In order to study the thermodynamical stability of a crystalline overlayer on a quasicrystalline surface, thin Al films are deposited on the five- and three-fold-symmetry surface of the Al70Pd20Mn10 quasicrystal. Subsequently, the decrease of the film thickness is monitored as a function of time at different substrate temperatures using Auger electron spectroscopy. We find that diffusion of Al into the substrate is negligible below roughly 280 K and 300 K for the two investigated surfaces, respectively. For higher temperatures, Arrhenius parameters are extracted from the diffusion data which suggest that Al absorption is mediated by a fast vacancy-diffusion process. (C) 2004 Elsevier B.V. All rights reserved.