ARTICLE INFO ABSTRACT Keywords:lntergranular corrosion defects formed after a 24h immersion in a 1 M NaCI solution in a 2024-T351 Al alloy were characterized using a combination of electron microscopy techniques. Results showed the dissolution of intergranular Cu-rich precipitates ail along the corroded grain boundaries. Cu species were incorporated inside the amorphous alumina oxide film identified in the corroded grain boundaries leading to the formation of structural defects in the oxide film. A 10-200 nm-thin metallic Cu-rich layer was also observed at the oxide{metal interface and at the tip of the intergranular corrosion defect.

Hydrogen was inserted into 2024 aluminum alloy by cathodic polarization in sulfuric acid at 25 C. Scanning Kelvin Probe Force Microscopy (SKPFM) measurements performed perpendicularly to the charging side revealed a potential gradient and confirmed the insertion of hydrogen over hundreds of microns. A hydrogen diffusion coefficient of 1.7 Â 10 À9 cm 2 s À1 was calculated from SKPFM measurements of H-charged samples for different durations. The evolution of the potential gradient during desorption of hydrogen in air, at room temperature and at 130 C was investigated. Additional experiments performed at a corrosion defect showed that SKPFM could detect both reversibly and irreversibly bounded hydrogen. These results show that SKPFM is a cutting-edge technique for hydrogen detection and localization at a local scale.

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.

To study the influence of hydrogen on the intergranular corrosion mechanism of a 2024 aluminium alloy, samples were hydrogen precharged by cathodic polarisation and then exposed to a NaCl solution. EBSD analyses and SEM observations showed that hydrogen increased the number of corroded interfaces and led to the embrittlement of low-angle grain boundaries which were not susceptible to corrosion without hydrogen precharging. The increase of the reactivity of the 2024 aluminium alloy in the presence of hydrogen gave a new insight into the intergranular corrosion mechanism: corrosion-induced hydrogen promoted the intergranular corrosion propagation and partially controlled the corrosion defect morphology.

corrosion defects formed after a 24h immersion in a 1 M NaCI solution in a 2024-T351 Al alloy were characterized using a combination of electron microscopy techniques. Results showed the dissolution of intergranular Cu-rich precipitates ail along the corroded grain boundaries. Cu species were incorporated inside the amorphous alumina oxide film identified in the corroded grain boundaries leading to the formation of structural defects in the oxide film. A 10-200 nm-thin metallic Cu-rich layer was also observed at the oxide{metal interface and at the tip of the intergranular corrosion defect.

In aeronautic industry, lifetime prediction of structural elements is a capital issue, in particular for the parts exposed to atmospheric corrosion processes. Tests exist to detect corrosion defects but only a few predictive tests allowing the corrosion defects propagation kinetics to be determined are developed and they need to be optimized. In this framework, tensile tests on pre-corroded samples are assumed to be useful. First results were obtained for AA 2024 samples pre-corroded by continuous immersion in a 1M NaCl solution for times ranging from 6h to 1200h. Results from tensile tests evidenced a decrease of the mechanical properties with the exposure time. Propagation depths of the corrosion defects were then derived from the results of mechanical tests. However, depending on the exposure conditions, a volume damage related to the corrosion-induced hydrogen absorption seemed to contribute to the loss of mechanical properties of the pre-corroded samples. To better understand, hydrogen content of pre-corroded samples was measured using an Instrumental Gas Analysis on a Horiba EMGA-621 W analyzer. Moreover, AA-2024 samples were hydrogenated by cathodic polarization in H2SO4solution to model the corrosion defect tip. Samples were then corroded by continuous immersion in 1 M NaCl solution. First, observations using optical microscope and scanning electron microscope allowed the morphology of the corrosion defects to be studied for the hydrogenated samples. Then, electrochemical characterizations of the hydrogenated samples were performed in order to determine the influence of hydrogen on the corrosion defect propagation kinetics. This work is supported by ANR-14-CE07-0027-01 – M-SCOT: Multi Scale COrrosion Testing.