JOAO VICTOR DE SOUSA ARAUJO

JOAO VICTOR DE SOUSA ARAUJO

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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.
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.
Galvanic and asymmetry effects on the local electrochemical behavior of the 2098-T351 alloy welded by friction stir welding
2020 - MILAGRE, MARIANA X.; DONATUS, UYIME; MOGILI, NAGA V.; SILVA, REJANE M.P.; VIVEIROS, BARBARA V.G. de; PEREIRA, VICTOR F.; ANTUNES, RENATO A.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; COSTA, ISOLDA
Scanning electrochemical microscopy (SECM) and scanning vibrating electrode technique (SVET) were used to investigate the electrochemical behaviour of the top surface of the 2098-T351 alloy welded by friction stir welding (FSW). The SVET technique was efficient in identifying the cathodic and anodic weld regions. The welding joint (WJ), which comprises the thermomechanically affected zone (TMAZ) and the stir zone (SZ), was cathodic relative to the heated affected zone (HAZ) and the base metal (BM). The reactivities of the welding joint at the advancing side (AS) and the retreating side (RS) were analyzed and compared using SECM technique in the competition mode by monitoring the dissolved oxygen as a redox mediator in 0.005 mol L−1 NaCl solution. The RS was more electrochemically active than the AS, and these results were correlated with the microstructural features of the welded alloy.
The effect of acid pickling on the corrosion behavior of a cerium conversion-coated AA2198-T851 Al-Cu-Li alloy
2020 - KLUMPP, RAFAEL E.; DONATUS, UYIME; ARAUJO, JOAO V.S.; REDÍGOLO, MARCELO M.; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
The effect of acid pickling pretreatments prior to cerium conversion coating process on the corrosion behavior of AA2198-T851 alloy substrates was investigated. Three acid pretreatments were employed: nitric acid (HNO3), phosphoric acid (H3PO4) and sulfuric acid (H2SO4). The cerium conversion coating process was performed using a batch solution composed of cerium nitrate and hydrogen peroxide. Microscopic techniques, electrochemical impedance spectroscopy, polarization resistance and open-circuit potential measurements were employed to investigate the effect of each acid pretreatment. The untreated and nitric acid pretreated substrates presented more defective cerium conversion layers than the substrates treated with phosphoric and sulfuric acids. Accordingly, the corrosion resistance of the untreated and nitric acid-treated substrates was very low, while that of the substrates treated with phosphoric acid and sulfuric acids were greatly improved. The sulfuric acid pickling treatment was the best pretreatment before cerium conversion coating among the investigated pretreatments on the AA2198-T851 Al-Cu-Li alloy.
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.
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.
Comparison of the corrosion resistance of an Al–Cu alloy and an Al–Cu–Li alloy
2019 - MILAGRE, MARIANA X.; DONATUS, UYIME; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; SILVA, REJANE M.P. da; VIVEIROS, BARBARA V.G. de; ASTARITA, ANTONELLO; COSTA, ISOLDA
In this study, the corrosion mechanisms of the AA2024-T3 and the AA2098-T351 were investigated and compared using various electrochemical techniques in 0.005 mol L−1 NaCl solution. The severe type of corrosion in the AA2098-T351 was intragranular attack (IGA) although trenching and pitting related to the constituent particles were seen. On the other hand, the AA2024-T3 exhibited severe localised corrosion associated with micrometric constituent particles, and its propagation was via grain boundaries leading to intergranular corrosion (IGC). Electrochemical techniques showed that the corrosion reaction in both alloys was controlled by diffusion. The non-uniform current distribution in both alloys showed that EIS was not a proper technique for comparing the corrosion resistance of the alloys. However, local electrochemical techniques were useful for the evaluation of the corrosion resistance of the alloys.
Comparison of the corrosion resistance of AA2024 and AA2098 alloys in different solutions
2018 - MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; GOMES, MAURILIO P.; DONATUS, UYIME; MACHADO, CARULINE S.C.; COSTA, ISOLDA
In this work the corrosion resistance of the AA2098-T351 and AA2024-T3 was evaluated and compared by electrochemical tests in 0.01 mol.L-1 of NaCl and 0.1 mol.L-1 of Na2SO4 with 0.001 mol.L-1 NaCl electrolytes. Monitoring of corrosion evolution in both alloys was carried out by electrochemical impedance spectroscopy (EIS) and polarization methods. The surface of the samples exposed to the test solutions was observed by microscopy after corrosion tests. The results showed different corrosion mechanisms in the two test solutions. In the sulfate containing electrolyte, the Al-Cu-Li alloy showed corrosion mechanism mainly associated with the micrometric particles at the surface, similarly to the AA2024-T3 alloy. However, in the chloride solution without sulfate, the AA2098-T351 alloy showed susceptibility to severe localized corrosion (SLC) besides the corrosion associated to the micrometric particles and the first type of corrosion was the main type of attack. The AA2024-T3 showed lower susceptibility to SLC than the AA2098- T351 alloy.