Sign in Get Instant Quote

Chem film or Alodine™

Chromate Conversion Coating

At a glance

Applicable Materials

Aluminum

Colors

Clear, Gold

Applications

Tools, hardware, electrical systems

Thickness

0.25-1.0 µm0.00001-0.00004 inches

About the Process

Chromate conversion coating, more commonly known as chem film or by its brand name Alodine™, is a chemical coating that passivates and protects aluminum from corrosion. It is also used as a base layer before priming and painting parts. The standard most commonly specified in engineering applications is MIL-DTL-5541F, which refers specifically to coating of aluminum alloys.

This protective layer is much thinner than an anodizing layer, and while both are created by immersion of parts into a bath, Chem film or Alodine™ is a simple chemical coating and the process does not use electrical current.

Chem film or Alodine™ is a slightly cheaper process than anodizing, though it is more prone to scratches, wear, and cosmetic damage. The most common color of the coating is an iridescent greenish-gold, and thus it may also be used for cosmetic purposes. However, this color comes from hexavalent chromium, which is toxic, so for RoHS compliance needs, there are clear versions of the coating available as well.

Design considerations

  • Plugging threaded/reamed holes not required unless tolerances are very tight, as thickness change is minimal.
  • Chem film or Alodine™ coatings offer a much greater electrical conductivity than bare aluminum
  • Media Blast parts before Chem film or Alodine™ to create a more consistent coating that hides small machine marks

YOU MIGHT ALSO BE INTERESTED IN

Design for Manufacturing and Assembly (DFMA): Principles, Best Practices, and Real-World Examples

There have been countless times when I’ve been putting something together and wondered, “Why was this designed this way?” If you’ve ever assembled your own prototypes or even furniture, you probably know what I mean. The best way to design for assembly is often to put prototypes together yourself throughout the process, but it helps […]

Learn More

Humanoid Robots in Manufacturing: Transforming Industrial Automation

Robotic humanoids are becoming increasingly common as critical hardware and software breakthroughs overcome long-standing barriers to creating viable and high-functioning systems. These robots are being increasingly adopted across manufacturing and related sectors to perform tasks traditionally handled by humans.  These humanoid robots are designed to replicate, substitute for, and enhance human capabilities. They are bringing […]

Learn More

Also of Interest