Principles of equal-channel angular pressing as a processing tool for grain refinement

Twenty-five years of ultrafine-grained materials: achieving exceptional properties through grain refinement

The texture formation in one pass of equal channel angular extrusion (ECAE) is investigated in comparison with that after simple shear deformation. The orientation of the die's intersection plane and the deviation of deformation from simple shear along this plane are the two main factors that together contribute to differences in measured ECAE textures from simple shear. With this in mind, an appropriate method for analysis of ECAE textures is developed. Using an idealized simple shear model for ECAE deformation, the ideal orientations and fiber textures for ECAE of both fcc and bcc materials are derived for any die angle. To demonstrate this method, two popular polycrystal models, finite element simulation, and orientation imaging microscopy texture measurements of copper are used to quantify the individual contributions of these two factors in actual ECAE deformation. The importance of comparing ECAE textures with the negative rather than positive shear texture is emphasized, otherwise interpretations of the ECAE experimental and simulated data can be misleading.

Texture formation during equal channel angular extrusion of fcc and bcc materials: comparison with simple shear

Samples of pure aluminum and an Al-6061 alloy were subjected to equal-channel angular pressing (ECAP) for up to eight passes at room temperature. The Vickers microhardness was recorded on the polished cross-sections of each as-pressed billet and the results are plotted in the form of color-coded maps to provide a pictorial depiction of the hardness distributions throughout the cross-sections. The results show the hardness increases by a factor of ∼2 in the first pass through the die but thereafter there is only a minor increase. The microhardness distribution is homogeneous in the unpressed condition but becomes inhomogeneous after a single pass and then reasonably homogeneous in subsequent passes. The results reveal some differences between the behavior of pure Al and the Al-6061 alloy. These results and microscopic observations are used to develop a model for the process of grain refinement during ECAP.

The evolution of homogeneity and grain refinement during equal-channel angular pressing: A model for grain refinement in ECAP

In this study, the deformation behavior of aluminium during equal channel angular pressing (ECAP) was calculated on the basis of a dislocation density-based model. The behavior of the material under ECAP, including the dislocation density and cell size evolution as well as texture development, was simulated using the finite element method (FEM). The simulated stress, strain and cell size were compared with the experimental data, which were obtained by ECAP for several passes in a modified Route C regime. Good agreement between simulation results and experimental data, including strain distribution, dislocation density and cell size evolution, strain hardening and texture development was obtained. As concerns the general trends, the stress was found to increase rapidly in the first ECAP pass, the strain-hardening rate then dropping from the second pass on. Calculations showed a non-uniform strain distribution evolving in the course of ECAP. The simulated cell size is also in good agreement with the experiment, particularly with the observed rapid decrease of the cell size during the first pass slowing down from the second pass onwards. Larger cells were found to form in the upper and the lower parts of the workpiece where the strain is smaller than in the middle part. Due to the accumulation of strain throughout the workpiece and an overall trend to saturation of the cell size, a decrease of the difference in cell size with the number of passes was predicted.

Dislocation density-based modeling of deformation behavior of aluminium under equal channel angular pressing

Finite element analysis of material flow in equal channel angular pressing

Experimental studies and finite element analysis of equal-channel angular pressing (ECAP) were carried out to clarify the deformation behavior in a sharp corner die and a round corner die under the condition without a frictional effect. It was found in both the experiment and the finite element simulation that the geometry of the die itself has a great influence on the homogeneity in deformation, resulting in more uniform shear deformation in the sharp corner die than in the round corner die under the condition without friction. The shear deformation was concentrated homogeneously on the diagonal plane of the sharp corner, which was in good agreement with the postulation of the conventional theory. In the case of the round corner die, however, plastic deformation was spread over a wide sector of the corner where shear deformation was confined to the inner part, and nonshear deformation was found in the outer part. The inhomogeneous deformation of the round corner die due to geometrical effects exhibited forward-curved flow in the outer part of the corner differently from backward-curved flow caused by frictional effects. The numerical analysis showed that more inhomogeneous distribution of stress was generated on the inlet cross section of the round corner, resulting in a variation of the normal stress from a compressive stress in the inner part to a tensile stress in the outer part. Tension followed by compression was a dominant deformation mode of the material during passing through the outer corner, and a gradual bending of the material occurred instead of shear deformation.

Effect of die shape on the deformation behavior in equal-channel angular pressing

Grain refinement of steel plate by continuous equal-channel angular process

The present invention relates to a continuous shear deformation device, in particular, which is capable of mass-producing shear deformed materials by continuously supplying a sharply bent channel type mold with materials, particularly, which have a variety of thickness from thin sheet to thick plate. The continuous shear deformation device in accordance with the present invention includes a sharply bent channel type mold and a rotary guide apparatus installed at the inlet of the mold for guiding materials into the mold by frictional contact with the materials. In addition, the present invention can additionally include a rotary guide for exiting the shear-deformed material.

Continuous shear deformation device

The present invention relates to a shear deformation device. To improve the productivity by solving the problem that the amount of shear deformation of a material is not uniform and sufficient due to the gap between the curved portion of the molding path and the lower parts of the material and omitting any additional process for removing irregularity and surface products on the surface of the material, there is provided a shear deformation device capable of scalping, characterized in that a scalping guide path which allows the surface of the material to be separated from the other portions of the material as the material is scalped at a predetermined thickness when passing through the curved portion during shear deformation is formed in the curved portion in communication with the molding path. In addition, there are provided additional constructions for effectively performing shear deformation by a small power by reducing the friction at the molding path excepting the curved portion. The present invention thusly constructed can be utilized for continuously and effectively mass-produce sheared materials.

Jong-Woo Park

Papers

Finite element analysis of material flow in equal channel angular pressing

Effect of die shape on the deformation behavior in equal-channel angular pressing

Grain refinement of steel plate by continuous equal-channel angular process

Continuous shear deformation device

Shear deformation device for scalping