Abstract
WC-12Co coatings (with and without Ni-5Al bond coats) as well as Ni-5Al coatings were deposited on Al 7075 by HVOF spraying. The corrosion behaviour of the coatings was investigated by salt spray testing for 40 days, followed by potentiodynamic tests in a 3.5% aqueous NaCl solution, at 25, 35 and 45°C.The thicker duplex coatings (500µm) were not susceptible to pit corrosion, at any temperature. A small fraction of the thinner duplex coatings (260µm) underwent localized corrosion, only at 45°C. Ni-5Al and a small fraction of WC-12Co single coatings showed low susceptibility to pit corrosion which increased with temperature increasing and thickness decreasing. The coating system Ni-5Al/WC-12Co exhibited the highest resistance to general corrosion, which was independent of the thickness at the two thicknesses tested.
