Sharif Digital Repository

Al-15wt.% Mg2Si composites were prepared by in situ casting and characterized in wear tests. Previous to the extrusion of specimens at 470°C - varying extrusion ratio (7.4, 14.1 and 25), the as-cast composites were homogenized at 500°C for 5h, followed by slow furnace cooling. The microstructure, hardness and sliding wear behavior were characterized for both, the as-cast and hot extruded composites. Results show that increasing the extrusion ratio causes a significant improvement in hardness and wear resistance. This is ascribed to the observed decrease in average size and better distribution of Mg2Si particles, in tandem with a remarkable decrease in porosity percentages, which goes from... 

The present study is concerned with introducing a new configuration of equal channel angular extrusion (ECAE) process nominated as multi-stage ECAE. This die configuration is not a real processing die and is just used to calculate strain in ECAE dies with outer curved corner. A solution is presented for evaluating total strain in those dies consisting of two or more ECAE sub-dies. The solution is extended for calculating strain in frictionless ECAE dies with outer curved corner. A complete agreement is found between calculated and previously published results by other authors. © 2006 Elsevier B.V. All rights reserved  

A thermo-mechanical model has been developed for modeling of hot extrusion processes. Accordingly, an admissible velocity field was first proposed by means of stream function method and then, extrusion pressure as well as temperature variations within the metal and the die were predicted employing a combined upper bound and Petrov-Galerkin finite element analysis. In order to evaluate the model predictions, hot extrusion of AA6061-10%SiCp was considered under both isothermal and non-isothermal conditions and the predicted force-displacement diagrams under various extrusion conditions were compared with the experimental ones and reasonable consistency was found between the two sets of results... 

An architectural modification method was utilized to improve fracture toughness of discontinuously reinforced aluminum (DRA) composites. Al-DRA composites having a structure similar to that of reinforced concrete were fabricated. The number of reinforcing DRA rods within Al matrix and volume fraction of SiC particles in DRA were altered to evaluate their effect on fracture behavior of these materials. It was found that architectural modification does not have any destructive influence on elastic modulus and yield strength of the composite. Moreover, the success of this method on toughness improvement strongly depends on the occurrence of debonding between Al and DRA regions upon loading  

Extrusion-based three-dimensional (3D) printing has recently become a major field that provides significant benefits, as it is principally employed to fabricate 3D scaffolds, exploiting soft biomaterials. The 3D printing hydrogel-based ink requires crucial properties, such as printability and printing fidelity to fabricate the appropriate structure. However, it typically uses trial and error techniques to achieve a three-dimensional structure, which wastes material and time. This study employed multiphysics simulation to predicate the potential printability of chitosan hydrogel as a desirable biomaterial used in tissue engineering. The flow was presumed to be laminar and two-phased in the... 

In this paper, with introducing and based on a new configuration of equal channel angular extrusion (ECAE) process, nominated as multi-stage equal channel angular extrusion, two relationships are derived to calculate the effective strain based on shear and principal strains. First, a solution is presented for evaluating the effective strain in multi-stage ECAE dies consisting of two or more ECAE sub-dies. Then, the solution is extended to calculate the effective strains in ECAE dies with outer curved corner. The effective strain based on shear strains shows an exact agreement with previously published results. The derived relationships were compared with each other, with the relationships... 

In this research, a new method for producing bimetallic rods is introduced. The method is a new application of equal channel angular extrusion (ECAE) process. Advantages of using this method can be expressed as; good dimensional control on both the core and clad layer, possibility of performing the process in more than one pass which can result in larger bonding strength, and the possibility of performing the process in different temperatures which is critical for producing most of the bimetallic joints as well as aluminum-copper joint. The shear strength obtained using this method is compared with the same final product produced by general extrusion process. While the shear strength after... 

Effort was made to characterise segregation tendency of mechanically stirred ZA27 alloy with back extrusion as a thixoforming process. At sufficiently high ram speeds, at which liquid phase flows forcefully, pooling of the heavy liquid phase owing to gravitational segregation contributes to homogeneity of back extruded products in terms of solid phase distribution, The amount of this contribution depends on the contact time of this liquid with solid skeleton during liquid exertion to the clearance. Hence, at high ram speeds, small rams which demand taller initial slugs are more efficient in minimising the segregation. However, in the case of low speed back extrusion tests, liquid impotency... 

In this study, hot extrusion of AA6061-5% SiCp composite was studied to determine the composite thermo-mechanical behaviour during deformation and the mechanical properties of extruded composite. Hot compression tests were first carried out to obtain the flow stress behaviour of the composite at different temperatures and strain rates. Then a mathematical model was used to estimate the required energy as well as to predict temperature and strain distributions during the process. Finally, hot extrusion experiments were performed in order to verify the predictions and, also, tensile and hardness testing were conducted to evaluate mechanical properties of extruded material. Comparison between... 

In this research in order to predict the strain distribution and extrusion load in equal channel angular extrusion (ECAE) process of circular cross section a new three dimensional kinematically admissible velocity field has been developed based on Bezier formulation. The strain distribution in deformation zone and the effects of various terms on extrusion load were determined. The results were compared both with the experimental and numerically predicted results reported in the literature. It was found that extrusion pressure decreases with increasing both the die angle and the outer curved corner angle and increases with increasing the friction coefficient. Also, it was exhibited that... 

The capability of backward extrusion (BE) method was assessed to achieve modified structures in AZ80 magnesium alloy. At first, 3D-Deform was employed to simulate the deformation flow through the deformed cup which gives an evidence from the flow behavior of the material. The material was processed via BE method at various temperatures of 250, 350, and 450 °C. Metallographic investigations were conducted in three different regions of the BE-processed cup (wall, bottom, and flow channel). The main feature observed at the wall of the BE cup was the presence of mechanical twins, the frequency of which was reduced by raising the process temperature. The flow localization in the form of shear... 

In this study, conductive sodium alginate/polyaniline/graphene (PAG) NGCs were fabricated utilizing a straightforward solution extrusion method. The 4 point-probe test revealed that the addition of PAG has increased the conductivity of the NGCs up to 9.7 × 10−3 S.cm−1. The results also showed a remarkable increase in the Young modulus and SEM images revealed that the suggested process could produce NGCs continuously and uniformly with desirable porosity. The Fourier-transform infrared spectroscopy spectrum proved a good interaction between PAG and the polymeric matrix. Furthermore, the addition of PAG slightly prevented biodegradation of the NGCs. Finally, the cell viability assay confirmed... 

In this study, conductive sodium alginate/polyaniline/graphene (PAG) NGCs were fabricated utilizing a straightforward solution extrusion method. The 4 point-probe test revealed that the addition of PAG has increased the conductivity of the NGCs up to 9.7 × 10−3 S.cm−1. The results also showed a remarkable increase in the Young modulus and SEM images revealed that the suggested process could produce NGCs continuously and uniformly with desirable porosity. The Fourier-transform infrared spectroscopy spectrum proved a good interaction between PAG and the polymeric matrix. Furthermore, the addition of PAG slightly prevented biodegradation of the NGCs. Finally, the cell viability assay confirmed... 

In this research, a general solution of volume constancy differential equation is presented based on the equation of deformation field for a general process. As the Bezier method is suitable for construction of complex geometries, the solution is used in conjunction with the Bezier method to analyze the equal channel angular extrusion (ECAE) process of rectangular cross section. Thus, a generalized kinematically admissible velocity field is derived from the equation of deformation zone such that the compatibility of the surface representing the deformation zone is fulfilled. The effects of die angle, friction between the billet and die wall, and the angle of outer curved corner, on extrusion... 

A simple method for estimating the apparent viscosity of semi-solid alloys was investigated. A drop weight of 50Kg and backward extrusion equipments were used to test the deformation. Backward extrusion was employed in a closed die system due to the very little separation of liquid from solid phases compared with other methods at very high deformation rate. The half of the calculated impact velocity, 700mm/s was considered as an average velocity for deformation during the test, since the slop of the velocity changes against time is constant in the middle stage of the deformation. The initial height of the sample and the thickness of the residual compressed solid at the bottom of the cup were... 

In the present work, hot workability of particulate-reinforced Al6061-20%SiC composite produced by direct hot extrusion technique was studied. Uniaxial hot compression test at various temperatures and strain rates was used and the workability behavior was evaluated from the flow curves and the attendant microstructures. It was shown that the presence of SiC particles in the soft Al6061 matrix deteriorates the hot workability. Bulging of the specimens and flow lines were observed, which indicates the plastic instability during hot working. Microstructure of the composites after hot deformation was found to be heterogeneous, i.e. the reinforcement clusters were observed at the flow lines. The... 

Back extrusion technique was employed to characterize phase segregation tendency of mechanically stirred ZA27 alloy at different deformation rates. Variation of segregation intensity with ram diameter was found to follow opposite trends at low and high ram speeds. At sufficiently high ram speeds, small rams are of better performance in minimizing segregation whereas at low ram speeds, large rams result in less pronounced segregation. In addition, increasing ram speed invariably decreases segregation degree. Back extrusion at very high shear rates provided via a Drop Extruder Apparatus capable of displacing ram at speeds in excess of 1m/s results in production of very homogeneous products in... 

In this research, deformation of material during equal channel angular extrusion (ECAE) is analyzed using an upper bound model. The model considers the effect of die angle and friction between the sample and the die walls on the geometry of dead metal zone and total strain. The relationship between the friction coefficient, the extent of dead metal zone and total strain is derived. It is found that strain decreases with increasing die angle and friction coefficient. Moreover, a critical value for friction coefficient is determined that when the friction coefficient is more than the critical, deformation zone and therefore, the dead metal zone forms which consequently total strain decreases.... 

In this research, deformation of material in equal channel angular extrusion (ECAE) process with outer curved corner is analyzed using an upper bound solution. The effects of die angle, friction between the sample and the die walls, and the angle of the outer curved corner, on the extrusion pressure are all considered in the analysis. It is found that the extrusion pressure decreases with increasing both the die angle and the outer curved corner angle and increases with increasing the friction coefficient. Moreover, a good agreement is found between the predicted and experimental results of extrusion pressure relating to two dies of different outer curved corner angles used in ECAE tests of...