Demonstration and Validation of Non-Chromate Aluminum Pretreatments

WP-200025

Objectives of the Demonstration

WP-200025 Project Graphic

Chromate-based aluminum pretreatments are heavily used throughout the Department of Defense (DoD) and aerospace communities to provide corrosion protection and an adhesive base for organic coatings. Hexavalent chromium is a known human carcinogen that is strictly regulated. The Environmental Protection Agency limits air emissions and regulates solid waste disposal from operations using hexavalent chromium, and the Occupational Safety and Health Administration regulates the amount of hexavalent chromium to which workers can be exposed. The Permissible Exposure Limit (PEL) for hexavalent chromium has been reduced from 50 micrograms per cubic meter (µg/m3) to 5 µg/m3. Such limits will increase the costs of using hexavalent chromium materials for the pretreatment of aluminum and aluminum alloys. This project demonstrated and validated the performance of alternative aluminum pretreatments that do not contain chromates on DoD, National Aeronautics and Space Administration (NASA), and private industry platforms in an effort to reduce and ultimately eliminate the use of hexavalent chromium in aluminum finishing operations. 

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Technology Description

WP-200025 Project Graphic
WP-200025 Project Graphic

Candidate alternatives were nominated based on previous research and development efforts conducted by the project participants. 

Pretreatment performance was initially evaluated using representative substrates and coating systems and standard accelerated laboratory tests. Acceptable candidates were then demonstrated in the field at various depots and manufacturing sites. Demonstrations were performed on weapons platforms from all of the military Services as well as various weapon systems original equipment manufacturers (OEM). Life cycle cost analyses were performed on each alternative. Toxicological, environmental, and occupational health and safety issues also were quantified. 

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Demonstration Results

With support from ESTCP, the Joint Group on Pollution Prevention, and leveraged organizational efforts, alternative materials and processes were identified through laboratory evaluations and their in-service performance was demonstrated and validated through field testing on military land and aircraft assets. Trivalent chromium pretreatment (TCP) films improve corrosion inhibition and paint adhesion. TCP can be applied by methods similar to chromate conversion coatings. Alodine™ 5700 pretreatment films improve paint adhesion. 5700 can be applied by methods similar to chromate conversion coatings. PreKote™ is an organic conversion coating used for surface pretreatment prior to painting. The solution is applied by a manual or automated scrubbing process. AC-130/131™ is a sol-gel conversion coating that improves paint adhesion. DoD, NASA, OEMs, and commercial industry partners are currently authorizing, transitioning and implementing these technologies for chromate replacement in aluminum finishing. The relevant military and commercial specifications also are being revised to promote the use of these alternatives.

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Implementation Issues

WP-200025 Project Graphic

Non-chromate aluminum pretreatments will help DoD and OEM facilities comply with local, national, and international environment, safety and occupational health regulations for hexavalent chromium. Eliminating hexavalent chromium from the pretreatment operations will reduce user liability and risk in the life cycle of the assets, while maintaining a high level of technical performance. Additional benefits will be realized with the implementation of these and other alternatives in the commercial finishing industry as many private sector operations follow DoD specifications and technology transitions. (Anticipated Project Completion - 2010)

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Project Documents

Points of Contact

Principal Investigator

Bill Nickerson

ONR 351

Phone: 703-501-6226

Program Manager

Weapons Systems and Platforms

SERDP and ESTCP

Project Documents

Document Types

  • Fact Sheet - Brief project summary with links to related documents and points of contact.
  • Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
  • Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
  • Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
  • Guidance - Instructional information on technical topics such as protocols and user’s guides.
  • Workshop Report - Summary of workshop discussion and findings.
  • Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
  • Model/Software - Computer programs and applications available for download.
  • Database - Digitally organized collection of data available to search and access.