On the Age-hardening of Aluminium-rich Al-Zn alloys

Abstract

(1) The phenomena of age-hardening were observed on the Al-rich Al-Zn alloys, when the zinc content exceeded 5%, and these alloys were divided into 2 kinds at 26% zinc, according to their properties. (2) Al-Zn series showed an eutectoid transformation at 256°C, and this transformation was observed on the alloys containing more than 20% zinc. The solubility of zinc in aluminium was found to be less than 5% at 110°C. Owing to these facts, the equilibrium diagram on the aluminium side was obtained. (3) It was found that age-hardening did not always concern a compound. The question is the solubility of a solid solution. (4) Age-hardening was considered to be due to the spontaneous crystallisation of a super-cooled solid solution. With this conception, the phenomena of hardening were explained. (5) As the mechanism of hardening it was found that the separaticn of a second phase in finely divided perticles gave rise to hardening on the one side, and on the other the disintegration of the grains.