Sharif Digital Repository

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... 

2024 Aluminum alloy has an abundant application in the aerospace and automobile industries. One of the most important problems of the alloy is hot cracking during the fusion welding process. It is stated that the solidified grains can be refined by a static magnetic field and an alternative electric field applied simultaneously during solidification. To make the alternative electric field, an alternative current was passed through the specimen. In order to prevent hot cracking, electromagnetic vibration was used. Then the effect of intensity of the static magnetic field and alternative electric current on joint was examined. Joining was carried out at electric currents of 40, 60, and 80A and... 

In this study, non-isothermal annealing of multi-directionally forged (MDF) aluminum alloy 2024 has been investigated. Two initial heat treatments have been considered, the solution treated (without S′/S (Al2CuMg)) and the over-aged (with S′/S (Al2CuMg)) conditions. DSC curves have shown that GPB zones/Cu-Mg co-clusters have been dynamically formed during MDF. This dynamic formation of these meta-stable phases has been modeled and in the presented model volume fraction of meta-stable phases has been calculated and its effect on the dislocation density has been considered. Although, hardness of solution treated sample has been increased by two-fold after MDF, hardness of over-aged sample has... 

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... 

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... 

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... 

Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium interlayer, has been investigated. Bonding experiments were carried out using two basic methods; Conventional and Temperature gradient TLP bonding. Optimum values of isothermal solidification temperature and time, pressure, surface roughness, heating rate and homogenizing conditions were determined in conventional TLP bonding experiments. Aluminum oxide layer was not removed before TLP bonding to prevent gallium attack.this layer is crashed during bonding. Al2O3 particles are not soluble in the liquid and are pushed into liquid by solidification front progression. These particles are accumulated in grain boundaries and in... 

In this study nanostructured composite from Al1050 and Al2024 were manufactured via accumulative roll bonding (ARB). Process was conducted in two different ways. In one approach the Al2024 sheets were annealed and in the other they were solution treated (ST). The sheets were degreased by acetone and wire-brushed, and then one Al2024 was placed between two sheets of Al1050, so three pieces of sheets were stacked to be 3 mm in thickness. The stacked sheets were rollbonded to produce the primary composite sandwich with thickness of 1 mm. Then, this sandwich was cut in the half and the two halves were degreased and wire-brushed and stacked to be 2 mm in thickness. Roll-bonding was conducted... 

In this study, temperature and Thermo-mechanical stress Distributions during and after TIG welding operations of AA2024 have been investigated by means of numerical simulation and experimental observations. Different geometries and initial microstructures, i.e. artificially and naturally aged alloys, have been selected. The model can determine the effect of welding parameters as well as mechanical fixtures on temperature and stress fields developed within metal being welded. Furthermore the subsequent aging behaviour of welded alloy (up to 70 days) has been evaluated employing hardness measurement and tensile testing. In addition, microstructural evolutions have been made utilising Scanning... 

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... 

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... 

An aerial structure can be at the disposal of the owners of damage or intellectual property during its lifetime, under the supervision of static and dynamic loads and providing information in the field of recognizing temperature, humidity and environmental pressure with high-speed gradient. Capable Composite patches are used to repair damaged areas. Composite patches have unique properties such as high strength to weight ratio and corrosion resistance. In structures modified with a composite patch, various failures occur during loading, including: fiber breakage, matrix fracture, separation of fibers from the matrix or the latest patch from the main structure and failure of the metal... 

The 2024 aluminum alloy is deformed by two passes of multi-directional forging at room temperature, 180 oC, 250 oC, 320 oC and 380 oC with initial state of solid solution. Microstructure, mechanical properties and the state of precipitates are investigated via optical and scanning electron microscopies, hardness test, shear punch test and differential scanning calorimetry. Fragmentation and distribution of the precipitates are observed after straining at different temperatures. Dynamic precipitation of GPB zones at room temperature and 180 oC are studied by DSC analysis. The increase of both hardness and strength and the formation of shear bands are related to the presence of GPB zones.... 

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... 

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... 

Aluminum alloys have became one of the most important metals in industries because of its good corrosion resistance and good machinability and high strength to weight ratio. But its properties are still in need to be improved for essentials affairs.in previous researches the effect of various factors before, between and after the multidirectional forging process has been investigated. But there is a gap between the effect of the isothermal final annealing and the effects of heating time between these studies. In this research the main focus is on microstructure improvement using severe plastic deformation and final annealing. First specimen deforms by 4pass of multi directional forging then...