Anodic degradation of Zn-Ni coatings in moderately alkaline NaCl solution

•Zinc dissolution in alkaline NaCl generates mud-crack patterns in Zn-Ni coatings.•Simonkolleite grows on the coating and on the underlying steel substrate.•The compactness of the simonkolleite layer is revealed by FIB-SEM.•The barrier properties of simonkolleite are reflected in its high impedance values.