Grain Refinement Mechanism and Its Effect on Strength and Fracture Toughness Properties of Al–Zn–Mg Alloy

  • P. K. MandalEmail author
Conference paper
Part of the Lecture Notes in Mechanical Engineering book series (LNME)


Grain refinement has a significant effect on the mechanical properties. Grain refinement in cast Al–Zn–Mg alloy tends to reduce porosity, size and number of the pores. This improves the mechanical properties, specially fracture toughness. Inoculation effect is most important factor during feeding of liquid metal. For these reasons, most cast aluminium alloys are grain refined. Fluidity is another factor that increases formation of a coherent equiaxed dendritic network at the flow front. The degree of grain refinement is dependent on the level of scandium (Sc) concentration and the Zn/Mg ratio. Grain refiner namely Al–Sc master alloy is added in small amounts (>0.2 wt% Sc) to molten aluminium alloys to control the grain structure in castings. Al3Sc particles act as nucleating sites for the formation of primary α-Al dendrites and promote a uniform and fine equiaxed structure. In addition, friction stir processing (FSP) is the most innovative solid-state surface modification technology that eliminates cast heterogeneity and refines grains under the depth of the processed zone of aluminium alloys. The basic principle is based on friction stir welding (FSW). Thus, three main causes for fine grains are severe plastic deformation, heat input and dynamic recrystallization. Therefore, FSP should result in heterogeneous nucleation and growth of Al3Sc precipitates for diffusional mechanisms, which explains the rapid growth of precipitates in the processed zone. It has been experimentally proven that after as-cast (AC) + FSP condition aluminium alloy enhance mechanical properties such as 0.2% proof strength is 89.81 MPa, ultimate tensile strength is 187.1 MPa, elongation is 3.42%, and fracture toughness (K IC) is 25.10 MPa\( \surd \)m. In the present study, further evaluation has been done with optical microscopy, EPMA, FESEM, SEM, and TEM of Al–Zn–Mg–Sc alloy.


Inoculation effects FSP Fracture toughness Al3Sc precipitates TEM analysis 



The author is very much thankful to the research scholars in Metallurgical and Materials Engineering Department, Indian Institute of Technology Roorkee (IITR), Roorkee, India, for helping and providing Instron Testing Machine for conducting fracture toughness testing.


  1. 1.
    Wu L-M, Seyfing M, Rettenmayr M, Wang W-H (2010) Characterization of precipitate evolution in an artificially aged Al–Zn–Mg–Sc–Zr alloy. Mater Sci Eng A 527:1068–1073CrossRefGoogle Scholar
  2. 2.
    Mandal PK (2016) Study on GP-zones formation in the Sc inoculated ternary Al–Zn–Mg Alloys. J Mater Metall Eng 6(2):53–69Google Scholar
  3. 3.
    Loffler H, Kovacs I, Lendvai J (1983) Review decomposition processes in Al–Zn–Mg alloys. J Mater Sci 18:2215–2240CrossRefGoogle Scholar
  4. 4.
    Fuller CB, Krause AR, Dunand DC, Seidman DN (2002) Microstructure and mechanical properties of a 5754 aluminium alloy modified by Sc and Zr additions. Mater Sci Eng A 338:8–16CrossRefGoogle Scholar
  5. 5.
    Huang J-W, Yin Z-M, Fang J-F, Nie B, Wang T (2007) Aging characteristics of 7A52 Al–Zn–Mg alloy. Mater Sci Forum 546–549:867–870CrossRefGoogle Scholar
  6. 6.
    Mandal PK (2015) Processing and characterization of Al3Sc precipitates in cast aluminium alloy by Foundry Route. J Adv Res Manuf Mater Sci Metall Eng 2(3&4):1–6Google Scholar
  7. 7.
    Milman Y (2006) Structure and mechanical behavior of Al-Sc alloys. Mater Sci 519–521:567–572Google Scholar
  8. 8.
    Gholami S, Emadoddin E, Tajally M, Borhani E (2015) Friction stir processing of 7075 Al alloy and subsequent aging treatment. Trans Nonferrous Met Soc China 25:2847–2855CrossRefGoogle Scholar
  9. 9.
    Wang K, Liu FC, Ma ZY, Zhang FC (2011) Realization of exceptionally high elongation at high strain rate in a friction stir processed Al–Zn–Mg–Cu alloy with the presence of liquid phase. Scripta Mater 64:572–575CrossRefGoogle Scholar
  10. 10.
    Costa S, Puga H, Barbosa J, Pinto AMP (2012) The effect of Sc additions on the microstructure and age hardening behaviour of as cast Al-Sc alloys. Mater Des 42:347–352CrossRefGoogle Scholar
  11. 11.
    Patel JB, Patil HS (2014) Simulation of peak temperature & flow stress during FSW of aluminium alloy AA6061 for various tool pin profiles. Int J Mater Sci Eng 2(1):67–71Google Scholar
  12. 12.
    Deng Y, Yin Z, Zhao K, Duan J, He Z (2012) Effects of Sc and Zr microalloying additions on the microstructure and mechanical properties of new Al–Zn–Mg alloys. J Alloy Compd 530:71–80CrossRefGoogle Scholar
  13. 13.
    Kumar N, Mishra RS (2013) Ultrafine-grained Al-Mg-Sc alloy via friction-stir processing. Metall Mater Trans A 44A:934–945CrossRefGoogle Scholar
  14. 14.
    Han NM, Zhang XM, Liu SD, He DG, Zhang R (2011) Effect of solution treatment on the strength and fracture toughness of aluminium alloy 7050. J Alloy Compd 509:4138–4145CrossRefGoogle Scholar
  15. 15.
    Vratnica M, Cvijovic Z, Rakin M (2004) Fracture toughness modeling in high-strength Al-based alloys. Mater Sci Forum 453–454:181–186CrossRefGoogle Scholar
  16. 16.
    Feng X, Liu H, Babu SS (2011) Effect of grain size refinement and precipitation reactions on strengthening in friction stir processed Al-Cu alloys. Scripta Mater 65:1057–1060CrossRefGoogle Scholar
  17. 17.
    Su J-Q, Nelson TW, Sterling CJ (2006) Grain refinement of aluminium alloys by friction stir processing. Phil Mag 86(1):1–24CrossRefGoogle Scholar
  18. 18.
    Mohan Kumar S, Pramod R, Shashi Kumar ME, Govindaraju HK (2014) Evaluation of fracture toughness and mechanical properties of aluminium alloy 7075, T6 with Nickel Coating. Procedia Eng 97:178–185CrossRefGoogle Scholar
  19. 19.
    Reddy AC, Rajan SS (2005) Influence of ageing, inclusions and voids on ductile fracture mechanism in commercial Al-alloys. Bull Mater Sci 28(1):75–79CrossRefGoogle Scholar
  20. 20.
    Ludtka GM, Laughlin DE (1982) The influence of microstructure and strength on the fracture mode and toughness of 7XXX series aluminium alloys. Metall Trans A 13A:411–425CrossRefGoogle Scholar
  21. 21.
    Yan A, Chen L, Liu HS, Xiao FF, Li XQ (2015) Study on strength and fracture toughness of Al–Zn–Mg–Cu–Ti(–Sn) alloys. J Min Metall Sect B: Metall 51(1):73–79CrossRefGoogle Scholar
  22. 22.
    Rhodes CG, Mahoney MW, Bingel WH, Calabrese M (2003) Fine-grain evolution in friction-stir processed 7050 aluminium. Scripta Mater 48:1451–1455CrossRefGoogle Scholar
  23. 23.
    Zhenbo H, Zhimin Y, Sen L, Ying D, Baochuan S (2010) Preparation, microstructure and properties of Al–Zn–Mg–Sc alloy tubes. J Rare Earths 28(4):641–646CrossRefGoogle Scholar

Copyright information

© Springer Nature Singapore Pte Ltd. 2018

Authors and Affiliations

  1. 1.Department of MetallurgyAmal Jyothi College of EngineeringKanjirappallyIndia

Personalised recommendations