Structural changes after heat treatment of an icosahedral phase of melt-spun Al—Pd—Mn alloys have been studied by X-ray powder diffraction and transmission electron microscopy. Around the compositions Al70Pd20Mn10and Al70Pd23Mn7, no phase transition occurs on annealing, and the icosahedral phase is stable up to the melting point. However, for the Al70Pd26Mn4sample, the icosahedral phase transforms into a 2/1 cubic approximant crystalline phase at 750°C. A decagonal quasicrystal is formed for a melt-spun Al75Pd20Mn5alloy.