| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeM |
| Session: | Thin Film Synthesis and Characterization II |
| Presenter: | Wonhwi Lee, POSCO, Republic of Korea |
| Correspondent: | Click to Email |
Electrogalvanized steel sheets are widely used in automobiles, building interior decorations and home appliances because of its excellent surface uniformity and formability. Among the wide areas of its applications, barely post-treated electrogalvanized steel sheets used in home appliances are processed no further treatments but to form essential resin coating layers for the functions of anti-fingerprinting or Chromate-free. In this case, it is a key quality to have uniformity and good whiteness of its surface.
However, the electrogalvanized zinc layer with partially oriented and enlarged grains is normally produced due to the epitaxial growth along the iron substrate. The oriented zinc grains on the surface lead to the dispersion of reflecting light that results in lowering whiteness.
In addition, iron oxide scales or oil stains remained on the substrate even after the all pre-treatments of rinsing, degreasing and pickling processes may induce poor uniformity of the galvanized surface.
To solve these problems which are derived from the iron substrate, some manufacturers have created a nickel nano-layer on a substrate. The deposition of the nickel layer on a substrate has brought a galvanized surface not only the uniformity but also the better whiteness. This is because the nickel layer significantly enhances the quality of deposited zinc since the condition of substrate is no longer transferable. Recently, however, its high cost as a raw material and harmful fumes during welding processes have arisen as critical problems to solve.
In this article, we suggest to deposite a thin film of a single or as an alloy of transition metals between the deposited zinc and the iron substrate. The thin layers were made by electrodeposition method and several transition metals were selected for the coating materials. These coating materials were electrodeposited with the coating weights in the range of 10 to 50mg/m2. The results show that the better whiteness and uniformity of the galvanized zinc can be achieved by the thin layer which minimizes the influences from the substrate and interrupts coarsening of zinc grains as well. Furthermore, it is a remarkable finding that the zinc grains are randomly oriented on the surface with much smaller sizes.