Chemical Film Coating: The Complete Guide

In this guide, you will learn everything about chemical film coating. Whether you want to learn about advantages, coating technique, quality standard specifications, or types of chromate conversion coating – you will find all information right here.

What Is Alodine?

Alodine is another name for chem film. It is a process where a conversion coating chemical prevents aluminum from rusting. This process is common in passivating aluminum.

Advantages Of Chemical Film Coating

Advantages Of Chemical Film Coating
Advantages Of Chemical Film Coating

Some of the main advantages of chemical film coating include:

  • For parts constructed of various materials; protection against erosion manufacturers typically uses a mixture of film covering as a protective coating.
  • Chemical films with minimal electrical impedance do not affect a material’s electrical conductivity. It holds especially for Class 3 fantasy films.
  • It is relatively easy to apply material films and coatings. It takes little effort to produce a high-quality covering.
  • It is cost effective hence you can save on your finances, especially with a limited budget.
  • Aids in providing equipment exposed to salty environments, such as seas and oceans, with resistance to salt spray.
  • It is suitable for mass production.

Materials Suitable For Chemical Film Coating

Materials Suitable For Chemical Film Coating
Materials Suitable For Chemical Film Coating

You can apply chemical film coating on any of the following materials:


The corrosion resistance of aluminum is already better than average, but this protection can be increased by coating it with a suitable material. In any case, a second, more obvious reason for chemical films on metal is to improve prep coatings’ ability to adhere to an aluminum part’s surface.


The high melting point, intrinsic resistance to corrosion, and superior thermal conductivity are just a few of the benefits of this thin metal found in the earth’s crust.  However, beryllium is also poisonous and can harm people’s lungs and respiratory systems. It is a valuable metal used in satellite constructions, heat sinks, computer components, and x-ray detectors.


Magnesium and similar alloys are becoming increasingly common materials in automotive and aviation applications. Magnesium is appealing for various applications since it is incredibly lightweight and has an excellent quality-to-weight ratio.  The material’s thickness is significant. Magnesium has a thickness of 66% that of aluminum and a quarter of that of iron.


The other most prevalent metal in the world is this one. Zinc is quite expensive and has a high level of corrosion resistance. Since this develops zinc patina during oxidation, it can erode up to 100 times slower than other metals. Additionally, it prevents harm.

Although this makes zinc ideal for plating, it does provide a challenge when zinc is a crucial component that functions correctly in the finished product.

Types Of Chromate Conversion Coating

Types Of Chromate Conversion Coating
Types Of Chromate Conversion Coating

The chemical makeup of the coating material is typically related to the type of chemical film coating.

Type 1 The MIL-DTL-5541

Hexavalent chromium, often known as hex chrome, is present. Until safer chemicals were introduced, this procedure was the norm for a long time. Being substances that cause cancer and environmental risks. OSHA and the EPA in the United States closely monitor exposure to hexavalent chromium.

For processing permits, always check with your state or county. The Hex chrome must be adequately ventilated and disposed of Hex chrome must be adequately ventilated and disposed of.   Suppose you use Type 1 with MIL-DTL-5541 spec work. The price of a Type 1 chemical film system may rise significantly if more ventilation is necessary.

Type 2 The MIL-DTL-5541

Without hex, it is known as chromating. This variety, commonly accepted as the norm across many industries, substitutes trivalent chromium, titanium, or zirconium for hexavalent chromium.

TCP-HF (hexavalent free), a hex-free solution, is provided by Chemeon. A global pioneer in hex-free trivalent chromium coating chemistries. They have been approved for usage in various aerospace and defense applications. Trivalent chromate conversion coating Technological advancements enable the method to offer several advantages over Type 1.

Classes Of Chromate Conversion Coatings

Classes Of Chromate Conversion Coatings
Classes Of Chromate Conversion Coatings

Chemical film coatings are classified according to their intended use. Two classes that are frequently employed in chemical film applications are described in the MIL-DTL-5541 specification.

Class 1A

This chromate coating offers unpainted. It is often thicker and darker than other classes. Besides, it provides highly effective protection against corrosion for things.

The paint coating methods cling better to aluminum and its alloys. Numerous vehicles for military and pieces of gear are painted with chemical agent-resistant coating (CARC) paint to provide further chemical agent protection.

Class 3

The two goals of this class of chromate coatings are: It is intended to lessen interference with electrical conductivity in addition to protecting against corrosion. These coatings typically have a thinner coating thickness and a lighter coating weight than Class 1A.

Normally, the Class 3 covering is only thin enough for the metal to maintain its conductivity. The phrase “alodine conductivity” is technically erroneous because the layer itself is not conductive.

Chemical Film Coating Process

Chemical Film Coating Process
Chemical Film Coating Process

Although manufacturing facilities differ, the basic steps in the chromate conversion process are as follows:

  • The surface is cleaned of dust, grease, oil, and production waste so that the conversion coating chemicals may cover it evenly. These cleaners typically consist of non-etch, slightly alkaline detergents that are heated at a reasonably high temperature before being thoroughly rinsed with water.
  • After thoroughly cleaning, the surface may undergo an acid or alkaline etch to remove alloying components that could impair the conversion coating reaction. It will depend on the specific aluminum alloy.

Generally speaking, this process enriches the surface, revealing more aluminum, which is helpful for castings and materials with heavier alloys. It’s crucial to avoid over-etching or material removal. Once more, a thorough water rinse comes after these etch.

  • After being etched, the surface is subjected to acid treatment. Depending on the particular aluminum alloy, the surface’s naturally occurring oxide deposit and desmut could affect the conversion coating reaction. Once more, a thorough water rinse comes after this deoxidation.
  • Chemical Film Coat The deoxidized, clean, and etched aluminum is now prepared for conversion coating. Historically, this was carried out in acidic hexavalent chromium solutions.

Nevertheless, more non-hexavalent baths have emerged and been incorporated into the appropriate standards over the previous ten years. After conversion coating, the components are cleaned and dried.

Factors Influencing Quality Of Chemical Film Coating Process

Material Type
Material Type

The type of material to which the coating is applied will typically also affect how the product looks. In contrast to an alloy treated with the same chemical, a purer substance will have a distinct final appearance and quality.

Material Quality And Purity
Material Quality And Purity

Due to the chemical makeup of the chemical film coating, any changes to the process will affect the results. Purer aluminum alloys, for instance, will provide higher corrosion resistance than a less pure alloy after applying chemical film coating.

Surface Quality
Surface Quality

Whether the substrate surface is polished or etched will affect how uniform the surface is when the chemical layer is applied. It is an additional factor that will influence the chemical coating process.

Chemical Film Class
Chemical Film Class

The outcome will depend on the chemical film’s class selection. Chemical films in Class 1A will be heavier and darker, while those in Class 3 will be lighter and thinner.

Chemical Film Coating Quality Standard Specifications

The MIL-DTL-5541_
The MIL-DTL-5541
  • It is chemical film coatings specification that is most frequently employed.
  • Aluminum and aluminum alloys with chemical conversion coatings to suit military requirements.
  • MIL-C-5541 was replaced in 2006
The ISO 8081
The ISO 8081
  • The aerospace procedure, general-purpose chemical conversion coating for aluminum alloys
  • It outlines specifications for creating and testing coatings.
The ASTM B921_
The ASTM B921
  • MIL-DTL-5541, The Standard Specification for Non-hexavalent Chromium Conversion Coatings on Aluminum and Aluminum Alloys and Type 2 are similar but not identical.
The AMS 2474_
The AMS 2474
  • Aluminum Alloy Chemical Treatment, Low Electrical Resistance Coating
  • The requirements for Aerospace, such as MIL-DTL-5541 Class 3
The ASTM B449_
The ASTM B449
  • Similar to MIL-DTL-5541, Type 1, but not the same
  • The Aluminum Chromate Standard Specification
The AMS 2473_
The AMS 2473
  • Usually, Aluminum Alloys and the General Purpose Coating: Chemical Film Treatment is an Aerospace specification similar to MIL-DTL-5541 Class 1A.

Applications Of Chemical Film Coating

Electrical Industry
Electrical Industry

Chemical films are applied to product housings by electronic manufacturers to prevent corrosion. By doing so, the interior and wiring components of the product are more likely to be stable and safe throughout time.

Aerospace Industry
Aerospace Industry

Any anodized surfaces on the aerospace aircraft will be repaired using chemical film coatings. For components and accessories of aircraft, this acts as a corrosion defense.

A cloud can be damaging to an airplane when it is traveling at high speeds and altitudes. Chemical film coating offers best protection.

Military And Defense
Military And Defense

The Department of Defense and the military use chemical films for various purposes, including priming parts and protecting machinery. The MIL-DTL-5541F requirements are a standard for this finishing technique, which also governs and classifies chemical film coatings and applications.

Maritime Industry
Maritime Industry

Boats and other watercraft need to be corrosion resistant to keep their parts from being destroyed by water. For boats used in saltwater settings, this is essential.

Chemical films’ anticorrosive qualities are widely valued for this and their use as a paint primer for hand-painted watercraft.

People Also Ask:

How Does Anodizing Compare To Chem Film?

Alodine (chem film) and anodizing vary because anodizing uses an electrolytic process, while on the other hand Alodine (chem film) does not. Aluminum is finished using the anodizing and alodine (chem film) procedures to increase corrosion resistance. Both alter the metal’s outermost layer of the surface.

What Makes Chemical Film?

Chem film, or chemical film, describes a chemical conversion coating most frequently related to coating aluminum with chromates. Alodine from Henkel and Iridite from MacDermid Enthone are the two most well-known brand names for this technique.

Is Chemical Film Coating Good For Aluminum?

Chem film, also known as chrome, aluminum chromate, alodine, or iridite, is a chemical conversion coating used to passivate metal. It maintains dimensions while providing corrosion protection for aluminum substrates and acting as a foundation for organic coatings.

Will Chemical Film Coating Prevent Corrosion?

Although it is acceptable for “general” corrosion in less harsh conditions, as Paul Tibbals noted later, it typically is insufficient to prevent galvanic corrosion.

Can You Chem Film Titanium?

Zinc, aluminum alloys, magnesium, steel, and other metals can all be used with chem film. Anodizing can be used on specialized metals like titanium, tantalum, niobium, and various metals.

More Resources:

Film Coating

Sheet Metal Finishing

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