  The mechanisms of dislocation/precipitate interactions were analyzed in an
Al-Cu alloy containing a homogeneous dispersion of $\theta'$ precipitates by
means of discrete dislocation dynamics simulations. The simulations were
carried out within the framework of the discrete-continuous method and the
precipitates were assumed to be impenetrable by dislocations. The main
parameters that determine the dislocation/precipitate interactions (elastic
mismatch, stress-free transformation strains, dislocation mobility and
cross-slip rate) were obtained from atomistic simulations, while the size,
shape, spatial distribution and volume fraction of the precipitates were
obtained from transmission electron microscopy. The predictions of the critical
resolved shear stress (including the contribution of solid solution) were in
agreement with the experimental results obtained by means of compression tests
in micropillars of the Al-Cu alloy oriented for single slip. The simulations
revealed that the most important contribution to the precipitation hardening of
the alloy was provided by the stress-free transformation strains followed by
the solution hardening and the Orowan mechanism due to the bow-out of the
dislocations around the precipitates.
