**Microstructures, Nanostructures and Image Analysis**

422 Recent Trends in Processing and Degradation of Aluminium Alloys

propagation: *i*) crack initiation in the vicinity of stress concentration; *ii*) crack propagation within the plasticity zone; *iii*) onset of generation of a narrow pre-fracture zone formed by

Schemes allowing description of deformation, damage accumulation, and failure of material under fatigue with account of the preliminary inelastic deformation of the material and

The work was financially supported by Russian Foundation for Basic research (No 08-01- 00220), in the context of the project No 23.16 included into the program of Presidium of Russian Academy of Sciences, and of *Integration Project of SB RAS, UB RAS, FEB RAS No*

Romaniv, O.N.; Yarema, S.Ya.; Nikiforchin, G.N.; Makhutov, N.A.; Stadnik, M.M. (1990).

Shaniavski, A.A. (2003). *Safety fatigue fracture of elements of aircraft constructions. Synergetic in engineering applications*. Monografiya, ISBN 5-94920-015-2, Ufa, Russia (in Russian) Laird, C.; Smith, G.C. Crack propagation in high stress fatigue. *The Philosophical Magazine, A.* 

Laird, C. The influence of metallurgical structure on the mechanism of fatigure crack

Kornev, V.M. Two-scale model of low-cycle fatigue. Change from quasi-ductile to brittle

Kornev, V.M. Distribution of stresses and crack opening displacement in the pre-fracture

Nikitenko, A.F. (1997). *Yield and long strength of metallurgical materials.* Institute of

Coffin, L.F.; Schenectady, N.Y. A Study of the effects of cyclic thermal stresses on a ductile metal. *Transactions of the ASME*. Vol.76., No.6., (1954), pp. 931-950, ISSN 0742-4795 Karpov, E.V. Deformation and fracture of a spheroplast under low-cycle loading at various

Kornev, V.M. Two-scale model of low-cycle fatigue. Embrittlement of pre-fracture zone material. *Procedia Engineering.* Vol.2, No.1, (2010), pp. 453-463, ISSN 1877-7058 Kornev, V.; Karpov, E.; Demeshkin, A. Damage accumulation in the pre-fracture zone under

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effect of stress concentration on crack initiation have been proposed.

**6. Acknowledgment** 

**7. References** 

Kiev, Russia (in Russian)

(1967), pp. 131-168, ISBN 0-8031-1250-5

pp. 53-62 (in Russian), ISSN 1683-805X

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119.

**18** 

*Tehran, Iran* 

Abbas Akbarzadeh

**Nanostructure, Texture Evolution and** 

**Mechanical Properties of Aluminum Alloys** 

*Department of Materials Science and Engineering, Sharif University of Technology,* 

Various research works have been conducted to replace heavy steel body constructions with lighter aluminum ones to achieve stronger energy consumption and environmental standards. The most important technical obstacle to this goal is the inferior ductility of most aluminum sheet alloys. It has been reported that control of the microstructure and the texture of materials is essential for improvement of their mechanical properties (Lee et al., 2002). Reducing the grain size of polycrystalline metallic materials to the nanosize (*d* < 100 nm, nanocrystalline) or submicron levels (100 nm< *d* <1 μm, ultra-fine grain) is an effective and relatively economic way of improving mechanical properties such as strength, toughness, or wear resistance in structural materials (Kim et al., 2006; Prangnell et al., 2001) which even can give rise to superplastic behavior under appropriate loading conditions (Pérez-Prado et al., 2004). Since it is practically difficult to reduce the grain size of many metallic materials such as aluminum alloys below 5 μm by a conventional cold working and recrystallization process, several new methods are developed to manufacture ultrafine grained (UFG) materials (Kim et al., 2006). These methods can be classified into two main groups namely bottom-up and top-down processes. In the bottom-up procedures, such as rapid solidification, vapor deposition and mechanical alloying, an ultra-fine microstructures is configured from the smallest possible constituents which are prohibited to grow into the micrometer domain (Pérez-Prado et al., 2004). In the top-down procedures, on the other hand, an existing microscale microstructure is refined to the submicrometer scale, e.g. by a process such as severe plastic deformation (SPD) (Pérez-Prado et al., 2004; Saito et al., 1999). The ancient Persian swords are the interesting examples of severe upset forging for

development of fine microstructures (Sherby and Wadsworth, 2001).

By now, various SPD processes such as accumulative roll bonding (ARB) (Saito et al., 1999), cyclic extrusion compression (CEC) (Richert J. & Richert M., 1986), equal channel angular pressing (ECAP) (Valiev et al., 1991), and high pressure torsion (HPT) (Horita et al., 1996) have been proposed and successfully applied to various materials. The common feature of these techniques is that the net shape of the sample during processing is approximately constant, so that there is no geometric limitation on the applied strain (Prangnell et al., 2001). Among these processes, accumulative roll bonding has some unique features. Firstly,

**1. Introduction** 

**Processed by Severe Plastic Deformation** 
