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{sup +} and Cr{sup +} 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 Cu{sub 1-x}Cr {sub x} solid solution, extending over sub-micrometer areas is highlighted for the first time. A discussion of the process leading to Cu{sub 1-x}Cr {sub x} formation is given.