Aluminium-copper alloys phase diagram

When the phase diagram for an alloy has the shape shown in Fig. 10.3 (a solid solubility that decreases markedly as the temperature falls), then the potential for age (or precipitation) hardening exists. The classic example is the Duralumins, or 2000 series aluminium alloys, which contain about 4% copper. 

G. Ghosh, Aluminium-chromium—copper, in Ternary Alloys A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams, G. Petzow and G. Effenberg, Ed., VCH Publishers, New York, 1992, pp. 311-319. 

When we compare, for example, the ordinary per cent, by weight equilibrium diagrams of the alloys of monovalent copper with, first, divalent zinc, second, trivalent aluminium, and, third, tetravalent tin, we find that each system is characterised by similar a, a + / , /3, /3 + y, y, etc., phase areas. We have already noted that the range of a-solid solution decreases with increasing valency of solute, and that the maximum solid solubility, in each case, occurs at an electron concentration of 1 4 (p. 69). 

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