Specification for Electrodeposited Coatings on Threaded Fasteners (Metric)

Abstract

This specification covers application, performance and dimensional requirements for electrodeposited coatings on threaded fasteners with metric screw threads. It specifies coating thickness, supplementary hexavalent chromate or trivalent chromite finishes, corrosion resistance, precautions for managing the risk of hydrogen embrittlement and hydrogen embrittlement relief for high-strength and surface-hardened fasteners. It also highlights the differences between barrel and rack plating and makes recommendations as to the applicability of each process. The coating material, coating thickness, chromate finish, and trivalent chromite finish shall be selected and designated. The electrodeposited coating shall cover all surfaces and shall meet the following requirements: the coating metal deposit shall be bright or semibright, smooth, fine grained, adherent and uniform in appearance; the coating shall be free of blisters, pits, nodules, roughness, cracks, unplated areas, and other defects that will affect the function of the coating; and the coating shall not be stained, discolored or exhibit any evidence of white or red corrosion products. Slight discoloration that results from baking, drying, or electrode contact during rack-plating, or all of these, as well as slight staining that results from rinsing shall not be cause for rejection. Corrosion resistance and embrittlement of coatings shall be determined by performing mechanical tests.