JOAO VICTOR DE SOUSA ARAUJO

JOAO VICTOR DE SOUSA ARAUJO

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Investigação da atividade eletroquímica de liga Al-Cu-Li após processo de soldagem por fricção e mistura
2023 - SILVA, REJANE M.P. da; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; RAMIREZ, OSCAR M.P.; MACHADO, CARULINE de S.C.; ANTUNES, RENATO A.; COSTA, ISOLDA
In this work, the local electrochemical activity of the zones coupled by Friction Stir Welding (FSW) of an Al-Cu-Li alloy was studied and the results were correlated to the microstructural characteristics of each zone. Electrochemical studies were carried out in the zones affected by welding using cyclic voltammetry (CV) and scanning electrochemical techniques (namely, SECM - Scanning Electrochemical Microscopy and LEIS – Local electrochemical impedance spectroscopy). The results showed that the welding joint (WJ) is predominantly cathodic relatively to the heat affected zones (HAZ). The HAZ was always anodic and showed the highest electrochemical activities among the tested ones. The high electrochemical activity of the HAZ was associated with the effect of galvanic coupling between the cathodic region (WJ) and the anodic region (HAZ). In addition, the advancing side (AS) presented increased electrochemical activity compared to the retreating one (RS).
Surface finishing effects on the corrosion behavior and electrochemical activity of 2098-T351 aluminum alloy investigated using scanning microelectrochemical techniques
2022 - SILVA, REJANE M.P. da; MILAGRE, MARIANA X.; IZQUIERDO, JAVIER; BETANCOR-ABREU, ABENCHARA M.; OLIVEIRA, LEANDRO A. de; ARAUJO, JOAO V. de S.; ANTUNES, RENATO A.; SOUTO, RICARDO M.; COSTA, ISOLDA
The effects of surface finishing on the corrosion behavior and electrochemical activity of AA2098-T351 (Al–Cu–Li alloy) were investigated on the basis of the correlation between surface chemistry, microstructure and electrochemical activity. The alloy was evaluated in the as-received and polished conditions. The morphology of the two types of surfaces was investigated using confocal laser scanning microscopy (CLSM), optical microscopy and optical 3D profilometry. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). Scanning microelectrochemical techniques (namely, localized electrochemical impedance spectroscopy (LEIS), the scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM) in potentiometric mode) were used to examine the electrochemical activity of the surfaces. The results showed that on the as-received surface, the near surface deformed layer (NSDL), which is composed of Mg-rich bands, influenced the corrosion activity of the alloy. Higher electrochemical activity and greater susceptibility to severe localized corrosion were related to the polished surface condition compared to the as-received one.
Electrochemical characterization of alloy segregation in the near-surface deformed layer of welded zones of an Al-Cu-Li alloy using scanning electrochemical microscopy
2022 - SILVA, REJANE M.P. da; IZQUIERDO, JAVIER; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; ANTUNES, RENATO A.; SOUTO, RICARDO M.; COSTA, ISOLDA
The development of heterogeneous electrochemical activity in the welded zones of aluminum alloy 2098-T351 by friction stir welding (FSW) associated with the formation of a near-surface deformed layer (NSDL) upon exposure to an aqueous chloride-containing solution was characterized using scanning electrochemical microscopy (SECM) in potentiometric operation. A solid-contact Mg2+ ion-selective microelectrode allowed in situ monitoring of the corrosion reactions sites for magnesium dissolution from different zones of the FSW weld upon exposure to a chloride-containing aqueous environment. In this way, localized corrosion reactions developing in the galvanically coupled joint/heat affected zones (WJ/HAZ) of the weld were detected and imaged with spatial resolution. The most active domains for local Mg2+ concentrations were associated with the HAZ of the retreating side (RS), and these corresponded to Mg oxidation from the Mg-enriched oxide bands in NSDL.
Compreendendo os mecanismos de corrosão de ligas de Al-Cu-Li
2022 - ARAUJO, JOAO V. de S.; SILVA, REJANE M.P. da; VIVEIROS, BARBARA V.; MILAGRE, MARIANA X.; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
In this study, the corrosion mechanism of an Al-Cu-Li alloy manufactured by two different treatment routes (T3 and T851) was evaluated by immersion and electrochemical tests in solutions containing chloride ions (Cl-). For both alloys, the formation of cavities on the surface was associated with micrometer-sized intermetallics (IM’s), however, in addition to this attack, the alloy submitted to T851 treatment also presented an attack called severe localized corrosion (SLC), caused by the preferential attack to the nanometric T1 (Al2CuLi) phase. The electrochemical concepts involved in these two types of attacks were discussed. During the IM’s corrosive process, whereas the O2 reduction occurred over the IM’s, the Al dissolution is favored around the particle, forming trenching and cavities (with 2 and 6 mm of depth). On the other hand, the mechanism associated with the SLC is related to the formation of a differential aeration cell followed by the evolution of H2, with greater depth of attack penetration (8 and 35 mm). Additionally, by the use of the Scanning Vibrating Electrode Technique (SVET), it was concluded that the higher anodic currents observed for the T851 temper were related to the relation between the anodic area (Aa) and the cathodic area (Ac).
TSA anodising voltage effects on the near-surface coarse intermetallic particles in the AA2024-T3 and AA2198-T8 alloys
2022 - ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; KLUMPP, RAFAEL E.; AYUSSO, VICTOR H.; DONATUS, UYIME; COSTA, ISOLDA
In this study, the behaviour of the micrometric particles of the AA2198-T8 alloy during anodising at various voltages and the effect of anodising voltage on the anodised surface morphology have been investigated in a tartaric-sulfuric acid anodising solution. The results were compared with that of the AA2024-T3 alloy. For the AA2198-T8 alloy, partial dissolution of these particles occurred at 0, 3 and 4 V. Besides, for potentials above 5 V, there is a preferential dissolution of the intermetallic particles. For the AA2024-T3 alloy, the results indicated a total dissolution of the micrometric particles at 0 V and a partial dissolution at 3 V, whereas above 4 V total dissolution occurred. Between 1 and 2 V, no dissolution was observed for both alloys. The preferential dissolution of the micrometric particles resulted in defects in the anodic film and cavities on the anodised surfaces.
Corrosion resistance of precipitation-hardened Al alloys
2021 - DONATUS, UYIME; BODUNRIN, MICHAEL O.; OLAYINKA, AYOTUNDE; MILAGRE, MARIANA X.; OLOYEDE, OLAMILEKAN R.; ARIBO, SUNDAY; ARAUJO, JOAO V. de S.; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
The corrosion resistance of conventional (AA2024-T3, AA6082-T6 and AA7050-T7451) and the new generation (AA2050-T84, AA2098-T351, AA2198-T8, and AA2198-T851) precipitation-hardened alloys has been studied and compared using electrochemical and non-electrochemical approaches. The AA6082-T6 was the most resistant alloy followed by the new generation Al-Cu-Li alloys, except the AA2050-T84. All the alloys exhibited pseudo-passivity, except for the AA2024-T3 alloy which presented the highest number of pitting sites per cm2 and also exhibited the most insidious form of corrosion amongst the alloys tested. However, the alloy with the highest corrosion depth was the AA2050-T84 alloy followed by the AA2024-T3 and AA7050-T7451 alloys. Intergranular corrosion was associated with rapid rates of penetration. In addition to the microstructural features of the alloys before corrosion, the modes of localized corrosion in the alloys were also influenced by evolving microstructural features (such as re-deposited Cu) during corrosion.
O processo de anodização do alumínio e suas ligas
2021 - ARAUJO, JOAO V. de S.; SILVA, REJANE M.P. da; KLUMPP, RAFAEL E.; COSTA, ISOLDA
Al and its alloys are found in several industrial applications. However, like most metals, this material is not immune to corrosion, being necessary to be protected against corrosion. One of the methods most commonly employed to improve the corrosion resistance of Al alloys is the anodizing process, which consists of thickening of the natural oxide (Al2O3) presents in Al through anodic oxidation. The anodizing process is accomplished by immersion of the Al alloy into an acid bath and passing an electric current through it. This process produces two layers: a barrier layer thicker than the natural oxide and a layer with regular arrangement of nanopores (porous layer). This duplex structure forms the anodized layer with a large specific surface area. With the advent of nanotechnology, this layer has been applied in other areas due to its low cost, stability, absence of toxicity, and biocompatibility. In this context, this paper addresses a historical and electrochemical review of the anodizing process of Al and its alloys, presenting the main events that culminated in the development of the current processes and the understanding of the relationship between the chemical reactions and the mechanisms that occur during nucleation and development of the oxide layer.
How microstructure affects localized corrosion resistance of stir zone of the AA2198-T8 alloy after friction stir welding
2021 - MACHADO, CARULINE de S.C.; DONATUS, UYIME; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; VIVEIROS, BARBARA V.G. de; KLUMPP, RAFAEL E.; PEREIRA, VICTOR F.; COSTA, ISOLDA
In this study, the microstructure and corrosion resistance of the stir zone (SZ) of the AA2198-T8 Al-Cu-Li alloy welded by friction stir welding (FSW) were investigated by microscopy, immersion tests and electrochemical techniques such as measurements of open circuit potential variation with time, and scanning vibrating electrode technique (SVET) measurements. A low chloride-containing solution (0.005 mol L−1 NaCl) was employed in the corrosion studies and severe localized corrosion (SLC) was observed in the SZ related to intergranular attack. The results were compared to those of the non-affected areas by FSW, also known as base metal (BM). In the BM, SLC was found and the type of attack related to it was intragranular. In both zones, BM and SZ, SLC was due to precipitates of high electrochemical activity, specifically T1 (Al2CuLi) phase in the BM, whereas TB (Al7Cu4Li) / T2 (Al6CuLi3) in the SZ. Scanning vibrating electrode technique (SVET) analysis was very useful in the study of SLC in the AA2198-T8 alloy showing the development of high anodic current densities at the mouth of the SLC sites.
Mecanismo de evolução de hidrogênio durante a corrosão da liga 2198-T8 em meio contendo cloreto
2020 - ARAUJO, JOAO V. de S.; SILVA, REJANE M.P. da; MILAGRE, MARIANA X.; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
Corrosion is still one of the most serious and frequent problems in industries. The phenomena involved in the corrosion mechanism of Al-alloys may be explained by formation of galvanic cells between the metal matrix and heterogeneities, such as precipitates, intermetallic phases leading to potential differences and electrochemical reactions. In the cathodic sites, the main reactions are oxygen reduction reaction, in aerated neutral environments, and hydrogen evolution in acid media. This last type of reaction might also occur in neutral solutions inside pits (anodic region). In this study, the mechanism of hydrogen evolution during corrosion of the 2198-T8 Al-Cu-Li alloy exposed in a chloride solution was investigated. The mechanism was related to the presence of T1 phase (Al2CuLi), which is the main strengthening phase in this material. This phase is highly active and, when exposed to corrosive media, leads to severe localized corrosion (SLC). One of the main characteristics related to SLC is hydrogen gas evolution which was confirmed by gel visualization. In this study, the hydrogen evolution mechanism inside the SLC sites was studied by scanning electrochemical microscopy (SECM).
Exfoliation and intergranular corrosion resistance of the 2198 Al–Cu–Li alloy with different thermomechanical treatments
2020 - ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; FERREIRA, RAPHAEL O.; MACHADO, CARULINE de S.C.; BUGARIN, ALINE de F.S.; MACHADO, IZABEL F.; COSTA, ISOLDA
In this study, the resistance to exfoliation and intergranular corrosion (IGC) of the 2198 Al–Cu–Li alloy submitted to different thermomechanical treatments (T3, T8, and T851) was investigated. The tests were carried out following the standard practices, ASTM G34‐18 and ASTM G110‐15, respectively. All the tested alloys showed susceptibility to exfoliation and some alloys showed susceptibility to IGC, but the artificially aged alloys presented a higher tendency to exfoliation. The extensive hydrogen evolution reaction (HER) was observed on the surfaces of artificially aged alloys when immersed in the EXCO solution. The HER resulted in an increase in solution pH with the time of immersion. Also, the weight losses related to the artificially aged alloys were higher than that of the naturally aged ones. The T8 treatment was the only condition that resulted in susceptibility to both, intergranular and transgranular corrosion, whereas the T851 treatment did not show IGC susceptibility, only transgranular corrosion. Finally, the 2198‐T3 condition showed the highest corrosion resistance among the thermomechanical treatments tested. The results of the 2198 alloy subjected to various treatments were compared with that of the 2024‐T3 alloy. This last alloy showed higher resistance to exfoliation and IGC as compared with the 2198 alloy.