Showing 7 results for Shahmiri
M. Ghalambaz,, M. Shahmiri, Y. H. K Kharazi,
Volume 4, Issue 1 (winter & spring 2007 2007)
Abstract
Abstract: Problems such as the difficulty of the selection of processing parameters and the large
quantity of experimental work exist in the morphological evolutions of Semisolid Metal (SSM)
processing. In order to deal with these existing problems, and to identify the effect of the
processing parameters, (i.e. shearing rate-time-temperature) combinations on particle size and
shape factor, based on experimental investigation, the Artificial Neural Network (ANN) was
applied to predict particle size and shape factor SSM processed Aluminum A.356.0 alloy. The
results clearly demonstrated that, the ANN with 2 hidden layers and topology (4, 2) can predict the
shape factor and the particle size with high accuracy of 94%.The sensivity analysis also revealed
that shear rate and solid fraction had the largest effect on shape factor and particle size,
respectively. The shear rate had a reverse effect on particle size.
M. Ghalambaz, M. Shahmiri,
Volume 5, Issue 3 (Summer 2008 2008)
Abstract
Abstract: Cooling slope-casting processing is a relatively new technique to produce semisolid cast
feedstock for the thixoforming process. Simple equipment, ease of operation, and low processing
costs are the main advantages of this process in comparison with existing processes such as
mechanical stirring, electromagnetic stirring, etc. The processing parameters of cooling slope
casting are length, angle and the material of the inclined plate and their combinations, which
usually affect the micro structural evolutions of the primary solid phase.
In order to clarify the effect of the processing parameters on the evolution of the particle size,
based on experimental investigation, Artificial Neural Network (ANN) was applied to predict the
primary silicon crystals (PSCs) size of semisolid cast ingot via a cooling slope casting process of
Al-20%(wt.%) Si alloy.
The results demonstrated that the ANN, with 2 hidden layers and topology (4, 3), could predict the
primary particle size with a high accuracy of 94%. The sensitivity analysis also revealed that
material of the cooling slope had the largest effect on particle size.
M. Shahmiri, S. Murphy,
Volume 5, Issue 4 (Autumn 2008 2008)
Abstract
Abstract: The microstructural features of the early stage of ordering of the intermetallic compound Pt2FeCu have been
examined using optical and transmission electron microscopy in conjunction with X-ray diffraction technique. It was
found that the compound has similar morphological alteration to that of FePt in which the ordering cannot be
suppressed by rapid quenching.
The early stage of ordering transformation was initiated at temperatures above the critical value of 1178 oC, by a
homogeneous nucleation of the intermediate short range ordered particles and ultra rapid directional-induced
heterogeneous growth (burst type). As the result of these combined mechanisms, twin –related ordered domains have
been formed which in turn minimize the strains produced by ordering reaction in polycrystalline material. The
individual grain was divided up by different sizes of twin-related ordered domain bonded with {101} habit planes.
B. Tolaminejad, A. Karimi Taheri, H. Arabi, M. Shahmiri,
Volume 6, Issue 4 (Autumn 2009 2009)
Abstract
Abstract: Equal channel angular extrusion (ECAE) is a promising technique for production of ultra fine-grain (UFG) materials of few hundred nanometers size. In this research, the grain refinement of aluminium strip is accelerated by sandwiching it between two copper strips and then subjecting the three strips to ECAE process simultaneously. The loosely packed copper-aluminium-copper laminated billet was passed through ECAE die up to 8 passes using the Bc route. Then, tensile properties and some microstructural characteristics of the aluminium layer were evaluated. The scanning and transmission electron microscopes, and X-ray diffraction were used to characterize the microstructure. The results show that the yield stress of middle layer (Al) is increased significantly by about four times after application of ECAE throughout the four consecutive passes and then it is slightly decreased when more ECAE passes are applied. An ultra fine grain within the range of 500 to 600 nm was obtained in the Al layer by increasing the thickness of the copper layers. It was observed that the reduction of grain size in the aluminium layer is nearly 55% more than that of a ECA-extruded single layer aluminium billet, i.e. extruding a single aluminium strip or a billet without any clad for the same amount of deformation. This behaviour was attributed to the higher rates of dislocations interaction and cell formation and texture development during the ECAE of the laminated composite compared to those of a single billet
M .shahmiri, , H. Arabi ,
Volume 6, Issue 4 (Autumn 2009 2009)
Abstract
Abstract:
The aims of this research were to investigate the effects of semisolid metal (SSM) processing parameters (i.e., shear rates –times – temperatures combinations) on the primary solidification products and isothermal holding duration, subsequent to cessation of stirring on the secondary solidification of Al-Si (A356) alloy.
The dendrite fragmentation was found to be the governing mechanism of the primary dendritic to non-dendritic transformation, via rosette to final pseudo-spherical shapes during the primary solidification
The secondary solidification of the liquid in the slurry was not only a growth phenomenon but also promoted by 1) fresh heterogeneous nucleation and growth of dendrites and 2) the dendritic growth of the primary solidification products in the remaining liquid. Upon cessation of stirring and gradual disappearance of the prior shear force, the slurry relaxed, and the secondary solidification products pertained to conventional solidification condition
M. Shahmiri,
Volume 13, Issue 4 (December 2016)
Abstract
Over the last few decades, there have been many mechanisms proposed to describe the formation of the non-dendritic microstructures during Semisolid Metal (SSM) processing; including dendrite fragmentation, spherical growth, cellular growth and recalescence. Dendrite fragmentation is the most popular mechanism of all these hypotheses. It is the purpose of the present article to examine the morphological evolution of the non-dendritic microstructures, based on models proposed by Flemings, Vogel, Cantor, and Doherty during SSM processing of the Al-Si (A356) alloy. Based on new microstructural evidences, including (1) - plastic deformation at the side arms by slip lines formation as a result of the thermal fatigue mechanism, (2) - crack formation at the root of the side arms and (3) – the interaction of a rapidly sheared hot viscous medium with these regions, i.e. erosion; it propose and hereby discuss a new mechanism called "fatigue –erosion", for dendrites fragmentation of the experimental alloy. Optical and Scanning Electron Microscopy (SEM) with EBSD and EDS, TEM, and AFM was used for the microstructural characterizations.
M. Shahmiri,
Volume 14, Issue 1 (March 2017)
Abstract
In the present work microstructural evolution of A356 Aluminum alloy using an inclined cooling plate casting process for thixoforming feedstock production is investigated. The resultant microstructure was evaluated and compared with those of the same alloy produced by the conventional casting process, i.e. directly cast in the same mold without using an inclined cooling plate. It was found that when alloy melt poured over an inclined cooling plate and subsequently cast in semisolid condition into a metallic mould resulted in fine rosettes and nearly globular α-Al primary phase uniformly distributed in an Al +Si eutectic matrix. The effect of the processing parameters such as the lengths and angles of the inclined cooling plate and their combinations were identified to produce alloy ingot with the most suitable microstructural constituent for thixoforming process
