Al–Cu–Zn Aluminum–Copper–Zinc system

Al–Cu–Zn Aluminum–Copper–Zinc system

518 Al-Cu-W Aluminum-Copper-Tungsten system A tungsten-bearing compound (possibly a ternary AlCuW compound or, more probably, WA112) forms a eutectic...

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518

Al-Cu-W Aluminum-Copper-Tungsten system A tungsten-bearing compound (possibly a ternary AlCuW compound or, more probably, WA112) forms a eutectic with aluminum and CuAl2. Tungsten additions raise the upper melting point, but have no effect on strength with or without heat treatment [11. REFERENCE 1.

M. R. Whitmore, etc., JIM 34, 419

Al-Cu-Zn Aluminum-Copper-Zinc system Al is the primary phase over a wide range. There are four invariant points on a monovariant line from the Al-CuAl 2 eutectic to the zinc end [1-11] (Table 3.21). Table 3.21

INVARIANT REACTIONS AT THE ALUMINUM-ZINC SIDE OF THE ALUMINUM-COPPER-ZINC SYSTEM

Reaction

Composition of phases %Cu %Zn %Cu %Zn %Cu %Zn liq.



(l)liq.-»Al + CuAl2

33.0

(2)liq. + Al^ZnAl

— ~ 86

(3)liq.—ZnAl + Zn



(4)liq. + CuZn5-^Zn (5)liq. + CuAl 2 —Al + T

1.7 15

Al 5.7



95



70 Zn 99

98.3

2.7

60

(6)liq. + T ^ A l + CuZn5 10.5 74 1.8 (7) liq. + Al->CuZn 5 + ZnAl 6(?) 84(?) (8)liq.->ZnAl + CuZn3 + Zn 3.71 89.3

1.5

CuAl2 52.5 — ZnAl — 71.6

821



655

72.0

82.2 CuZn5 12.5 87.5 CuAl2 52 2 CuZn5 23 72

ZnAl 78.1

CuZn5 15.5 83.3

97.3 Al 1.5 65.0

Temperaature Ref. %Cu %Zn (°K)

716

55 55.5

T

697 13

693

8

14

669

8

Zn 2.75 96

652.5 11

The ternary phase T has a field of existence of 56-58% Cu, 10-30% Zn [8]. Two different structures, denoted by T and T', were determined for this phase, but no twophase field was detected. The structure at the aluminum end is very similar to the Cu4NiAl7 phase; therefore, it is probable that, as in the aluminum-copper-nickel alloys, the structure of the ternary phase changes more or less continuously with change of composition and the two structures T and T' represent the extremes, with inbetween structures formed in the intermediate alloys. The T structure is toward the copper-zinc side and has a formula close to Cu5Zn2Al3 (60.1% Cu, 24.7% Zn). It is

519

Wt.96Zn (a)

Wt.%Zn (b)

Fig. 3.27. The aluminum-zinc side of the aluminum-copper-zinc diagram: (a) liquidus; (b) phase distribution at 650 °K cubic; space group Pm3m; 2 atoms to the unit cell; with a weak ordering of the CsCl type. The parameter of the basic unit lattice changes from a = 2.91 x 10~10m at 57% Cu, 10% Zn, to a = 2.94 x 10- 10 m at 57% Cu, 25% Zn [8]. The T structure, which is at the aluminum end and has a possible formula Cu 3 ZnAl 3 (56.7% Cu, 19.2% Zn), has a deformed body centered cubic lattice, with strong superlattice lines of the CsCl type. Its Vickers hardness is 6 500MN/m 2 [12]. Diffusion of zinc into the Al-CuAl 2 eutectic results in the formation of T phase [12b]. CuZn 5 [78-87% Zn) can dissolve up to 5% Al. It is hexagonal close packed; space group P66/mmc; parameters a = 2.74 x 10 _10 m and c = 4.29 x 10"10m when containing 82% Zn and no aluminum [13]. It has a Vickers hardness of 1 500MN/m 2 [12]. The CuAl2 phase can dissolve up to 2 - 3 % Zn, with little change in lattice parameter and properties; the Zn phase can dissolve up to 1.25% Al and 2.75% Cu at eutectic temperature (652 °K) [8]. The solubility of copper in the ZnAl phase should be of the order of 1.5% at 633 °K [8]. The distribution of the phases in the solid state is complicated by the presence of two aluminum solid solutions (see 'Aluminum-Zinc system'). Figure 3.27(b) shows the probable distribution of phases at 650 °K.

520 The solubility of copper and zinc at various temperatures is given in Table 3.22. According to [14], the solubility of copper in aluminum is increased by zinc additions: at 730 °K the solubility is 2.8% Cu at 0% Zn and 3.6% Cu at 9% Zn. The eutectoid transformation ZnAl—>A1 + Zn is slowed down by copper additions [6, 15]. Zinc additions slow the diffusion of copper in aluminum [16, 17]. Table 3.22

SOLUBILITY OF COPPER AND ZINC IN ALUMINUM AT VARIOUS TEMPERATURES [8]

Temperature (°K) (°F) 700 650 625 600 550 500

800 710 665 620 530 440

Composition %Cu %Zn 2.7 1.8 1.5 1.3 0.7 0.45

70 47 43 29 14 6

Age hardening of aluminum-copper alloys is not appreciably affected by zinc additions [3, 16, 18-21]. Additions of copper to aluminum-zinc alloys reduce the rate of precipitation substantially (see 'Aluminum-Zinc system'). For the properties of the alloys see Part 4.

REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 12b. 13. 14. 15. 16. 17. 18. 19. 20. 21.

J. L. Haughton, etc., JIM 26, 532; 28, 645 D. Hanson, etc., CA 20, 569 H. Nishimura, JIM 40, 497; 41, 438; 43, 447 M. Hamasumi, etc., IIM 43, 447 H. Burkhardt, JIMMA 3, 520 E. Gebhardt, JIMMA 9, 274, 276; 10, 139, 244 K. Löhberg, JIMMA 10, 319 W. Köster, etc., JIMMA 9, 272, 273; 10, 244 E. Gebhardt, JIMMA 17, 428 H. Watanabe, JIMMA 25, 909 E. Weisse, etc., JIMMA 10, 244 Hanemann, 1952 M. R. Jackson, etc., Met A 6, 130976 Pearson, 1 D. J. Strawbridge, etc., /. Inst. Metals, 1947/48, 74, 191 M. L. Fuller, etc., JIMMA 2, 13, 681; 3, 38 V. I. Arkharov, etc., JIMMA 21, 781; 24, 773; 27, 375, 376, 647 J. S. Kirkaldy, Met A 3, 130892 N. N. Buinov, etc., JIMMA 26, 314 L. D. Kharitonova, JIMMA 28, 232 O. D. Shashkov, etc., JIMMA 31, 929 Y. Baba, MA 2, 1365