No abstract

Copper-zinc alloy coatings were deposited on mild steel substrates using sodium citrate electrolytes at room temperature and under direct current. For the bath composition studied, factorial design was used to verify the influence of deposition parameters, such as current density and mechanical stirring, on the cathodic efficiency, the contents of copper and zinc, and the amount of hydrogen evolution. Moreover, the four responses were simultaneously studied by using an optimization methodology. The results suggest that the optimum point for reaching good quality copper-zinc alloy deposits from the proposed citrate electrolytes are 29 A m -2 and 247 rpm for bath 3 and 13 A m -2 and 67 rpm for bath 4. Applying these conditions, a yellowreddish coating was obtained from bath 3, while a bright red deposit was produced from bath 4.

Copper-cobalt alloy coatings were deposited on mild steel substrates using sodium citrate electrolytes at room temperature and under direct current. A set of cathodic polarization curves was plotted by varying the mechanical stirring speed of the solution (0-400 rpm), using a range of current densities during the electrodeposition experiments. Factorial design was used to verify the influence of these deposition parameters on the cathodic efficiency, the copper and cobalt content in the coating, the corrosion current density of the coating/substrate system, and the efficiency of the coating in protecting the substrate. The electroplating experiments showed that, with the studied bath composition, high stirring speed and low current density lead to greater cathodic current efficiency and copper-rich coatings. On the other hand, high current density and low stirring speed yields coatings with high cobalt content and a lower cathodic efficiency. Our results show that the studied parameters affect the corrosion current density and the coating efficiency of the coating/ substrate system in opposite ways. The best results were obtained increasing the current density and decreasing the mechanical stirring speed. Additionally, three samples were produced in selected deposition conditions. The coatings morphologies were compact, and their grain sizes seemed to enlarge with increasing stirring speed and decreasing current density.

Alternative electrolytes, such as citrate baths, are now studied, aiming to reduce the toxicity and the cost of the electroplating process while maintaining the decorative qualities and anticorrosive properties of the coatings. For this purpose, brightening and/or leveling compounds are usually added to the base citrate bath. In this work, Cu-Zn alloys were electroplated on mild steel substrates from electrolytes containing sodium citrate and additives (benzotriazole and cysteine) at constant stirring speed. The results showed that coatings produced from baths containing additives were brighter than those obtained from the base citrate bath. Additionally, the presence of benzotriazole directly influenced the coating composition and the properties of the deposited alloy: the amount of zinc in this coating increased excessively, and the coating/substrate corrosion presented a poor anticorrosive performance.