Improvement in Coating Quality and Corrosion Characteristics of Galvanized Steels by Pre-Electrodeposition of Cu

A dual-phase steel was electrodeposited with Cu prior to reduction annealing in order to improve coating quality and resultant corrosion characteristics of the galvanized material. This pre-eletrodeposition process allowed a tenfold reduction in coating defects (typically found in uncoated areas and empty pores), thereby yielding a 8.4% coating weight gain and a noticeable decrease (24%) in the average spangle diameter. However, the Cu pre-electrodeposition layer acted as an inter-diffusion barrier, thereby limiting Fe-Al interactions during galvanization, and resulted in the formation of imperfect Fe-Al compounds. Nevertheless, this Cu layer could extend the incubation time of the Fe-Zn phases. Consequently, the presence of this Cu electrodeposition layer could effectively prevent concentration polarization, thereby decreasing corrosion current density even after 4 days of immersion in 3.5% NaCl solution. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.010211jes] All rights reserved.