Materials Science Forum Vols. 667-669

Abstract: A two-phase Ti-Al material was fabricated by severe plastic deformation. Particles of finely mixed elemental Ti and Al were mechanically milled and then consolidated by equal channel angular pressing. The bulk material has a unique interpenetrating structure of Ti and Al phases with multiple scales from micro to nano. Compared to its coarse structured counterpart, the multiscale structured material exhibited a significant increase in strength without compromising plasticity.

Abstract: Experiments were conducted to evaluate the feasibility of using a new ECAP die configuration in which there are arcs of curvature at the intersection of the two channels at both the outer and inner points. The experiments used a configuration in which the radii of curvature were identical at both the outer and inner points since calculations suggest this corresponds to an optimum configuration. High-purity aluminum was pressed using this special die and hardness measurements were taken on cross-sectional planes after pressing. The results show the new die configuration leads to less homogeneity than with conventional ECAP dies.

Abstract: In this paper, a systematic investigation of equal channel angular extrusion/Pressing (ECAE, ECAP) process on the AZ31 alloy and die design is performed by using numerical simulation. The stress distributions on the die were obtained, and general consideration of the die during the whole pressing process was given. The numerical results revealed that effective stress distribution at the corner of the cavity and the extruded load during extrusion processes was effect by channel angles and friction factor. From the simulations, it was found that the closer the die corner is, the higher stress value results can be acquired. And the effective stress concentration in ECAP die cavity corner. The extruding load fell rapidly when the angular angle increasing. With the increase of friction factor, extruding load also increased significantly. The proposed method can serve as preconditions to analyze the abrasion and fatigue of ECA Pressing die. Besides, this method also provides a feasible way for other die stress analysis.

Abstract: Finite element simulation of the effects of mould angle and friction condition on the equal channel angular pressing (ECAP) for AZ80 magnesium alloy were investigated by using DEFORM-3D program. The results show that the curve of load-displacement was divided into several stages including rapid increasing stage, load fluctuation, rapid increasing stage, steady stage and rapid drop stage. Firstly, when the angle decreased from 150°to 90°, the maximum load increased, and the same as energy consuming. In addition, the average effective strain increased with the decreasing of mould angle after single extrusion, while the degree of effective strain uniformity of the sample decreased and keep greater strain grads between inner and surface part. Secondly, the work load ascended with the increasing of the friction coefficient from 0 to 0.3, and one part of load overcome the friction and the other part is used for deformation of the sample. With the increment of friction coefficient, the average effective strain keeps steady value, while the degree of effective strain uniformity of the sample decreased. As mentioned above, large angle mould and low coefficient of friction should be adopted during ECAP deformation for AZ80 magnesium alloy.

Abstract: The aim of the present work was to compare microstructures and mechanical properties of nano-Al alloys fabricated by two different methods: (i) SPD induced grain refinement, (ii) plastic consolidation of nano-powders or nano-crystalline ribbons. SPD grain refinement has been implemented by hydrostatic extrusion, HE. The ribbons were rapidly solidified using a melt spinning methods. Plastic consolidation of powder and ribbons was conducted by warm extrusion. The results of the studies show that by applying various fabrication routes for a given chemical composition, diverse nano-structures can be obtained, which differ in terms of grain size and shape, grain boundary character and dislocation density. As a result, the alloys also differ significantly in the mechanical properties. The findings are discussed in terms of the possibilities for optimizing properties of the bulk-nano-metals.

Abstract: An earlier study showed that high-pressure sliding (HPS) is effective for grain refinement of pure Al in a rectangular sheet form using the principle of high-pressure torsion. In this study, the HPS is applied for grain refinement of an Al-3%Mg-0.2%Sc alloy and an AZ61 Mg alloy. HPS was conducted under a pressure of 1 GPa with sliding distances of 10 to 30 mm at room temperature for the Al alloy and at 473 K for the Mg alloy The average grain size is ~300 nm for both the Al and Mg alloys, respectively. Tensile tests showed that a superplastic elongation of ~1500% is achieved in the Al-3%Mg-0.2%Sc alloy at 573 K with an initial strain rate of 3.3x10-3 s-1 and of ~600% in the AZ61 alloy at 573 K with an initial strain rate of 1x10-3 s-1.

Abstract: A hypothesis for two-stage character of deformation under load via the simple shear scheme is suggested. At the first stage in the shear strain range , where - the strain parameter, the metal microstructure changes in the way similar to that during elongation. At the second stage at accidental multi-scale rotative motions, similar to turbulent motions in liquids, take place in the metal. This stage of deformation is the proper simple shear. The results of experiments are presented, which testify in favor of the suggested hypothesis.

Abstract: Equal Channel Angular Swaging (ECAS) is a new severe plastic deformation process which combines the conventional equal channel angular pressing (ECAP) and the incremental bulk forming process rotary swaging. The tool system consists of two rotary swaging dies with an angled channel that contains four shear zones, generating severe plastic strain per pass. The crucial advantages compared to conventional ECAP are a significant reduction of friction and axial forces plus the potential to be extended to continuous processing. Thus, ECAS has high potential for a cost-efficient production of bulk UFG materials. In the present paper the principles of ECAS are introduced and first experimental results for the processing of copper are presented.

Abstract: By the method of severe plastic deformation at high strain rate of coarse-grained copper under explosively dynamic loading, nanocrystalline copper with the average grain size less than 200 nanometer was fabricated. The mechanism of grain-refining was investigated by means of transmission electron microscopy. Finally, the deformation processes were simulated using Ls-Dyna3d finite element program and the effects of the strain, strain rate as well as temperature rise on grain-refining were analysed systematically. The results show that it is feasible to fabricate nanocrystalline copper by explosively dynamic plastic deformation of coarse-grained copper; twin crystal and dislocation are the main mechanism of grain-refining; higher strain and lower temperature rise are beneficial to the grain refining; the distribution of the grain size is not uniform along the loading direction.

Abstract: Multi-pass ECAP process of pure Al for square samples (Φ＝90º, Ψ＝37º, pressing speed of 1mm/s), was simulated by using 3D finite element method (FEM).The distribution of equivalent strain for two and four passes was compared. The results showed that route A leads to non-uniform distribution of equivalent strain during multi-pass ECAP. The distribution of equivalent strain is uniform in BC route, but the value of equivalent strain is larger in C route. The simulation results were compared with the experimental ones with previous work in the literature. The simulation also shows that equivalent strain and load increase with pass increasing.