Copper-aluminium phase diagram

The aluminium-copper phase diagram is shown below. 

Fig. 20.43 Aluminium-rich end of the aluminium-copper 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. 

Figure 6.46(a) shows part of the phase diagram of the Al-Cu system. One prerequisite for precipitation hardening is the existence of a two-phase region where the matrix phase (in the example, aluminium with copper in solid solution) is in equilibrium with the precipitation phase (a copper-rich phase in the example), a so-called miscibility gap (see section C.3). 

Mar] Markiv, V.Ya., Bumashova, V.V., Rybov, V.P., The Systems Titanium-Iron-Aluminium, Titanium-Nickel-Aluminium and Titanium-Copper-Aluminium (in Russian), Akad. Nauk Ukr. SSR, Metallofizika.,46, 103-110 (1973) (Phase Diagram, Phase Relations, Experimental,, , 24)... 

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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