Effect of anodic treatment on the composition and structure of electrodeposited Zn–Cr alloy coatings

The anodic behaviour of Zn–Cr alloy coatings, containing 14–28 at.% of Cr is investigated in 1 M Na2SO4 solution using electrochemical methods. The alterations of the composition and structure caused by anodic treatment, are examined by means of EDX, XRD, XPS and SEM. Independently of the initial Cr content in the alloys the η-Zn phase and depleted of Cr bcc Γ-(Zn,Cr) phase are dissolving at potentials more positive than that of Zn. Further dissolution of the Γ-(Zn,Cr) phase is established at a potential close to the potential of trans-passive dissolution of Cr. A thin Γ-(Zn,Cr) layer, containing about 40 at.% of Cr, remains and is mechanically disintegrated after the potential of oxygen evolution is reached. [Copyright &y& Elsevier]