Deformation of the material during CYCLIC EXPANSION EXTRUSION (CEE) is investigated using upper-bound theorem. The analytical approximation of forming loads agrees very well with the FEM results for different amounts of chamber diameter, friction factor and also for lower die angles. However, the difference between analytical and numerical solution increases at higher die angles, which is explained by the formation of dead-metal zones at these angles. The results show that the forming load increases at higher friction coefficients, higher chamber diameters, and lower amounts of corner fillet radius, but for the die angle there is a maximum value of load at about 60o. Forming load is enhanced by the increase of the die chamber diameter and friction factor. Increasing the die chamber diameter causes higher strains and, therefore, higher rate of homogenous work. The load slightly decreased by an increase of the die corner radius because of the lower and more homogeneous strain distribution in the material.

Strain distribution of Al 1100 was numerically investigated during CYCLIC EXPANSION EXTRUSION (CEE) process using finite element method (FEM). Die angle, corner fillet radius and die chamber diameter were considered as die parameters and friction factor and number of passes as process parameters. The effects of these parameters were investigated on the effective strain and strain homogeneity in the CEE process. Results showed that the decrease of friction factor along with the increase of die angle, corner fillet radius and number of passes lead to more homogeneous strain distribution, while chamber diameter has an optimal effect on the homogeneity. Material flow diagram of the deformation zone demonstrated that shear strains have a significant contribution to accumulated effective strain especially adjacent to the outer region of the sample. In comparison, in the central region of the CEE processed sample, normal strains exist as a dominant deformation route. Also, the results revealed that all the parameters except corner fillet radius (r) influence on the equivalent strain value.

Fine grain materials exhibit excellent mechanical properties and are widely used in various industries. One way to produce fine grain bar is by using the severe plastic deformation techniques. CYCLIC EXTRUSION and EXPANSION of the sample is used as one of the methods of severe plastic deformation for production of fine-grained bars. As the length of piece increases, the friction force increases, so that the required force for shaping operation is increased to such an extent that the process cannot be performed. For solving this problem, the “ CYCLIC EXTRUSION and EXPANSION under Hydrostatic Pressure” is proposed as a new method of severe plastic deformation for production of long-length fine-grained bars. In this method, the forming operation was done by using a pressure oil, so the hydrostatic compressive stresses are applying to the material and improve the mechanical properties. Also, the results of simulation of finite elements of this method show the effect of friction coefficient on the forming force and independence of the forming force from the bar length due to the hydrostatic process. Therefor the process is capable of producing rods of long length and fine structure. Results of pure copper rebar underwent this process showing that the yield strength and final strength increased by 200% and 33%, respectively. Also, the sample hardness increased substantially by 120%, and the distribution of relatively homogeneous hardness in rebar diameter was obtained. The microstructure results showed a fine-grain after the process, with the grain size reduced to 8μ m in center and 5μ m in outer diameter.

It is generally known that severe plastic deformation processes with back pressure not only apply higher hydrostatic stress and more deformation compared to what a regular process can apply to a workpiece but also prevent surface defects in the workpiece during the process. Hydrostatic CYCLIC EXPANSION EXTRUSION (HCEE) was developed recently for processing long ultrafine-grained metals and alloys. This process applies relatively higher hydrostatic pressure and prevents the formation of defects at the same time dramatically decreases the processing load by eliminating the friction. However, increasing the compressive hydrostatic pressure leads to enhance the mechanical properties by minimizing the initiation and propagation of defects. So, back pressure may be considered as a solution. In this paper, first, morphological investigation of HCEE processed aluminum without back pressure is conducted. Second, the plastic deformation behavior of the aluminum sample during this recently introduced process for producing longer samples with different external back pressures is investigated using the finite element method. The homogeneity within the workpiece was analyzed in terms of contours, path plot, and statistics of strain distribution under different conditions regarding back pressure. The simulation results shed some lights on the optimum design of HCEE for homogeneous and large severe plastic deformation.

Magnesium and its alloys have received much attention not only in the aerospace and electronics industry, but also in medical applications due to its low density, excellent physical properties, and biocompatibility. However, magnesium and its alloys have low ductility and poor strain hardening ability because of the hexagonal crystal structure with the limited number of slip systems at room temperature. Therefore, it seems necessary to improve their ductility and other mechanical properties via novel technologies. In this research, hydrostatic CYCLIC EXPANSION EXTRUSION has been used to produce ultrafine-grained magnesium rod. Properties of produced rods have been investigated morphologically and mechanically. The numerical investigation has also been performed to show the effects of hydrostatic pressure on strain distribution. Due to the brittleness of magnesium, the process has been conducted at elevated temperatures. Also, due to the fluid limitation at high temperatures, melted polyethylene has been used as the fluid in the process. The results showed that the yield and ultimate strength increased by 54% and 43% after only one pass of the hydrostatic CYCLIC EXPANSION EXTRUSION process, respectively. Also, elongation increased by 46%. Furthermore, microhardness has also increased with an average of 57 Hv to 70 Hv. The microstructure result showed that the grains become ultrafine-grained after only one pass of the process. Finite element investigation revealed that high hydrostatic pressure has a good effect on improving the strain distribution and the microstructure. This process seems very appropriate for industrial applications due to its ability to produce long ultrafine-grained rods.

In present study, an improved severe plastic deformation process named improved tube CYCLIC EXPANSION EXTRUSION process has been introduced. The idea of this process is taken from the conventional tube CYCLIC EXPANSION EXTRUSION process, and in this novel process, it is tried to solve some important problems of the conventional process. Improved tube CYCLIC EXPANSION EXTRUSION process is capable of severe plastic deforming and improving microstructure and mechanical properties of tubular components. Also, this process can be considered for producing relatively long tubes. For this purpose, the improved tube CYCLIC EXPANSION EXTRUSION process was successfully performed on AZ91 magnesium alloy tubes, up to two passes. Then, the microstructure evolution and the mechanical properties improvement were scrutinized. The results showed that the microstructure and mechanical properties were improved considerably. In this way, after two passes of this process, an ultrafine grained (UFG) microstructure was formed, and the values of ultimate strength (UTS), hardness (Hv) and ductility (EL%) became 3. 6, 1. 83 and 1. 8 times higher, respectively. Also, the comparison of the results of the improved tube CYCLIC EXPANSION EXTRUSION process with those of the conventional tube CYCLIC EXPANSION EXTRUSION process indicated that ultimate strength and hardness of the improved process were near to those of the conventional process, but the value of elongation to failure of the improved process is considerably higher than the value of the conventional process. This can be considered as one of the important advantages of the improved process over the conventional process.

Hydrostatic tube CYCLIC EXPANSION EXTRUSION process is a newly invented severe plastic deformation technique for producing long ultrafine-grained and nanostructured tubes with higher mechanical properties. In the present research, this process was applied through two passes at room temperature on the commercial purity copper. Then, the hardness, tensile properties, fracture surface and microstructure of the samples were evaluated. The main goal of this research was to achieve a material with a simultaneous high strength and desirable ductility. In this process, the utilization of pressurized fluid between the die and the tube leads to first, the desired improvement of mechanical properties due to the effects of hydrostatic compressive stress. Second, the reduction of a required deforming force to eliminating the friction between the die and the tube leads to the facilitation of producing relatively long ultrafine-grained and nanostructured tubes. After two passes of process, a nearly equiaxed and homogeneous ultrafine-grained (UFG) microstructure was observed. The yield strength and ultimate strength increased from 75 MPa and 207 MPa to 310 MPa and 386 MPa, respectively. However, elongation to failure decreased from 55% to 37%. Also, the hardness value of the tube increased significantly from 59 Hv to 143 Hv, and the uniform distribution of hardness was obtained through the thickness of the tube. The fractography evaluations revealed that the predominantly ductile fracture happened in all samples of tensile testing. The hydrostatic tube CYCLIC EXPANSION EXTRUSION process can be utilized as a practical industrial method for producing relatively long ultrafine-grained tubes.

CYCLIC EXTRUSION compression angular pressing (CECAP) is a novel severe plastic deformation (SPD) method applied to improve the mechanical and metallurgical properties of materials. In this research, finite element analysis and response surface method were considered for CP-Ti in CECAP process. Temperature, input EXTRUSION diameter, exit EXTRUSION angle, shear factor and longitudinal distance of input EXTRUSION to the ECAP region were selected as input parameters to study strain distribution in the current process. The analysis of variance (ANOVA) was developed for current work, and the results showed that input parameters of input EXTRUSION diameter and shear factor, and the interaction of the temperature and longitudinal distance of input EXTRUSION to ECAP region, and the shear factor and longitudinal distance of input EXTRUSION to ECAP region considerably affect the strain distribution. Hardness measurement in section A at the points near the center and outer surfaces of the sample showed the hardness of 21 and 24 HRC respectively. At this point, the maximum difference for hardness was achieved at about 12% throughout the cross section which is in suitable agreement with the strain distribution model. Moreover, the optical microscope (OM), both current CDECAP and conventional CECAP, showed that the majority of deformed grains were enlarged. The average deformed grain size for the current CECAP was reduced to 100 nm, which is considerably smaller than the conventional CECAP with an average grain size of 300 nm. Furthermore, the load-stroke diagram was achieved by executing experimental tests and comparing the results achieved the numerical model. The results showed a good agreement between them.

Pure copper pipes have various applications in industries. It is necessary to improve their mechanical properties. The main strengthening mechanism in this case is severe plastic deformation in order to achieve ultrafine-grain microstructure. In this research, the deformation method of tube CYCLIC EXTRUSION-compression (TCEC) was used. The design of punch and mould was performed by Solidwork and Mo40 steel was used for manufacture of both mould and punch. Then, the pure copper tube at ambient temperature and 750 °C deformed in one pass. Investigation of microstructural evaluation and hardness measurement on the cross-sectional surface and side surface of the pipe showed that in the case of cold TCECed pipe, the microstructure of the cross-section is slightly fine-grain and compared to the raw sample, a substantial hardness improvement (60%) was achieved. In the microstructure, orientation of grains and material flow were also observed in the direction of EXTRUSION. In the hot SPD treatment, the cross-sectional area of ​​the sample significantly was fine-grained and the hardness of this part increased considerably by about 93% compared to the raw sample.