Angular Pressing Research Articles

A study of disperse structures in metals and alloys exposed to powerful shock waves

The structure of iron-base steels and alloys loaded with plane and spherical shock waves and of copper and titanium after dynamic angular channel pressing is considered. It is shown that shock wave loading (alone or in combination with other methods of treatment) yields disperse structures in metals and alloys, including nanocrystalline ones, due to very rapid straining processes and phase transformations that occur with a great number of nucleation centers.

Angular Extrusion of Double-Metal Ingot

Relatively high mechanical strength and simultaneously good plasticity of a crystalline material are determined by the state of its internal structure, preferably nano- or ultra-fine grained one. To achieve the above combination of properties, various manners of plastic deformation and heat treatment are applied in practice. One of the most effective processes in this field is severely plastic deformation, e.g. by the method of equal angular channel pressing (ECAP). During the ECAP, favourable effects of grain fragmentation and the formation of specific orientation relations can be attenuated by the process of structure recovery, especially, when the real temperature of angular extrusion is elevated for physical or technological reasons. An attempt to modify the ECAP technology was considered, to avoid the unfavourable temperature effects and to increase at the same time the efficiency of manufacturing the ultra-fine structure of material. Extrusion of dual-material (AZ31 + Al) ingot was performed at room temperature. As it seems, the well known difficulties with plastic deformation of materials with hexagonal lattice symmetry, like AZ31 alloy, have been decreased. Both experimental and methodological aspects of the angular extrusion of the dual-material ingot and chosen microstructure characteristics (texture, stress, morphology) are presented. On the basis of the suggested modification, the text discusses an explanation of physical origins of the microstructure evolution in the investigated material revealed by experiments.

Enhanced superplastic deformation behavior of ultrafine‐grained Ti‐6Al‐4V alloy

AbstractThe mechanical behavior of the Ti‐6Al‐4V ELI alloy in both conventional grain size (CG) and ultrafine‐grained (UFG) conditions under tension and compression at elevated temperatures (500–800 °C) is considered. Grain refinement by equal‐channel angular pressing (ECAP) followed by multicycle extrusion was observed to result in a considerable improvement of superplastic characteristics of Ti‐6Al‐4V ELI alloy. The alloy exhibits a superplastic deformation behavior already at 600 °C. The enhanced regime of superplasticity allows more efficient forming of parts and components. In addition, the UFG microstructure and, consequently, enhanced mechanical properties are kept after superplastic forming.

Influence of Thermal Condition of ECAP on Microstructure Evolution in Low Carbon Steel

Commercial low carbon steel AISI 1010 was subjected to Equal Angular Channel Pressing (ECAP) at different temperatures. The paper describes the refinement of the coarse grained ferrite microstructure to submicrocrystalline range by large plastic strain. The steel was deformed in an ECAP tool with a channel angle φ = 90°, at different temperature in the ranging between 150 – 300°C. The number of passes at each temperature was N = 3. Optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the formation of substructure and ultrafine grains in the deformed specimens. The TEM study reveals that at the lowest ECAP temperature of 150°C extensively elongated ferrite grains with dense dislocation network dominate in the structure. The randomly scattered polygonized subgrains have been observed. The activation of dynamic recovery process, even at the lowest temperature of equal channel pressing, contributed to the formation of individual polygonized grains. As the temperature of ECAP processing was increased the process of dynamic polygonization and recrystallization occurred more effectively and the submicrocrystalline structure was formed by sectioning of elongated ferrite grains. The formation of such predominant submicrocrystalline structure resulted in strength increase of the low carbon steel.

Boss Formability of Nano-Structured Aluminium Alloys at Elevated Temperatures

Together with conventional alloys, ultra-fine or nano-structured aluminum alloys were prepared by equal channel angular rolling (ECAR) and pressing (ECAP). Formability of cylindrical bosses was investigated by compression tests of a closed die. Finite element (FE) analysis was also carried out to investigate the effect of die friction on the forming behavior. Cylindrical bosses with the aspect ratio over three were formed in a closed die at elevated temperatures even under a frictional condition, although more uniform deformation was expected under a frictionless condition by the FE simulation. Boss formability increased with increasing temperature and decreasing strain rate, and fine structured aluminum alloys had superior boss formability to the conventional alloys. Near-net shape forming of a simplified cellular phone case was performed at elevated temperatures using a set of closed dies. A nano-structured aluminum alloy showed higher formability in all aspects of bosses, sidewalls and face thickness than conventional alloys.

Achieving a Superplastic Forming Capability through Severe Plastic Deformation

AbstractProcessing by severe plastic deformation (SPD) leads to very significant grain refinement in metallic alloys. Furthermore, if these ultrafine grains are reasonably stable at elevated temperatures, there is a potential for achieving high tensile ductilities, and superplastic elongations, in alloys that are generally not superplastic. In addition, the production of ultrafine grains leads to the occurrence of superplastic flow at strain rates that are significantly faster than in conventional alloys so that processing by SPD introduces the possibility of using these alloys for the rapid fabrication of complex parts through superplastic forming operations. This paper examines the development of superplasticity in various aluminum alloys processed by equal‐channel angular pressing (ECAP).