MARIANA XAVIER MILAGRE

MARIANA XAVIER MILAGRE

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Exfoliation susceptibility of aluminum alloys joined by Friction Stir Welding (FSW)
2018 - MILAGRE, MARIANA X.; DONATUS, UYIME; MACHADO, CARULINE S.C.; ARAUJO, JOAO V. de S.; MOGILI, VISHNU; ASTARITA, ANTONELLO; COSTA, ISOLDA
In the present study, the exfoliation susceptibility of a commercial Al-Cu-Li alloy of the third generation, AA2098-T351, joined by FSW was investigated according to ASTM G34 standard practice and the results were compared with the results of the parent material. Susceptibility to exfoliation attack was classified by the depth of attack penetration. The cross-sections of the samples after test were observed by optical and scanning electron microscopy (SEM) to evaluate the penetration depth of corrosion attack. A comparison to conventional Al-Cu alloys (AA2024-T3/T351) was carried out and the results showed that the Al-Cu-Li alloy tested (AA2098-T351) was more susceptible to exfoliation. Besides, exfoliation susceptibility varied with each welded zone and the active zones remained active for long periods of time after removal from the test solution when the attack continuously propagated in the corrosion front.
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.
Influência da composição da solução de tratamento de superfície na resistência à corrosão da liga AA2024-T3
2019 - KLUMPP, RAFAEL E.; SILVA, REJANE M.P. da; DONATUS, UYIME; MACHADO, CARULINE de S.C.; AYUSSO, VICTOR H.; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; COSTA, ISOLDA
Os tratamentos de superfície de ligas de alumínio em soluções contendo íons de terras raras têm se mostrado promissores para a substituição dos tratamentos que utilizam íons de cromo hexavalente em sua composição. A composição das soluções de tratamento com terras raras é um fator importante na propriedade de proteção à corrosão da camada superficial formada. Neste trabalho, o efeito da adição de peróxido de hidrogênio à solução de tratamento para proteção à corrosão da liga AA2024-T3 foi investigado por técnicas eletroquímicas e microscópicas. Os resultados mostraram que a adição do peróxido de hidrogênio altera a morfologia da camada, o mecanismo de formação desta e resulta em propriedades de proteção levemente inferiores às da camada formada na ausência de peróxido.
Effect of galvanic coupling on the corrosion susceptibility of friction stir weldment of AA2198-T851 alloy
2018 - COSTA, I.; DONATUS, U.; MILAGRE, M.X.; MACHADO, C.S.C.; ARAUJO, J.V.S.
The AA2198-T851 alloy is a new generation Al-Li alloy which finds application in the aerospace industry. Its preference over conventional Al alloys is premised on the fact that it exhibits better strength to weight ratio and improved fatigue resistance due to the addition of Li as a major alloying element. However, it is a relatively new alloy and its processing-structure-property-performance relationship is far from being established. This is very true for the relationship between its structure and corrosion resistance which is very scarce in the literature. Our recent findings have revealed that this alloy is highly susceptible to severe localized corrosion which is caused by the abundance of active hexagonal T1 (Al2CuLi) particles in its microstructure. The corrosion susceptibility is further promoted by the non-uniform precipitation of these particles which are often preferentially concentrated in bands aligned parallel to the {111}Al. Furthermore, bulk zonal heterogenities with pronounced non-uniform distribution of the active T1 particles are created when this alloy is welded using friction stir welding. The friction stir welding process is a solid state welding process that has been adjudged to be the best welding technique for Al alloys. Nonetheless, this process generates different zones in the weldments of Al alloys. Thus, zones exhibiting different electrochemical characteristics and severe galvanic interactions can occur when the weldment is exposed to a corrosive media. The galvanic interactions can lead to a faster propagation of attack in the most susceptible region of the weldment, which in this case is the parent material (with the highest volume fraction of the T1 particles). To establish this, the galvanic interactions between the zones of the weldment have been investigated by separately exposing the parent material and the stir zone of the weld and then by exposing the entire weldment using NaCl and EXCO solutions. Optical, scanning electron and transmission electron microscopes were also employed in the study. The results revealed that the parent material of the weldment was the most susceptible (as previously mentioned) and appeared to corrode at a faster rate when coupled to the more cathodic stir zone, thermomechanically affected zone and the heat affected zones of the weldment (with lower volume fraction of the T1 particles). The modes of corrosion in the zones of the weld were also observed to be different. However, the most susceptible region corroded intragranularly with the grain boundaries exhibiting more noble electrochemical characteristics.
The effect of FSW on microstructure and intergranular corrosion of the AA2198- T8 alloy
2018 - MACHADO, C.S.C.; DONATUS, U.; ARAUJO, J.V.S.; KLUMPP, R.E.; MILAGRE, M.X.; GIORJAO, R.A.R.; MOGILI, N.V.V.; COSTA, I.
In this investigation, the intergranular corrosion (IGC) resistance of the AA2198-T8 alloy welded by friction stir welding (FSW) was investigated by ASTM G110-97 test. The different zones resulting from FSW showed distinct resistances to intergranular attack depending on the heating and/or mechanical effects produced by welding. The base metal (BM) was the most susceptible to IGC whereas the thermomechanically affected zone (TMAZ) and the stir zone (SZ), presented the highest resistances to IGC comparatively to the other zones. The results of IGC tests were correlated with those of thermal simulation, microhardness measurements, transmission electron microscopy (TEM) and optical microscopy (OM). The dissimilarities in corrosion resistance of the various zones were associated to differences in hardening phase quantities between the various zones. In the BM and HAZ, T1 phase, the main hardening phase, was found at grain boundaries and it resulted in IGC susceptibility. The slight IGC observed in the SZ and TMAZ was not associated with T1 phase which was rarely found but to another precipitate (T2 phase) which was found preferentially located at the grain boundaries in these zones.
Comparação da resistência a corrosão localizada de ligas de alumínio pela técnica de varredura com eletrodo vibratório (SVET)
2018 - MILAGRE, M.X.; ARAUJO, J.S.; MACHADO, C.S.C.; DONATUS, U.; COSTA, I.
As ligas Alumínio-Cobre-Lítio (Al-Cu-Li) foram desenvolvidas como substitutas para as ligas convencionais de Al-Cu. Apesar de apresentarem melhor módulo específico também são suscetíveis à corrosão localizada. As técnicas eletroquímicas convencionais são ferramentas úteis para entender o comportamento de corrosão das ligas de Al, no entanto elas dão uma resposta global dos fenômenos de corrosão. Neste trabalho, a técnica de varredura com eletrodo vibratório (SVET) foi utilizada para comparar os mecanismos de corrosão de algumas ligas de Al. Os ensaios com SVET foram realizados em solução de NaCl 0,005 mol L-1 durante 24 h e os mapas foram obtidos a cada 2 h para as ligas AA2024-T3, AA2098-T351 e AA2198-T851. Os resultados mostraram diferentes mecanismos para cada liga sendo que as ligas Al- Cu-Li maiores densidades de corrente associadas a corrosão severa localizada em relação a liga AA2024-T3.