Contribution of Hydrogen to the Intergranular Corrosion Damage in a 2024 T351 Aluminum Alloy

Abstract

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.