We have investigated the segregational properties of polycrystalline Al(Cu) alloys in the composition range of 0.04 to 0.5 at. % Cu using medium energy ion scattering. While Cu does not segregate to the bare surface, significant quantities of Cu are found at the interface between the Al(Cu) and aluminum oxide. By measuring the interfacial Cu concentration as a function of temperature, we have determined that the segregational energy is 0.21±0.03 eV. ©1996 American Institute of Physics.