CAIO PALUMBO DE ABREU

CAIO PALUMBO DE ABREU

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Microstructural characteristics of the Al alloys
2020 - ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; FERREIRA, RAPHAEL O.; MACHADO, CARULINE de S.C.; ABREU, CAIO P. de; COSTA, ISOLDA
Microstructure characteristics of two high-strength aluminum alloys, the 2024-T3 Al–Cu–Mg, and the new generation Al–Cu–Li alloy 2198, in the T8 and T851 tempers, were investigated in this study. For this purpose, microstructural and statistical analyses were carried out. The results showed equiaxed grains for the 2024-T3 and 2198-T851 alloys, whereas, elongated grains for the 2198-T8. Besides, the 2198-T851 alloy displayed slip bands in the grains due to the stretching stage, “51”. The 2024-T3 alloy showed at least two types of constituent particles, Al–Cu–Mg and Al–Cu–Mn–Fe–(Si); whereas Al–Cu–Li alloys showed only one type, Al–Cu–Fe, in their composition. Statistical analyses showed that the percentage of area covered by constituent particles was larger in the 2024-T3 alloy compared to the 2198 in both tempers, T8 and T851. On the other hand, the Al–Cu–Li alloys showed higher microhardness values relatively to the Al–Cu one. The differences among the nanometric phases present in Al–Cu and Al–Cu–Li alloys were analyzed by transmission electron microscopy. All the results were related to the different chemical composition and industrial thermomechanical processing of each alloy.
Effect of friction stir welding (FSW) on the electrochemical behavior and galvanic coupling of AA2024-T3 and AA7475-T651
2020 - BUGARIN, A.F.S.; ABREU, C.P. de; TERADA, M.; MELO, H.G. de; COSTA, I.
In this study, the local electrochemical activity of AA2024-T3 and AA7475-T761 joined by friction stir welding (FSW) was investigated as a function of time by electrochemical tests in 0.01 mol L−1 NaCl solution using a mini cell. The welding procedure resulted in increased electrochemical activity of the weld affected zones of both alloys, which electrochemical activities increased with immersion time, as demonstrated by the electrochemical behavior. In the heat affected zone (HAZ) and the thermomechanically affected zone (TMAZ) of AA7475-T651 the increased activity was due to precipitation of η phase at the grain boundaries stimulated by thermomechanical effects. On the other hand, the enhanced activity in the TMAZ/HAZ of the AA2024-T3 was associated to a large concentration of copper rich cathodic particles broken by tool rotation that were spread along this zone. However, the zone of highest electrochemical activity was the stir zone (SZ) and this was ascribed to galvanic coupling between the two alloys, AA2024-T3 and the AA7475-T651, where the former acted as cathodic and the latter as anodic area.
Corrosion resistance evaluation of the different zones on the AA2024-T3 and AA7475-T651 alloys welded by FSW
2017 - ABREU, C.P.; MELO, H.G. de; PEBERE, N.; MOGILI, N.V.V.; COSTA, I.; VIVIER, V.
The aeronautic industry has a great interest in joining dissimilar aluminium alloys used in different parts of an aircraft. The Friction Stir Welding (FSW) process has been considered an effective alternative to conventional techniques for the welding of high strength alumin-ium alloys. However, this procedure results in zones with different microstructures due to thermal and thermomechanical effects involved during the joining process, leading to the formation of the thermomechanically affected zone (TMAZ), the heat affected zone (HAZ), the stir zone (nugget), and the unaffected base metal (BM). As the corrosion resistance of materials depends on their microstructures, the aim of this study was to investigate the intrin-sic corrosion resistance of the different zones of the AA2024-T3 and AA7475-T761 alloys welded by FSW, without considering the coupling effects between the different zones. This was achieved by evaluating the corrosion resistance of each individual zone in 0.1 M Na2SO4 + 1 mM NaCl solution by electrochemical techniques, such as open circuit potential meas-urements, polarization curves, and electrochemical impedance spectroscopy, using an elec-trochemical cell with an exposed area of 0.78 mm2. The electrochemical results showed that the lowest corrosion resistance was associated to the nugget zone, on which a galvanic cou-pling between the 2024 and 7475 alloys takes place. The corrosion resistance was also low-ered on the TMAZ of both alloys. This behaviour was associated to the enhanced precipita-tion of the η phase (MgZn2) at the grain boundaries in the 7475 alloy and to the coarsening of S phase (AlCuMg) precipitates in the 2024 alloy, both processes favoured by the thermome-chanical effects in these specific zones as demonstrated by TEM analysis.
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.
Multiscale electrochemical study of welded al alloys joined by friction stir welding
2017 - ABREU, CAIO P. de; COSTA, ISOLDA; MELO, HERCILIO G. de; PEBERE, NADINE; TRIBOLLET, BERNARD; VIVIER, VINCENT
Friction stir welding (FSW) is an efficient way to join high strength aluminum alloys. However, FSW generates different microstructural areas in contact that may give rise to galvanic couplings, affecting the corrosion resistance of the assembly. In the present work, a multiscale electrochemical study of the 7475-T651 and 2024-T3 aluminum alloys butt-joined by FSW was carried out.Much lower impedances were associated with the FSW affected zones compared to the two aluminum base metals tested individually. Corrosion of the welded system resulted in the establishment of galvanic coupling, shown by local electrochemical impedance spectroscopy (LEIS) measurements, at which the AA7475 behaves anodically with respect to the AA2024. A Zn deposit was observed on the intermetallic particles of the AA2024 after 24 h of immersion in the electrolyte resulting from the galvanic coupling, which seems to reduce the galvanic coupling effects. Such a behavior in combination with LEIS results allowed a description of the galvanic coupling development between two different aluminum alloys (AA2024-T3 and AA7475-T761) butt-welded by FSW as a function of time from the early stage of immersion.