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Chromate conversion coating services

Chromate conversion coating, more commonly known as chem film or by its brand name Alodine, is a type of conversion coating, used on aluminum as a corrosion inhibitor, as a primer for paint due to increased adherence or to preserve electrical conductivity.

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Surface preparation Colors Applicable materials Thickness Cosmetic availability Visual appearance
As machined (Ra 3.2μm / Ra 126μin) Clear/ slight yellow tint Aluminum (7xxx series not recommended) None No Machining marks are visible
Bead blasted (Glass beads #120) Clear/ slight yellow tint Aluminum (7xxx series not recommended) None Cosmetic on request Machining marks are completely removed on “cosmetic” parts but may be visible on “non-cosmetic” parts

Example of chromate conversion coated parts

Chromatic Conversion Coating
As machined
Chromatic Conversion Coating
Bead blasted

Design considerations for chromate conversion coating:

  • When applying chromate conversion coating, the dimensions of the part can be controlled, enabling it to maintain the requested tolerances. 

  • Chromate conversion coating can be applied to aluminum alloys, however, steel and iron parts cannot be coated directly.

What is chromate conversion coating?

Chromate conversion coating is a chemical coating for metal that has many benefits. It protects aluminum from corrosion, serves as a primer for painting and preserves electrical conductivity, making it a useful finish for parts used in the aerospace, automotive and construction industries. At Hubs, we only use chromium-free, RoHS-compliant chromate conversion coating.

How does chromate conversion coating work?

Chromate conversion coating involves adding chromic acid to a metal in a chemical process that results in a thin, protective outer layer. This enhances a metal’s durability and makes it more resistant to corrosion.

Protolabs Network offers chromate conversion coating for aluminum parts to improve functional properties. To find out more, contact

Here’s how we apply chromate conversion coating:

  • Parts are cleaned and degreased to remove any contaminant

  • Parts are then rinsed to eliminate any residue of detergent

  • Aluminum parts are immersed in a tank containing the chemical solution 

  • Parts are removed when a film of the desired thickness coats the surface 

  • Parts are then rinsed again

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