes that meet higher optical standards can be used.

The Holzapfel Group offers a variety of enhanced forms of the conventional anodising process to produce anodised aluminium surfaces suitable for a broad range of applications. In addition to anodisation in a variety of colours and anodisation with individual visual designs, a process for treating hybrid components (metal-plastic composites) is now available, too. We have also developed a partial anodising process.

Description of the anodising process

Unlike electrolytic precipitation, the anodising process does not precipitate a layer or coating onto the component, but rather transforms the top layer of aluminium by means of oxidation, forming an extremely tough, wear-resistant surface 10-20 µm thick with many capillary-like pores. As the anodisation process causes the aluminium oxide layer to grow from the surface into the metal, its adhesion to the substrate is particularly good, which means that the oxide layer is firmly bonded to the aluminium base material. As the oxide layer is transparent, the metallic appearance of the aluminium remains intact.
Anodised coatings also insulate very well because the surface layer consists of aluminium oxide, which, unlike the base material, does not conduct electricity.

Highly decorative surface effects can be achieved by mechanically or chemically pre-treating the surfaces prior to anodising.

Anodised surfaces are produced in baths with electrolyte liquids using an external source of electricity (rectifier), whereby the components to be coated are switched as anodes. For this reason, anodised layers are also referred to as "anodic layers" and the process is called anodisation, which is carried out using a rack.