Obtenção e caracterização de revestimentos metálicos de Zn-Ni-P depositados sobre o aço API 5L X65.

Abstract

This work presents a study of a metallic coating of the Zn-Ni-P alloy obtained on an API 5L X65 steel substrate and its main characterizations regarding chemical composition, crystalline and grain structure and resistance to corrosion. Zn-Ni-P alloy is a current proposal for comparison with the protection methodologies currently used in the petroleum, aeronautics and even automotive industries that often present toxic chemical elements in their composition, such as Cadmium. The interest in the comparison arises from the understanding that corrosion protection techniques are in constant evolution and study to offer the lowest possible risk in the accomplishment of the tasks, be it human or environmental risk. Zn-Ni alloys are known to provide a cathodic type protection to ferrous substrates, increasing the interest of evaluating the behavior of the corrosion resistance of the substrate + coating set in an environment that simulates the corrosive action. The coatings studied were obtained from the electrodeposition technique with variation of current density and temperature, in a range of 34 to 76 mA / cm² and 38 to 64ºC, respectively. The coatings were characterized regarding the structure and morphology of the deposit on the steel surface. Analysis of the structure showed a uniform crystalline structure, in most of the experiments, and the appearance of oxides. The study of the morphology revealed the presence of small and compacted nodules for the best result of resistance to corrosion. As for the evaluation of the corrosion resistance, the coatings were submitted to a corrosive medium, a solution of NaCl (3.5%) simulating the sea water. For the best result a resistance of 6,119γ kΩ and corrosion current of β7,β81 μA was obtained.