Chrome-Free Modifications for MIL-DTL-16232, Phosphate Coating, Heavy, Manganese or Zinc Base

Heavy phosphate coatings provide both corrosion and wear resistance for steel assemblies. A chromic acid sealer is required for enhancing corrosion resistance of the coating per MIL-DTL-16232. It has been known for quite some time that hexavalent chromium (Cr6 ) is a risk to both human health and the environment. In April 2009, a memo was released from the Office of the Secretary of Defense specifically directing the military to approve the use of alternatives to Cr(VI) where they can perform adequately for the intended application and operating environment. This effort examines the efficacy of non-Cr6 sealers to replace and meet the performance of the previously required chromic acid. Eleven candidate sealers, along with the baseline sealer, were tested. Several alternative sealers demonstrated performance similar to or better than the baseline Cr6 . The results of this work allowed for the MIL-DTL-16232 specification to be updated to allow alternative sealers to Cr6 where allowed.