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:
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ASTM B449 [Nadcap Accredited]
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MIL-C-5541 [Nadcap Accredited]
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MIL-DTL-5541 [Nadcap Accredited, ROHS Compliant]
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MIL-DTL-5541 Type II [Nadcap Accredited]
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MIL-DTL-81706 [Nadcap Accredited, ROHS Compliant]
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MIL-C-13924
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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
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Talk to an industry expert about the best solution for your application.
Resources
AOTCO Acquires Modern Metal Finishing
Archeological Discovery Shows AOTCO’s History of Metal Plating
AOTCO Launches New Type I Chromic Acid Anodizing Line
Services & Capabilities

Electroplating
Electroplating
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.
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Anodizing
Anodizing
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.
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Passivation
Passivation
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.
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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.
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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.
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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.
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