Sub-types:
Type II Anodizing (also called “clear” or standard anodizing)
Type III Anodizing (also called “hard coat” anodizing)
2.1 Type II Anodizing
Applications:
Used for decorative and functional finishes on aluminium parts, where moderate wear/corrosion resistance and good appearance are required.
Advantages:
Adds an oxide layer that improves corrosion resistance and wear compared to untreated aluminium.
Allows dyeing or colouring, so aesthetics can be part of the specification.
Dimensionally modest change because coating thickness is lower.
Appearance:
Can be clear or coloured (black, blue, red, etc. depending on dye), typically matte to satin finish. The oxide layer is thinner, so the surface can have a refined look.
Applicable Materials:
Aluminium and aluminium alloys.
Important Notes:
Coating thickness is typically in the range ~0.00007-0.001 in (≈1.8-25 µm) depending on process parameters.
Because of the porous nature of the anodized layer, sealing is often required (to improve corrosion resistance, dye stability).
Although colourable, the resulting finish may still show substrate marks or machining features—pretreatment and cleaning still matter.
Not ideal for high-abrasion applications; for those, consider Type III.
2.2 Type III Anodizing
Applications:
Used when high hardness, superior wear resistance, and significant corrosion resistance are required—e.g., aerospace structural parts, marine, heavy-duty equipment.
Advantages:
Much thicker and denser oxide layer leads to improved abrasion resistance, longer life in harsh environments.
Often used for functional rather than purely decorative purposes.
Appearance:
Because of the thicker coating, surfaces are usually not dyed (or if dyed then less colour variety) and may have a more industrial look (darker, less reflective).
Applicable Materials:
Aluminium and aluminium alloys.
Important Notes:
Coating thicknesses can range significantly higher than Type II: e.g., up to ~0.001-0.006 in (≈25-150 µm) in certain processes.
The thicker layer may require allowance in dimensional tolerances (stock removal or maskings).
Dyeing capability is limited; also sealing and correct process controls are more critical.
Cost will be higher than Type II; also process control must be stricter.
