Sharif Digital Repository

The present study is concerned with introducing a new configuration of equal channel angular extrusion (ECAE) process nominated as multi-stage ECAE. This die configuration is not a real processing die and is just used to calculate strain in ECAE dies with outer curved corner. A solution is presented for evaluating total strain in those dies consisting of two or more ECAE sub-dies. The solution is extended for calculating strain in frictionless ECAE dies with outer curved corner. A complete agreement is found between calculated and previously published results by other authors. © 2006 Elsevier B.V. All rights reserved  

A thermo-mechanical model has been developed for modeling of hot extrusion processes. Accordingly, an admissible velocity field was first proposed by means of stream function method and then, extrusion pressure as well as temperature variations within the metal and the die were predicted employing a combined upper bound and Petrov-Galerkin finite element analysis. In order to evaluate the model predictions, hot extrusion of AA6061-10%SiCp was considered under both isothermal and non-isothermal conditions and the predicted force-displacement diagrams under various extrusion conditions were compared with the experimental ones and reasonable consistency was found between the two sets of results... 

In this study, a general methodology has been developed to design the proper bearing in order to eliminate the curvature of the final product in extrusion process. Three smooth curved (advanced-surface) dies with non-symmetric T-shaped sections and different off-centricities have been studied. For each die, the proper bearing has been designed and physical and numerical modeling have been performed to validate the design. The design procedure is as follows: A formulation, based on Bezier curves, has been used to determine the exit velocity profile. Since the result of Bezier method is different from the actual velocity profile, the Chitkara corrective function has been modified and applied... 

In this study, hot extrusion of AA6061-5% SiCp composite was studied to determine the composite thermo-mechanical behaviour during deformation and the mechanical properties of extruded composite. Hot compression tests were first carried out to obtain the flow stress behaviour of the composite at different temperatures and strain rates. Then a mathematical model was used to estimate the required energy as well as to predict temperature and strain distributions during the process. Finally, hot extrusion experiments were performed in order to verify the predictions and, also, tensile and hardness testing were conducted to evaluate mechanical properties of extruded material. Comparison between... 

High energy vibratiory mill was used to produce Nanocrystalline Al-20 wt% Ti powders by mechanical alloying. The milled powders were then consolidated by hot extrusion at 530°C. Produced bulk nanocomposite samples were studied by XRD analysis, optical microscopy (OM), Field Emission Scanning Electron Microscopy (FESEM), EDS spectroscopy, densitometry and hardness tests. Three point bending on SENB specimens was applied under quasi static condition to determine the fracture toughness and also investigate the fracture surface using SEM. The results indicated that after extrusion a fully dense Al-Al3Ti nanocomposite with the crystallite size of 200-400 nm is produced in which the Al3Ti... 

An Al-5 wt% Ti composite was fabricated via powder metallurgy and hot extrusion from initial pure Al and Ti powders. The effect of subsequent heat treatment at 600 °C for different time intervals on microstructure and mechanical properties was investigated. XRD and EDS analyses showed the in-situ formation of Al3Ti intermetallic. SEM micrographs demonstrated the formation of core-shell structured particles in Al matrix for composites heat treated up to moderate heating times (4 h). Generation of voids and pores in the heat treated composites was considered as a result of the Kirkendall effect. Mechanical properties of composites were studied by hardness and tensile testing methods at room... 

The most applicable configuration of the equal channel angular extrusion (ECAE) dies is the axi-symmetric one. However, most of the previous analytical solutions are focused on the plane strain conditions. In this research, an upper bound model is used to investigate the deformation of the material during axi-symmetric ECAE. The analysis considers the effect of die angle, friction between the sample and the die walls, and the angle of the outer curved corner of the die, on the extrusion pressure. It is found that increasing the die angle and outer curved corner angle and decreasing the friction coefficient results in decreasing extrusion pressure. The proposed model is verified using two... 

The twist extrusion process is a rather new route to produce highly strained materials. In this process, severe plastic deformation is applied by large shear strains. In this regard, prediction of materials behaviour and extrusion pressure is of importance to die designers and engineers. In this article, utilizing an admissible velocity field together with the upper bound technique, the required energy for twist extrusion is predicted. The proposed model is capable of considering the effect of various parameters such as die geometry and friction conditions. In addition, the model anticipates the critical die design parameters. To verify the proposed model, the predictions are compared with... 

In this work, nanostructured aluminum titanate (Al2TiO5 or AT) was synthesized by the citrate sol gel method. Then, different volume fractions of this ceramic were blended with Al powder through different durations of the high-energy vibratory milling. The effect of mechanical milling on the thermal degradation of AT in exposure to Al and formation mechanism of in-situ Al2O3 and Al3Ti particles were explored in three conditions: (i) in the powder form; (ii) after annealing of green compact; and (iii) after hot extrusion. In the powder form, it was shown that the mechanical milling is able to significantly diminish the thermal stability of AT, so that the required temperature for the Al3Ti... 

Mechanical alloying and hot extrusion techniques were employed to produce in-situ fully dens Al-Ti composites without applying any heat treatment. The focus of this study is the investigation of fracture toughness in produced composites in order to improve it and to explain the mechanisms responsible for the fracture. The morphology of milled powders was studied by Scanning Electron Microscopy (SEM). The microstructure of the extruded composites was examined by Optical Microscopy (OM) and Field Emission Scanning Electron Microscopy (FESEM). Moreover, the density and hardness of samples were investigated. Three point bending test of the single edge notched beam (SENB) samples was applied to...