Al-Cu-Zn (Aluminum-Copper-Zinc)
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Phase Diagram Evaluations: Section II
Al-Cu-Zn (Aluminum-Copper-Zinc) V. Raghavan
Since the previous review of this system by [1992Gho], several thermodynamic descriptions have become available [1998Lia, 2002Mie, 2003Bor], with the last study reporting in addition new experimental measurements. The description of [1998Lia] is the most detailed treatment available for Al-rich alloys.
Binary Systems The Al-Cu phase diagram [1993Sau, Massalski2] depicts a number of intermediate phases: CuAl2 (C16-type tetragonal, denoted h), CuAl (monoclinic, g), Cu5Al4(LT) (monoclinic, f), e2 (NiAs-type hexagonal), e1(bcc), Cu3Al2 (rhombohedral, d), Cu9Al4(HT) (c0), Cu9Al4(LT) (D83-type cubic, c1), and Cu3Al (bcc, b). In the above, HT = hightemperature and LT = low-temperature. The Al-Zn phase diagram [1993Che] contains no intermediate phases. A miscibility gap occurs in the Al-based face centered cubic (fcc) solid solution below 351 C, where the fcc phase splits into (Al)Õ and (Al)’’. The monotectoid reaction (Al)’’ M
(Al)Õ + (Zn) follows at 277 C. The Cu-Zn phase diagram [1993Kow, Massalski2] is characterized by a series of peritectic reactions, which yield CuZn (b, bcc), Cu5Zn8 (c, D82-type cubic), CuZn3 (d, B2, CsCl-type cubic), and CuZn4 (e, cph). Zn (cph) has an axial ratio c/a much larger than e and the two coexisting cph phases are modeled separately with different interaction parameters [1993Kow]. The b phase orders to a CsCl-type B2 phase (bÕ) through a second-order transition below ~460 C.
Ternary Phases A ternary phase with rhombohedral symmetry and with the nominal composition Al4Cu3Zn (denoted s) is known in this system [Pearson3]. The homogeneity range of s and its temperature dependence are not clearly defined [1998Lia]. The structurally-related, low-temperature form sÕ was found to be stable between 400 C and room temperature by [2005Hao]. [1998Lia] omitted sÕ in their thermodynamic description.
Fig. 1 Al-Cu-Zn computed liquidus projection [1998Lia]
Journal of Phase Equilibria and Diffusion Vol. 28 No. 2 2007
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Section II: Phase Diagram Evaluations
Fig. 2 Al-Cu-Zn computed isothermal section at 700 C [1998Lia]
Fig. 3 Al-Cu-Zn computed isothermal section at 600 C [1998Liaa]
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Journal of Phase Equilibria and Diffusion Vol. 28 No. 2 2007
Phase Diagram Evaluations: Section II
Fig. 4 Al-Cu-Zn computed isothermal section at 500 C [1998Lia]
(a)
(b)
Fig. 5 Al-Cu-Zn computed vertical sections at (a) 20 mass% Cu and (b) 20 mass% Zn [1998Lia]
Computed Ternary Phase Equilibria [1998Lia] reexamined the experimental data from the literature and presented an assessed liquidus projection and two isothermal sections at 700 and 500 C, based mainly on the results of [1932Bau, 1941Kos1,1941Kos2, 1960Arn]. In addition to the above assessed diagrams, the activity measurements of [1985Seb] for Al in Cu-lean liquid alloys and of [1986Sug] for Zn in Cu-rich liquid alloys were used in the optimization. In the thermodynamic modeling, the
liquid, fcc, cph (Zn), cph (e) and bcc phases were treated as disordered sol
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