Skip to content

Conversion Coating
Chem Film

What is Conversion Coating & Chem Film?

Conversion Coatings - often referred to as Chem Film or Chromate - are a category of surface treatments that can bring a variety of benefits, including surface corrosion protection even at low electrical resistances, increased paint adhesion capability, and decorative purposes.

Chem Films are created via electrochemical or chemical reaction of metals, where the chosen treatment superficially converts the material into a thin adhering coating of an insoluble compound.

Conversion Coatings are uniquely flexible in that, depending on your final surface finishing goals, Chem Film treatments can be appropriate for pre-process, post-process and as a finishing process itself.

At AOTCO, we offer both Hexavalent Chem-film and, RoHS Hex-Free Chem-film coatings

Conversion Coating Specs AOTCO Provides:

  • ASTM B449 [Nadcap Accredited]

  • MIL-C-5541 [Nadcap Accredited]

  • MIL-DTL-5541 [Nadcap Accredited, ROHS Compliant]

  • MIL-DTL-5541 Type II [Nadcap Accredited]

  • MIL-DTL-81706 [Nadcap Accredited, ROHS Compliant]

  • MIL-C-13924

  • MIL-DTL-13924

Types of Conversion Coatings

Hexavalent Chem Film (“Type I”)

  • The traditional process used in creating a Conversion Coating
  • Contains hexavalent chromium
  • Typical color specification (class) for traditional hexavalent chromate ranges from “clear” to “gold”

ROHS Chem Film (“Type II”)

  • A more environmentally friendly option
  • Does not contain Lead, Cadmium, Hexavalent Chromium, Mercury or PBB/PBDE compounds
  • ROHS chem-film is always “clear” in color, but longer exposure to the solution can make the coat more visibly discernible in daylight

Note: If no type is specified, Type I will be used.

Classes of Conversion Coatings

Class 1A

  • For maximum protection against corrosion on unpainted items, and increased adhesion on painted items
  • These coatings will generally be thicker and darker in appearance
  • Class 1A is commonly used on tanks, tubing, and component structures where only exterior protection is required

Class 3 

  • For protection against corrosion where low electrical resistance is required
  • These films are generally lighter in appearance, and of a thinner thickness in order to maintain low electrical resistance
  • Class 3 is frequently used in electrical components such as circuit boards or connectors.
Metals Suited to Chem Film Treatments
  • Steel Alloys (black oxide is a common treatment)
  • Aluminum
  • Beryllium
  • Magnesium
  • Zinc

A Helpful Note

“Alodine” (Chem Film) vs. Anodize

  • Alodine is a trade name for chemical conversion coating of aluminum
  • Because the name sounds like anodize, there is sometimes confusion between the two coatings
  • While both are coatings created by immersion, the Chem Film treatment is much thinner than Anodizing and is created without use of electrical current
  • Unlike anodizing, Chem Films provide a conductive coating and are sometimes used in conjunction with masking in anodized parts

Ready to get started?

Talk to an industry expert about the best solution for your application.


Join AOTCO at D2P Mohegan Sun | Southern New England

Spring has arrived to New England and that means it is time to get ready for fresh lobstah, the Boston Marathon, and fun at the Southern New England Design-2-Part Show....

AOTCO President Speaks At Harvard Business School Association

During a recent roundtable discussion at the Harvard Business School Association of Boston event, AOTCO's President, Matthew Smith, shared the remarkable journey of the...

Join AOTCO at MRO Americas 2024 | NADCAP Plating & Anodizing

Looking to secure your supply chain's NADCAP plating and anodizing services to drive innovation? Join AOTCO Metal Finishing at MRO Americas in Chicago!

Services & Capabilities

Plating Substrates
Pre- & Post-Process Treatments
Dedicated Outsourced Finishing



Electroplating is a process by which one metal is deposited onto a base metal (substrate). These deposited metals offer a variety of benefits including thermal and electrical conductivity, corrosion resistance and more. AOTCO electroplates a wide variety of both standard and exotic metals.

Learn More



Sometimes called a “conversion coating” Anodizing is an electrolytic process in which an oxide (anodic) layer is chemically built on the surface of the substrate material, providing anti-corrosion and other benefits. AOTCO offers, Type I, Type 2, Type 3 and Titanium anodizing services.

Learn More



Passivation is a term for a variety if processes that make a metal (most commonly stainless steel) or other substance unreactive, or passive, by altering the surface layer or coating the surface with a thin inert layer. AOTCO performs both citric and black oxide passivation techniques to a range of specifications.

Learn More

Plating Substrates

Plating Substrates

AOTCO plates on a wide variety of Common, Exotic and Non-Metallic substrates, bringing exceptional expertise to magnesium, titanium, beryllium, BeCu, TeCu, tungsten and more. In some cases we pass as high as 450 degrees celsius, allowing for high temperature soldering, brazing, or post machining operations after plating.

Learn More

Pre- & Post-Process Treatments

Pre- & Post-Process Treatments

Pre-Process: In addition to offering both mechanical & chemical cleaning options, AOTCO specializes in creating solutions for complicated, difficult and tight-tolerance masking challenges. Post-Process: For clients with specialized needs AOTCO offers laser marking and engraving options, including color change caused by chemical or molecular changes, charring, foaming, melting, ablation, and more.

Learn More

Dedicated Outsourced Finishing

Dedicated Outsourced Finishing

Part of our cornerstone goal of building long-term, collaborative & solution-oriented partnerships, AOTCO will devote reserved physical and human resource capacity for our clients with long-term finishing and deadline requirements. For these partnerships our commitment is that AOTCO manages the process, while YOU control the results.

Learn More