Testing and evaluation of nonchromated coating systems for aerospace applications

The advanced corrosion resistant aircraft coatings program (ACRAC) is part of the Air Force strategy to improve performance and reduce environmental i mpact of coatings used on Air Force weapon systems. The program addresses t he Air Force near and mid-term strategies to eliminate chromate corrosion i nhibitors and reduce steps in the outer mold line coating process. Evaluati on of the coating process (surface preparation, conversion coating, primer, topcoat) as a system is a key feature of the ACRAC program. Results to dat e indicate that the current-state-of-the-are nonchromated coating systems a re significantly less effective than those with chromate. A chromate conver sion coating is required for the nonchromate primer system to meet minimum requirements. Sol-gel-process based conversion coatings can replace chromat e conversion coatings provided a chromated primer is used. Several approach es to incorporating inhibitors into sol-gel coatings are discussed. Electro chemical methods for testing coating performance are discussed and a new pr ocedure based on impedance spectroscopy for evaluating active damage repair is presented. (C) 2001 Published by Elsevier Science B.V.