  In certain naturally aged aluminum alloys, significant strengthening can be
obtained due to the decomposition of a super-saturated solid solution into
clusters. The origins of such strengthening remain unclear due to the challenge
of differentiating solute cluster strengthening from solid solution or
precipitate strengthening. To shed light on the origin of cluster strengthening
in aluminum alloys, the interaction between the smallest possible type of
clusters (i.e. dimers) and moving dislocations in a model Al-Mg alloy is
studied using atomistic simulations. Additionally, theoretical models for both
the parelastic and dielastic interactions between clusters and dislocations is
used to identify which factor among order strengthening, elastic interaction,
and change of stacking fault energy controls cluster strengthening. The
comparison of the results from these models to that of the atomistic
simulations show that in the case of Mg dimers, the strength of the strongest
ones are dominated by the dielastic contribution through the change of stacking
fault energy.
