10) S. Fujikawa and Ken-ichi Hirano: Trans. JIM 17 (1976) 93â102. ... 23) G. W. Roper and D. P. Whittle: Metall. Sci. 14 (1980) 21â28. 24) L. S. Darken: Trans.
Materials Transactions, Vol. 43, No. 2 (2002) pp. 232 to 238 c 2002 The Japan Institute of Metals
Quaternary Diffusion in 7000 Aluminum Alloys Tomoshi Takahashi1 , Yoritoshi Minamino2 and Toshimi Yamane3 1
Department of Materials Science and Engineering, Niihama National College of Technology, Niihama 792-8580, Japan Department of Adaptive Machine Systems, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan 3 Department of Mechanical Engineering, Hiroshima Institute of Technology, Hiroshima 731-5143, Japan 2
Quaternary and ternary interdiffusion experiments of 7000 aluminum alloys have been performed at 725 and 755 K. The concentration profiles indicate that the diffusion distance of Cu is shorter than those of Zn and Mg in the solid solutions. The direct interdiffusion coefficients Al , D ˜ Al ˜ Al ˜ Al D˜ ZnZn MgMg are positive, and indirect coefficients DZnMg , DMgZn are negative in the ternary Al–Zn–Mg alloys. The effective interdiffusion eff ˜ coefficients in 7000 aluminum alloys are in the order D > D˜ eff > D˜ eff . When the concentration distribution of Zn and Mg are Zn,C
Mg,C
Cu,C
eff 4 = D˜ CuCu = almost constant and the concentration of Cu approaches zero in the Al–Zn–Mg/Al–Zn–Mg–Cu couple, it is obvious that D˜ Cu,C ∗ ˜ DCu(Al–Zn–Mg) . The ratio values of indirect to direct diffusion coefficients suggest that attractive interactions of Zn–Mg and Cu–Mg exist in the Al–Zn–Mg–Cu alloys.
(Received September 7, 2001; Accepted December 10, 2001) Keywords: aluminum-zinc-magnesium-copper alloy, quaternary diffusion, diffusion couple, interaction
1. Introduction
2. Experimental Procedures
Most practical alloys are composed of more than two elements. For example, the “7000 series aluminum alloys” have as many as 8 or more components. The 7000 series aluminum alloys have been originated from Extra super duralmin, and are the promising structural materials.1, 2) In order to obtain superior mechanical properties in such aluminum alloys, the alloys are heat-treated for recovering, recrystallization, homogenization, aging, precipitation, etc. Diffusion is a basic and important factor for understanding and discussing such phenomena and heat treatments. Therefore, it is necessary to obtain the information for diffusion in such Al-base alloys with multicomponents.3) Many experimental studies of diffusion in Al-base binary alloys have been performed3–5) in order to determine only one interdiffusion coefficient. On the other hand, a few investigations of diffusion have been made in Al-base ternary alloys6–8) in which four coefficients were required to represent interdiffusion. Especially, the number of studies on diffusion in practical ternary Al–Zn–Mg alloys is very small in spite of its importance; three reports on the impurity diffusion coefficients of Zn or Mg in this Al–Zn–Mg alloy system9–11) and two reports on the interdiffusion12, 13) have been published. Recently, the authors have reported the nine interdiffusion coefficients in the quaternary Al–Zn–Mg–Cu alloys.13) The purposes of the present work are (a) to determine the ternary interdiffusion coefficients by Matano-Kirkaldy method14, 15) in the α-phase region of the ternary Al–Zn–Mg system at 725 K, (b) to determine the effective interdiffusion coefficients by Dayananda method16, 17) in the 7000 aluminum alloys at 755 K, (c) to clarify the relation between the interdiffusion coefficients and the effective interdiffusion coefficients on the basis of the results of quaternary interdiffusion coefficients by Thompson-Morral Method18) in the α Al–Zn– Mg–Cu solid solutions, and (d) to discuss the thermodynamic interactions between solute atoms in α Al–Zn–Mg–Cu solid solutions.
Commercial alloys used in the present work were 1050 pure aluminum, 7003 and 7075 aluminum alloys produced by Showa Aluminum Co. Ltd. In the 7003 and 7075 aluminum alloys, the main solute elements are Zn, Mg, Cu, and small amounts of the other elements such as Mn, Cr, Ti etc. are added. Quaternary and ternary alloys with compositions of 7050 aluminum alloys (laboratory alloys) were prepared from 99.99 mass%Al, 99.998 mass%Zn, 99.99 mass%Mg and a Al–39.61 mass%Cu mother alloy by high frequency induction melting in an argon atmosphere. The commercial and laboratory alloys were annealed at 773 K for 432 ks for homogenization and grain coarsening. The These alloys have a single phase of α-phase solid solution. The grain diameter of commercial alloys was about 0.3 mm, and that of laboratory alloys was about 0.7 mm. The alloy ingots were cut into 5 mm×5 mm diffusion plates of about 3 mm in thickness. The surfaces of the alloy plates were metallographically polished with SiC paper, 0.3 µm alumina powder and diamond paste. The polished plates for diffusion couples were hold together by means of stainless steel clamps. The terminal compositions of diffusion couples are listed in Table 1(a). The quaternary diffusion couples are designated P1-P3 and M1-M3 according to the combination of commercial and laboratory alloys, respectively, as listed in Table 1(b). The terminal compositions of ternary Al–Zn–Mg diffusion couples have been reported in elsewhere.13) The assembled diffusion couples were vacuum-sealed into a Pyrex tube. The quaternary and ternary diffusion couples were annealed at 755 K for 73.53 ks and 725 K for 86.84 ks, respectively, and then quenched in ice water. The annealed diffusion couples were cut at their center parallel to the diffusion direction in order to expose sections which had no oxidation and evaporation of elements, and then they were mounted in synthetic resin. The exposed section of each couple was metallographically polished. In order to obtain diffusion profiles in the diffusion couples, the characteristic X-
Quaternary Diffusion in 7000 Aluminum Alloys
233
Table 1 (a) Compositions of commercial 1050 and 7000 aluminum alloys (at%). Al
Si
Fe
Cu
Mn
Mg
Cr
Zn
Ti
Zr
Commercial 1050 Commercial 7003 Commercial 7075
Bal. Bal. Bal.
0.087 0.080 0.060
0.111 0.090 0.090
0.004 0.080 0.684
D˜ Mg,C > D˜ Cu,C . D˜ Zn,C (3) When the concentration distribution of Zn and Mg are almost constant and the concentration of Cu approaches zero in the Al–Zn–Mg/Al–Zn–Mg–Cu couple, it is obvious that eff 4 ∗ = D˜ CuCu = D˜ Cu(Al–Zn–Mg) . D˜ Cu,C (4) The ratio values of indirect to direct diffusion coeffi-
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cients suggest that attractive interactions of Zn–Mg and Cu– Mg exist in the Al–Zn–Mg–Cu alloys. Acknowledgments This work was financially supported by Iketani Science and Technology Foundation, Tokyo 100, Japan, and the Light Metal Educational Inc., Osaka 541-0056, Japan. The authors are deeply indebted to the supports. Chemical analysis of the aluminum alloys was performed by Showa Aluminum Co. Ltd., Oyama 323-0811. The authors would like to thank Mr. Satoshi Hozumi of the company for his assistance of the chemical analysis. REFERENCES 1) See, for example, G. Itoh: The Structure and Property in Aluminum Alloys (Japanese), (Japan Inst. Light Metals, Tokyo, 1991) pp. 296– 322. 2) A. Deschamps, Y. Brecht and F. Livet: Mater. Sci. and Technol. 15 (1999) 993-1000. 3) S. Fujikawa: J. Japan Light Metals 46 (1996) 202–215. 4) Y. Minamino and T. Yamane: Diffusion in Materials (Japanese), Seminar Text of The Japan Inst. Metals, Japan, (1993) pp. 21–27. 5) H. Mehrer and N. Stolica: Diffusion in Solid Metals and Alloys, Landolt-Boernstein Ed., by H. Mehrer (Springer-Verlag, Berlin, 1991) pp. 600–625. 6) T. Takahashi, M. Katoh, Y. Minamino and T. Yamane: J. Japan Inst. Light Metals 39 (1989) 287–292. 7) T. Takahashi, A. Takahashi, H. Araki, T. Tanaka, Y. Minamino, Y. Miyamoto and T. Yamane: J. Japan Inst. Metals 58 (1994) 1364–1371. 8) T. Takahashi, H. Yasuda, H. Araki, Y. Minamino, T. Yamane and S. Saji: J. Japan Inst. Light Metals 44 (1994) 69–74. 9) S. Fujikawa: Diffusion of magnesium in Al–Zn–Mg alloys, ALUMINUM ALLOYS, Their Physical and Mechanical Properties, Ed., by T. Sato, S. Kumai, T. Kobayashi and Y. Murakami (The Japan Inst. Light Metals, Vol. 2, 1998) pp. 671–681. 10) S. Fujikawa and Ken-ichi Hirano: Trans. JIM 17 (1976) 93–102. 11) D. Beke, I. Godeny, F. J. Kedves and G. Groma: Acta Metall. 25 (1977) 539–550. 12) T. Takahashi, T. Yamane, H. Araki, Y. Minamino, T. Inoue, Y. Miyamoto and A. Takahashi: J. High Temperature Society of Japan 23 (1997) 275–
281. 13) T. Takahashi, Y. Minamino, K. Hirao and T.Yamane: Mater. Trans., JIM 40 (1999) 997–1004. 14) J. S. Kirkaldy: Can. J. Phys. 35 (1957) 435–440. 15) J. S. Kirkaldy, J. E. Lane and G. R. Masson: Can. J. Phys. 41 (1963) 2174–2186. 16) M. A. Dayananda and D. A. Behnke: Scri. Metall. Mater. 25 (1991) 2187–2191. 17) M. A. Dayananda : Defect and Diffusion Forum 95–98 (1993) 521– 534. 18) M. S. Thompson and J. E. Morral: Acta Metall. 34 (1986) 2201–2203. 19) I. Uchiyama, A. Watanabe and S. Kimoto: X-ray Micro Analyzer (Japanese), (Nikkan Kogyo Newspaper Co., Tokyo, Japan, 1974) pp. 127–196. 20) H. Soejima: Electron Probe Micro Analyzer (Japanese), (Nikkan Kogyo Newspaper Co., 1987) pp. 338–402. 21) A. D. LeClaire and G. Neumann: Diffusion in Solid Metals and Alloys, Landolt-Boernstein Ed., by H. Mehrer (Springer-Verlag, Berlin, 1991) pp. 151–156. 22) T. R. Heyward and J. I. Goldstein: Metall. Trans. 4 (1973) 2335–2342. 23) G. W. Roper and D. P. Whittle: Metall. Sci. 14 (1980) 21–28. 24) L. S. Darken: Trans. AIME 180 (1949) 430–438. 25) I. Araki, M. Kanno and Qi CUI: J. Japan Inst. Light Metals 43 (1993) 539–544. 26) Y. Baba: J. Japan Inst. Metals 31 (1967) 513–518. 27) S. Fujikawa, K. Hirano and Y. Baba: Bulletin Japan Inst. Metals 7 (1968) 494–504. 28) R. D. Sisson, Jr. and M. A. Dayananda: Metall. Trans. A 8A (1977) 1849–1856. 29) Y. Minamino, T. Yamane, S. Saji, K. Hirao, S. B. Jung and T. Kohira: J. Japan Inst. Metals 58 (1994) 397–403. 30) J. S. Kirkaldy, Zia-Ul-Haq and L. C. Brown: ASM Trans. Q. 56 (1963) 834–849. 31) T. Tanaka, N. V. Gokcen, P. J. Spencer, Z. Morita and T. Iida: Z. Metallkde. 84 (1993) 100–105. 32) T. Tanaka, N. V. Gokcen, K. C. Hari Kumer, S. Hara and Z. Morita: Z. Metallkde. 87 (1996) 779–783. 33) M. Shimoji and K. Niwa: Acta Metall. 5 (1957) 496–501. 34) A. K. Niessen, F. R. de Boer, R. Boom, p. F. de Chatel, W. C. M. Mattens and A. R. Miedema: Calphad 7 (1983) 51–70. 35) T. Iida and R. I. L Guthrie: The properties of Liquid Metals, (Clarendon Press, Oxford, 1988) pp. 14–71. 36) T. Iida and R. I. L Guthrie: The properties of Liquid Metals, (Clarendon Press, Oxford, 1988) pp. 14–100.
