Difference in the Hot Compressive Behavior and Processing Maps between the As-cast and Homogenized Al-Zn-Mg-Cu (7075) Alloys

doi:10.1016/j.jmst.2016.04.006

Abstract

Abstract: The deformation mechanisms and processing maps of the as-cast Al-Zn-Mg-Cu (7075) aluminum (Al) alloy were studied and compared with those of the homogenized 7075 Al alloy in the temperature range of 573-723?K and in the strain rate range of 10^-3-10?s^-1 to explore a possibility for directly using the as-cast 7075 Al alloy as a billet for hot working. The as-cast and homogenized 7075 Al alloys had similar grain sizes and showed similar high-temperature deformation behaviors. The as-cast 7075 Al alloy, however, exhibited higher power efficiencies and smaller unstable flow regions compared to the homogenized 7075 Al alloy because of the presence of secondary phases (MgZn₂) segregated at the dendritic interfaces in the as-cast microstructure, which were formed during non-equilibrium solidification. These segregated phases provided nucleation sites for dynamic recovery or continuous dynamic recrystallization, and as a result a fine and more homogeneous (sub)grain structure could be obtained from the as-cast microstructure compared to the homogenized microstructure. The current work suggested the possibility and advantage of using as-cast microstructures for hot working of aluminum alloys with high content of solutes.

Key words: Al-based alloys, Processing map, Hot compression, As-cast microstructure, Segregation, Recrystallization

S.Y. Park, W.J. Kim. Difference in the Hot Compressive Behavior and Processing Maps between the As-cast and Homogenized Al-Zn-Mg-Cu (7075) Alloys[J]. J. Mater. Sci. Technol., 2016, 32(7): 660-670.

Figures/Tables 14

SEM micrographs of the (a,b) as-cast and (c,d) homogenized 7075 Al alloys at low and high magnifications.

Types of phases and their phase fraction in the 7075 Al alloy calculated using the (a) non-equilibrium and (b) equilibrium and models.

HR-XRD results for the as-cast and homogenized 7075 Al alloys.

Image quality (IQ) and inverse pole figure (IPF) maps of the (a) as-cast and (b) homogenized 7075 Al alloys.

True stress (σ) vs. true strain (ε) curves obtained from the compression tests of the as-cast 7075 Al alloy performed at various strain rates at (a) 573?K, (b) 623?K, (c) 673?K, and (d) 723?K.

True stress (σ) vs. true strain (ε) curves obtained from the compression tests of the homogenized 7075 Al alloy performed at various strain rates at (a) 573?K, (b) 623?K, (c) 673?K, and (d) 723?K.

Plots of ln ε ? - ln σ 0.4 for the (a) as-cast and (b) homogenized 7075 Al alloys. The plots of ln ε ? - ln σ 0.4 for the (c) as-cast and (d) homogenized 7075 Al alloys.

Plots of ln ε ? - lnsinh ( α σ 0.4 ) for the (a) as-cast and (b) homogenized 7075 Al alloys. The plots of lnsinh α σ 0.4 - 1000 / T for the (c) as-cast and (d) homogenized 7075 Al alloys.

Plots of ln Z vs. lnsinh α σ 0.4 for the (a) as-cast and homogenized 7075 Al alloys. The plots of ln Z vs. lnsinh α σ at different strains (0.2, 0.4, 0.6 and 0.8) for the (b) as-cast and (c) homogenized 7075 Al alloys.

Plots of ln Z vs. lnσ0.4 for the (a) as-cast and (b) homogenized 7075 alloys.

Processing maps for the as-cast 7075 Al alloys at strains of (a) 0.2, (b) 0.4, (c) 0.6 and (d) 0.8.

Processing maps for the homogenized 7075 Al alloys at strains of (a) 0.2, (b) 0.4, (c) 0.6 and (d) 0.8.

η values of the as-cast and homogenized 7075 Al alloys as a function of the strain rate at ε?=?0.8.

IQ, IPF and grain boundary map images of the (a, b, c) as-cast and (d, e, f) homogenized 7075 Al alloys after the compression tests at 673?K at three different strain rates of 10-3, 10-1 and 10?s-1. In the grain boundary maps, low angle boundaries (2°-15°) are in blue and high angle boundaries (>15°) are in red.

References

[1] A. Heinz, A. Haszler, C. Keidel, S. Moldenhauer, R. Benedictus, W.S. Miller. Mater. Sci. Eng. A Struct. Mater, 280 (2000), pp. 102-107
[2] Y.C. Lin, L.T. Li, Y.X. Fu, Y.Q. Jiang. J. Mater. Sci, 47 (2012), pp. 1306-1318
[3] M.R. Rokni, A.Z. Hanzaki, A.A. Roostaei, A. Abolhasani. Mater. Des, 32 (2011), pp. 4955-4960
[4] M. Rajamuthamilselvan, S. Ramanathan. J. Alloys Compd, 509 (2011), pp. 948-952
[5] M.R. Rokni, A. Zarei-Hanzaki, A.A. Roostaei, H.R. Abedi. Mater. Des, 32 (2011), pp. 2339-2344
[6] Y.C. Lin, L.T. Li, Y.C. Xia, Y.Q. Jiang. J. Alloys Compd, 550 (2013), pp. 438-445
[7] M.A.J. Taleghani, E.M.R. Navas, M. Salehi, J.M. Torralba. Mater. Sci. Eng. A Struct. Mater, 534 (2012), pp. 624-631
[8] Y.B. Yang, Z.M. Zhang, X.B. Li, Q. Wang, Y.H. Zhang. Mater. Des, 51 (2013), pp. 592-597
[9] Z.C. Sun, L.S. Zheng, H. Yang. Mater. Charact, 90 (2014), pp. 71-80
[10] M.T. Mandarjani, A. Zarei-Hanzaki, H.R. Abedi. Mater. Sci. Eng. A Struct. Mater, 637 (2015), pp. 107-122
[11] Z. Zhao, J. Cui, J. Dong, B. Zhang. J. Mater. Process. Technol, 182 (2007), pp. 185-190
[12] R. Nadella, D. Eskin, L. Katgerman. Mater. Sci. Technol, 23 (2007), pp. 1327-1335
[13] L. Backerud, E. Krol, J. Tamminen. Solidification Characteristics of Aluminium Alloys. Wrought Alloys, vol. 1, TangenTrykk A/S, Oslo (1986)
[14] L. Backerud, G. Chai, L. Arnberg. Solidification Characteristics of Aluminum Alloys. Foundry Alloys, vol. 2, American Foundrymen's Society, Des Plaines, USA (1996)
[15] O.D. Sherby, R.H. Klundt, A.K. Miller. Metall. Trans. A, 8 (1977), pp. 843-850
[16] Y. Deng, Z. Yin, J. Huang. Mater. Sci. Eng. A Struct. Mater, 528 (2011), pp. 1780-1786
[17] S.D. Liu, J.H. You, X.M. Zhang, Y.L. Deng, Y.B. Yuan. Mater. Sci. Eng. A Struct. Mater, 527 (2010), p. 1200
[18] H.J. Frost, M.F. Ashby. Deformation-Mechanism Maps. Pergamon Press, Oxford, UK (1982)
[19] O.D. Sherby, P.M. Burke. Prog. Mater. Sci, 13 (1967), pp. 325-390
[20] Y.V.R.K. Prasad, H.L. Gegel, S.M. Doraivelu, J.C. Malas, J.T. Morgan, K.A. Lark, D.R. Barker. Metall. Trans. A, 15 (1984), pp. 1883-1892
[21] Y.V.R.K. Prasad. Mater. Sci. Eng. A Struct. Mater, 243 (1998), pp. 82-88
[22] T.Y. Kwak, H.K. Lim, W.J. Kim. J. Alloys Compd, 644 (2015), pp. 645-653
[23] T.Y. Kwak, H.K. Lim, W.J. Kim. J. Alloys Compd, 658 (2016), pp. 157-169
[24] H. Ziegler. Progress in Solid Mechanics. I.N. Sneddon, R. Hill (Eds.)John Wiley and Sons, New York (1963), pp. 93-191
[25] S. Gourdet, F. Montheillet. Acta Mater, 51 (2003), pp. 2685-2699
[26] W.H. van Geertruyden, W.Z. Misiolek, P.T. Wang. Mater. Sci. Eng. A Struct. Mater, 419 (2006), pp. 105-114
[27] F.J. Humphreys. Metall. Sci, 13 (1979), pp. 136-145
[28] F.J. Humphreys. ActaMetall, 25 (1977), pp. 1323-1344 Affiliated with Department of Materials Science and Engineering, Stanford University
[29] O.D. Sherby, E.M. Taleff. Mater. Sci. Eng. A Struct. Mater, 322 (2002), pp. 89-99