(Hughes Missile Systems Company)
Project Number: J-95-OC-001
Status of Project: Completed in 1997
Technology Survey
Conversion coating is the chemical treatment of metal surfaces to produce an adherent coating composed of chromates, oxides, phosphates, or other protective chemicals. Chromate conversion coatings are produced by combining chromium compounds (including hexavalent chromium) with other water-soluble inorganic materials. During the treatment process, the surface of the metal is changed to a layer of chromium salts to produce the desired decorative or functional properties.
Although chromate conversion coating offers many advantageous coating properties, its use of hexavalent chromium is strictly regulated due to the compound's toxicity and suspected carcinogenicity. Regulations pursuant to the CAA, CWA, and RCRA contain provisions regulating waste streams from metallic finishing operations that contain hexavalent chromium. In addition, worker exposure to hexavalent chromium in the work place is regulated by the OSHA based on permissible exposure limits.
Alternatives to chromate conversion coatings are now available. To identify alternatives, NDCEE/CTC, Johnstown, Pennsylvania was tasked to perform a Technology Survey. Alternatives were limited to coatings that pass one or more of the corrosion resistance or contact electrical resistance performance requirements of MIL-C-5541E ("Chemical Conversion Coatings on Aluminum and Aluminum Alloys") or MIL-C-81706 ("Chemical Conversion Coating Materials for Coating Aluminum and Aluminum Alloys"). Twenty commercially available or near-commercially available alternatives were identified. A description of each alternative, the testing that has been performed, and associated environmental, health, and safety concerns are presented. Note that, in most cases, only regulated or HazMats are listed as constituents of the alternatives, due to trade-secret issues. However, when available, all constituents are listed. Also included with the discussion of each alternative are relevant abstracts obtained from a brief and general literature search on several databases, and a point of contact in the manufacturing or researching company.
To view the Technology Survey for Alternatives to Chrome Conversion Coatings for Aluminum Alloys 2024, 6061, 7075, and Ion Vapor Deposition of Aluminum on Steel, dated January 29, 1998, please click here. This document is now Appendix A of the PAR.
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