Severe plastic deformation methods are of great interest in industrial forming applications, as they give rise to significant refinement in microstructures and improvements in mechanical and physical properties. In the &ldquo / Equal Channel Angular Extrusion (ECAE)&rdquo / , which is the most common method for production of ultrafine grained bulk samples, very high plastic strains are introduced into the bulk material without any change in cross section. This study is composed of two main parts. Part I focuses on the plastic deformation behavior of Al alloys by modeling ECAE with Msc. Marc finite element software. A series of numerical experiments were carried out for the die angles of 90° / , 120° / , and 150° / , different friction conditions, and different round corners. Besides, the effects of strain hardening characteristics of the material, strain hardening coefficient (K) and exponent (n) of Hollomon&rsquo / s law, on corner gap formation and strain homogeneity in equal channel angular pressing process were investigated quantitatively. The results were compared and verified with those of the upper bound analysis. The numerical results showed that the process performance can be improved by modifying the die corner curvature accordingly, without running time consuming simulations. On the other hand, the aim of Part 3 is to investigate the texture evolution, mechanical response and the corresponding mechanisms, in terms of the flow stress anisotropy and tension-compression asymmetry in the ZK60 Mg alloy. The alloy was processed using ECAE, with different processing routes and temperatures, in order to produce samples with a wider variety of microstructures and crystallographic textures. Several mechanical tests and microstructure examinations were carried out / and the flow stress anisotropy and tension-compression asymmetry of the as-received and processed samples were measured. It was found that the initial texture has a strong effect on the resulting textures / and the textures, combined with the microstructure effect, define the mechanical properties of processed samples. Thus, the tension-compression asymmetry and the flow stress anisotropy variations in the processed samples are attributed to the generated textures and it is possible to control these properties by controlling the processing route and temperature.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12614036/index.pdf |
| Date | 01 January 2012 |
| Creators | Karpuz, Pinar |
| Contributors | Gur, Cemil Hakan |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Ph.D. Thesis |
| Format | text/pdf |
| Rights | Access forbidden for 1 year |
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