X-RAY STUDY OF THE ALUMINIUM-ZINC SYSTEM

Abstract

The Al-Zn alloys covering the range of the β and the γ field have been studied roentgenographically with both ordinary and precision cameras, with which the powder photograms of the alloys have been taken not only at room-temperatures but also directly at high temperatures.
From the lattice constant-concentration curves obtained, it is confirmed that the β phase is merely a continuation of the γ phase; the solid solubility of zinc in the latter phase has been determined.
By adding a small amount of Mg in the alloy, the intermediate stages during the decomposition of quenched β due to aging h ave been studied. The results showed that the eutectoid-transformation of the β phas e is simply a process of decomposition into a and y, which are in the equilibrium concentration, and that no intermediate metastable phase exists during the process. It should be noticed, however, that the lattice constant of quenched β decreases anomalously during aging and that the complete decomposition of the said phase is hardly attainable at ordinary temperature. The complicated changes in physical properties of the quenched alloys due to aging have been explained crystallographically.