XXXVI. The primary solid solution of silver in aluminium

Abstract

The solid solubility curve for the primary solid solution of silver in aluminium has been re- determined, using pure materials. In contrast to the reports of previous workers, the solubility curve is not smooth, but exhibits a marked change in direction in the region of 49·4 per cent by weight of silver, at a temperature of 526°C. The maximum solid solubility is 55·6 per cent by weight of silver at the eutectic temperature of 566°C. The solidus curve shows an inflexion at approximately the same composition as that at which the anomaly in the solubility curve occurs. The results are discussed, and it is shown that the change in direction of the solubility curve occurs at the same electron : atom ratio as the peak of the (α+α₁) miscibility gap in the aluminium-zinc system. It is concluded that in both systems there is a tendency, caused by a factor of electronic origin, towards the separation of the solid sohltion into two face-centred cubic phases at an electron:atom ratio of 2·6. In the aluminium-silver system, however, the whole solubility curve lies at slightly too high a temperature for the formation of an (α+α₁) region such as occurs in the aluminium-zinc system, but the tendency towards this affects the form of the curve, introducing a change in direction. The relationship between the aluminium-zinc and aluminium-silver systems is described in terms of free-energy curves, and the structure of the Brillouin Zone for aluminium, which the present work suggests is still imperfectly known.