Abstract: The structure of Al-Mn-Zn-Mg alloy powder annealed at 800℃ has been studied by transmisston electron microscopy(TEM).An approximant phase(named as C-phase) to the decagonal phase was found and its crystal structure was determined It belongs to c-center orthorhombic lattice with a=2.35 nm,b=3.27 nm and c=1.22 nm.We stillfound a hexagonal phase with a=0.7) nm and c=0.79 nm,(named as phase) in the annealed alloy powder.The annealed alloy powder is composed of the C-phase,the phase,the decagonal phase and Al solid solution.

Key words: quasicrystal, crystalline structure, Al-Mn-Zn-Mg alloy powder