Corrosion-Induced Hydrogen Embrittlement in AA2024

Abstract

Embrittlement of aluminum alloy 2024 caused by corrosion-induced hydrogen evolution and trapping is discussed in this article. The current literature on corrosion mechanisms, hydrogen trapping, and mechanisms of hydrogen embrittlement is briefly reviewed. Accelerated corrosion tests followed by thermal desorption spectroscopy enabled the identification of hydrogen traps in the microstructure of the material. The nature of these traps was identified by controlled experiments involving solution treatments and plastic deformation prior to corrosion, in order to alter the alloy microstructure. The high-temperature trap is related to the S–CuMgAl2 phase. In the absence of this phase, hydrogen is trapped in vacancies, which liberate hydrogen at even higher temperatures. The lower temperature trap is related to dislocations. The hydrogen trapped at dislocations increases with plastic strain up to a certain strain and then decreases. The hydrogen generated by corrosion diffuses in the interior of the material and establishes a hydrogen-affected zone beneath the corrosion layer. Removal of the corrosion layer leads to complete restoration of yield strength but only partial restoration of ductility. Removal of the corrosion layer and heating at a high enough temperature to activate all traps for hydrogen desorption leads to complete restoration of ductility. A mechanism of corrosion-induced hydrogen embrittlement is suggested.