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Using localized electrochemical impedance spectroscopy (LEIS) for corrosion of high mechanical strength aluminum alloys welded by FSW

Grant number: 16/20572-7
Support type:Scholarships in Brazil - Post-Doctorate
Effective date (Start): March 01, 2017
Effective date (End): August 31, 2018
Field of knowledge:Engineering - Materials and Metallurgical Engineering
Principal Investigator:Hercílio Gomes de Melo
Grantee:Fernanda Martins Queiroz
Home Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Associated research grant:13/13235-6 - Investigation on the localized corrosion and the fatigue corrosion resistance of high strength aluminum alloys joined by friction stir welding (FSW), AP.TEM

Abstract

The high-strength aluminum alloys are widely used in the aircraft industry due to its high strength to density ratio that directly affects fuel consumption and the need of maintenance. Therefore, the 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, stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ), besides the base metal (BM). These zones affect the mechanical properties of the materials and can nucleate the localized corrosion phenomena, with the possibility of galvanic coupling due to changes in the microstructure as grain refinement and recrystallization, changes in the grain boundaries, dissolution and precipitation of the hardening precipitates and dispersoids. The Localized Electrochemical Impedance Spectroscopy (LEIS) helps to understand the corrosion processes of these welded alloys. It is known that the main cause of the localized corrosion of aluminum alloys are the intermetallic particles (IMs), which are far below the LEIS probes resolution available, not only the commercially but also the produced in the laboratory, that only differentiate activity between regions with tens of micrometres of magnitude. Thus, for these studies, an alternative is the models electrodes representing galvanic couples. Regarding the study of aluminum alloys, models electrodes have been used by research groups in LISE (Paris), Cirimat (Toulouse) and LEC (Brazil), employing pure metals for obtaining experimental data and/or simulation, highlighting the current distribution calculation and potential on the pair of metals. These studies evaluated the corrosion behavior of Cu-rich IMs and simulate the effect of of Al-Cu-Mg IMs, in an AA2024 alloy, using Al/Cu and Al/Mg models electrodes, respectively. The results of these studies showed the interfaces alkalinization between the different metals and corrosion mechanisms could be proposed in agreement with the simulations. Few studies involving LEIS are available in the literature for FSW welded alloys, and these results indicate the response of a galvanic coupling between the different zones of the material. About FSW, the zones created during the process are in order of mm2, so commercial equipments and their probes are sensitive to the corrosive processes, including the detection of existence of galvanic effects between the different regions. Considering the scarce number of studies about the subject, the aim of this study is to evaluate by LEIS the corrosion behavior of the different zones generated by FSW, initially for the 2024-T3 alloy, through a commercial system. A detailed observation of the microstructure, obtained from the welded joint will be the support for understanding the mechanisms involved in the corrosion processes. From these data model electrodes may be proposed to simulate the microstructure and galvanic couple representative of a similar joint of AA2024-T3. The interaction of the local research group with LISE (Paris) and Cirimat (Tolouse) groups allow discussion and exchange of information on the results and LEIS technique. In addition, to obtaining results for the project is intended to support the other components of the research group to use the LEIS. (AU)

Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
TERADA, MAYSA; QUEIROZ, FERNANDA M.; COSTENARO, HELEN; AYUSSO, VICTOR H.; OLIVIER, MARJORIE; COSTA, ISOLDA; DE MELO, HERCILIO G. Effect of Cerium Addition to a Hydrothermal Treatment on the Corrosion Protection of the Tartaric-Sulfuric Acid Anodized AA2524-T3. CORROSION, v. 75, n. 9, p. 1110-1117, SEP 2019. Web of Science Citations: 0.
QUEIROZ, FERNANDA MARTINS; DONATUS, UYIME; PRADA RAMIREZ, OSCAR MAURICIO; DE SOUSA ARAUJO, JOAO VICTOR; GONCALVES DE VIVEIROS, BARBARA VICTORIA; LAMAKA, SVIATLANA; ZHELUDKEVICH, MIKHAIL; MASOUMI, MOHAMMAD; VIVIER, VINCENT; COSTA, ISOLDA; DE MELO, HERCILIO GOMES. Effect of unequal levels of deformation and fragmentation on the electrochemical response of friction stir welded AA2024-T3 alloy. Electrochimica Acta, v. 313, p. 271-281, AUG 1 2019. Web of Science Citations: 1.

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