FERNANDA MARTINS QUEIROZ

FERNANDA MARTINS QUEIROZ

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On the effects of hydrothermal treatments on the corrosion resistance of the TSA anodized AA7475-T761 alloy
2016 - ALMEIDA, THALLIS L.; QUEIROZ, FERNANDA M.; TERADA, MAYSA; COSTA, ISOLDA; CAPELOSSI, VERA R.
The effect of hydrothermal treatment time on sealing and corrosion resistance of the AA7475-T761 anodized aluminium alloy has been investigated in this study. The hydrothermal treatments tested are environmental compatible without chromium ions involved. Anodizing was carried out by a tartaric-sulphuric anodizing (TSA) process and this was followed by hydrothermal treatments for partial sealing, in various solutions. The effect of propyleneglycol (PRG) and/or cerium ions in the hydrothermal treatment solution was evaluated. Four treatment times were tested, specifically, 2.5, 5.0, 7.5 and 10 min. The corrosion resistance of the anodized and treated samples was evaluated by Electrochemical Impedance Spectroscopy (EIS) and the anodic layers formed were characterized by Scanning Electron Microscopy (SEM). The EIS results showed that the hydrothermal treatments in solutions with cerium ions resulted in similar impedances for periods of treatment from 5 to 10 min whereas in the solutions with PRG the impedance increased with time of treatment from 2.5 to 10 min showing a slower kinetics of anodic layer sealing. However, the fastest kinetics of sealing were associated to the treatments that combined two steps, one in PRG and other in cerium containing solutions with similar impedances obtained from 2.5 to 10 min of treatment. Surface evaluation by SEM showed that the porosities in the anodic layer were not sealed for the periods of hydrothermal treatments corresponding to 2.5 min. The presence of cerium in hydrothermal treatment had a beneficial effect on the stability of the anodic layer formed and provided a healing effect on the corroding sites.
EIS study of the microstructure influence on the corrosion behaviour of AA 2198-T3 compared to AA 2198-T851 alloy
2016 - ARAUJO, J.V. de S.; QUEIROZ, F.M.; TERADA, M.; ASTARITA, A.; COSTA, I.
This paper deals with the study of the influence of the temper state on the electrochemical behavior of an high strength aluminum-lithium alloy. In particular the corrosion resistance of the AA2198 alloy in both T3 and T851 temper condition, has been evaluated by immersion tests as a function of immersion time in NaCl 0.01 mol.L-1. The evolution of the electrochemical behavior was monitored by electrochemical impedance spectroscopy (EIS) and surface observation by optical microscopy and Field Emission Gun- Scanning Electron Microscopy. The results indicated a higher electrochemical activity associated to the T851 treatment comparatively to the T3 one and this was ascribed to the more heterogeneous microstructure related to the first treatment. Severe localized corrosion was seen on the AA2198-T851 alloy after only few hours of exposure to the test medium. This type of corrosion was of the crystallographic type and was related to T1 (Al2LiCu) which is more electrochemically active than the matrix leading to localized attack. Pitting attack was seen on the AA2198-T3 alloy along the surface and it was located at the matrix-precipitates interface. The EIS results supported a faster kinetics and lower impedances associated to the AA2198-T851 comparatively to the AA2198-T3 alloy according to the surface observation along the test period.
On the effects of hydrothermal treatments on the corrosion resistance of the TSA anodized AA7475-T761 alloy
2016 - ALMEIDA, THALLIS L.; QUEIROZ, FERNANDA M.; TERADA, MAYSA; COSTA, ISOLDA; CAPELOSSI, VERA R.
The effect of hydrothermal treatment time on the sealing and corrosion resistance of the anodized AA7475-T761 aluminium alloy has been investigated in this study. The treatments tested are environmental compatible and has not chromium ions involved. Anodizing was carried out by tartaric-sulphuric anodizing (TSA) and this was followed by hydrothermal treatments for partial sealing, either with or without propyleneglycol (PRG) and/or cerium ions. Four different treatment times were tested, specifically, 2.5, 5.0, 7.5 and 10 min. The corrosion resistance of the treated samples was evaluated by Electrochemical Impedance Spectroscopy (EIS) and the anodic layers formed by anodizing and hydrothermal treatments were characterized by Scanning Electron Microscopy (SEM). The EIS results indicated that the best corrosion resistance was related to the treatments that combined hydrothermal treatments in boiling water with PRG for 10 minutes or boiling water with PRG and cerium ions for 5 min. The SEM images for the samples showed the formation of a homogeneous anodic layer and the thickness is approximately 3 m. It was noticed that the porosities were not completed sealed by the treatments tested and this was on purpose in order to allow coating adhesion to the anodic layer.
EIS behavior of anodized and primer coated AA2198–T851 compared to AA2024–T3 exposed to salt spray CASS test
2016 - QUEIROZ, F.M.; BUGARIN, A.F.S.; HAMMEL, N.P.; CAPELOSSI, V.R.; TERADA, M.; COSTA, I.
In this investigation, the corrosion behavior of AA2198–T851 was compared to AA2024–T3 by electrochemical impedance spectroscopy and the surface of both alloys was analyzed by Field Emission Gun (FEG) scanning electron microscopy (SEM) and Xray energy dispersive analysis (EDX). Electrochemical impedance spectroscopy (EIS) results for the uncoated surface of both alloys showed higher pitting susceptibility associated to the AA2198–T851 alloy comparatively to the AA2024–T3. In order to improve the corrosion resistance of both alloys, tartaric sulphuric acid anodising (TSA) was carried out with both alloys followed by primer application. The corrosion resistance of the anodized and primer coated samples was also evaluated by CASS salt spray test followed by EIS tests at increasing periods of exposure to the CASS test. The results showed larger amounts of corrosion products associated to the primer coated AA2198–T851 alloy comparatively to the AA2024–T3 alloy. Diffusionwas only indicated in the EIS results of the AA2198–T851 samples likely because of large amounts of porous corrosion products on the exposed surface of this alloy to the corrosive environment.
Caracterizacao de revestimento 'galvannealed' por 'stripping' eletroquimico
2003 - QUEIROZ, F.M.; COSTA, I.
Estudo do comportamento de corrosao dos intermetalicos presentes na liga AA2024-T3, por meio de tecnicas de microscopia associadas a tecnicas eletroquimicas
2008 - QUEIROZ, FERNANDA M.
A liga de alumínio AA2024-T3, amplamente utilizada na indústria aeroespacial, apresenta elevada resistência mecânica conferida pela adição de elementos de liga, principalmente o Cu, que formam precipitados finamente distribuídos e coerentes com a matriz, durante o processo de envelhecimento controlado. No entanto, durante este processo, também se formam intermetálicos (IMs) maiores com composição e atividade eletroquímica diferentes da matriz, tornando a liga altamente suscetível a processos de corrosão localizada. A literatura apresenta diversos trabalhos sobre o estudo da corrosão da AA2024-T3 associada à presença dos IMs, porém, o tema ainda é bastante controverso, e muitos aspectos precisam ser estudados com mais detalhes ou mesmo ainda desvendados. Nos últimos anos, técnicas de microscopia de alta resolução, como a microscopia eletrônica de transmissão (TEM) e microscopia eletrônica de varredura (MEV), associadas à espectroscopia por energia dispersiva de raios X (EDS) e a microscopia de força atômica (AFM) bem como técnicas eletroquímicas convencionais e localizadas têm auxiliado nestas pesquisas. Na presente tese serão apresentados os resultados dos estudos realizados sobre a corrosão da liga AA 2024-T3 em soluções de cloreto de baixa concentração. A investigação foi realizada aliando as técnicas de caracterização anteriormente descritas com técnicas eletroquímicas tradicionais: acompanhamento do potencial de circuito aberto (OCP) com o tempo, curvas de polarização (CP) e espectroscopia de impedância eletroquímica (EIS) e técnicas com elevado poder de resolução espacial: como a técnica do eletrodo vibratório de varredura (SVET). A caracterização microestrutural confirmou a heterogeneidade dos IMs, e como contribuições principais, evidenciou a existência de fases secundárias (cristalinas ou não) no interior dos próprios IMs e que a matriz da liga nas proximidades dos IMs apresenta microestrutura variável, todos estes aspectos podendo contribuir de maneira sinérgica para o complexo comportamento de corrosão exibido pelos IMs. Além do mais, mostrou-se que na corrosão os IMs estão submetidos a ataque eletroquímico e químico, este último ocasionado por aumento local do pH. Os resultados dos testes eletroquímicos convencionais mostraram que nas condições empregadas no presente estudo a corrosão da liga é dominada pelo comportamento de corrosão dos IMs, e que, dentro deste contexto, o transporte de oxigênio até os sítios catódicos formados pelos IMs, ao invés da concentração de cloretos, parece ser a etapa controladora da velocidade de corrosão. Por outro lado o tratamento da região em altas freqüências dos diagramas de EIS se mostrou um importante aliado na compreensão dos processos que ocorrem na interface quando da corrosão da liga. No que se refere às técnicas localizadas, a viabilidade do uso da técnica do eletrodo vibratório de varredura (SVET) para estudo do início da corrosão na AA2024-T3 foi avaliada e um sistema para aquisição de dados experimentais por espectroscopia de impedância localizada (LEIS) foi montado e validado. A SVET confirmou que a atividade eletroquímica da liga AA2024-T3 se inicia desde os primeiros instantes de imersão do material no eletrólito teste.
Caracterizacao eletroquimica, quimica e morfologica de aco 'galvannealed' comercial
2003 - QUEIROZ, FERNANDA M.
Investigation of the corrosion behaviour of AA 2024-T3 in low concentrated chloride media
2008 - QUEIROZ, F.M.; MAGNANI, M.; COSTA, I.; MELO, H.G. de
Electrochemical behaviour of electrogalvanized steel with a conversion treatment at room temperature
2012 - TOMACHUK, C.R.; QUEIROZ, F.M.; COSTA, I.