  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{\deg}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.
