The anodic oxidation of aluminum is a process of electrolytic oxidation. In the process, the surface of the aluminum
and the aluminum alloy will be normally converted into a layer of oxidation film with functional performance of
protection, decoration and others. The anodic oxidation of aluminum starting from the definition only includes the
process of generating the anodic oxidation film.

♦Why does it need the anodic oxidation?

To overcome the defects of the surface hardness and wear resistance, enlarge the application scope and increase
the service life, surface treatment technology is to be a necessary step for the use of the aluminum alloy. And the
anodic oxidation technology is applied widest and most successful now.

♦Principles

Taking the work piece of the metal or alloy as the anode to form the oxidation film on the surface with the electrolytic
way. The metal oxidation film change the state and performance of the surface, like surface coloration, improving
the resistance to the corrosion, increasing the abrasive resistance and hardness as well as protecting the metal
surface. For example, the anodic oxidation of aluminum is to put the aluminum into the corresponding electrolyte
(such as sulfuric acid, chromic acid and oxalic acid) as the anode, under the effect of the specific conditions and
the impressed current for electrolysis. The aluminum or the alloy is oxidized at the anode. Aluminum oxide is formed
on the surface. The general thickness of the film for the interior decoration is 3~10μm and 15~25μm for the exterior
decoration. Hard anodizing film could reach the thickness of 40~200μm. The hardness and the abrasive resistance
of the aluminum or its alloy after the anodic oxidation have been increased, reaching 220~500 kg/mm2; good heat
resistance, the melting point of the hard anodizing film is as high as 2300K; good insulativity, the resistance of
breakdown voltage is as high as 2000V; increasing the corrosion resistance, no corrosion in the slat mist of
ω=0.03NaCl for thousand hours. A lot of micropores on the thin layer of the oxidation film could absorb various
lubricants, applicable to manufacture the engine cylinder or other wear parts. The film could be colorated various
beautiful and colorful colors with the strong adsorption capacity of the micropore. Nonferrous metal or its alloy
(such as aluminum, magnesium and their alloys) all could be treated with anodic oxidation. This method is widely
used in the mechanical part, parts of plane and automotive, precise instrument, radio equipment, daily necessities
and architecture decoration.

♦The function of anodic oxidation

Protection
Decoration
Insulativity
Improving the adhesion with the organic coating.
Improving the adhesion with the inorganic coating.
Other functions in the development

♦Process flow chart

Pre:decorative aluminum foil

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