Equal channel angular pressing with converging billets—Experiment

Processing by severe plastic deformation (SPD) may be defined as such metals forming procedure in which a very high strain is imposed on a bulk material. This paper investigates the effect of different equal channel angular pressing (ECAP) routes and number of ECAP passes on resulting microstructure, mechanical properties and creep behaviour of selected materials. The distinction between various ECAP routes (A, B and C) and the difference in number of ECAP passes applied may lead to variations both in the macroscopic distortions of the individual grains and in the capability to develop a reasonably homogeneous and equiaxed ultrafine-grained microstructure. Experimental materials were processed by ECAP at room temperature using a die with an internal angle of 90° between the two parts of the channel. The ECAP pressing was performed by different routes up to 12 ECAP passes. Tensile creep tests were conducted at temperatures 473 - 673 K and at different applied stresses on ECAP materials and, for comparison purposes, on their unpressed states. Microstructure of samples was characterized by scanning electron microscope (SEM) equipped with the electron backscatter diffraction (EBSD) unit. In conclusion, the ECAP processing route and number of applied ECAP passes could play an important role in creep behaviour and their effect may be different for particular materials. The highest differences in processing routes were revealed for materials especially at lower number of ECAP passes. However, a little apparent dependence of the creep properties was observed during subsequent pressing.

Equal channel angular pressing (ECAP) has been conducted on as-extruded Mg-Zn-Y alloy containing quasicrystal phase at a temperature of 523 K. The optical images indicate that after 8 ECAP passes through route BA, the grain size of the extruded alloy is decreased sharply; and the coarse eutectic icosahedral quasicrystal phases (I- phases) are broken and dispersed in the alloy; and the distributions of Zn and Y elements become more homogeneous. These can be attributed to the shear effect during the ECAP processing. TEM micrographs show the grain refinement, the evolution of broken and dispersed I- phases and dispersion precipitation of nano I-phases during 1- ,4- and 8- pass ECAPed Mg-Zn-Y alloy. And the mechanism of grain refinement is also discussed.

The influence of ageing and Equal Channel Angular Pressing (ECAP) on the microstructure and mechanical properties of Mg-2.5%Tb-0.78%Sm alloy has been examined. The microhardness changes during ageing at 200ºC show a slight increase. The aged microstructure at maximum hardness contains Mg12(Tb,Sm) - metastable β’ phase of size about 2-10 nm as dispersed precipitates. The orientation relationship between β’ phase and the matrix was found as follows:(0001)Mg || (1¯10)β′, [21¯10]Mg || [116]β′. The ECAP passes were performed by two procedures: “I” - four passes at 350ºC; “II” - one pass at 370ºC, second pass at 340ºC and third pass at 310ºC. The grain size was reduced about 200 times as a results of ECAP process according “I” and “II” procedure. The grain refinement by ECAP improves significantly the compression yield strength and hardness. The Hall-Petch relationship was confirmed basing on microhardness measurements and the grain size after ECAP. The Mg24(Tb,Sm)5 and Mg41(Sm,Tb)5 particles smaller than 150 nm are located mainly at grain and subgrain boundaries and they prevent grain growth during ECAP processing. The microstructure evolution during ECAP can be described as dynamic recovery and continuous and discontinuous dynamic recrystallization.

Abstract. This article is focused on a 2-D fluid dynamics description of punch shape geometry improvement for Equal Channel Angular Extrusion (ECAE) or Equal Channel Angular Pressing (ECAP) of viscous incompressible continuum through acute-angled Segal 2θ-dies with 2θ < 90°. It has been shown both experimentally with physical simulation and theoretically with computational fluid dynamics that for the best efficiency under the stated conditions, the geometric condition required is for the taper angle 2θ0 of the inclined oblique punch to be equal to the 2θ angle between the inlet and outlet channels of the Segal 2θ-die. Experimentally and theoretically determined rational geometric condition for the ECAP punch shape is especially prominent and significant for ECAP through the acute angled Segal 2θ-dies. With the application of Navier-Stokes equations in curl transfer form it has been shown that for the stated conditions, the introduction of an oblique inclined 2θ0-punch results in dead zone area downsizing and macroscopic rotation reduction during ECAP of a viscous incompressible continuum. The derived results can be significant when applied to the improvement of ECAP processing of both metal and polymer materials through Segal 2θ-dies.

The dendritic microstructure of Cu–Ni–Cr alloys is typically associated with low formability. Previous studies have demonstrated that equal channel angular pressing (ECAP) can refine the microstructure and enhance mechanical properties. However, when only a single ECAP pass is applied, uniform microstructural evolution and hardness distribution cannot be fully achieved. In this study, the effects of different ECAP processing routes on microstructural evolution and hardness were systematically investigated. The following three secondary ECAP routes were considered: (i) 90° rotation along the longitudinal axis (2P-L90), (ii) 180° rotation along the longitudinal axis (2P-L180), and (iii) 180° rotation along the transverse axis (2P-T180). Microstructural evolutions were observed for all planes, and the microhardness at three positions on each plane was measured. After the second ECAP pass, uniformity in both microstructural evolution and hardness was achieved through the 2P-L180 processing route. A uniform hardness of approximately 287 HV was obtained, representing increases of approximately 64.87% and 5.93% compared with the initial and single-pass ECAP specimens, respectively. The secondary dendrite arm spacing and hardness further evidenced the influence of ECAP processing routes on the deformation of dendritic microstructures in each plane, in contrast to the behavior of non-dendritic materials, particularly in planes subjected to tensile loading. Specifically, hardness improvements were achieved mainly under compressive loading. Therefore, achieving hardness uniformity across all planes remained difficult with the ECAP processing routes suggested in earlier studies. The findings of this study support the adoption of 2P-L180 processing route for Cu–Ni–Cr alloys as a guideline for improving both hardness and its uniformity in materials with dendritic microstructures.

Mechanical properties of an Al-Zn-Mg alloy processed by ECAP and heat treatments

A (Bi,Sb)2Te3 alloy powder was sintered via a pulse discharge sintering process followed by a rotary-die equal channel angular pressing (ECAP) process. It was found by x-ray diffraction analysis that the as-sintered material shows preferentially orientated microstructure, which were considerably eliminated by following ECAP processes. Generally, the Seebeck coefficient of the material was reduced by ECAP processing, which was attributed to the increased carrier concentration after the severe plastic deformation. Electrical conductivity increases after ECAP, which was also originated from the increased carrier concentration. The figure of merit of the material in different conditions shows higher value in the transverse direction. In the transverse samples, those after ECAP processing showed increased figures of merit, which reached 3.85 × 10−3/K in the material after 4 passes of ECAP.

Influence of Route-R on wrought magnesium AZ61 alloy mechanical properties through equal channel angular pressing

Consolidation of commercial pure aluminum powder by torsional-equal channel angular pressing (T-ECAP) at room temperature

Effect of equal channel angular pressing on AZ31 wrought magnesium alloys

Effect of ECAP temperature on microstructure and mechanical properties of Al–Zn–Mg–Cu alloy

Fatigue damage generation in ECAPed oxygen free copper

The automobile industry uses magnesium for load-bearing components due to its low density, durability, and ductility. This study investigated a nanocomposite containing Nb2O5 (3 and 6 wt%) nanoparticles as reinforcement with AZ31 magnesium alloy made by stir casting. A severe plastic deformation was conducted on the cast samples via equal-channel angular pressing (ECAP) after homogenization at 410 °C for 24 h and aging at 200 °C for 10 h. The microstructural distributions and mechanical properties of the magnesium metal matrix composites (MMCs) reinforced with Nb2O5 nanoparticles were investigated via ECAP. With the increase in the number of ECAP passes, the grain sizes became uniform, and the size of secondary phases reduced in the pure Nb2O5/AZ31 MMC. The grain size decreased remarkably after the ECAP process from 31.95 µm to 18.41µm due to the dynamic recrystallization during plastic deformation. The mechanical properties of hardness, ultimate tensile strength, and elongation effectively improved after each ECAP pass. The maximum values achieved for the Nb2O5/AZ31 composite subjected to ECAP were 64.12 ± 12 HV, 151.2 MPa, and 52.71%.

Grain refinement mechanism analysis and experimental investigation of equal channel angular pressing for producing pure aluminum ultra-fine grained materials

Effect of initial microstructure on the processing of titanium using equal channel angular pressing