Sharif Digital Repository

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... 

Nanocrystalline steel was developed by severe cold-rolling and subsequent annealing of HSLA steel with an original microstructure of lath martensite. Specimens are austenitized at 1000 ºC for 30 min followed by quenching in brine. The quenched specimens are cold rolled with 80% to 90 % reduction and then annealed at temperatures from 400 to 700ºC for 10 to 120 min.The specimens annealed at temperature 500oC for 60 min showed the multiphased ultrafine structure composed of equiaxed ultrafine ferrite grains with the mean grain size of 180 nm, nano-carbides distributed uniformly and blocks of tempered martensite. The produced nanostructured steel exhibited a yield stress and UTS, of 1280 MPa... 

Friction stir spot welding (fssw) is a newly-developed solid state joining technology. In this study, normal fssw is applied to join the AlMg6 aluminum alloy sheets with 3 mm thickness and then the effect of the rotational speed and dwell time on microstructure and mechanical properties is discussed. The hardness profile of the welds exhibited a W-shaped appearance and minimum hardness was measured in the HAZ. The results of tensile/shear tests indicate that the joint strength increases and after a special rotational speed it decreases. Also the strength increases and after a special dwell time it decreases . At the rotational speed of 1500 rpm and dwell time of 6 sec, the... 

In recent years, the use of high specific strength aluminum alloys in automotive and aerospace industries is in progress due to their energy savings. On the other hand, the carbon nanotubes (CNTs), due to their ultra-high strength and modulus of elasticity, have been considered as an excellent reinforcement for the metal matrix composites used in these industries. For production of these materials, the severe plastic deformation (SPD) has been known as a method of grain refinement to increase the strength and ductility. In this research, the composites of AlMg6 reinforced with CNT were produced by accumulated roll bonding (ARB) known as a SPD technique and their properties were compared... 

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... 

Carrying out severe plastic deformation by different ways cause increasing the wear resistance of some alloys and decreasing the wear resistance of some other alloys. So far, many researches have been done on strength and microstructure of low carbon steel sheets after severe plastic deformation by constrained groove pressing method. However, the effect of the mentioned method on the wear resistance of low carbon steel is not investigated. In current research, the effect of severe plastic deformation by constrained groove pressing, annealing (at 300℃,400℃ and 500℃ for 20 minutes then cooling in air) after severe plastic deformation and also rapid annealing (at molten metal with temperature... 

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,...