JOAO VICTOR DE SOUSA ARAUJO

JOAO VICTOR DE SOUSA ARAUJO

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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.
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.
Correlating the modes of corrosion with microstructure in the friction stir welded AA2198-T8 alloy in aqueous hydrogen peroxide-chloride medium
2019 - MACHADO, CARULINE de S.C.; DONATUS, UYIME; MILAGRE, MARIANA X.; MOGILI, NAGA V.V.; GIORJÃO, RAFAEL A.R.; KLUMPP, RAFAEL E.; ARAUJO, JOAO V. de S.; FERREIRA, RAPHAEL O.; COSTA, ISOLDA
In this study, different types of localized corrosion in the friction stir welding (FSW) zones of an AA2198-T8 when the alloy is subjected to a corrosion test in a hydrogen peroxide–chloride solution (according to ASTM G110 standard) has been investigated. The corrosion modes were correlated with microstructure, especially with respect to the T1 phase and coarse Al-Cu-Fe phase distribution across the weldment. Simulated thermal profile and microhardness measurements were used to establish the variations in T1 phase distribution. Two types of corrosion were observed in the FSW zones: intense pitting and intergranular corrosion—type I; and the formation of cavities and trenches—type II. Type I is associated with the T1 phase while type II is associated with Al-Cu-Fe coarse intermetallics. Both types were found on the base metal (BM) and heat affected zone, but the type I reduced in the latter toward the stir zone (SZ). The SZ/thermomechanically affected zone (TMAZ) exhibited only type II. Also, Cu enrichment was observed around the type II sites in the SZ/TMAZ. Furthermore, an inverse correlation between microhardness and corrosion resistance which was related to T1 phase concentration in the different zones was also observed. Moreover, the SZ and BM were isolated and evaluated by an immersion test and electrochemical analysis using the ASTM G110 test solution. The results indicated galvanic coupling effects, as the SZ was strongly attacked when exposed separately compared to when it was coupled with the other zones.
Estudo da influência dos tratamentos termomecânicos T8 e T851 na microestrutura e no comportamento de corrosão da liga AA2198
2018 - ARAUJO, JOAO V. de S.; XAVIER, MARIANA M.; MACHADO, CARULINE S.C.; QUEIROZ, FERNANDA M.; COSTA, ISOLDA
Al-Cu-Li alloys present advantages in relation to conventional Al-Cu alloys in applications for aerospace industry due to their low density and good mechanical properties. The mechanical properties of these alloys depend on their microstructure and this is affected by the thermomechanical treatments to which the materials are submitted during their fabrication process. In the present study, the effects of T8 and T851 thermomechanical treatments on the corrosion resistance of the AA2198 alloy were compared. The main hardening precipitate in Al-Cu-Li alloys is the T1 phase, (Al2CuLi). The presence of this precipitate in the AA2198-T8 and T851 alloys was analyzed by transmission electron microscopy (TEM). The microstructure of both alloys was evaluated by Vickers micro hardness and differential scanning calorimetric (DSC) measurements and the results obtained were correlated. The results showed higher density of T1 phase for the T851 condition. Besides, microstructural characterization revealed elongated grains for the T8 condition and equiaxed grains for T851 condition. These results were related to the corrosion behavior of both alloys by immersion and gel visualization tests.
Estudo da influência dos tratamentos termomecânicos T8 e T851 na microestrutura e na resistência à corrosão da liga AA2198
2018 - ARAUJO, JOAO V. de S.; XAVIER, MARIANA M.; MACHADO, CARULINE S.C.; QUEIROZ, FERNANDA M.; COSTA, ISOLDA
Ligas de Al-Cu-Li têm mostrado grandes vantagens em relação às convencionais ligas de Al-Cu usadas na indústria aeroespacial, devido as boas propriedades mecânicas e baixa densidade. As propriedades mecânicas destas ligas dependem de sua microestrutura e esta por sua vez dos tratamentos termomecânicos na qual as ligas são submetidas durante o processo de fabricação. Neste estudo os efeitos de dois tratamentos termomecânicos, T8 e T851, na resistência a corrosão da liga AA2198 foram comparados. O principal precipitado endurecedor destas ligas, a fase T1 (Al2CuLi), foi analisada por microscopia eletrônica de transmissão (TEM). Os resultados de microestrutura, microdureza e calorimetria diferencial de varredura (DSC) mostraram diferenças para as ligas com os dois tratamentos. A liga submetida ao tratamento T851 mostrou maior densidade de fase T1. Além disso, a caracterização microestrutural revelou grãos alongados para o tratamento T8 e grãos equaxiais para tratamento T851. Estes resultados foram comparados com os do ensaio de imersão e de visualização em gel.
Avaliação da resistência a corrosão intergranular da liga AA 2198-T851 soldada pelo processo FSW
2016 - MACHADO, C.S.C.; MILAGRE, M.X.; ARAUJO, J.V.; TERADA, M.; COSTA, I.
In this work, the intergranular corrosion resistance of the Al-Cu-Li AA2198- 851 alloy, welded by friction stir welding (FSW) has been evaluated by ASTM G110-97 procedure. There was no susceptibility to intergranular corrosion of this alloy in the tested conditions.
Influência dos tratamentos termomecânicos t851 e t3 na resistência à corrosão localizada da liga AA2198
2016 - ARAUJO, JOAO V. de; COSTA, ISOLDA