Phase formation in the AuCu‐Al thin‐film system has been studied by nuclear backscatering of energetic ions and by x‐ray diffraction techniques. At temperatures between 150° and 220 °C Au2Al or Al2Cu are formed initially from Au‐rich or Cu‐rich solid solutiions, respectively. The growth kinetics are slower than in the corresponding bilayers of Al‐Cu or Al‐Au while the sequence of compound formation is unchanged.