Corrosion resistance of electroplated zinc alloy coatings

Abstract
Zinc alloy electrodeposits containing 0 to 25% of Ni or Co have been prepared in the laboratory and carefully characterised with respect to composition and structure. Corrosion behaviour has been studied using salt spray and electrochemical methods. Results obtained have been compared to those found when testing a selected range of commercially produced deposits. The optimum range of compositions for maximum corrosion resistance was found to be 12 to 13% Ni and in excess of 1.0% Co. The corrosion process was found to be under anodic control and dezincification led to an improved barrier layer and a reduced rate of anodic dissolution. The influence of conversion coating treatments (commercial and laboratory formulations) has also been investigated and found to improve corrosion resistance significantly.

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