Evaluation of Environmentally Acceptable Multi-Layer Coating Systems as Direct Substitutes for Cadmium Plating on Threaded Fasteners

Cadmium has been identified by the United States Army's Tank and Automotive Command as a threat to worker health and the environment. Based on already completed cadmium substitute testing, an evaluation program was conducted to quantify the performance of environmentally acceptable, multi-layer coatings that could be directly substituted for cadmium on threaded fasteners. The performance issues investigated included coating system lubricity and corrosion control performance. Data were generated from both natural marine atmosphere exposure tests and laboratory evaluations. Test specimens were prepared by applying sacrificial plating layers and lubricous topcoat materials to commercially available 1/2-20 UNC Fine, Grade 5 fasteners. Experimental analyses included realistic torque-tension curve development, marine atmosphere exposure testing, and ASTM B 117 salt fog evaluations. Program findings indicate that ASTM B 633 zinc coatings (without the Type II or III chromate passivation treatment) exhibited torque tension behavior that was directly comparable to that of the cadmium experimental controls. Corrosion control performance test results indicated that regardless of underlying plating chemistry, systems topcoated with Everlube 6108 performed as well as the cadmium experimental controls.