JOAO VICTOR DE SOUSA ARAUJO

JOAO VICTOR DE SOUSA ARAUJO

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Intergranular corrosion susceptibility of Al-Cu-Li alloys
2017 - MILAGRE, MARIANA X.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.; ASTARITA, ANTONELLO; PEBERE, NADINE; VIVIER, VINCENT; COSTA, ISOLDA
In the present study, the intergranular corrosion (IGC) susceptibility of commercial Al-Cu-Li alloys of the third generation (AA2098-T351, AA2198-T3 and AA2198-T851) was compared with that of the AA2024-T3 alloy according to ASTM G110 test. In addition, anodic and cathodic polarization curves were carried out in the ASTM G110 test solution at room temperature. The cross-section of the samples after the ASTM G110 test was observed by scanning electron microscopy (SEM) to evaluate the extension of the corrosion attack. The susceptibility to intergranular attack of the tested alloys was ranked according to the attack by IGC and from the anodic and cathodic polarization curves. The results showed that the AA2024-T3 and the AA2198-T3 alloys presented higher susceptibility to intergranular corrosion comparatively to the other alloys tested (AA2098-T351 and AA2198-T851). The AA2098-T351 alloy was associated to the highest resistance to intergranular attack among the alloys evaluated. A correlation was seemingly established between the stress relief treatment of the alloy and its corresponding susceptibility to intergranular or intragranular corrosion.
Effects of chloride ion concentration on the corrosion behavior of the AA2198-T8 alloy
2019 - MACHADO, CARULINE de S.C.; SILVA, REJANE M. da; ARAUJO, JOAO V. de S.; DONATUS, UYIME; MILAGRE, MARIANA X.; KLUMPP, RAFAEL E.; ROSSI, JESUALDO L.; COSTA, ISOLDA
In this work, the influence of chloride ions concentration on the corrosion behavior of the AA2198-T8 alloy was evaluated. Immersion test and electrochemical analyses were performed in sodium chloride solutions of three concentrations, 0.001 mol L-1, 0.005 mol L-1 and 0.01 mol L-1. The results showed that the AA2198-T8 alloy was susceptible to localized corrosion (LC) and to severe localized corrosion (SLC) in all conditions investigated. The electrochemical results obtained by open circuit potential measurements, cyclic voltammetry and potentiodynamic polarization curves were associated with the corroded microstructure of the alloy. Although electrochemical techniques allowed differentiating the corrosion resistance as a function of chloride concentration, the result was strongly influenced by the corroded/uncorroded area ratio related to the SLC.
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.
Macro and microgalvanic interactions in friction stir weldment of AA2198-T851 alloy
2019 - DONATUS, UYIME; SILVA, REJANE M.P. da; ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; ABREU, CAIO P. de; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
The galvanic interactions within and between the friction stir weld zones of the AA2198-T851alloy have been investigated using electrochemical and microscopy techniques. The parentmaterial (PM) was the most anodic region and exhibited pronounced severe localized corro-sion (SLC) both when coupled and isolated. The stir zone was the most resistant to corrosionand exhibited no SLC when coupled, but exhibited SLC when isolated. Profiles associatedwith dissolved oxygen consumption and hydrogen generation currents across the weldmentwere inversely related because the anodic (PM) region produced higher hydrogen bubblesand, interestingly, consumed more dissolved oxygen compared with the other regions.
Exfoliation corrosion susceptibility in the zones of friction stir welded AA2098-T351
2019 - MILAGRE, MARIANA X.; DONATUS, UYIME; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; FERREIRA, RAPHAEL O.; SILVA, REJANE M.P.; ANTUNES, RENATO A.; COSTA, ISOLDA
In the present study, the exfoliation susceptibility of the weld zones in friction stir weldedAA2098-T351 was compared with that of the base metal (BM) according to ASTM G34 stan-dard practice. Friction stir welding (FSW) had a significant effect on the microstructure of theAl alloy tested and the susceptibility to exfoliation was strongly affected by the microstruc-ture. Different features of corrosion attack and exfoliation susceptibility were observed whenthe zones affected by FSW were tested isolated or coupled. Also, the near-surface deformedlayer had an important effect on the Al alloy susceptibility to exfoliation. These are themain findings of this work. The corrosion features were correlated with the microstructuralmodifications related to the welding process and with the electrochemical response. TheT1 phase morphology, distribution and size were critical for exfoliation susceptibility. Thestir zone (SZ) was the zone most resistant to exfoliation. However, resistance to exfoliationvaried with the temperatures reached in the heat affected zones (HAZs). The HAZ exposedto the lowest temperatures during welding, HAZ (LT), was the most susceptible to exfoli-ation, whereas the HAZ exposed to the highest temperatures, HAZ (HT), presented highresistance to exfoliation, similarly to the SZ. The ASTM-G34 practice was an effective anduseful method in identifying the different exfoliation resistances of the BM and the vari-ous zones affected by FSW. The results of this practice were supported by electrochemicalimpedance spectroscopy (EIS) tests.
Microstructural characterization and corrosion behavior of a commercial friction stir welded AA2024-T3
2018 - QUEIROZ, FERNANDA M.; ARAUJO, JOAO V.S.; TERADA, MAYSA; LAMAKA, SVIATLANA; COSTA, ISOLDA; MELO, HERCILIO G. de
Friction Stir Welding (FSW) arises as a great development by removing rivets, fasteners and lap joints areas, consequently, decreasing the aircraft weight. However, during the welding process, the plastic deformation and heat generation at the joint and surrounding areas lead to three distinct microstructural zones, namely, nugget or stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ), besides the base metal (BM). In these zones the microstructure of the material can be profoundly modified and localized corrosion phenomena can be more easily developed, which can be enhanced by local galvanic coupling due to changes in the microstructure as grain refinement and recrystallization, changes in the grain boundaries, dissolution and precipitation of hardening precipitates and dispersóides. In the present work, a commercial friction stir welded AA2024-T3 had its microstructure characterized by Electron Backscatter Diffraction (EBSD) technique and optical microscopy (OM). The corrosion behavior was investigated by exfoliation corrosion (EXCO) test and the intergranular corrosion susceptibility according to ASTM G110-97. After all tests, the samples were observed by scanning electron microscopy (SEM). EBSD results revealed the evolution of microstructure as a result of FSW. The base metal showed elongated grains along the rolling direction with a pancake-like non-recrystallized structure. The SZ undergone dynamic recrystallization showing finer equiaxed grains as a result of a significant plastic deformation and heating during the welding process. The TMAZ of the advancing side showed recrystallized finer grains, while the TMAZ of the retreating side showed coarse grains. Finally, the HAZ of both advancing and retreating sides showed grains typically elongated caused by the thermal input. The EXCO and intergranular tests showed a more intense attack in the TMAZ of the retreating side in agreement with the corrosion morphology observed by SEM.
Effect of surface treatments on the localized corrosion resistance of the AA2198‐T8 aluminum lithium alloy welded by FSW process
2019 - MACHADO, CARULINE de S.C.; KLUMPP, RAFAEL E.; AYUSSO, VICTOR H.; DONATUS, UYIME; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; MACHADO, GLAUSON A.F.; COSTA, ISOLDA
In this work, the effect of eight types of surface treatments on the corrosion resistance of friction stir welded samples of an AA2198‐T8 Al‐Cu‐Li alloy were tested and compared in an attempt to find suitable alternatives to toxic and carcinogenic hexavalent chromium treatments. All the samples were anodized and subjected to different post‐anodizing treatments. The post‐anodizing treatments were (1) hydrothermal treatment in Ce (NO3)3 6H2O solution; (2) hydrothermal treatment in Ce (NO3)3 6H2O solution with H2O2; (3) hydrothermal treatment in boiling water; (4) hexavalent chromium conversion coating; and (5) immersion in BTSE (bis‐1,2‐(triethoxysilyl) ethane. The corrosion resistance of the treated samples was evaluated by immersion tests in sodium chloride solution (0.1 mol L−1 NaCl) and electrochemical impedance spectroscopy (EIS) of the friction stir weldment. The results showed that among the alternative treatments, the Ce‐containing solutions presented the best corrosion resistance, especially when used without peroxide.
Thermomechanical treatment and corrosion resistance correlation in the AA2198 Al–Cu–Li alloy
2019 - ARAUJO, JOAO V. de S.; BUGARIN, ALINE de F.S.; DONATUS, UYIME; MACHADO, CARULINE de S.C.; QUEIROZ, FERNANDA M.; TERADA, MAYSA; ASTARITA, ANTONELLO; COSTA, ISOLDA
The influence of T3, T8 and T851 thermomechanical treatments on the microstructure and corrosion resistance of the AA2198 was investigated. Differential scanning calorimetry and scanning electron microscopy were used for microstructural characterisation, whereas electrochemical methods were employed to analyse the corrosion behaviour of the alloy. The morphology and composition of constituent particles were similar for the T3 and T8 thermomechanical treatments but varied in the T851. There was an inverse relation between T1 phase density and corrosion resistance. The T3 treatment with the highest corrosion resistance was the one with the lowest density of T1 phase. The mechanisms of corrosion varied with the thermomechanical treatments.
The effect of manufacturing process induced near-surface deformed layer on the corrosion behaviour of AA2198-T851 Al–Cu–Li alloy
2019 - DONATUS, UYIME; ARAUJO, JOAO V. de S.; MACHADO, CARULINE de S.C.; MOGILI, NAGA V.V.; ANTUNES, RENATO A.; COSTA, ISOLDA
The effect of the near-surface deformed layer on the corrosion behaviour of AA2198-T851 Al–Cu–Li alloy has been investigated using microscopy and electrochemical techniques. This shows that a deformed layer developed by rolling was more active but only exhibited superficial attack compared to a mechanically polished surface, which produced severe localised corrosion associated with the presence of hexagonal T1 particles. The rolled surface became increasingly corrosion resistant with time, but when coupled, galvanically enhanced severe localised corrosion sites developed on the surface over time.
Effect of unequal levels of deformation and fragmentation on the electrochemical response of friction stir welded AA2024-T3 alloy
2019 - QUEIROZ, FERNANDA M.; DONATUS, UYIME; RAMIREZ, OSCAR M.P.; ARAUJO, JOAO V. de S.; VIVEIROS, BARBARA V.G. de; LAMAKA, SVIATLANA; ZHELUDKEVICH, MIKHAIL; MASOUMI, MOHAMMAD; VIVIER, VINCENT; COSTA, ISOLDA; MELO, HERCILIO G. de
The effect of unequal levels of deformation and fragmentation on the electrochemical response of friction stir welded AA2024-T3 has been investigated using electron backscatter diffraction, scanning electron microscopy, global and localized electrochemical techniques. The friction stir welding process introduced unequal distribution and fragmentation of coarse intermetallic particles, such that more clusters of these particles were present in the thermomechanically affected zone of the weld. This resulted in a higher susceptibility to severe localized corrosion in this region when compared with the others. Results from electrochemical measurements using a microcell could not be clearly correlated with the corrosion behaviour because no significant differences were observed using these techniques. On the other hand, LEIS and SVET results were in agreement and correlated with the corrosion evolution at the surfaces of the tested samples.