Study On Grain Refinement Of Aluminum Rod Of Large-Size Processed By Equal Channel Angular Pressing

Equal Channel Angular Pressing (ECAP) is one kind of severe plastic deformation method, which can refine grain size by introducing the simple shear deformation into the workpice and has been proved to be an effective method for obtaining various bulk ultrafine-grained materials. It has been attracting more and more attention in material field. At present, ECAP technique is mainly used to process sample of small-size about 10mm in diameter. Due to the limitation of fabrication size, its application in industries has been greatly impeded.In this paper, the large-size pure aluminum samples of 30mm in diameter were pressed at room temperature by 4 passes with ECAP dies self-designed. The change law of extrusion force and the microstructure evolution during ECAP were investigated. The mechanical properties of pure aluminum after ECAP, the uniformity of deformation and its influencing factors were also researched. Further more, the grain refining mechanism of pure aluminum during ECAP and the industrialization of ECAP were discussed.The results show that the load required to drive the deformation varies with the increasing displacement, according to the following five steps when there exists residual sample: rapid increase, rapid decrease, slow increase, slow decrease and load rising slightly. And the mechanical properties of pure aluminum are greatly improved by ECAP process. After 4 passes of ECAP in route Bc, the grain size of pure aluminum has been refined from 40-50μm to about 5μm. It is found that the shearing deformation, the large cumulative of strain and dislocation movements are the main causes for grain refining during ECAP. Hardness method research results show that the deformations of sample in head and tail are extremely inhomogeneous, the deformation at the top is similar to that in the middle, and the deformation at the bottom is very different with the top and the middle. In addition, residual sample plays a role of backward extrusion during ECAP, and makes the deformation and strain distribution more uniform.