Anodic oxidation concept:
The process of formation of an oxide layer on aluminum products due to the action of an external current under the corresponding electrolyte and specific processing conditions.
Anodic oxidation, unless otherwise specified, generally refers to the anodic oxidation of sulfuric acid.
1. The role of anodic oxidation
1) Protector
2) Decorative
3) Insulating
4) Improves adhesion with organic coatings
5) Improves adhesion strength with inorganic coatings
6) Other functions under development
2. Aluminum alloy chemical conversion film treatment
(chemical oxidation, chromization, passivation)
Aluminum alloy chemical conversion film is obtained by chemical oxidation. See US military standard MIL-C-5541.
Why is chemical conversion film treatment necessary?
A) Increases the corrosion resistance of aluminum alloy.
B) Stabilizes resistance. (A customer once requested conductive oxidation to stabilize the contact resistance and conductive function)
C) The chemical conversion film is thin (about 0.5~4um), soft, conductive, porous and has good adsorption capacity. It is generally used as a base coat for paints or other coatings.
D) Does not change the mechanical properties of the material.
E) The equipment is simple, easy to operate and economical.
F) Does not affect the dimensions of the part.
Conversion film thickness:
The chemical conversion film on the surface of the aluminum alloy is quite thin, about 0.5~4um. Conversion film is a type of gel that is difficult to measure directly.
Normally, it is only necessary to weigh the quality of the part before and after chemical oxidation, or evaluate the corrosion resistance of the oxide film by surface color and salt spray test.
Anti-corrosion function after scratching:
The chemical conversion film on the surface of the aluminum alloy is a kind of gel. This gel may move after the conversion film is scratched.
The gel around the scratch mark will move to the scratched surface, combine, continue to prevent the aluminum alloy from being corroded, and even have anti-corrosion function.
Color:
The color of aluminum alloy chemical conversion film is gray, white, grass green, golden yellow, rainbow. The final color of the conversion film is determined by the conversion film solution and the operating process.
3. Difference between anodic oxidation and conductive oxidation
1) Anodic oxidation is carried out under high voltage. It is an electrochemical process; Conductive oxidation (also called chemical oxidation) does not require electricity and can be embedded in medicine. It is a pure chemical reaction.
2) Anodic oxidation is time-consuming, often requiring tens of minutes, while conductive oxidation requires only tens of seconds.
3) The film generated by anodic oxidation is a few micrometers to tens of micrometers and is hard and wear-resistant, while the film generated by conductive oxidation is only 0.01 ~ 0.15 micrometers, the wear resistance is not very good, but it is can conduct electricity and resist atmospheric corrosion, which are its advantages.
4) The oxide film is originally non-conductive, but because the conductive oxide film is very thin, it becomes conductive.
