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Microstructure and Mechanical Characterization of Heat Treated Stir Cast Silica (Sea Sand) Reinforced 7XXX Al Alloy MMCs

Authors: S. S. Sharma, Jagannath K, P. R. Prabhu


Metal matrix composites consists of a metallic matrix combined with dispersed particulate phase as reinforcement. Aluminum alloys have been the primary material of choice for structural components of aircraft since about 1930. Well known performance characteristics, known fabrication costs, design experience, and established manufacturing methods and facilities, are just a few of the reasons for the continued confidence in 7XXX Al alloys that will ensure their use in significant quantities for the time to come. Particulate MMCs are of special interest owing to the low cost of their raw materials (primarily natural river sand here) and their ease of fabrication, making them suitable for applications requiring relatively high volume production. 7XXX Al alloys are precipitation hardenable and therefore amenable for thermomechanical treatment. Al–Zn alloys reinforced with particulate materials are used in aerospace industries in spite of the drawbacks of susceptibility to stress corrosion, poor wettability, poor weldability and poor fatigue resistance. The resistance offered by these particulates for the moving dislocations impart secondary hardening in turn contributes strain hardening. Cold deformation increases lattice defects, which in turn improves the properties of solution treated alloy. In view of this, six different Al–Zn–Mg alloy composites reinforced with silica (3 wt. % and 5 wt. %) are prepared by conventional semisolid synthesizing process. The cast alloys are solution treated and aged. The solution treated alloys are further severely cold rolled to enhance the properties. The hardness and strength values are analyzed and compared with silica free Al – Zn-Mg alloys. Precipitation hardening phenomena is accelerated due to the increased number of potential sites for precipitation. Higher peak hardness and lesser aging time are the characteristics of thermo mechanically treated samples. For obtaining maximum hardness, optimum number and volume of precipitate particles are required. The Al-5Zn-1Mg with 5% SiO2 alloy composite shows better result.

Keywords: reinforcement, Hardness, Precipitation Hardening, matrix, thermomechanical, dislocation

Digital Object Identifier (DOI):

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[1] De Sanctis M, "Structure and properties of rapidly solidified ultrahigh strength Al–Zn–Mg–Cu alloys produced by spray deposition”, Material Science Engineering 1991; A141:103–21.
[2] Duan X, Hao Y, Yoshida M, Ando T, Grant N. J, "Liquid dynamic compaction of aluminum alloy 7150”, International Journal of Powder Metallurgy 1993;29(2): 149–59.
[3] Lengsfeld P, Juarez-Lslas J. A, Cassada W. A, Lavernia E.J. "Microstructure and mechanical behavior of spray deposited Zn modified 7XXX series Al alloys”, International Journal of Rapid Solidification 1995; 8: 237–65.
[4] Li X. Z, Hansen V, Gjonnes J, Wallenberg L. R, "HREM study and structure modeling of the g0 phase, the hardening precipitates in commercial Al–Zn–Mg alloys”, Acta Mater 1999;47(9):2651–9.
[5] Troeger L. P, Starke E. A., "Microstructural and mechanical characterization of a superplastic 6xxx aluminum alloy”, Material Science Engineering A 2000; 277: 102–13.
[6] Berg L. K, Gjonnes J, Hansen V, Li X. Z, Knutson-wedel M, Waterloo G, et al. "GP-zones in Al–Zn–Mg alloys and their role in artificial aging” Acta Mater 2001;49:3443–34651
[7] Song R. G, Zhang Q. Z, "Heat treatment optimization for 7175 aluminum alloy by genetic algorithm. Material Science Engineering, C 2001; 17:133–7.
[8] TangenStian, Sjolstad Knut, Nes Erik, FuruTrond, Marthinsen Knut, "The effect of precipitation on the recrystallization behavior of a supersaturated, cold rolled AA3103 aluminium alloy”, Material Science Forum 2002;396–402:469.
[9] Lee S. H, Saito Y, Sakai T, Utsunomiya H, "Microstructures and mechanical properties of 6061 aluminum alloy processed by accumulative roll-bonding”, Material Science Engineering A 2002;325:228–35.
[10] Robson J. D, "Optimizing the homogenization of zirconium containing commercial aluminium alloys using a novel process model”, Material Science Engineering A 2002; 338:219–29.
[11] Chen S. P, Kuijpers NCW, van der Zwaag S, "Effect of microsegregation and dislocations on the nucleation kinetics of precipitation in aluminium alloy AA3003”, Material Science Engineering A 2003;341:296.
[12] Starink M. J, Wang S. C, "A model for the yield strength of overaged Al–Zn–Mg–Cu alloys”, Acta Mater 2003;51:5131–50.
[13] Chen K. H, Liu H. W, Zhang Z, Li S, Todd R. I, "The improvement of constituent dissolution and mechanical properties of 7055 aluminum alloy by stepped heat treatments”, Journal of Material Process Technology, 2003; 142:190–6.
[14] Dumont D, Deschamps A, Brechet Y, "On the relationship between microstructure, strength and toughness in AA7050 aluminum alloy”, Material Science Engineering A 2003; 356: 326–36.
[15] Wang D, Nia D. R, Ma Z. Y, "Effect of pre-strain and two-step aging on microstructure and stress corrosion cracking of 7050 alloy”, Material Science Engineering A, 2008.