Anodized Aluminum Processing Observation and Measurement Using Digital Microscopes

A thin oxide film (approximately 2 nm) naturally forms on aluminum when it comes into contact with air. Therefore, it is commonly believed that aluminum does not rust easily.
However, this film is extremely thin, so chemical reactions may cause aluminum to corrode depending on the environment. Anodized aluminum processing is a type of surface processing in which this oxide film is artificially formed on aluminum.

A : Plating layer B : Growth film C : Penetrating film D : Aluminum material
Half the anodized aluminum film grows on top of the aluminum surface. The other half penetrates into the aluminum surface.

Anodized aluminum processing is a type of surface processing in which an anodic oxide film is formed on the surface of aluminum.
Plating is another type of surface processing, but whereas plating causes a film of another metal to form on the aluminum surface, anodized aluminum processing causes a growth film to form on top of and a penetrating film to form underneath the aluminum surface.

A : In air B : In electrolytic solution
C : Original aluminum surface D : Barrier layer

Passing an electric current through aluminum causes the microscopic dents and protrusions on the surface to dissolve (penetrating into the surface) while at the same time causing an oxide film to form. As time passes, a 3D structure known as a cell forms.

• 1
  In air, an oxide film approximately 2 nm thick forms naturally.
• 2
  The barrier film grows.
• 3
  Holes 10 to 20 nm thick open up.
• 4
  Oxidation and the dissolution of the film proceed simultaneously, elongating the holes.
• 5
  The film grows proportionally to the time electrolysis is applied.