Recent Alternatives to Chromate Conversion Coatings

NCMS Project #: 170604


  • 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.


  • 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.


  • 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


FInal Report