  Grain boundary energies in different elements are correlated. The
proportional scaling constants relating the energies of
crystallography-equivalent boundaries in any two f.c.c. elements are nearly
constant, with the notable exception of aluminum where these constants are
known to vary significantly. However, the origins of the exceptional behavior
of aluminum are not understood. Previously, we reported that for fcc metals
there is a preference for boundaries to shift their tilt axis across the (1-10)
plane towards [112] and to ultimately form low energy [112] core shifted
boundaries (CSBs). By comparing grain boundary energies in copper and aluminum
with different tilt axis in (1-10) plane, we now report the existence of a
well-defined scaling behavior for the case of low angle boundaries. In
contrast, the scaling constant for high angle boundaries is essentially fixed
regardless of their tilt axis shift. This results in a gradual change in the
scaling constants from low angle to high angle boundaries, which is responsible
for the apparent exceptional scaling behavior found in aluminum. An analysis of
structure evolution during core shifting points to the significance of
boundary-core dissociation, a form of correlated relaxation of individual atoms
at boundaries, in controlling the scaling of the boundary energies.
