Qualification of Trivalent Chromate as a Hexavalent Chromate Alternative for Propellant and Cartridge Actuated Devices; Final rept

摘要

A low toxicity trivalent chromate conversion coating (TCP) over a zinc-phosphate conversion coat was qualified to replace toxic hexavalent chromate conversion coating (CCC) on zinc-nickel plated steel. Unpainted test panels exhibited at least 42 days of resistance to cyclic salt fog. These panels lasted at least 4 days when subjected to cyclic sulfur dioxide and cyclic salt fog testing with full red rust evident on the seventh day. Painted and scored TCP panels previously subjected to 10 days of humidity and 120 days of salt cyclic fog were subject to 78 days of cyclic sulfur dioxide and salt fog. This paint was still largely intact with only moderate score corrosion and paint blistering near the score. Breakaway torque required to unscrew adhesively bonded TCP over zinc-phosphate conversion coated zinc-nickel plated exceeded their initial assembly torque on representative propellant actuated device and cartridge actuated device parts.