Cerium-based conversion coatings as alternatives to hex chrome

Rare-earth compounds are corrosion inhibitors for aluminum alloys that show promise as replacements for hexavalent chromate compounds. Cerium-based conversion coatings can be applied with spontaneous spray or immersion processes as well as an electrolytic process. The coatings can meet military standards by providing corrosion protection for up to 14 days in ASTM B117 salt spray. As with any surface finishing operation, the performance is a function of the parameters used in the deposition, but the process is reproducible and robust. Development efforts are continuing to optimize the deposition process, to enhance the long-term corrosion resistance of chromate-free systems, and to integrate CeCCs into non-chromate coating systems that include primers, topcoats, or multifunctional UV-curable coatings in addition to CeCCs.