Estudo da liga de Zn-Ni-Cu-P obtida por eletrodeposição em aço 1020 para aplicação como revestimento metalico.

Abstract

The corrosion process is constantly transforming metallic materials so that their durability and performance no longer satisfy their intended purpose. One way to minimize corrosion in metallic materials is to coat them with other materials. Electrodeposition is a method widely used to obtain metallic coatings resistant to corrosion and mechanical wear. Through electrodeposition it is possible to obtain metallic alloys, which are generally prepared in order to improve the properties of their initial constituents. The proposed study aims to optimize the current density, bath temperature and phosphorus concentration variables and obtain the Zn-Ni-Cu-P alloy, characterizing it in terms of morphology, alloy composition, structure, microhardness and corrosion resistance. For the optimization of the alloy electrodeposition process, a 23 full factorial design was used. The electrodeposition process of the alloy on a 1020 steel substrate was studied, using a bath containing copper sulfate, zinc sulfate, nickel sulfate, sodium citrate, sodium hypophosphite and cyanide-free. A Zn-Ni-Cu-P coating was obtained for the first time by the electrodeposition process. It was observed that the increase in current density favored the increase of Ni, Cu and P and the decrease of the Zn content. The increase in temperature caused an increase in the content of Ni, Cu and P and a decrease in the content of Zn. The increase in sodium hypophosphite concentration favored an increase in Zn, Ni and P and a decrease in Cu content. The coatings were shiny and adherent to the steel substrate. The surface morphology of the coatings showed amorphous behavior and the presence of nodules and cracks on the surface. Regarding the corrosion tests, it was found that the nickel content in the coatings obtained directly affected their corrosion resistance, since an increase in the nickel content decreased the corrosion resistance of the coatings. The optimal values found through linear potentiodynamic polarization were: cathodic current density of 55 mA/cm2, temperature of 50 oC and phosphorus concentration of 0.07 M; with these parameters it was possible to reach a corrosion potential of -0.614 V, a polarization resistance of 1.730λ KΩ and a corrosion current of 18.θ4η ȝA. The electrochemical impedance tests confirmed the results obtained by the potentiodynamic polarization tests.