The influence of quenching rate on the kinetics of transformations of metastable phases in the Al-30 wt.% Zn alloy

The effect of quenching rate on the precipitation process in the Al-30 wt. % Zn alloy has been studied by the X-ray diffraction and electron microscopy. No effect has been observed both on the T-T-T curve for the transformation of coherent into semicoherent phase and on the isothermal growth of precipitates of these phases. The significant dependence has been, however, found when the ageing of the investigated alloy led to the formation of incoherent phases. The T-T-T curves for _R and _R transformations are shifted to the shorter ageing times with the increased quenching rate. The slopes of these T-T-T curves yielding parallel straight lines remain unchanged. The role of coherency stresses and of quenched-in strains in the investigated processes is discussed.In conclusion the authors would like to express their appreciation to Doc. Dr. V.Syneek, CSc. for his valuable discussions and to Ing. V.íma for the preparation of Al-Zn alloys. Our thanks are also due to Mr. V.Petr and Mr. Z.iký for their help in the heat-treatment and X-ray diffraction measurements of the investigated samples, and to Mr. P.Vyhlídka for the homogeneity control of the Al-Zn alloys.