Abstract: Through microstructure observation and X-ray diffraction analysis, the equilibrium phase constituents of Al-Zn alloy that contains 2 at.pct Cu at room temperature have been determined as Al-based solid solution (α), Zn-based solid solution and Al4Cu3Zn phase (T'-phase), which are different from α phase, Zn phase and CuZn4 phase originally believed. It is determined that the products of discontinuous precipitation transformation below 277℃ are not the equilibrium phase constituents, but the metastable phases made up of α phase, Zn phase and CuZn4 phase. The phase constituents after discontinuous precipitation of AlZn-2Cu alloy would transform to the ones in equilibrium status: Al-based solid solution (α) in fcc structure, Zn-based solid solution in hcp structure and A4Cu3Zn phase (T'-phase) ultimately through plastic deformation at room temperature and re-heating treatment below 277℃

Key words: Al-Zn-Cu alloy, Discontinuous, precipitation, Phase constituents, Deformation