Cu–Cr alloys, irradiated with a low-energy, high-current electron beam, are analyzed by high-resolution secondary ion mass spectrometry. Mass spectra and images of Cu+ and Cr+ surface distributions finely reveal the regions enriched in Cu and Cr. For electron beam energies above a threshold value, the formation of a non-equilibrium Cu1−xCrx solid solution, extending over sub-micrometer areas is highlighted for the first time. A discussion of the process leading to Cu1−xCrx formation is given.