Sharif Digital Repository

One of the most common processes in shaping profiles with various cross-sections (with parallel surfaces), is a direct extrusion process. Always in the process, minimize the extrusion pressure and reduce the output profile curvature form of the main goals of researchers. Minimize the extrusion pressure in the mold design using nonlinear, many relationships are presented. Also, to reduce the output profile curvature of the mold, extrusion molding is used mostly at the outlet of the bearing. The purpose of this research is suitable for bearing design eliminates the curvature of the final product is extrusion. In this study interior design templates and profiles bearing acts simultaneously on... 

In this thesis, equations related to large deformation of a polymer were derived by considering viscoelastic effects. To express type of material behavior which includes elastoplastic and viscoelastic property at the same time, two-layer viscoplastic model was used. An axisymmetric model was used for modeling problem in finite element software. By derivation of parameters related to two layer model and entering them in finite element software and also entering other properties required to model the forming process, modeling was performed by special profile connecting input and output sections. Due to favorable properties of spline functions, profiles used in die geometry, were selected from... 

In this study, a two-hole die with unsymmetrical T-shape holes has been investigated. At first, a kinematically admissible velocity field in outlet of die has determined. Then, appropriate length of die has calculated by upper bound method. Finally, suitable position of holes has achieved in aspect of minimum pressure and curvature. To calculate curvature of exit profile, a realistic deviation function has been defined. To validation of results, finite element simulation and physical modeling have been used. Analytical, experimental and finite element results have decent agreement to each other  

In this work, minimization of the exit profile curvature in multi-hole extrusion die was studied by specifying an appropriate location for exit holes using analytical, finite element and experimental approaches. First by considering linear dead metal zone in flat multi-hole dies, the velocity field constructed. Then based on an objective function, the deviation of the exit profile obtained for any positioning of the exit holes. Additionally, the deviation obtained from theoretical method was verified with the result of the commercially available bulk forming simulation software (Deform 3D v5). Also to verify the result the direct extrusion process was simulated physically by plasticine.... 

The extrusion process of flat dies in non-symmetrical sections is among processes which in spite of enormous applications, has not been thoroughly understood due to complexities of analyzing the section deformation process. In these dies, a zone is formed during egression of billet from die in which the material is stationary and accordingly the material on profile of this zone shears. This zone is called the dead metal zone. Dead metal zone is a natural non-linear die and it is pragmatic to obtain the value of the deviation. In the present work, determine the curvature of the exit profile by using prediction of the dead metal zone profile is target. The dead metal zone profile is assumed... 

One of the most practical deformation processes has been used to produce profiles with a diversity of shapes is forward extrusion. Minimizing the extrusion pressure along with reducing the curvature of the final product have always been the main concerns of the researchers in this area. To achieve the former, researchers have designed nonlinear dies and proposed various equations to determine proper die profile. To accomplish the latter, they have used bearing at the exit section of the extrusion die. The primary object of the current study is to design a proper bearing in order to eliminate the curvature of the final product in extrusion process. The effects of both bearing and die profile... 

Magnesium and its alloys have gained much attention in medical applications, especially bio-degradable stents. However, they have not been used extensively due to their natural limitations, such as weak mechanical properties. WE43 magnesium alloy has gained attention as a bio-alloy due to its high temperature and good corrosion resistance. The present study aims to use a combination of ECAP and direct tube extrusion to fabricate thin wall tubes with good mechanical properties using WE43 magnesium alloy. In the first phase, the ECAP process at 370°C were conducted up to 4 passes on the homogenized samples to reach ultrafine grain structure. Subsequent to ECAP, direct tube extrusion at 230 °C,... 

In this study, in situ Al-Al3Ti-Al2O3 nanocomposite has been fabricated on thermal decomposition of tialite (Al2TiO5 or AT) precursor in the aluminum matrix through powder metallurgy method. The high-temperature mechanical property of Al-Al3Ti-Al2O3 on this procedure has been investigated. In the first step nano-structured tialite were synthesized through citrate sol-gel methods. Then 3.5 wt.% tialite powder was mixed with aluminum by high energy vibratory milling for 3 hours. In the next step, green compacts of mechanically milled powder mixtures were sintered at 530°С for 6 hours under argon atmosphere. In the final step, hot extrusion as a consolidation method reduces the sample voids,... 

In the present work, at first Al-20 wt% Ti nanocomposite was fabricated via mechanical alloying in high energy vibratiory mill for 1-4 hours. Particles morphology, crystallite size changes and phases transformation were investigated during mechanical alloying. Next, the powders which mechanically alloyed for 2 and 4 hours was compressed by hot extrusion at 500 ℃. The extruded specimens were investigated by different tests such as density, hardness, tensile and differential scanning calorimetry (DSC). Microscopic analysis and phases transformation were also investigated by optical microscopy (OM), field emission electron microscope (FESEM) and X-ray diffraction. Then, the samples were heat... 

In this study insitu Al-Al3Ti-Al2O3 nanocomposite has been fabricated based on thermal decomposition of tialite (Al2TiO5) precursor in aluminium matrix through powder metallurgy method. Also the effect of high energy mechanical milling and hot extrusion on this procedure has been investigated. In the first step nano-structured tialite were synthesized through citrate sol gel methods. Then, different volume fraction of tialte was mixed with aluminium by high energy vibratory milling. The results of X-ray differaction analysis, scanning electron microscopy and differential thermal analysis showed that mechanical milling can degrade stability of tialite and cause strain-induced decomposition,... 

The aim of this research was to fabricate an in-situ Al-Al3Ti nanocomposite from pure microsized aluminum and titanium powders by mechanical alloying and hot extrusion without any usage of nanometric particles or applying secondary heat treatments. The focus of the present research was fabricating a nanocomposite material with high strength, modulus and hardness accompanied with high fracture toughness that could be comparable with aluminum alloys in terms of fracture toughness. Mechanical alloying and hot extrusion techniques were employed to produce in-situ fully dense Al-Ti composites. Platenary and high energy vibratiory mill was used to produce composites with different percent of... 

In the present research, a novel method for the fabrication of Al/Al3 Ti-Al2O3 composites and nanocomposites based on the thermal degradation of the refectory ceramic “Aluminium Titanate (AT)” or Al2TiO5 by powder metallurgy route. This research encompasses some precise subsequent steps. At first stage, nanostructured aluminium titanate nanofibers and particles were synthesized via a citrate sol gel process in which citric acid was used as a chelating agent. At second step, the possible chemical reactions between Al and aluminium titanate were taken into consideration both in powder form and in bulk form. Thermal analysis results indicated that it is feasible to decompose aluminium titanate... 

In this study in-situ Al/Al3Ti was fabricated by mechanical alloying, hot extrusion and subsequent heat treatment. First, initial pure powders of Al and Ti were mechanically alloyed with 5 weight percentages of Ti for 40 hours. The as-hot extruded samples containing 5 wt% of initial Ti particles, were exposed to heating at 600 oC for various time intervals up to 10 hours. Microstructure analysis by OM and SEM proved that in-situ Al3Ti phase was formed as a layer around Ti particles by solid reactive diffusion between Al and Ti particles. After 10 hours of heating, all the Ti particles were consumed and transformed to Al3Ti. Mechanical properties of samples were investigated by Brinell... 

In this study, hot extrusion of AA2017-10%SiC¬p composite during deformation process and effect of deformation parameters on mechanical properties have been investigated. At the first step, hot compression tests have been carried out to obtain the flow behavior of the material at different temperatures and strain rates. The activation energy of hot deformation was calculated 296 Kj/mol. In the next step, by using a finite element model in ABAQUS software and the results of uniaxial hot compression test behavior of AA2017 and AA2017-10%SiC¬p during hot and warm extrusion have been investigated. By using it temperature gradient and velocity field and strain distribution were predicted. In the... 

This research focused on mechanical properties of Al-TiB2 composite in as cast, heat treated and extruded condition. The composites were produced by mixing Al-Ti and Al-B master alloyes. Since some engineering parts during service are supposed to tolerate severe wear conditions, in this research abrasive wear condition was wxamined using pin on disk method. In a fixed load and abrasive disk, composites showed better resistance against wear in comparison with matrix alloy. Furtheremore, T6 heat treatment made composites more resistant against abrasive wear. Finally the best wear resistance was accompolished when composite was extruded and then heat treated. While increase in reinforcement... 

The use of aluminum and its alloys in different industries is increasing. To increase the deformability of Aluminum alloys, it is usually deformed at high temperatures. In Such working conditions, the chemical composition, temperature of deformation, strain rate and high temperature activating phenomena will affect the microstructure and final properties of the material. In this thesis the hot and cold deformation behavior of a Al-11.77%Si-0.2%Mg are evaluated. In the cold deformation, the alloy was first annealed and then ECAEed. The mechanical properties and the related microstructure were evaluated via the microhardness test. The results indicated that the alloy could not be deformed... 

Aluminum alloys are widely used in many applications in aerospace and automotive industries. Therefore, the study of the effects of different parameters such as chemical composition, temperature, strain, strain rate and recovery and recrystallization phenomena being more effective on controlling of microstructure and final properties of product, are more important. In this research, deformation behavior of AlMg6 alloy has been studied from two theoretical and experimental views as described below: In ambient temperature deformation, the mechanical properties in correlation on the microstructures developed at different temperatures have been assessed. The results of tensile test demonstrated... 

In this research, the extrusion of composite AA6061-SiC has been investigated and the temperature distribution field and energy required for the process has been predicted. In this regard, to predict the flow behavior of material, hot extrusion tests conformed at various ranges of temperatures and strain rates. Afterward, the finite element method coupled with the upper bound technique to calculate the temperature distribution and energy required during hot extrusion. This model has also used for wire drawing and cold extrusion processes. The present model is capable of considering various process parameters such as speed of extrusion, reduction and the initial billet/die temperature on the... 

A new method for production of bimetallic rods, utilizing the equal channel angular extrusion (ECAE) process has been introduced before by previous researchers, but no attempt has been made to assess the effect of different temperatures and holding times in order to achieve a diffusional bond between the mating surfaces. In present research copper sheathed aluminum rods have been ECAEed at room temperature and subsequently held at a constant ECAE pressure, at different temperatures and holding times to produce a diffusional bond between the copper sheath and the aluminum core. The bonding quality of the joints was examined by shear strength test. The microstructure examinations were carried... 

In recent years, more attention was devoted to ECAE process than any other Severe Plastic Deformation (SPD) process. Repeatability of the process and high mechanical properties of the exit profile are the reasons of this attention. ECAE process carried out with conventional extrusion process, provides more strain and back pressure. In this thesis an analytical model based on upper Bound analysis and Bezier interpolation functions is presented and the effects of process parameters were studied. According to the presented model, reduction of inner corner angle φ, increases strain, strain rate and press force. Reduction of the outer corner angle ψ, causes the same effect. Moreover, decreasing...