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Hydrogen Isotope Trapping in Al-Cu Binary Alloys

The trapping mechanisms for hydrogen isotopes in Al-X Cu (0.0 at.% < X < 3.5 at.%) alloys were investigated using thermal desorption spectroscopy (TDS), electrical conductivity, and differential scanning calorimetry. Constant heating rate TDS was used to determine microstructural trap energies and occupancies. In addition to the trapping states in pure Al reported in the literature (interstitial lattice sites, dislocations, and vacancies), a trap site due to Al-Cu intermetallic precipitates is observed. The binding energy of this precipitate trap is ($18\pm3$) kJ$\cdot$mol$^{-1}$ ($0.19 \pm 0.03$ eV). Typical occupancy of this trap is high; for Al-2.6 at.% Cu (a Cu composition comparable to that in AA2219) charged at 200°C with 130 MPa D$_2$ for 68 days, there is ca. there is $3.15\times10^{-7}$ mol D bound to the precipitate trap per mol of Al, accounting for a third of the D in the charged sample.