Electrodeposited Zn-Ni alloy coatings show a maximum resistance to salt spray corrosion at 12% to 15% Ni. To gain an increased understanding of this behavior, we studied the corrosion mechanisms of 13% Ni coatings in sodium chloride solutions with electrochemical, microscopic, x-ray, and Auger electron spectroscopic methods. We observed that the Zn-Ni alloy initially corrodes with the preferential dissolution of zinc. As the coating dezincifies, tensile stresses are created in the coating causing development of a fine network of cracks. As corrosion progresses, the coating transforms into a composite barrier layer consisting of a micro cracked nickel-rich metallic phase and zinc corrosion products. This behavior contrasts with that of pure zinc coatings which corrode by a simple mechanism of uniform dissolution. The superiority of Zn-Ni alloy coatings in salt spray corrosion appears to result from slower anodic dissolution kinetics and some barrier protection afforded by the remaining composite layer.


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    Title :

    Corrosion Mechanism of Zn-Ni Alloy Electrodeposited Coatings


    Additional title:

    Sae Technical Papers


    Contributors:

    Conference:

    SAE Automotive Corrosion and Prevention Conference and Exposition ; 1983



    Publication date :

    1983-12-05




    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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