Chromate conversion coatings have been routinely applied on aluminum-based surfaces in order to improve corrosion characteristics and adhesive properties. The conventional chromate conversion coating process uses highly oxidizing toxic hexavalent chromium, or Cr+6, compounds and ferricyanide. The metal finishing industry has been developing less toxic alternative coatings in order to comply with environmental regulations and substance restriction legislation, such as the European Union’s Restriction of Hazardous Substances directive, or RoHS.

One promising alternative is the trivalent chromium–based environmentally friendly conversion coating. This white paper, provided by METALAST, will describe a new trivalent chromium process for chromate conversion on aluminum with high corrosion protection, good paint adhesion, low cost, quick and simple processing, and all while meeting the stringent requirements of military specifications. It is QPL (Qualified Product List) approved by the United States Navy–Defense Standardization Program under Governing Spec MIL-DTL-81706-B.

In addition, this article will outline various chromate conversion techniques for aluminum. Furthermore, it will address a new, environmentally friendly, cost-efficient, and performance-oriented chromate conversion coating with a unique and patented trivalent chromium pre- and post-treatment chemistry for aluminum.