Thin‐film reactions of Al/V with and without 4 at. % Cu in the Al have been studied by Rutherford backscattering, x‐ray diffraction, scanning electron microscopy, and Auger electron spectroscopy after vacuum annealing in the temperature range 300–500 °C. In the Al/V system, the intermetallic phase VAl3grows as (time)1/2with an activation energy of 2.1±0.2 eV. The presence of Cu in the Al retards the VAl3growth and alters the phase sequence.