Sharif Digital Repository

According to the conducted research, severe deformation of low-carbon steel sheets using the constrained groove pressing method causes a decrease in grain size and increases the strength and hardness of the sample after one pass. However, continuing this process in subsequent passes does not significantly increase strength and hardness, and sometimes it remains constant. Therefore, in this project, cold rolling has been used to improve the strength of the steel sheet and improve the surface smoothness of the final piece. After severe deformation and rolling due to the high applied strain, the strength of the sample increased and the percentage of its elongation decreased. Therefore,... 

Nowadays, modeling the behavior of materials during forming processes is so important. The role of most of them is to investigate and predict the evolutions of microstructure and mechanical properties of materials during plastic deformation. Previous researches have demonstrated that the best parameter to investigate these evolutions is the dislocation density of materials. In this study, first, the dislocation-based models, which investigate the material parameters evolutions during plastic deformation, were investigated and it was revealed that among all presented models, only the two internal variables models can investigate the behavior of materials during severe plastic deformation. ... 

Al-Mg alloys are used in many industrial fields, thus improvement of their mechanical properties is so important. Expressing mathematical models on the basis of physical and microstructural properties can be useful for this purpose. In this research, in order to study the microstructural evolutions and mechanical properties of the material, a dislocation based model and microstructural parameters such as grains and subgrains during plastic deformation and subsequent annealing are considered. In addition, a modification is used to make the model capable of justify the solute atom and temperature effect simultaneously. This makes the results to be more precise and accurate considering... 

Mechanical properties of commercial purity copper sheets are improved and grain size of material is refined into Nano scale after using a severe plastic deformation technique called constrained groove pressing (CGP). Since there are high levels of stored energy and non-equilibrium grain boundaries in nanostructure, annealing behavior and thermal stability of material should be investigated. Although there is not a clear distinction between annealing phenomena, it is essential to determine the intervals of annealing phenomena in order to control their sequences on mechanical properties and nanostructure. Also mechanisms of annealing phenomena should be determined to realize annealing behavior... 

Severe Plastic Deformation (SPD) Processes have drawn lots of attention due to their ability to refine grain size and develop some properties of bulk metals and alloys. After deformation, however, ductility and formability of metals are reduced. Annealing has been used as a solution for improvement of these characteristics after deformations even after SPD processes. On the other hand, there is a possibility that during annealing grains could grow, therefore it can neutralize the effect of SPD process. Consequently, predicting behavior and evolution of microstructure during annealing finds an important role. In this research, accordingly, vertex model have been used in order to predict... 

So far many investigations was performed in the field of energy absorption of mono and bi-layer sheets. As respects, severe plastic deformation process causes grain refinement and strength increase, there is not any study in feild of energy absorption of the severely plastic deformed sheets. The aim of this project was to investigate energy absorption of constrain groove pressed sheets by using different methods such as tensile test and wedge tear test. In this project, low carbon steel was processed by constrain groove press and mechanical properties of sheets was investigated, by using tensile test. It has been observed that ductility reduced and strength increased with increasing the... 

Improvement of mechanical properties and microstructure of 2024 aluminum alloy by performing a severe plastic deformation method, called multidirectional forging (MDF), and heat treatment was the aim of this research. In this work the effects of heat treatment before and after deformation on mechanical properties and microstructure of the alloy were studied.
Microstructure evolution during severe plastic deformation was considerably affected by the precipitates and non-shearable particles. On the other hand, the severe plastic deformation had different effects on precipitates in the microstructure and precipitation processing after deformation. Fragmentation, scattering and dissolution... 

Nowadays, modeling the deformation behavior of materials is an indispensable tool to describe the evolutions of microstructure and mechanical properties of materials during deformation. As previous investigations have shown, the dislocation density is the most appropriate parameter for investigating the deformation behaviour of materials. In present research, considering the effect of stacking fault energy (SFE), the deformation behavior is investigated. In this regard, at first a thermodynamics based modeling of deformation is presented. Previous studies have shown that due to heterogeneous distribution of dislocations during severe plastic deformation, it is needed to use multi-variable... 

A low-carbon steel, containing 0.05 C, 0.203 Mn and 0.0229 Si (all in wt%) rapidly annealed in temperature range 300 ºC - 900 ºC, after severe plastic deformation (SPD) by constrained groove pressing (CGP). Microstructure evolution was investigated by Scanning Electron and Optical Microscopy. Mechanical properties were evaluated by hardness measurements and Shear Punch Testing (SPT). The result showed a thermal stability at 300 ºC and 400 ºC, which recrystallization did not occurred in these temperatures up to 2 h holding time. By annealing at 500 ºC and 600 ºC, the onset of recrystallization observed after holding times of 10 min and 20 s, respectively. Predicting the kinetic of... 

Lots of researches have been carried out on the severe plastic deformation (SPD) and annealing of the aluminum up to now. Due to the different annealing behavior of the severely deformed metals and on the other hand the necessity to the rollig for producing the thin SPD sheets, so the purpose of the recent study is producing the thinned sheets with applying the temperature simultaneously. Dislocations density increases by SPD so it confines their movement and cause to the higher strength of the material. Rolling of the SPDed sheets increase the mechanical properties. Grain boundary energy increases with this mechanical improvement and results in lower ductility. So, it is necessary to... 

Metallurgical phenomena modeling help the researchers to understand the influence and contribution of different factors on the alloys properties. One of the most interesting phenomenon is the aging process occuring in age-hardenable alloys like 2xxx aluminium series. A factor which has high impact on aging and there are not proper models for evaluating that, is the contribution of plastic deformation. This factor has contribution not only on the dynamic precipitation (during deformation) but also on the natural aging after plastic deformation. So in this research a model containing the role of plastic deformation on dynamic precipitation and the contribution of dynamic precipitation on total... 

Commercial pure copper sheets after primary annealing were severely deformed to amount of 2.32 by Constrained Groove Pressing (CGP) method. These sheets were undergone to electrical current at different heating times of 0.5, 1, 2, and 3 seconds up to four maximum temperatures of 150, 200, 250, and 300 °C without holding time. In order to compare the annealing by electrical current and without electrical current, four other samples were heated to 300 °C with holding times of 60, 90, 120, and 150 seconds in salt bath. Then, samples microstructure evolutions, hardness and shear stress values were investigated. Generally, the results depicted that inducing electrical current can accelerate the... 

Severe Plastic Deformation (SPD) has been used as an effective approach to access fine grain (FG) and ultra-fine grain (UFG) materials.the Temperature of SPD is a dominant parameter to controlling ultimate properties. SPD at room-temperature and the high temperature was used widely in literature but the low-temperature process (sub-zero and cryogenic temperatures) was not used comparably. In this study, Low-temperature Multi-Directional Forging (LMDF) was applied on commercially pure aluminum and room-temperature MDF (RMDF) was attained for contrast temperature effects, and resulting in more fine grains. The grain refinement was attributed to the fragmentation process with a limitation in... 

Aluminum alloys have many applications in various industries such as automotive and aerospace due to their high strength to weight ratio. Today, much research is being done on the strength of metals and alloys after severe plastic deformation. Among these studies, limited work has been done on the hot deformation behavior of alloys that have undergone a severe plastic deformation process. In this research, aluminum alloy 2024-O is subjected to various passes under a type of severe plastic deformation process called multi-directional forging. Samples were divided into zero passes (annealed), one pass, three passes and five passes. After preparing pressure samples from them, hot pressure with... 

Many researches have been done on the severe plastic deformation of 2024 aluminum alloy, but there is limited information on the effect of severe plastic deformation for this alloy in the over-aged condition. In this study, the effect of severe plastic deformation and annealing heat treatment on the microstructure and strength of the over-aged AA2024 has been investigated. 1, 3, 5 and 7 two-dimensional multi-directional forging passes carried out to the over-aged samples at room temperature as one of the methods of severe plastic deformation process. After applying strain, samples were subjected to annealing heat treatment at 200, 300 and 400 °C for 30 minutes and then quenched in water. For... 

In this study, the solution treatment of severely deformed AA 2024-O and its post-severe plastic deformation is investigated. The investigation was performed in two cases of pre-multi directional forging (pre-MDF) and post-multi directional forging (post-MDF) on the solution treatment. After applying pre-MDF, finding kinetics of temperature and solution time caused that natural aging to be studied as a treatment after solid solution. By measuring the difference in hardness before and after natural aging in pre-MDFed and un-MDFed samples, 500℃ and 5 minutes were found to be the most desirable temperature and time in terms of mechanical properties and microstructure. Continuous... 

Severe plastic deformation (SPD) processes, in addition to increasing the strength of alloys, reduce their ductility. Aluminum alloy 2024 in the initial annealing state (420°C, 150 minutes) is failed after 5 passes if subjected to the multi-directional forging (MDF) process at room temperature. Therefore, in this project, with initial effective strains of 1 and 2, intermediate annealing was used at temperatures of 150°C, 250°C and 350°C (20 minutes) between process passes. This not only maintains the major strength created in this alloy after the initial passes but also provides the capability of applying more passes in this process. After each step, the microstructural examination was... 

So far, a lot of research has been done on the hot behavior of different alloys; These studies have generally been performed using tensile, compression and torsion tests and isothermal conditions, which have greatly contributed to the understanding of the mechanisms of deformation at high temperatures. Due to the fact that in real deformation processes, it is less common for the material to experience isothermal conditions during deformation, so in this project, the aim is to investigate the behavior of 2024 aluminum-alloy in non-isothermal hot compression test. In this regard, non-isothermal hot pressure test was performed from 300℃ to 600℃ و temperature range and at different deformation... 

Low carbon steel is widely used in the automotive industry by improving ductility and minimizing hardness to achieve greater strain. Applying severe plastic deformation to metals and alloys increases strength and decreases ductility. In the process of severe plastic deformation, the pressure is limited in the grooved form. Low carbon steel, after two passes of severe plastic deformation, experiences a rapid drop in strength in addition to ductility, which may indicate the presence of microcracks. Therefore, in this research, annealing between passes during the pressure process in the form of limited grooves has been used so that without a serious decrease in strength, some ductility... 

So far, much research has been done on severe plastic deformation of aluminum alloy 2024, but there is limited information on the effect of artificial aging for this alloy in the supersaturated, post-MDF state. As one of the methods of extreme plastic deformation process, multidirectional forging process (single pass) has been performed on different alloys including aluminum alloy 2024 at ambient temperature. Alloy 2024 was subjected to solution treatment at 500°C for 1 hour and multi-directional forging process was immediately performed on it. Then, at temperatures of 100, 140, 190, 240, and 290 °C, the aging process was continued for one hour until artificial aging. In order to investigate...