The corrosion-protective traits of electroplated multilayer zinc-iron-chromium deposits

A novel kind of three-layer zinciron-cbromium electroplated coating was tested and proven to possess good corrosion protective characteristic as well as acceptable decorative properties. A citric-chloride bath containing Fe(III)-complexes is suggested for electrodeposition of iron intermediate layer on the zinc deposit surface. Due to the low acidity (pH 5) and medium operating temperature (20-30°C), the electrolyte involved has no a strong etching effect and can be used for direct iron deposition on zinc. A finish chromium layer is deposited from formate-sulfate trivalent bath. The zinc layer corrodes through the pores of Fe and Cr layers and protects the steel substrate against corrosion. The iron and chromium layers decelerate the corrosion rate of zinc. The finish chromium layer provides with good decorative properties, and the intermediate iron layer ensures adhesion of chromium to the zinc.