The change of microstructure with temperature of the title alloys has been studied in situ by X-ray powder diffraction. It has been found that the temperature dependence of microstructure of the alloys, rapidly quenched from the solid-solution temperature, T_ss, to room temperature, RT, is quite different from that of the alloys slowly cooled from T_ss to RT. The area between two curves showing that dependence for the given phase during the first heating from RT to Tss and first cooling from T_ss to RT is much smaller for the slowly-cooled alloys than for the rapidly quenched alloys. That area slightly increases with the increase of the Zn content in the alloys. The temperature dependence of microstructure of the alloys during the second heating from RT to Tss and second cooling from Tss to RT differs little from that during the first cooling from T_ss to RT. The ideal equilibrium state cannot be reached either by slow cooling of the alloys from T_ss to RT, or by a prolonged ageing at RT of the rapidly quenched alloys. The observed sequence of phase transitions in alloys during heating from RT to T_ss is different from that which could be expected according to the phase diagram of the system Al-Zn accepted in the literature. During cooling from T_ss to RT, a temperature hysteresis is observed in reversal phase transitions
