Recent Alternatives to Chromate Conversion Coatings

NCMS Project #: 170604

Problem:

When aluminum is given the standard treatment for corrosion resistance (chromium conversion coating), active hexavalent chromium remains on the surface of the metal.
New regulations in the European Union may restrict the operation of aircraft treated with hexavalent chromium in all of its member states.
No good commercially available alternative exists for conversion coating of the high copper content aluminum alloys currently in use for structural aerospace applications.

Benefit:

Process alternatives are now available when the European Union acts to restrict the use of hexavalent chromium.
Similar regulatory restrictions may eventually be developed in the U.S.

Solution/Approach:

Seventeen hexavalent chromium-free alternatives from seven different suppliers were tested on six aluminum alloys.
Test samples were subjected to standard testing for salt-fog corrosion resistance, conductivity, and paint adhesion.
Two alternative coatings were found to give promising results on the most demanding application (a high-strength aerospace alloy).

DOD Participation:

U.S. Army (Corpus Christi Army Depot)

Industry Participation:

CAI Resources
Integrated Technologies
NCMS