Zn Ni Alloy Coatings Research Articles

Galvanic corrosion behaviour of electrodeposited zinc and Zn–Ni coatings coupled with aluminium alloys

Abstract The galvanic corrosion characteristics of detached electrodeposited pure zinc and Zn–Ni alloy coatings have been investigated on coupling with two aerospace aluminium alloys. Zinc alloys containing up to 24 wt-% nickel were coupled with an Al–Cu alloy, 2014–T6, and an Al–Zn–Mg alloy, 7075–T6, under total immersion conditions in quiescent 600mM NaCl solution. It was found that zinc alloys containing 5–14 wt-% nickel corroded preferentially on coupling with the aluminium alloys and reduced the corrosion rates of the aluminium alloys below those found in the uncoupled state. While pure zinc and Zn–Ni alloys containing <5 wt-% nickel also corroded preferentially on coupling with the aluminium alloys, in such cases the aluminium alloys suffered an accelerated rate of corrosion over that found in the uncoupled state as a result of, it is suggested, the formation of strongly alkaline conditions at the aluminium alloy surface. For zinc alloys containing over 14 wt-% nickel, aluminium alloy corrosion was ...

Galvanic corrosion behaviour of electrodeposited Zn–Ni coatings coupled with steel

AbstractThe galvanic corrosion behaviour of detached electrodeposited Zn–Ni alloy coatings has been investigated during coupling with bare steel under two experimental conditions: total immersion in 600mM NaCl solution and exposure to neutral saltfog. Open circuit potential measurements made in NaCl solutions indicated that zinc alloys containing less tha approximately 14 wt-% nickel have potentials which remain negative with respect to steel over long immersion periods, suggesting that the coatings would behave sacrificially. This was confirmed by the galvanic current measurements which showed thatfor extended periods of time, zinc alloy coatings containing less than 14 wt-% nickel were sacrificial towards steel under both total immersion and salt fog conditions. Howeve,~ when the nickel level was increased above 14 wt-%, predominantly non-sacrificial corrosion behaviour was exhibited and steel corrosion was accelerated.

The corrosion resistance of electrodeposited zinc-nickel alloy coatings

The corrosion behaviour of electrodeposited zinc-nickel (Zn-Ni) alloy coatings has been studied in aqueous chloride environments. The corrosion rates of detached zinc alloys containing up to 25% Ni by weight were determined using linear polarisation techniques. The corrosion rate of Zn-Ni alloys was found to decrease with increasing Ni content over the compositional range studied. Galvanic corrosion measurements have indicated, however, that Zn-Ni alloy coatings become less sacrificial toward steel as the Ni content is increased. These results are used to interpret the corrosion behaviour of electroplated steel in a neutral salt fog environment.

Fatigue behaviour of short-alumina-fibre-reinforced AZ91 magnesium alloy metal matrix composite: Llorca, N., Bloyce, A. and Yue, T.M. Mater. Sci. Eng. A Mar. 1991 A135, (1–2), 247–252

Zn–Ni alloy coatings were plated on AZ91 magnesium alloy using a pulse potential electrodeposition method after zinc immersion and Zn–Cu plating. The density and frequency of electric current, deposition time and ton / toff have large effects on chemical composition, thickness of the Zn–Ni coatings. The Zn–Ni coatings provide very good corrosion protective function to inner AZ91 magnesium alloy. The good corrosion resistance of Zn–Ni coatings is attributed to the existence of the γ-phase and the homogeneous and compact structure of the coatings. Chromating treatment can further improve the corrosion resistance of Zn–Ni coatings.

MORPHOLOGY AND PROPERTIES OF ELECTRODEPOSITED ZN-NI ALLOY COATINGS ON MILD STEEL

Zinc-nickel alloys electrochemically deposited on mild steel under various deposition conditions were investigated. The effect of plating variables (bath composition, pH, current density) on the coating composition, morphology, corrosion property and microhardness were investigated. Modified morphology with perfect crystal growth, uniform arrangement of crystals, refinement in crystal size and hence bright deposit was obtained from sulfate Bath-3 containing 30 g/l H3BO3 at a current density of 75 mA/cm2. Corrosion resistance as well as microhardness of Zn-Ni alloy coatings increased with the increase of %Ni in the deposit for all the sulphate baths studied. Optimum conditions for good deposition are also discussed. Keywords: Zn-Ni alloy, electrodeposition, morphology, corrosion resistance. doi: 10.3329/jme.v40i1.3468 Journal of Mechanical Engineering, Vol. ME40, No. 1, June 2009 9-14