Environmental hydrogen embrittlement associated with decohesion and void formation at soluble coarse particles in a cold-rolled Al–Cu based alloy

The combined effect of solution treatment temperature and severely cold rolling on the hydrogen partitioning and related fracture mechanism was investigated using constant heating rate thermal desorption spectroscopy to determine hydrogen desorption energies and occupancies in a cold-rolled 2219 aluminum alloy. The alloy was solution-treated, subsequently rolled by 90% at room temperature and subjected to tensile tests performed in dry nitrogen gas and in humid air with relative humidity of 90% at initial strain rates of 1.67 x 10^-6 and 1.67 x 10^-4 s^-1. The specimens tested at a lower strain rate exhibited embrittlement in humid air environment. Besides interstitial lattice sites, dislocations, and vacancies which have been known as trap sites in pure Al, a trap site originated from coarse Al₂Cu particles and negligible trapping by fine Al₂Cu particles were observed. The hydrogen desorption energy of the coarse Al₂Cu particles is 56.59 kJ/mol, indicating that the particles act as a relatively strong trap site for hydrogen. Based on the obtained results and tensile testing at humid air and inert atmosphere, it is firstly reported that the high-hydrogen concentration induced by environment leads to the decohesion accompanied by void formation at Al₂Cu coarse particles which promotes the premature fracture.