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    Mechanical properties of severely plastic deformed aluminum sheets joined by friction stir welding

    , Article Materials Science and Engineering A ; Volume 543 , 2012 , Pages 243-248 ; 09215093 (ISSN) Khorrami, M. S ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    Abstract
    The severely plastic deformed aluminum sheets were joined by friction stir welding (FSW). The technique used for imposing the severe strain to the sheets was constrained groove pressing (CGP) process. The specimens with three different imposed strains by CGP, which lead to different initial microstructures, were joined at various rotation (. ω) and traveling (. V) speeds. The microhardness measurements and microstructure investigations were carried out. It was revealed that after FSW process of the specimens strained by CGP process, grain growth and correspondingly hardness reduction were observed at the stir zone. Also, transverse tensile test was performed at all conditions. For the CGPed... 

    Microstructure generation of severely deformed materials using Voronoi diagram in Laguerre geometry: Full algorithm

    , Article Computational Materials Science ; Volume 50, Issue 9 , July , 2011 , Pages 2698-2705 ; 09270256 (ISSN) Jafari, R ; Kazeminezhad, M ; Sharif University of Technology
    2011
    Abstract
    A new Voronoi diagram in Laguerre geometry based on closed-pack non-overlapping circles was proposed. This diagram was used to simulate microstructure of severely deformed materials at different applied strains. Grains size and their fractions were introduced by controlling the size and distribution of nuclei. Edge number distribution and neighboring cells edge number along with area distribution of the simulated Voronoi cells were determined. The edge number distribution was observed to fit gamma distribution more accurately. However, due to high inhomogeneity in the microstructure of the deformed samples at low strains, edge number distribution could not be matched by any distribution... 

    Effect of rolling speed on the occurrence of strain aging during and after warm rolling of a low-carbon steel

    , Article Journal of Materials Science ; Volume 45, Issue 13 , July , 2010 , Pages 3405-3412 ; 00222461 (ISSN) Koohbor, B ; Ohadi, D ; Serajzadeh, S ; Akhgar, J. M ; Sharif University of Technology
    2010
    Abstract
    In this study, effect of rolling speed on strain aging phenomena in warm rolling of a carbon steel has been investigated. For this purpose, by using a mathematical model and predicting temperature and strain rate fields, the possibility of occurrence of dynamic strain aging during the warm rolling was first evaluated. In the next stage, warm-rolled samples were aged up to 11 months at room temperature for studying the kinetics of static strain aging, while mechanical tests as well as microstructural evolutions have been performed to determine the effect of strain aging on material behavior. The results indicate that dynamic strain aging may not occur for the employed rolling program;... 

    Thermal stability during annealing of friction stir welded aluminum sheet produced by constrained groove pressing

    , Article Materials and Design ; Volume 45 , 2013 , Pages 222-227 ; 02613069 (ISSN) Sarkari Khorrami, M ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    Abstract
    The severely deformed aluminum sheets with strain of 2.32 were successfully joined by friction stir welding (FSW) process. Welding was carried out at various rotation speeds of 600, 800, and 1000. rpm at traveling speed of 200. mm/min corresponding to various revolution pitches of 0.33, 0.25, and 0.20. mm/r, respectively. In order to investigate the thermal stability of the joints, annealing was carried out at temperature of 200 °C for 1. h. Microstructure examinations revealed that severely deformed samples were quite unstable upon FSW process. However, during annealing it was found that in contrast to regions of heat affected zone (HAZ) and thermo mechanical affected zone (TMAZ) where... 

    Work hardening and mechanical properties of severely deformed AA3003 by constrained groove pressing

    , Article Journal of Manufacturing Processes ; Volume 14, Issue 1 , 2012 , Pages 20-25 ; 15266125 (ISSN) Khakbaz, F ; Kazeminezhad, M ; Sharif University of Technology
    2012
    Abstract
    A severe plastic straining method, called constrained groove pressing, is used to improve the microstructure and mechanical properties of non-hardenable 3003 Al-Mn alloy. Williamson-Hall method is utilized to measure the grain size from X-ray diffraction patterns of deformed samples. The results show that ultra-fine grained 3003 alloy having grain size of 580 nm can be successfully produced by constrained groove pressing at room temperature. Mechanical properties of sheets, examined by tensile test, are approximately exhibited 170% improvement in comparison with those of annealed sample. Also, comparing the achieved results with those of aluminum 1100 alloy confirms the rapid rate of grain... 

    A new microstructural model based on dislocation generation and consumption mechanisms through severe plastic deformation

    , Article Computational Materials Science ; Volume 50, Issue 3 , January , 2011 , Pages 1123-1135 ; 09270256 (ISSN) Hosseini, E ; Kazeminezhad, M ; Sharif University of Technology
    2011
    Abstract
    A new model on the evolution of dislocation structure of cell forming metals and alloys through severe plastic deformation is presented. Following previous approaches, the model considers a cellular dislocation structure consisted of two phases: cell interiors and cell walls. The model distinguishes edge and screw dislocations in terms of three categories: mobile dislocations, immobile dislocations in cell interiors and immobile dislocations in cell walls. Then considering physical and geometrical assumptions for each dislocation category, an evolutional law is derived, based on some dislocation interaction mechanisms such as dislocation generation, annihilation, locking and migration. The... 

    Kinetics of static strain aging after temper rolling of low carbon steel

    , Article Ironmaking and Steelmaking ; Volume 38, Issue 4 , 2011 , Pages 314-320 ; 03019233 (ISSN) Koohbor, B ; Serajzadeh, S ; Sharif University of Technology
    Abstract
    In this study, static strain aging behaviour of cold rolled steel strips was considered with emphasis on the distribution of residual hydrostatic stress developed during temper rolling. In order to assess residual stress distribution produced by the temper rolling, a three-dimensional model was first employed. Then, samples were rolled at a reduction of 4% under single and double pass rolling programmes and the kinetics of static strain aging phenomenon as well as the required activation energies were then evaluated using hardness and tensile tests on the deformed samples. Considering the predicted residual hydrostatic stress distribution, it was found that tensile hydrostatic stresses... 

    Constrained groove pressing of low carbon steel: Nano-structure and mechanical properties

    , Article Materials Science and Engineering A ; Volume 527, Issue 16-17 , 2010 , Pages 4043-4049 ; 09215093 (ISSN) Khodabakhshi, F ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    2010
    Abstract
    In this study a severe plastic deformation method called constrained groove pressing (CGP) is used for imposing a high magnitude of strain into the low carbon steel sheets. Microstructural changes during process are examined by X-ray diffraction and optical observations. The grain size evolution during severe plastic deformation is studied using Williamson-Hall analysis on XRD pattern of the deformed samples. In effective strain of 4.64, ferrite grains with a submicron size of 200-300nm are achieved. The results show that constrained groove pressing can effectively refine the coarse-grained structure to an ultra fine grain range. Mechanical properties changes due to microstructure evolution... 

    Nanostructure and mechanical properties of 0-7 strained aluminum by CGP: XRD, TEM and tensile test

    , Article Materials Science and Engineering A ; Volume 526, Issue 1-2 , 2009 , Pages 219-224 ; 09215093 (ISSN) Hosseini, E ; Kazeminezhad, M ; Sharif University of Technology
    2009
    Abstract
    Commercial purity aluminum sheets are subjected to a severe plastic deformation technique called constrained groove pressing. In this study for the first time by using some technical optimizations, a strain magnitude of 6.9 is imposed to the sheets. The grain size evolution during severe plastic deformation is studied using Williamson-Hall analysis on X-ray diffraction pattern of the deformed samples. These results and transmission electron microscopy observations show that constrained groove pressing process can effectively refine the coarse-grained structure to an ultrafine grain range. The results of mechanical tests show that imposing strain in range of 0-5.75 causes to strengthening of...