Avaliação da resistência à corrosão de revestimentos de Zn-Mn eletrodepositados sobre aço carbono 1020 em meio de cloreto de colina e uréia

Abstract

Binary Zn-Mn alloys are widely used in corrosion protection of carbon steel due to their ability to form compact corrosion products when exposed to corrosive media. This work evaluated the morphology, composition, efficiency and corrosion resistance of Zn-Mn coatings electrodeposited from eutectic solvent, choline chloride and Urea (1ChCl:2U), free of additives, on carbon steel at different rotation speeds: 100, 300 and 500 rpm. The chemical analysis of the coatings showed that the increase in rotation speed promoted an increase in the Zn content in the layer, while the deposition of Mn is inhibited. The electrodeposit with the highest Mn content in the layer was obtained from bath II (1ChCl:2U + 0.4 mol L-1 Zn2+ + 0.4 mol L-1 Mn2+), at 100 rpm, under the potential of -1.5 V, at 70°C. The micrographs showed that the morphology of the coatings is affected by the increase in the electrode rotation speed, making them less rough, more homogeneous and less dense, presenting the form of small nodular grains in the agglomerated form, The XRD results revealed crystalline structures of Zn and Mn, with the absence of intermetallic phases constituting the coatings. Despite the electrodeposition efficiency of the Zn84Mn16 coating (bath II) having presented a relatively low deposition current efficiency, approximately 40%, it was found that in the linear polarization test (PPL), it showed a resistance to polarization of 128.6 Ω cm2, a higher value compared to pure Zn, 95.39 Ω cm2. Furthermore, in prolonged immersion tests in 3.5 % NaCl, the Zn84Mn16 coating proved to be 3 times more resistant than pure Zn, suggesting that the increase in Mn the layers optimizes the anticorrosion behavior of Zn-Mn coatings.