Aluminium Anodizing

* English *, Materiales y tratamientos — Por Gladys el 6 Octubre 2007 a las 7:16 pm

Anodizing is an electrochemical process that can also be applied to checking fixtures to give them better aesthetic and mechanical properties finishings. This superficial treatment can only be carried out on aluminium; it is a forced oxidation thanks to which the base aluminium generates an aluminium oxyde protective layer (A12O3) on its surface. The thickness of this layer can freely range between a few microns to to 25 or 30 microns for protection anodizing and up to 100 microns for hard anodizing. This thickness is regulated by the UNE-38010 norm. The process consists in submitting the aluminium to a bath of acid, generally sulfuric. When the electric power goes through it, oxygen is liberated and goes to the anode that generates, by reacting to the aluminium, an oxyde layer which thickness varies according to the duration of the passing of the electric power. Then, the anodized aluminium is dived into hot water, to shut the pores present on the surface and thus finalise the process. The operational life of this finishing is proportional to the obtained anode layer thickness.

The aluminium oxyde can get a great hardness varying between 7 and 8 on the Mhos scale; it is very stable and resists to environmental corrosive agents.

The layer generated by the electrochemical process gets integrated to the metal, and cannot as such be scratched or cut off.

Anodized aluminium presents various advantages:

No maintenance is necessary.
An increased protection against moisture, dust, etc.
An improved surface hardness against blows.
A decorative finishing, several colours can be obtained.
Resistant to abrasion and wear and tear.
Resistant to corrosion.

The following graphs display the difference between an electroplating process – during which a deposit is created on a metal through an electrolitic process – and an anodizing process. The main difference lays in the fact that for the first process, the part thickens according to the duration of the treatment, whereas for the second process, the surface begins to thin beyond 60 minutes of treatment. This complicates things a little, compared to chemical nickel treatment, to overlap parts with very adjusted dimensional tolerances.