Aspects of the phase transformation during aging of Zn-11% Al and Zn-27% Al alloys

The purpose of this work is to study the complex evolution observed during aging and the effect of alloying elements in ZA12 and ZA27. The results confirm the existence of the cellular reaction which appears very quickly: after 1 h at 100 deg C the quench alpha sub 1 phase has nearly decomposed and the lamellae have begun to appear. Evidence of the second stage of aging is shown by the aged Zn--10.2% Al which exhibits fine precipitates alpha ' sub m FCC in alpha ' lamellae. When the aging time is increased diffusion of Zn inside these particles increases the difference in crystalline parameters leading to alpha ' HCP precipitates and finally to eta HCP. The aging is completed when the fine microstructure alpha ' sub m has disappeared leading is large globular grains of alpha and Beta