Use of amperometric and potentiometric probes in scanning electrochemical microscopy for the spatially-resolved monitoring of severe localized corrosion sites on aluminum alloy 2098-T351

Amperometric and potentiometric probes were employed for the detection and characterization of reactive sites on the 2098-T351 Al-alloy (AA2098-T351) using scanning electrochemical microscopy (SECM). Firstly, the probe of concept was performed on a model Mg-Al galvanic pair system using SECM in the amperometric and potentiometric operation modes, in order to address the responsiveness of the probes for the characterization of this galvanic pair system. Next, these sensing probes were employed to characterize the 2098-T351 alloy surface immersed in a saline aqueous solution at ambient temperature. The distribution of reactive sites and the local pH changes associated with severe localized corrosion (SLC) on the alloy surface were imaged and subsequently studied. Higher hydrogen evolution, lower oxygen depletion and acidification occurred at the SLC sites developed on the 2098-T351 Al-allo

On the local corrosion behavior of coupled welded zones of the 2098-T351 Al-Cu-Li alloy produced by Friction Stir Welding (FSW): An amperometric and potentiometric microelectrochemical investigation

Electrochimica Acta 373 (2021) 137910, 12 pp. https://doi.org/10.1016/j.electacta.2021.137910.The galvanic coupling effects and the local electrochemical activity developed along the welded zones in FSWelded 2098-T351 Al-Cu-Li alloy have been investigated using localized electrochemical methods supported by surface analytical characterizations. The investigation was carried out in the coupled welding joint/heat affected zones (WJ/HAZ) for both the retreating (RS) and the advancing (AS) sides. The correlation between surface chemistry, microstructural features and electrochemical activity of these welded zones has been studied. The results showed the development of galvanic interactions within and between the WJ and the HAZ regions that were visualized using the Scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM). SVET analyses showed that the HAZ was more susceptible to the development of anodic sites compared to WJ. SECM in amperometric operation mode showed that the WJ coupled to HAZ presented higher oxygen consumption and greater cathodic activity compared to HAZ. Furthermore, SECM in the potentiometric operation mode showed alkalization on the WJ and increased acidity on the HAZ, mainly at severe localized corrosion (SLC) sites. Based on SVET and SECM results in combination surface analysis, it is proposed that the micro-galvanic cells formed within these welded zones are due to the presence of secondary phases in the 2098-T351 alloy and their interactions with the adjacent matrix

Galvanic coupling effects on the corrosion behavior of the 6061 aluminum alloy used in research nuclear reactors

The 6061 alloy is used in different thermomechanical conditions in research nuclear reactors. Nuclear fuel plates are manufactured by the picture frame technique (PFT) and the 6061 alloy is used as cladding for the nuclear fuel “sandwiches”. After the process, these nuclear plates are placed in a case composed of 6061-T6 alloy. In this work, the galvanic effects of coupling the 6061 alloy in the T6 and PFT conditions on the corrosion behavior was investigated in solutions of different chloride contents. The results showed that galvanic corrosion was favored due to the different microstructural features related to these two thermomechanical conditions of the 6061 alloy. The 6061 alloy in the PFT condition was cathodic to the alloy in the T6 condition. Local electrochemical techniques were useful in characterizing the electrochemical behavior of the coupled alloys

Development of an Al3+ ion-selective microelectrode for the potentiometric microelectrochemical monitoring of corrosion sites on 2098-T351 aluminum alloy surfaces. R.M.P. da Silva, J. Izquierdo, M.X. Milagre, R.A. Antunes, R.M. Souto, I. Costa.

A novel potentiometric Al3+− ion selective microelectrode (ISME), with internal solid contact, based on the use of a neutral carrier morin as ionophore is reported. The ability of the ISME to image local ion concentration distributions was tested on aluminum alloy surfaces freely corroding in an aqueous solution containing chloride ions. The microelectrode was then used as the sensing tip for scanning electrochemical microscopy (SECM) in potentiometric operation to monitor the reactive sites associated with the dissolution of aluminum that developed in the 2098− T351 Al− Cu− Li alloy as a result of welding by the Friction Stir Welding (FSW) process. The ISME detected differences in the local concentrations of Al3+ species arising from the 2098− T351 Al− Cu− Li alloy (base material) and from the coupled weld joint/heat affected zones (WJ/HAZ) of the alloy produced by the FSW process. More active domains for Al3+ dissolution were found in the HAZ regions coupled to WJ, more specially in the HAZ of the advancing side (AS). These results demonstrate that the Al3+− ISME presented in this work can be used to monitor corrosion sites on aluminum alloys surfaces with combined chemical and spatial resolution

Development of an Al3+ ion-selective microelectrode for the potentiometric microelectrochemical monitoring of corrosion sites on 2098-T351 aluminum alloy surfaces Autores: R.M.P. da Silva, J. Izquierdo, M.X. Milagre, J.V.S. Araujo, R.A. Antunes, R.M. Souto, I. Costa

The development of heterogeneous electrochemical activity in the welded zones of aluminum alloy 2098-T351 by friction stir welding (FSW) associated with the formation of a near-surface deformed layer (NSDL) upon exposure to an aqueous chloride-containing solution was characterized using scanning electrochemical microscopy (SECM) in potentiometric operation. A solid-contact Mg2+ ion-selective microelectrode allowed in situ monitoring of the corrosion reactions sites for magnesium dissolution from different zones of the FSW weld upon exposure to a chloride-containing aqueous environment. In this way, localized corrosion reactions developing in the galvanically coupled joint/heat affected zones (WJ/HAZ) of the weld were detected and imaged with spatial resolution. The most active domains for local Mg2+ concentrations were associated with the HAZ of the retreating side (RS), and these corresponded to Mg oxidation from the Mg-enriched oxide bands in NSDL

Surface finishing effects on the corrosion behavior and electrochemical activity of 2098-T351 aluminum alloy investigated using scanning microelectrochemical techniques R.M.P. da Silva, M.X. Milagre, J. Izquierdo, A.M. Betancor-Abreu, L.A. de Oliveira, J.V.S. Araujo, R.A. Antunes, R.M. Souto, I. Costa

The effects of surface finishing on the corrosion behavior and electrochemical activity of AA2098-T351 (Al–Cu–Li alloy) were investigated on the basis of the correlation between surface chemistry, microstructure and electrochemical activity. The alloy was evaluated in the as-received and polished conditions. The morphology of the two types of surfaces was investigated using confocal laser scanning microscopy (CLSM), optical microscopy and optical 3D profilometry. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). Scanning microelectrochemical techniques (namely, localized electrochemical impedance spectroscopy (LEIS), the scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM) in potentiometric mode) were used to examine the electrochemical activity of the surfaces. The results showed that on the as-received surface, the near surface deformed layer (NSDL), which is composed of Mg-rich bands, influenced the corrosion activity of the alloy. Higher electrochemical activity and greater susceptibility to severe localized corrosion were related to the polished surface condition compared to the as-received one