A differential scanning calorimetry and Vickers microhardness study of phase transformations in an Al–Zn–Mg alloy

Abstract

Precipitate phase formation following different thermal cycles has been investigated on an age-hardenable Al–4.8 wt% Zn–1.3 wt% Mg alloy to obtain the best hardness conditions. Differential scanning calorimetry and microhardness measurements have been performed. It has been evidenced that a distribution of Guinier–Preston zones and their partial transformation into an intermediate phase lead to the highest hardness. The formation of equilibrium phases acts as an obstacle to an increase in the hardness in the various cycles examined. The different stabilities of the coherent structures formed in the course of thermal treatments is discussed and a multistage procedure is claimed to be the best condition for obtaining high hardness within a reasonable heat treatment time.

Acknowledgements

E. Di Russo and Istituto Sperimentale Metalli Leggeri (ISML) are greatly acknowledged for fruitful discussions and for the sample preparation. The work has been partially supported by a national Ministero Istruzione UniversitáRicerca–Fondo Incentivazione Ricerca di Base program.