Hydrogen mapping in an aluminum alloy using an alternating current scanning electrochemical microscope (AC-SECM)

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. A B S T R A C TMeasurements using an alternating current scanning electrochemical microscope (AC-SECM) were performed on a 2024 aluminum alloy pre-charged with hydrogen. A gradient in AC current magnitude was observed over several hundreds of microns on the side perpendicular to the charging side. After heat treatment at 130°C for 2 h, the current gradient disappeared. Comparison with scanning Kelvin probe force microscopy (SKPFM) measurements confirmed that the increase in AC current magnitude observed with AC-SECM was due to the presence of hydrogen in the material. Fitting of localized impedance spectra with a suitable equivalent circuit showed the influence of H on the corrosion rate. AC-SECM is thus a powerful new method to detect hydrogen and study its effect on corrosion at the micrometer scale.

Influence of hydrogen on the propagation of intergranular corrosion defects in 2024 aluminium alloy

“…The H enrichment of those interfaces enhances their electrochemical reactivity (Fig. 6d), promoting their dissolution, as shown by AC-SECM measurements [28] so that IGC defects can progress laterally and become more and more branched when the duration of exposure to the chloride solution increased (insert in Fig. 2a).…”

“…The samples were 1 cm 3 cubes, the precharging duration was 40 h and the precharging potential was -0.8 V vs SCE; these parameters allowed a sufficient amount of H to be introduced inside the sample in a reasonable amount of time. The precharging side was polished with diamond paste down to 3 μm with distilled water as a lubricant before precharging; it was chosen to be perpendicular to the elongated grain direction (L) [27,28]. Therefore, one of the long transverse (LT) -short transverse (ST) sides of the samples was exposed to the electrolyte; all the other sides were protected by a varnish.…”

“…Further, Lafouresse et al have performed alternative current scanning electrochemical microscope (AC-SECM) measurements on H-precharged AA 2024 samples and have shown an increase of the local reactivity, i.e. higher local currents associated with a lower effective resistance, due to the H diffusion inside the samples [28].…”

“…However, to the author knowledge, except for Lafouresse et al [28] and Schaller et al [29,30], there are very few publications that provide data concerning the influence of H on the electrochemical reactivity of the materials. However, if H is introduced around a corrosion defect and if it can modify the electrochemical reactivity of the material, then it could have an influence on the corrosion defect growth and then on its morphology.…”

The local electrochemical behavior of the AA2098‐T351 and surface preparation effects investigated by scanning electrochemical microscopy

“…SECM is a well‐established scanning technique, with high resolution to monitor corrosion processes, where a microelectrode is positioned close to a surface for localized detection of electrochemically active species . SECM and SECM integrated with electrochemical atomic force microscopy (SECM/AFM) have been applied to study the local corrosion of aluminum alloys in different situations. However, the use of SECM to investigate the local corrosion processes and the influence of the near surface deformed layer (NSDL) and its removal by polishing on the local electrochemical activities of the on new generation Al‐Li alloys, such as the AA2098, is rare in the literature.…”