When it comes to military and defense components, specialized standards are in place to ensure consistent quality, performance, and long life cycles even in very challenging types of applications.
Chromium conversion, which may also be called chem film, Iridite or Alodine, is a common coating used on weapons, vehicles, telecommunication, aerospace and other industries that fall within the military and defense sector. When these parts or components are fabricated with aluminum alloys, they are required to have chromium conversion MIL-C-5541 coating.
The Standard
The MIL-C-5541 is a specific standard formally known as the Military Specification, Chemical Conversion Coatings on Aluminum and Aluminum Alloys standard. As with most of the military and defense standards (DoD), there is a comparable ISO standard which is ISO 8081:1985.
The standard outlines the differences in coating including the hexavalent chromium coating (typically yellow) or the coating without hexavalent chromium (typically clear).
The standards also identify the class of coating, which refers to the thickness. This will vary based on the need for protection against corrosion as well as the need for low electrical resistance.
While the chromium conversion MIL-C-5541 coating requirements are specific to the Department of Defense applications, they are widely used outside of the DoD in a wide range of industries.
The Advantages
As mentioned above, by using the chromium conversion MIL-C-5541 standard it is possible to provide a coating for an aluminum alloy that offers a range of benefits and advantages. In addition to corrosion resistance and low electrical resistance, it will also provide a foundation coating for the application of additional plating or even for paint.
This is a very thin layer coating, which means virtually no distortion of the dimensions of the part or component. In DoD and aerospace applications, retaining the tight tolerances on parts or components is a significant advantage offered by chromium coating to the MIL-C-5541 standard.