Improving the Semisolid Deformation Behavior and Thixoformability of AZ61 Magnesium Alloy Through Controlling the Strain Induced Melt Activation Process

Document Type : Research Paper


1 School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran

2 School of Metallurgy & Materials Engineering, Iran University of Science and Technology (IUST), Tehran, Iran


The present work deals with the microstructure globularization, coarsening behavior and the correlated kinetics during strain-induced melt activation process of AZ61 magnesium alloy. In this study, the effect of pre-strain, temperature and holding time have been considered, and the evolutions were numerically discussed based on Lifshitz-Slyozov-Wagner (LSW) and Ostwald ripening mechanisms. The treated microstructures (undeformed, globular, non-globular, and coarsened) were then hot compressed at a semisolid temperature range to assess the thixotropic flow behavior of the material. A unique microstructure encompassing fine α-Mg globules uniformly distributed in the matrix and surrounded by a liquid phase was developed by imposing 45% pre-strain and holding it at 555°C for 8 min. The lowest deformation resistance belonged to the specimens holding globular microstructures, while those with undeformed characteristics possessed the highest flow stress during thixoforming. The semisolid flow response was discussed considering the flow of liquid that incorporates solid particles (FLS); sliding between solid particles (SS), and plastic deformation of solid particles (PDS) mechanisms. The influence of the shape factor (in globular structure) and the grain size (in coarsened structure) on the thixotropic flow behavior of the experimented alloy were also illustrated.


[1]    M. Kohzu, F. Yoshida, H. Somekawa, Fracture mechanism and forming limit in deep-drawing of magnesium alloy AZ31, Materials Transactions, 42(7) (2001) 1273-1276.
[2]    S.H. Hsiang, J.L. Kuo, An investigation on the hot extrusion process of magnesium alloy sheet, Journal of Materials Processing Technology, 140(1-3) (2003) 6-12.
[3]    Y. Nishikawa, K. Matsumura, A. Takara, Development of the outer cases for television set with magnesium alloy, Materia Japan, 39(3) (2000) 278-280.
[4]    S. Kleiner, O. Beffort, A. Wahlen, P.J. Uggowitzer, Microstructure and mechanical properties of squeeze cast and semi-solid cast MgAl alloys, Journal of Light Metals, 2(4) (2002) 277-280.
[5]    S. Kleiner, O. Beffort, P. J. Uggowitzer, Microstructure evolution during reheating of an extruded Mg-Al-Zn alloy into the semisolid state, Scripta Materialia, 51(5) (2004) 405-410.
[6]    Z. Zhao, Q. Chen, H. Chao, S. Huang, Microstructural evolution and tensile mechanical properties of thixoforged ZK60-Y magnesium alloys produced by two different routes, Materials & Design, 31(4) (2010) 1906-1916.
[7]    P. Kapranos, P.J. Ward, H.V. Atkinson, D.H. Kirkwood, Near net shaping by semi-solid metal processing, Materials & Design, 21(4) (2000) 387-394.
[8]    D. Liu, H.V. Atkinson, H. Jones, MTDATA thermodynamic prediction of suitability of alloys for thixoforming, Proceeding S2P 8th International Conference, 2004.
[9]    E. Tzimas, A. Zavaliangos, A comparative characterization of near-equiaxed microstructures as produced by spray casting, magneto-hydrodynamic casting and the stress induced, melt activated process, Materials Science and Engineering: A, 289(1-2) (2000) 217-227.
[10]  E. Tzimas, A. Zavaliangos, Evolution of near-equiaxed microstructure in the semisolid state, Materials Science and Engineering: A, 289(1-2) (2000) 228-240.
[11]  Y. Birol, A357 thixoforming feedstock produced by cooling slope casting, Journal of Materials Processing Technology, 186(1-3) (2007) 94-101.
[12]  R. Haghayeghi, E.J. Zoqui, A. Halvaee, M. Emamy, An investigation on semi-solid Al–7Si–0.3Mg alloy produced by mechanical stirring, Journal of Materials Processing Technology, 169(3) (2005) 382-387.
[13]  S. Luo, Q. Chen, Z. Zhao, Effects of processing parameters on the microstructure of ECAE-formed AZ91D magnesium alloy in the semi-solid state, Journal of Alloys and Compounds, 477(1-2) (2009) 602-607.
[14]  T.J. Chen, G.X. Lu, Y. Ma, Y.D. Li, Y. Hao, Microstructural evolution during partial remelting of equal channel angular pressed ZW21 magnesium alloy, Journal of Alloys and Compounds, 486(1-2) (2009) 124-135.
[15]  A. Khosravani, H. Aashuri, P. Davami, A. Narimannezhad, R. Hadian, Liquid segregation behavior of semi-solid AZ91 alloy during back extrusion test, Journal of Alloys and Compounds, 477(1-2) (2009) 822-827.
[16]  B. Nami, S.G. Shabestari, S.M. Miresmaeili, H. Razavi, Sh. Mirdamadi, The effect of rare earth elements on the kinetics of the isothermal coarsening of the globular solid phase in semisolid AZ91 alloy produced via SIMA process, Journal of Alloys and Compounds, 489(2) (2010) 570-575.
[17]  M.R. Rokni, A. Zarei-Hanzaki, H.R. Abedi, N. Haghdadi, Microstructure evolution and mechanical properties of backward thixoextruded 7075 aluminum alloy, Materials & Design, 36 (2012) 557-563.
[18]  T.J. Chen, Y. Hao, J. Sun, Microstructural evolution of previously deformed ZA27 alloy during partial remelting, Materials Science and Engineering: A, 337(1-2) (2002) 73-81.
[19]  S.B. Hassas-Irani, A. Zarei-Hanzaki, B. Bazaz, A.A. Roostaei, Microstructure evolution and semi-solid deformation behavior of an A356 aluminum alloy processed by strain induced melt activated method, Materials & Design, 46 (2013) 579-587.
[20]  E. Tzimas, A. Zavaliangos, Mechanical behavior of alloys with equiaxed microstructure in the semi-solid state at high solid content, Acta Materialia, 47(2) (1999) 517-528.
[21]  J.G. Wang, H.Q. Lin, Y.Q. Li, Q.C. Jiang, Effect of initial as-cast microstructure on semisolid microstructure of AZ91D alloy during the strain-induced melt activation process, Journal of Alloys and Compounds, 457(1-2) (2008) 251-258.
[22]  F. Czerwinski, A. Zielinska-Lipiec, The melting behaviour of extruded Mg–8%Al–2%Zn alloy, Acta Materialia, 51(11) (2003) 3319-3332.
[23]  F. Czerwinski, Near-liquidus molding of Mg–Al and Mg–Al–Zn alloys, Acta Materialia, 53(7) (2005) 1973-1984.
[24]  Z. Zhao, Q. Chen, C. Hu, D. Shu. Microstructure and mechanical properties of SPD-processed an as-cast AZ91D+ Y magnesium alloy by equal channel angular extrusion and multi-axial forging, Materials & Design, 30(10) (2009) 4557-4561.
[25]  K. Ding, L. Hengcheng, J. Qiumin, T. Yun, Effect of hot extrusion on mechanical properties and microstructure of near eutectic Al–12.0% Si–0.2% Mg alloy, Materials Science and Engineering: A, 527(26) (2010) 6887-6892.
[26]  J.F. Jiang, L.I.N. Xin, W.A.N.G. Ying, J.J. Qu, S.J. Luo, Microstructural evolution of AZ61 magnesium alloy pre-deformed by ECAE during semisolid isothermal treatment, Transactions of Nonferrous Metals Society of China, 22(3) (2012) 555-563.
[27]  N. Haghdadi, A. Zarei-Hanzaki, S. Heshmati-Manesh, H.R. Abedi, S.B. Hassas-Irani, The semisolid microstructural evolution of a severely deformed A356 aluminum alloy, Materials & Design, 49 (2013) 878-887.
[28]  F. Czerwinski, Size evolution of the unmelted phase during injection molding of semisolid magnesium alloys, Scripta Materialia, 48(4) (2003) 327-331.
[29]  Q. Chen, J. Lin, D. Shu, C. Hu, Z. Zhao, F. Kang, S. Huang, B. Yuan, Microstructure development, mechanical properties and formability of Mg-Zn-Y-Zr magnesium alloy, Materials Science and Engineering: A, 554 (2012) 129-141.
[30]  D.G. Eskin, V.I. Savran, L. Katgerman, Effects of melt temperature and casting speed on the structure and defect formation during direct-chill casting of an Al–Cu alloy, Metallurgical and Materials Transactions A, 36(7) (2005) 1965-1976.
[31]  S. Ashouri, M. Nili-Ahmadabadi, M. Moradi, M. Iranpour, Semi-solid microstructure evolution during reheating of aluminum A356 alloy deformed severely by ECAP, Journal of Alloys and Compounds, 466(1-2) (2008) 67-72.
[32]  D. Fan, S.P. Chen, L.Q. Chen, P.W. Voorhees, Phase-field simulation of 2-D Ostwald ripening in the high volume fraction regime, Acta Materialia, 50(8) (2002)1895-1907.
[33]  F. Czerwinski, On the generation of thixotropic structures during melting of Mg-9%Al-1%Zn alloy, Acta Materialia, 50(12) (2002) 3267-3283.
[34]  Z. Fan, Semisolid metal processing, International Materials Reviews, 47(2) (2002) 49-85.
[35]  C.P. Chen, C.Y. Tsao, Semi-solid deformation of non-dendritic structures Phenomenological behavior, Acta Materialia, 45(5) (1997) 1955-1968.
[36]  H. Yan, B. Zhou, Thixotropic deformation behavior of semi-solid AZ61 magnesium alloy during compression process, Materials Science and Engineering: B, 132(1-2) (2006) 179-182.
[37]  H.R. Abedi, A. Zarei-Hanzaki, S.M. Fatemi-Varzaneh, A.A. Roostaei, The semi-solid tensile deformation behavior of wrought AZ31 magnesium alloy, Materials & Design, 31(9) (2010) 4386-4391.
[38]  E.R.D. Freitas, E.G. Ferracini Júnior, V.P. Piffer, M. Ferrante, Microstructure, material flow and tensile properties of A356 alloy thixoformed parts, Materials Research, 7(4) (2004) 595-603.
[39]  E.J. Zoqui, MH. Robert, Structural modifications in rheocast Al-Cu alloys by heat treatment and implications on mechanical properties, Journal of Materials Processing Technology, 78(1-3) (1998) 198-203.
[40]  M. Easton, D. StJohn, Grain refinement of aluminum alloys: Part I. The nucleant and solute paradigms-a review of the literature, Metallurgical and Materials Transactions A, 30(6) (1999), 1613-1623.