Equal Channel Angular Extrusion (ECAE) has great potential for developing ultrafine
grain structure consisting of homogeneous and equiaxed grains dominated by high
angle grain boundaries. In addition, the ECAE-processed specimens retain their original
cross-section, providing capabilities of multi-passing. However, the process is
discontinuous as the length of the billet is limited due to potential buckling of the
extruding ram. This problem provides an opportunity of making the process continuous.
The objectives of this study were to examine the feasibility of a process obtained by
combining ECAE and Equal Channel Angular Drawing (ECAD), evaluate the potential
of the combined process for continuous processing of sheet metal, and to analyze the
mechanical response of sheet metal subjected to the ECAE and ECAD techniques using
numerical study. Numerical analyses of ECAE and ECAD were performed using the
commercial FE analysis package ABAQUS/explicit. Experimental data and analytical
models available in literature were used to validate the numerical results. Parametric
studies on the effects of drawing angle, and sheet thickness to die radius ratio (t/r), on
reduction in thickness, strain uniformity and resulting microstructure are presented. Numerical results indicate that ECAD through a closed channel should be preferred
over conventional drawing (open channel) operation as reduction in thickness is
decreased by 2-3% after a single pass. In the experimental study, it was observed that
during ECAD, the reduction in thickness increases by 2.5-3.5% per pass. Also, a higher
reduction is observed in route C compared to route A. Use of sharper die corners
(higher t/r ratios) and smaller channel intersection angles tend to increase this thickness
reduction, and results in an increase in hardness i.e., results in strengthening. ECAD
most likely results in a non-uniform microstructure with low fraction of high angle
grain boundaries. In addition, for a given pass, the average hardness of the ECADprocessed
samples is approximately half that of ECAE-processed samples. This
suggests that ECAD alone may not be commercially viable. However, a significant
improvement in minimizing reduction in thickness is achieved by providing a little gap
between the sheet metal and support plates.
From the numerical analyses, the proposed continuous process appears to be
effective in retaining continuity of the drawing operation, minimizing the percent
reduction in thickness and imparting higher plastic strains. It is believed that an
experimental study of the process will reveal some more promising information.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-08-7140 |
| Date | 2009 August 1900 |
| Creators | Murudkar, Rahul R. |
| Contributors | Wang, Jyhwen, Hartwig, Karl T. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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