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In recent years, automotive component manufacturer's use of autodeposited coatings has dramatically increased due to the performance, cost-effectiveness, versatility and environmental advantages that this technology offers. Although historically used to coat only steel substrates, the increased use of zinc and zinc alloy coatings presents further market opportunity for autodeposition of coatings. Due to differences in chemical reactivity between steel and zinc, obtaining high quality coatings by acidic chemical deposition (autodeposition) has required some process development innovations. In this paper, the procedure of coating deposition on galvanized surfaces is described and compared to the deposition on steel. Corrosion performance of autodeposited coatings on galvanized steel is evaluated by a cyclic corrosion test and compared to the performance of another widely used coating for galvanized substrates.

In recent years, automotive component manufacturers' use of autodeposited coatings has steadily increased due to the performance, cost-effectiveness, and environmental advantages that this technology offers. This paper presents a comparison of corrosion performance test results for autodeposited coatings and several other commonly used coatings employed to protect vehicle underbody components.

The corrosion resistance of 0 to 15% Ni-Zn electroplated alloy coatings was examined using salt-spray, cyclic corrosion and electrochemical tests. Our findings support those of previous investigations showing that the single phase (gamma) 11 to 15% Ni-Zn coatings provide the best barrier protection for unpainted applications, while the pure Zn coatings provide the highest level of galvanic protection. However, we have found that dual phase (gamma + eta) 9% Ni-Zn coatings appear to provide the best compromise between galvanic and barrier corrosion protection, and a minimum amount of paint delamination. In addition, we found that deformation, similar to body panel stamping, does not have a significant effect on the corrosion resistance of the pure Zn and low Ni-content coatings. However, deformation does produce cracking and a reduction in corrosion resistance for unpainted samples having higher Ni-content coatings.