Marine Corrosion Tests of Galvanic Coatings for Ship Instruments. XI. Gold and Palladium Coatings on Brass

The corrosion peculiarities and the protective and decorative characteristics of gold and palladium coatings were investigated in containers simulating the casings for ship's equipment of watertight and splashproof types. The coatings (3 and 6 μm thick) were applied to 62 brass specimens either directly or with a 12 μm-thick silver sublayer (Ag12/Au3, Ag12/Pd 2, μm). The specimens plated were tested by exposure for 14–20 years at coastal corrosion stations in cold (Murmansk), moderately humid (Vladivostok), and humid subtropical (Batumi) climates. The dezincification products of the brass substrate emerging through the pores of the coating form stains and salt films on its surface. Clogging the pores, the products become responsible for the blistering of the plate. The corrosion weight loss linearly correlate with the surface accumulation of chlorides; the thicker the coating, the smaller the damaged area of the substrate, but the deeper the corrosion centers. The technical service life of protective coatings is refined.