Chem Film (Alodine)




AMS 2743









Electrical Conductivity


Good Corrosion Resistance


Excellent Paint Adhesion




Chem Film

Chem film or Alodine is a chemical conversion coating that’s mostly used to protect aluminum from corrosion. It’s primarily used to passivate aluminum as it protects this metal and serves as a base for paint coatings. It leaves aluminum unaffected, so it’s easier to put paint over it without changing anything.

Chem film goes by several different names and designations:

  • Chromate conversion coating
  • Alodine
  • Iridite coating
  • Yellow iridate

Chem film is applied by dipping, brushing, or by spraying it. Many often combine it with Type II Anodizing as it can help repair many different yet small damages done to anodized surfaces.

Besides the protection against corrosion it can offer, as well as making a base for later painting, chem film also protects aluminum against the loss of electrical conductivity.

Where is Chem Film Used?

Chem film is used on:

  • Heat sinks
  • Automotive wheels
  • Most aluminum hardware and other aluminum components used by people every day

Alodine is heavily used in the aerospace industry and many applications used in this vital industry:

  • Aircraft hulls
  • Side and torsion struts
  • Shock absorbers
  • Landing gear
  • Parts of the flight control system (the rudder system, wing portions, etc.)

Other industries that also benefit from chem film are the electrical, military and defense, and the maritime industry.

Besides aluminum, metals like copper, cadmium, tin, magnesium, and zinc-plated steel, and iron substrates can also benefit from chromate coating.

After application, the thickness of the chromate conversion coating doesn’t change the dimensions of the parts at all.

Additionally, the coating can also improve the adhesion of both paint and primer by a significant amount, as long as you apply it to the surface of the aluminum before the primer.

In the end, it’s worth mentioning that chem film is not intended for decorative use and it also has very little abrasion resistance, making it unnecessary for use in decorations.


Chromate conversion coatings are the most widely used coating for corrosion protection of Aluminum and Aluminum alloys minimizing surface oxidation. It is commonly used for an undercoat for paint or adhesive applications due to the excellent bonding properties it provides. Class 1A coatings give maximum corrosion protection with the highest electrical surface resistance while class 3 coatings have lower corrosion protection and provide lower electrical surface resistance.

ADV applies both standard hexavalent (clear and yellow) and RoHS compliant Trivalent (TCP) to Aluminum.

The Trivalent Chromium Process (TCP) provides a non hexavalent chromate conversion coating compliant with RoHS, ELV and WEEE directives. It compares favorably with the hexavalent coatings providing a conversion coating that fulfills the corrosion, paint and electrical requirements of the different specifications.

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