Environmentally Friendly Anticorrosion Coatings for High Strength Fasteners

WP-1617

Objective

WP-1617 Project Graphic

Bulk application of thin film zinc rich primer (left) plus electrodeposition topcoat (center) yields superior corrosion performance (1000 hours B117 Salt Spray), without toxic metals or risk of hydrogen embrittlement.

Traditionally, high-strength steel fasteners have been used with cadmium electroplated coatings followed by a hexavalent chrome rinse. The environmental and health hazards associated with cadmium and hexavalent chromium are well established, and significant legislation has been put in place to limit their continued usage. It is critical that suitable replacement technologies be identified that can provide these high performance characteristics in a cost-effective manner.

The objective of this project was to develop new environmentally benign coating technologies that could eliminate the need for cadmium or hexavalent chromium coatings on high-strength fasteners. These technologies would provide a coatings system for high-strength, corrosion resistant fasteners for use on both legacy weapon systems and new weapon platforms.

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Technical Approach

In this project, a multilayer coating system was developed that consisted of a conventional zinc phosphate pretreatment followed by a zinc flake-based primer, then a cationic electrodeposition topcoat. Additionally, a silver aluminum-based topcoat was developed for application where electrodeposition equipment was not available. The bulk of the work focused on developing novel inorganic binders and zinc flake technology for the sacrificial zinc primer. This primer is superior over current zinc rich primers for corrosion performance and adhesion when used with the cationic electrodeposition topcoat. The topcoats were formulated for adequate torque/tension performance and color variations.

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Results

The multilayer coating system exhibits excellent corrosion resistance and represents a viable, environmentally friendly alternative to cadmium/chromium coatings for high-strength fasteners. The primary system includes zinc phosphate conversion coating, dip-spin application of an inorganic zinc rich primer, followed by an epoxy topcoat applied by cationic electrodeposition. An alternative aluminum rich topcoat has also been developed for dip-spin application where electrocoat is not available. Both coating systems meet the minimum 1000 hours of salt spray performance, meet torque/tension requirements, and are free of cadmium, chromium, lead, and nickel. The electrodeposition topcoat offers an environmentally benign coating alternative and is an excellent method for bulk application such as fasteners.

The coatings and processes were tested in production-scale environments and are ready for commercial distribution. Testing and approvals to automotive, industrial, and construction specifications are under way with positive results. The zinc rich plus electrocoat finish has been used commercially in a dip-drain application successfully.

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Benefits

Eliminating hazardous materials currently used in anticorrosion coatings for high-strength fasteners will improve the life-cycle costs as well as environmental and health issues associated with the manufacture and maintenance of DoD weapons systems. The environmentally benign coating technologies developed would impart high-end sacrificial corrosion resistance without the use of hazardous chrome or cadmium and without embrittlement of fasteners.

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Project Documents

Points of Contact

Principal Investigator

Mr. Matt Scott

PPG Industries Inc.

Phone: 412-492-5594

Fax: 412-492-5522

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.