Improved Metal-Rich Coatings for Corrosion Prevention

Hexavalent chromium has long been an indispensable component of corrosion-preventing coating systems.  Although, hexavalent chromium compounds (chromates) offer outstanding corrosion protection, they are known carcinogens and an EPA priority pollutant.  OSHA recently lowered the acceptable exposure limits for chromates, and as a result, chromates are a major source of exposure to hazardous waste and their use is become increasingly discouraged.

Over the past several years, much effort has been focused on finding viable alternatives to chromates for the coatings industry.  One approach is to employ a metal-rich primer in the overall protection scheme; like the use of zinc-rich coatings for steel substrates.  These metal-rich primers offer galvanic corrosion protection whereby the metal particles are oxidized preferentially to the substrate.  In particular, one new application of metal-rich primers is the use of magnesium-rich primers for the protection of aluminum substrates.  While the overall performance of the Mg-rich primer is good compared to other non-chromate systems, recent modifications by NAVAIR have improved the corrosion protection offered to aluminum.  This improvement can be applied to other metal-rich coatings in order to increase their performance as well.  This presentation will focus on the performance of improved metal-rich primers in accelerated corrosion testing, with comparisons to chromate and other non-chromate coating systems.