Department of Defense Issues Final Procurement Rule on Minimizing the Use of Materials Containing Hexavalent Chromium
The U.S. Department of Defense in early May issued its final procurement rule governing military uses of hexavalent chromium. During the multi-year review of the issue, NASF technical and policy committees provided input to inform the Pentagon’s decision.
What does the rule cover and what is exempt?
The rule only covers hexavalent chromium-containing materials that remain on or in the component. It does not cover processes that use hexavalent chromium solutions, if they do not leave hexavalent chromium in the coating. In addition, the rule uses the familiar definition of a homogeneous material, which is explicitly defined to include coatings, but is meant to exclude heat treatments and other surface modifications, which are considered to be part of the bulk material.
Conversion coatings are explicitly exempt, because they are intrinsically inhomogeneous, whether on aluminum and magnesium alloys, or on coatings such as Zn, Cd and anodize.
- Conversion coating and chromate converted coatings
- Hard chromium plating
- Chromic acid anodizing
- Chromate washes, etches, pickling and stripping solutions, etc.
- Low chromate metallic ceramics (<0.1% Cr6+)
- Chromium diffusion heat treats (such as chromizing and some carbonitriding processes)
- Chromated primers (for aircraft skins and components)
- Aircraft fuel tank internal coatings
- Wet install fastener sealants (used on Naval aircraft)
- Other chromated sealants (used to seal panels, covers, electronics, etc.)
- Chromated metallic-ceramic paints containing >0.1% Cr6+ (MIL-C-81751, used in turbine engines)