Evaluation of hydrogen adsorption on Zn-Ni alloy coating by electrochemical desorption technique and its permeability on AISI 1020 steel

The objective of this study was to assess the impact of Ni composition in a Zn-Ni coating on the retention of hydrogen and the reduction of its permeability in a low-carbon alloy steel. The methodology used in this study has been modified and adapted from the electrochemical desorption methodology proposed by Zakroczymski [19]. In addition to the advantages of this method mentioned by this author, the present work uses this technique to evaluate the influence of the barrier formed by the Zn-Ni coating on the permeability of hydrogen in the base metal, thereby mitigating its deleterious effects. For the different Ni compositions that are obtained in the Zn-Ni coating, the results of the SEM and EDS analyses indicated that higher nickel concentrations were conducive to grain refinement, resulting in more uniform and compact deposits. The X-ray diffraction (XRD) analysis yielded diffractograms displaying well-defined peaks, indicative of a γ-phase cubic crystalline structure. Nevertheless, while there has been a favourable improvement in the anti-corrosion parameters associated with the increased Ni composition in the coating, it remains imperative to assess the degree of hydrogen content retained throughout the electrodeposition process. It is well known that the nickel content of the coating is a factor in the amount of hydrogen adsorbed during the electroplating process. This, in turn, has the potential to influence the permeation of the coating into the base metal as a result of the synergistic effect of the coating composition. The intensity of the hydrogen adsorption energy is thus dependent upon the aforementioned factors. It is essential to exercise caution with similar base metals that require anti-corrosion protection to prevent them becoming brittle due to hydrogen. In accordance with the findings a reduction in permeation was observed for an intermediate composition of 17.27 wt.% Ni. It was suspected that the interaction between the two elements of the coating may result in a modification of the ratio of reversible and irreversible hydrogen trap sites, which could directly influence the permeation of hydrogen into the base metal.