**8. Acknowledgments**

This research was carried out under the project number MC 4.04203 in the framework of the Research Program of the Materials innovation institute M2i (www.m2i.nl). The authors acknowledge Mr. K. Kwakernaak and Mr. E.R. Peekstok for assistance in microstructure examination.

### **9. References**


1) The particles distributed along the grain boundaries which constitute more than 70% of the secondary phases present in the as-cast structure of the AA7020 aluminum alloy are Al17(Fe3.2,Mn0.8)Si2 particles. The low melting point phases are indeed present in the as-cast microstructure of the AA7020 aluminum alloy, which may cause incipient melting at 576 °C. These phases contain Al-Cu-Mg-Zn and dissolve during homogenization at 550 °C for 2 h. 2) The width of the grain boundary particles remains unchanged during homogenization at low temperatures. It however decreases at higher temperatures. The extent of the dissolution is more dependent on homogenization temperature than on time. The evolution mechanisms of the GB particles during homogenization consist of spheroidization during homogenization at low temperatures and thinning, discontinuation and full dissolution

3) Four different types of dispersoids are formed in the AA7020 aluminum alloy variants during homogenization. In addition to the well-known Al3Zr dispersoids, three other types of dispersoids are also present in the homogenized microstructure of the AA7020 aluminum alloy. The number densities of Zr- and Cr-containing dispersoids are large in the grain interior and very small in the grain boundary regions. These two types of dispersoids appear to be fully spherical and are formed at all the homogenization conditions. The Mncontaining dispersoids form only when the homogenization temperature is equal to or higher than 510 °C and holding time longer than 4 h. The number density of these dispersoids is close to zero in the grain interior but becomes high in the grain boundary regions. The number density and sizes of the Zr-containing dispersoids increase with

This research was carried out under the project number MC 4.04203 in the framework of the Research Program of the Materials innovation institute M2i (www.m2i.nl). The authors acknowledge Mr. K. Kwakernaak and Mr. E.R. Peekstok for assistance in microstructure

[1] ASM Handbook, 10th ed., vol. 14, Metal Forming, ASM International, Metals Park, OH

[2] T. Sheppard, *Extrusion of Aluminum Alloys*, Kluwer Academic Publishers, Dordrecht

[3] A.R. Eivani, Modeling of Microstructural Evolution during Homogenization and

[4] N.A. Belov, D.G. Eskin and A.A. Aksenov, *Multicomponent Phase Diagrams: Applications* 

[5] L.L. Rokhlin, T.V. Dobatkina, N.R. Bochvar and E.V. Lysova, *J. Alloys Compd.* 367, 10

*for Commercial Aluminum Alloys*, Elsevier Science, New York (2005).

[6] S.T. Lim, Y.Y. Lee and I.S. Eun, *Mater. Sci. Forum* 519-521, 549 (2006). [7] C. Mondal and A.K. Mukhopadhyay, *Mater. Sci. Eng. A* 391, 367 (2005). [8] R.K. Gupta, N. Nayan and B.R. Ghosh, *Cana. Metall. Q.* 45, 347 (2006).

Simulation of Transient State Recrystallization leading to Peripheral Coarse Grain Structure in Extruded Al-4.5Zn-1Mg Alloy, PhD Thesis, June 2010, Delft, The

(TDFD) at high temperatures.

**8. Acknowledgments** 

examination.

**9. References** 

(1992).

(1999).

(2004).

Netherlands.

increasing Zr content of the alloy and homogenization time.


[45] Alphabetical indexes for experimental patterns, Sets 1-52, International Center for

[47] ASM Handbook, 10th ed., vol. 2, *Non-Ferrous Alloys*, ASM International, Metals Park,

[48] R.T. DeHoff and F.N. Rhines, *Quantitative Microscopy*, McGraw-Hill, New York (1968). [49] A.R. Eivani, H. Ahmed, J. Zhou, J. Duszczyk, Metal. Mater. Trans. A. 40, 717 (2009). [50] R.W. Cahn and P. Haasen, *Physical Metallurgy*, North Holland, Amsterdam (1996). [51] D. Gaskell, *Introduction to the Thermodynamics of Materials*, Taylor & Francis Co., New

[54] M. Dumont, W. Lefebvre, B. Doisneau-Cottignies and A. Deschamps, *Acta Mater.* 53,

[57] ASM Handbook, 10th ed., vol. 3, *Alloy Phase Diagrams*, ASM International, Metals Park,

[62] A.R. Eivani, H. Ahmed, J. Zhou, J. Duszczyk, C. Kwakernaak, Mater. Sci. Tech. DOI

[67] Y. Du, Y.A. Chang, B. Huang, W. Gong, J. Jin, H. Xu, Z. Yuan, Y. Liu, Y. He and F.Y. Xie,

[68] A.R. Eivani, S. Valipour, H. Ahmed, J. Zhou, J. Duszczyk, Metal. Mater. Trans. A. 42,

[69] A.R. Eivani, H. Ahmed, J. Zhou, J. Duszczyk, Adv. Mater. Res. 89-91, 177 (2010).

[63] A.R. Eivani, H. Ahmed, J. Zhou, J. Duszczyk, Mater. Sci. Eng. A. 527, 2418 (2010). [64] A.R. Eivani, S. Valipour, H. Ahmed, J. Zhou, J. Duszczyk, Metal. Mater. Trans. A. 40,

[52] R. Nadella, D.G. Eskin, Q. Du and L. Katgerman, *Prog. Mater. Sci.* 53, 421 (2008). [53] A.R. Eivani, H. Ahmed, J. Zhou, J. Duszczyk, Mater. Sci. Tech. 26, 215 (2010).

4015.

OH (1992).

York (2003).

2881 (2005).

OH (1992).

2435 (2009).

1109 (2011).

[66] N. Saunders, *Z. Metallkd* 80, 894 (1989).

*Mater. Sci. Eng. A* 363, 140 (2003).

[46] M. Cooper, *Acta Crystallogr.* 23, 1106 (1967).

[55] G. Sha and A. Cerezo, *Acta Mater.* 52, 4503 (2004).

[56] A. Melander and P.A. Persson, *Acta Metall.* 26, 267 (1978).

[59] E. Ho and G.C. Weatherly, *Acta Metall.* 23, 1451 (1975).

[58] M. Conserva, E. Di Russo and A. Giarda, *J. Metall.* 6, 367 (1973).

[61] M. S. Zedalis and M. E. Fine, *Metall. Trans. A.* 17, 2187 (1986).

10.1179/026708310X12635619988267 (2010).

[60] A.R. Eivani, H. Ahmed, J. Zhou, J. Duszczyk, Phil. Mag. 42, 1109 (2010).

[65] J. Murray, A. Peruzzi and J.P. Abriata, *J. Phase Equilib.* 13, 227 (1992).

Diffraction Data (ICDD), 2005, Powder Diffraction File Number (PDF no.) 01-071-
