The temperature dependence of microstructure in Zn-Al alloys, transferred to the equilibrium state by quenching from the solid solution temperature, T_SS, to room temperature (RT) and prolonged ageing at RT, was studied in situ by X-ray powder diffraction. Instead of the phase transitions expected according to the phase diagram, namely α (M/β) + β → α' + α(M/α') → α_SS for the alloy with 54 at% Zn and α(M/β) + β → α'+β → α_SS for the alloy with 62 at% Zn, the following sequence was observed for both alloys: α(M/β) + β → α' + β+ α(M/α', β) → α'+β → α_SS. In the cooling run, a temperature hysteresis in reversal phase transitions was observed. During a repeated heating, the microstructure depended on the previous thermal treatment of the alloys
