Trivalent Chromium Process (TCP) as a Sealer for MIL-A-8625F Type II, IIB, and IC Anodic Coatings

This report documents evaluations of trivalent chromium compositions TCP as sealers for MIL-A-8625F Type II, IIB, and IC anodic coatings conducted from March 2001 through December 2007 by Materials Engineering, AIR-4.3.4, at NAWCAD Patuxent River, Maryland, and the In-Service Support Center at Fleet Readiness Center FRC Southeast, Jacksonville, Florida. Key performance criteria evaluated are bare, or unpainted, corrosion resistance in ASTM B 117 neutral salt fog NSF and ASTM G 85 Annex 4 acidified salt fog SO2 SF, painted corrosion resistance in NSF and SO2 SF, and paint adhesion. The performance of TCP as a sealer was compared to standard sealers like dichromate and water which are commonly used in aerospace and other industries. Paint adhesion was performed with commonly used high-solids and water-borne chromated and chromate-free primers qualified to MIL-PRF-23377 and MIL-PRF-85582. In these series of evaluations, TCP performs as good as or better than chromate in corrosion resistance and equal to chromate in paint adhesion. TCP is far superior to water for sealing. An additional benefit is that the TCP is applied at ambient conditions for 5 to 10 min. Chromate and water sealers are applied at 190 deg F to 200 deg F for up to 25 min.