R. Luri

A New Configuration for Equal Channel Angular Extrusion Dies

Equal channel angular extrusion or pressing (ECAE or ECAP) is a process used in order to impart severe plastic deformations to processed materials with the aim of improving their mechanical properties by reducing the grain size. The grain size reduction leads to mechanical properties improvement. In the present study, a new die configuration is proposed for the ECAE process. The advantage of this die geometry is that it allows us to obtain higher plastic strain in each ECAE passage than traditional ECAE dies. It is important to optimize the die geometry, as the main aim of the ECAE process is to impart severe plastic deformations to the processed materials. Consequently, the higher the deformation, the better the improvement on the mechanical properties of the processed materials. In order to determine how variations on geometry affect the plastic strain of the processed materials finite element modeling (FEM) is used. Both analytical and FEM methods will allow us to affirm that by using this new die configuration it is possible to achieve higher deformation values per ECAE passage.

Development of Nanostructured Armco-Fe by Equal Channel Angular Extrusion (ECAE)

The Equal Channel Angular Extrusion or Pressing (ECAE/ECAP) process has been developed over these last years in order to obtain nanostructured materials by means of severe plastic deformation. These applications have been mainly focused on light alloys while its application to iron and steel has not been so common. This is due to the difficulties that their ECAE processing implies, as much higher values for the processing force are required. In this present study, the results achieved when Armco-Fe is processed by ECAE at room temperature are shown. In addition, a comparative study on the variation in the mechanical properties (yield stress, ultimate tensile strength, and elongation at break) is shown when different thermal treatments are employed. Specific combinations are also shown of the thermal treatments which lead to a higher value of elongation and mechanical strength in relation to the starting material. Furthermore, an analysis of the obtained results is made by optical and scanning electron microscopy techniques.

Comparative Analysis of Actual Processing Conditions in ECAE between FEM and Both Analytical and Experimental Results

Equal Channel Angular Extrusion (ECAE) process is a severe plastic deformation (SPD) process whose principal purpose is to impart high values of deformation to the processed material, which leads to a grain size reduction and hence to an improvement in its mechanical properties. Although the strain achieved is important in the process, the required force and the extrusion pressure are equally important design factors. Like other metal-forming processes, a compromise solution between the strain achieved and the force required has to be applied. In this study, both the finite element method (FEM) and analytical methods based on the upper bound method (UBM) were used for modelling and comparing the forces required in the ECAE process when strain-hardening materials are considered. In addition, experimental results were carried out in order to validate the FEM modelling. Several FEM simulations, with different geometric parameters, were run, and by using design of experiments (DOE) tools, a mathematical model was obtained. By using this model, the processing extrusion pressure can be predicted. In order to compare the actual behaviour of processed materials with FEM and analytical results, a 5083-AA was chosen as processed material. Nevertheless, the methodology developed could be applied to different materials with strain hardening.

FEM Modelling and Experimental Analysis of an AA5083 Turbine Blade from ECAP Processed Material

This present research work deals with the design by finite element method (FEM) of the dies required for the isothermal forging of a Francis turbine blade taking into account that the starting material has been previously nanostructured through severe plastic deformation by equal channel angular extrusion. This nanostructured material possesses improved mechanical properties and hardness, better forgeability, and, under specific conditions, a superplastic behavior. Once this material is obtained, its flow rule has been determined through compression tests at different temperature values along with its subsequent fitting with artificial neural networks. Later on, these rules will be employed in the FEM simulations included in this present study. Furthermore, the results of the processing of these materials are shown comparing the properties of the mechanical components after their isothermal forging at different temperature values both with predeformed and non-predeformed material. This work is at the cutting-edge of technology because there are only a few technical papers about forging applications of nanostructured material.

Upper Bound Analysis of the ECAE Process by Considering Strain Hardening Materials and Three-Dimensional Rectangular Dies

Equal channel angular extrusion (ECAE) or pressing is a process used to introduce severe plastic deformations to processed materials with the aim of improving their mechanical properties by reducing the grain size. At present, there are no analytical studies that have considered strain hardening materials in order to determine the required force to carry out the process. All the existing papers have only considered nonstrain hardening materials. Furthermore, all those studies have been done by considering plane strain conditions. In this work, an upper bound analysis of the required force for performing the ECAE process is made by considering a full three-dimensional geometry with a rectangular cross section. From this analysis, the influence of the geometric and the material parameters is studied by considering both friction and strain hardening materials. By using the upper bound method, an analytical formulation was obtained and the influence of all the parameters was determined. With this work, it is possible to have a wider knowledge of the influence of the main affecting parameters in the ECAE process and to optimize them.

Grain Refinement of Pure Copper by ECAP

Pure commercial Cu of 99,98 wt % purity was processed at room temperature by Equal- Channel Angular Pressing (ECAP) following route Bc. Heavy deformation was introduced in the samples after a considerable number of ECAP passes, namely 1, 4, 8, 12 and 16. A significant grain refinement was observed by transmission electron microscopy (TEM). Tensile and microhardness tests were also carried out on the deformed material in order to correlate microstructure and mechanical properties. Microhardness measurements displayed a quite homogeneous strain distribution. The most significative microstructural and mechanical changes were introduced in the first ECAP pass although a gradual increment in strength and a slight further grain refinement was noticed in the consecutive ECAP passes.

Analysis and modelling by finite element method of the equal channel angular extrusion pressure

Abstract Equal channel angular extrusion (ECAE) is a process used to impart severe plastic deformation within the material billet. This has a great deal of interest because of the improvement achieved in the mechanical properties of the material to be processed. In this study, a finite element method (FEM) analysis has been used in order to find out how the geometrical parameters of the ECAE dies and the part affect the punch force. This is important in order to predict the force required to perform the process accurately. By solving several finite element models with different geometries, a mathematical model for the extrusion pressure was obtained, and it has been possible to study the influence of the geometry on the processing force. From this, a better die design can be made. FEM modelling has been validated by comparison with experimental results. This comparison has shown a good agreement between both of them (a difference lower than 8 per cent). Moreover, the error obtained with an analytical analysis based on the upper bound method has been determined by comparison of analytical and FEM results. This has shown that the difference between analytical and FEM results was less than 9 per cent.

Study of ECAE Process by Using FEM

In this work, the strain field attained by using a severe plastic deformation (SPD) process called equal channel angular extrusion (ECAE) is studied by the finite element method (FEM). The three-dimensional model with circular section includes shear friction between the part and the die, the material strain hardening behaviour and a rigid-deformable contact between the billet and the die. In the ECAE process the part is extruded through two channels with similar diameter that intersect at an angle. When the extrusion process has been performed, the processed material remains it cross section, so there is not any geometric limitation to achieve the desired plastic strain. There are different ways of processing the material by using the ECAE process; those ways of processing are called routes. In this work two passages of route C have been simulated. Using route C means that the billet has been rotated 180º between each passage. Deformations imparted to the processed material have been calculated and a comparison with experimental results has been carried out.

Simulation and analysis of isothermal forging of AA6063 obtained from material processed by equal channel angular pressing severe plastic deformation

In this research study, a comparative examination on the mechanical properties of AA6063 has been carried out after having been processed by isothermal forging, using plane-shape dies and starting from different initial deformation states. It introduces the novelty of employing experimental data obtained from the isothermal forging so as to model the flow rules of AA6063 processed by equal channel angular pressing taking temperature into account and using artificial neural networks to this end. Subsequently, these flow rules are employed to model the behaviour of AA6063 by means of finite element simulation. Furthermore, a validation of the experimental results is made with those obtained from the simulations using the flow rules attained with the neural networks. It is shown that it is possible to achieve higher precision than with traditional fitting methods of flow rules. In addition, this study presents the novelty of carrying out a comparative study between different starting material states, prior to forging, including among these material previously processed by the severe plastic deformation process, which is referred to as equal channel angular pressing. Moreover, the experimental results obtained when processing the aluminium alloy by equal channel angular pressing are compared to those states, which correspond to the traditional way of working on aluminium alloys, which can be quenched and aged for the purpose of improving their mechanical properties.

Analysis on the Manufacturing of an AA5083 Straight Blade Previously ECAE Processed

Over these past few years, there have been a large number of technical papers published related to the problem of improving the mechanical properties of materials obtained through severe plastic deformation. Nevertheless, the number of technical papers dealing with improvement in the mechanical properties of mechanical components manufactured from submicrometric grain size material has not been so proficient. Therefore, in this present research work, a straight blade has been manufactured starting from AA-5083 previously processed by ECAE twice (N2) with route C. This material will be manipulated so as to be isothermally forged at different temperature values. This present research work shows the results that are inherent in an improvement in the mechanical properties and the microstructure achieved in the thus obtained components, compared with the starting material. In addition, the optimum forging temperature to achieve these components will be determined. As shown in this research work, it is possible to obtain submicrometric grain size mechanical components with a higher mechanical strength than those obtained in nonultrafine grained materials. The originality of this research work lies in the manufacturing of actual mechanical components from ECAE processed material and the analysis of their properties.