Zn-ni Alloy Electrodeposition Process Of Hydrogen Permeation Behavior And Corrosion Resistance

Because of the excellent corrosion resistance, Zn-Ni alloy coating has been used widely in the fields of automobile, aviation and electronics, as a promising candidate of Zn or Cd coating, recently. Zn-Ni alloy coating is mostly prepared by electrodeposition, where the local hydrogen embrittlement occurs easily because of the hydrogen co-deposition. So the technique used for investigating hydrogen permeation behavior or eliminating and inhabiting hydrogen permeation through steels have become a keen subject for the surface engineering researchers.In the present paper, the behaviors of hydrogen permeation during the electrtrodeposition of Zn-Ni alloy from chloride and sulfate-chloride baths were investigated using an electrochemical hydrogen permeation technique, in order to obtain a suitable Zn-Ni alloy bath and operating conditions with a low susceptivity of hydrogen embrittlement.Firstly, according to the results of corrosion resistance of Zn-Ni alloy coatings examined using salt spray test, the plating parameters of Zn-Ni alloy electrodeposition from chloride and sulfate-chloride baths were optimized. Secondly, the behavior of hydrogen permeation during the electrodeposition of Zn-Ni alloy from this two baths was investigated using an electrochemical hydrogen permeation technique. The characteristics of hydrogen permeation are explained in terms of the hydrogen coverage during the electrodeposition of Zn-Ni alloy and the porosity of Zn-Ni alloy deposits. The results indicated that the current of hydrogen permeation from chloride bath is smaller than that from sulfate-chloride bath. The currents of hydrogen permeation in either chloride or sulfate-chloride bath increase with increasing the temperature of the bath tested. Finally, hydrogen-charged samples coated with Zn-Ni alloy were tested using hydrogen-induced hysteretic fracture method, and the micrographs of the fractures were examined using scanning electron microscopy (SEM), which were in good agreement with the results obtained by electrochemical hydrogen permeation test.In summary, the electrochemical hydrogen permeation is capable of monitoring and investigating the behavior of hydrogen permeation during the electrodepodition of Zn-Ni alloys. The results from the test can be used to estimate the hydrogen brittleness resistance. Combining the results obtained from corrosion resistance test with that from electrochemical hydrogen permeation test, the electroplating parameters of Zn-Ni alloy coating with excellent properties in both corrosion resistance and hydrogen-resistance were worked out.