Endothermic quasicrystalline-to-crystalline phase transition in Al<SUB>6</SUB>CuMg<SUB>4</SUB>

Electron microscopic and differential scanning calorimetric (DSC) studies have been performed to investigate the phase transitions in the rapidly solidified Al6CuMg4 alloy system. We present evidence, for the first time, that anendothermic quasicrystalline to crystalline transition occurs in this system around 340&#176; C. This is an unexpected feature-for conventional wisdom would lead one to expect exothermic behaviour as was seen in Al86Mn14-and points to the fact that stability of certain quasicrystalline phases may be much larger than hitherto expected. Some comments on the recently reported large quasicrystal for the Al6CuLi3 system are also made in the light of our observation