Improved surface morphology and corrosion resistance for galvannealed coatings by pre-electroplating iron

Dual-phase steel was electroplated with Fe prior to reduction annealing to improve surface quality and corrosion characteristics after galvannealing. This pre-electroplating process caused remarkable reduction in surface cracks and induced δ-phase formation over the surface of the galvannealed coating. Moreover, the degree of Fe–Zn alloying significantly increased, resulting in a thicker coating. Consequently, the corrosion potential increased and corrosion current decreased in the highly polarized anodic reaction. Further, spontaneous passivation occurred, resulting in a very low corrosion rate.

► Galvannealed steel pre-electroplated with Fe.
► Fe pre-electroplating on dual-phase steel for the suppression of oxide formation during reduction annealing.
► Fe pre-electroplating remarkably reduced in surface defects and improved homogeneity of the galvannealed coating.
► Degree of Fe–Zn alloying increased, resulting in a thicker coating.
► Corrosion resistance increased and, further, spontaneous passivation occurred.