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.

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Abstract:The most important difficulties when the behaviour of a part that is subjected to external mechanical forces is simulated deal with the determination of both the material thermo-mechanical properties and its boundary conditions. The accuracy of the results obtained from the simulation is directly related to the knowledge of the flow stress curve. Therefore, the determination of a material flow rule which is valid for both a wide temperature range and different initial deformation conditions in the starting material presents a great deal of interest when simulation results close to the experimental values are required to be obtained. In this present study, a novel flow stress curve is proposed that is able to accurately predict the behaviour of both materials with no previous accumulated strain and materials that have been previously subjected to severe plastic deformation processes. Moreover, it is possible to use it both for hot and cold working. The results are analysed in a wide test temperature range, which varies from room temperature to 300 • C, and from material previously processed by angular channel extrusion or with no previous strain accumulated. It is shown that the flow rule proposed is effective to model the material behaviour in a wide temperature range and it makes it possible to take the recrystallization phenomena that appear in previously deformed materials into account. In addition, the results obtained are compared with those predicted by other flow rules that exist in the prior literature. Furthermore, the study is complemented with finite element simulations and with a comparison between simulation and experimental results.

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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.

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