The anodizing of Aluminium is a forced growth of an oxid film through an electrochemical reaction that modifies the surface improving its original properties.
It’s achieved by submitting the Aluminium to be treated to an anodic oxidation with an electrolitic process in which the Aluminium forms the anodic electrode in an acid electrolyte.
The result of the reaction depends basically on the electrolyte, the reaction products, the bath temperature and the treatment duration.
As much as the layer grows, the electrical resistance increases and, consequently, the growth speed decreases. When the growth speed is like the dissolution speed
(due to the solubility of the reaction products), the film thickness remains constant.
The HARD anodizing is produced when working in conditions of high current density and solution temperatures near 0ºC which allows the obtainance of thicker layers, high hardness and minimum porosity.