Equal Channel Angular Extrusion Process Research Articles

Texture evolution and serrated failure of AZ31B alloy subjecting to equal channel angular extrusion

Equal channel angular extrusion (ECAE) is considered the most promising method for improving strength and ductility. The microstructures after ECAE have been extensively studied for Mg alloys relating to mechanical properties. However, the changes in texture and their relationship with the prior conditions, extrusion conditions and extrusion directions are rarely studied. In the current work, the changes in texture of AZ31B Mg alloys were investigated along the normal direction (ND), transverse direction (TD), and rolling direction (RD) after ECAE processing one pass. The results revealed a rule that the AZ31B alloy follows for texture changes, where the basal texture (namely the focused c-axis) orients 45º or nearly orients 45º, regardless of the pre-extrusion texture, extrusion temperature, and extrusion rate. Interestingly, serrated failure sorely occurs along the ND for all extrusion conditions, due to the basal slip in an unfavorable orientation and the shear plane not parallel to either pyramidal slip directions.

Equal channel angular extrusion (ECAE): Die design, affecting variables and development of mechanical behavior and properties of bio-metals

There are numerous practices for producing nanocrystalline (NC) and ultrafine-grained (UFG) metals, composites, polymers and alloys; amongst which Equal Channel Angular Extrusion (ECAE) is one of the renowned techniques in metal forming processes under the severe plastic deformation process (SPD) in which a massive plastic strain is enforced on a bulk material. The novelty of this work is the design and fabrication of a split type of die specifically for carrying out ECAE on difficult-to-deform bio-metals. The die is designed for a channel angle of 120°. The study provides a detailed discussion of the pre and post-extrusion tests, process flowchart, and operational variables. This work offers a valuable opportunity to investigate the implications of the ECAE process for other challenging-to-deform metals. Additionally, the ultrafine-grained materials produced through ECAE have potential applications in industries such as automobile, power, and aerospace.

Lamellae orientation and structure evolution of reinforced poly(lactic acid) via equal channel angular extrusion

AbstractThe aim of this study was to improve the mechanical performance of biodegradable poly(L‐lactic acid) through equal channel angular extrusion (ECAE). Changes in morphology induced by the ECAE shear deformation in poly(lactic acid) (PLA) were investigated. Differential scanning calorimeter results suggested a significant improvement in crystallinity of ECAE‐deformed PLA depending on its thermal condition and deformation force. Two‐dimensional wide angle X‐ray diffraction measurement and polarized FTIR spectroscopies of ECAE‐deformed PLA revealed a structural network in the crystalline region, and the taut tie molecules (TTMs) connecting lamellae also stretched. Scanning electron microscope results showed that the macro‐fibrils were generated, and the oriented structures were arranged along the nominal shear direction at a certain angle. Both the inclined macro‐fibrils structure and the oriented TTMs within fibrils were beneficial in improving mechanical performance. Finally, the mechanical property tests showed that the mechanical properties of PLA were improved overall. The tensile strength, elongation, impact strength, and bending strength increased by 28%, 123.8%, 224.3%, and 47.6%, respectively. Meantime, a transition from brittle fracture to ductile fracture was observed from the original PLA billet to ECAE‐deformed one. Therefore, the ECAE process represents a promising approach for comprehensively reinforced PLA.

Enhancing Mechanical Properties of Molybdenum with Equal Channel Angular Extrusion Processing

Enhancing Mechanical Properties of Molybdenum with Equal Channel Angular Extrusion Processing

Recrystallization mechanisms, grain refinement, and texture evolution during ECAE processing of Mg and its alloys

This article presents key findings from a study of the microstructural evolution and grain size refinement of equal-channel angular extrusion (ECAE)-processed Mg and Mg-based alloys. Firstly, we delineate the experimental trends and material characteristics of grain size distribution and texture of as-cast pure Mg and rolled AZ31B which were processed via ECAE. We then identify and describe the primary controlling mechanisms of dynamic recrystallization (DRX) and twinning and how their interaction affects the overall refinement process. Secondly, using preliminary results from ongoing studies of other Mg-based model binary and ternary systems, with access to precipitation hardening mechanisms, we present new opportunities and beneficial outcomes that could affect and control the material's microstructural properties. Thirdly, we provide a summary of prior and concurrent modeling and simulation efforts that capture and emulate the experimentally observed trends of DRX and illustrate their predictive capability. We then, within a Materials-by-Design and Optimization framework, conclude with implications for future developments in Mg alloy research.

On the Hybrid Modeling of Phenomenological Damage Evolution in Low Carbon Steels During Equal Channel Angular Extrusion Process

On the Hybrid Modeling of Phenomenological Damage Evolution in Low Carbon Steels During Equal Channel Angular Extrusion Process

Effect of Equal-channel angular pressing on mechanical Properties: An overview

Equal-channel angular pressing (ECAP) is also known as Equal-channel angular extrusion (ECAE) process. ECAP is a Severe plastic deformation process which can produce ultrafine grains with superior mechanical properties. There is a very significant role of number of passes in the ECAP process, mechanical properties and grain refining is depending on it. This study is focused on the influence of the number of passes and processing routes on hardness, tensile strength and elongation of different alloys, so only mechanical properties are mentioned under this review. Among all the processing route of the ECAP process, BC route shows the maximum strength. Some limitations or disadvantages related to the ECAP process are also discussed in this study.

Evolution of microstructural deformation mechanisms under equal-channel angular extrusion loading conditions: a molecular dynamics case study of single crystal titanium

ABSTRACT Classical molecular dynamics simulations have been performed to investigate the microstructural evolution of single crystal titanium under equal channel angular extrusion process (ECAE). The ECAE loading condition has been simulated by constraining deformation along two directions and applying shear along one direction. We find that for the case where shear is applied along direction, the material yields at higher value of stress in comparison to the case where shear is applied along direction. The and twins activate for the case where shear is applied along direction and the deformation is primarily accommodated by twinning, dislocation slip and structural phase transformation. The ω-phase volume fraction increases, reaches a peak and then decreases. The decrease in ω-phase volume fraction indicates that the ω-phase is not stable. For the case where shear is applied along direction, no twinning occurs and the deformation is primarily accommodated by the dislocation slip.

Repeated equal-channel angular extrusion of polypropylene: Processing routes and back-pressure influence

Multi-pass equal channel angular extrusion (ECAE) process of polypropylene was investigated at room temperature using a 90° die-angle tooling outfitted with a back-pressure. The process was repeated until eight times using two different extrusion orientation routes: route A where the sample orientation is kept constant between each extrusion and route C where the sample is rotated by 180°. The crystalline textures were examined by WAXS measurements and the changes on the mechanical response were observed by full-field strain measurements during tensile tests. The use of a back-pressure turns the deformation behavior, along the flow direction of the ECAE products, from highly heterogeneous (characterized by a peculiar periodic shear-banding behavior) to roughly homogeneous and leads to completely different plastic processes in the crystalline phase. The textural differences subsequent to the multi-pass processing and the use of a back-pressure are the source of significant differences in tensile response along the flow direction. The observations show that the polypropylene processed via route C reaches more easily a saturation state than that obtained via route A with a strong beneficial influence of a back-pressure.

Severe plastic deformation of commercially pure aluminum using novel equal channel angular expansion extrusion with spherical cavity

Abstract Equal channel angular expansion extrusion with spherical cavity (ECAEE-SC) was introduced as a novel severe plastic deformation (SPD) technique, which is capable of imposing large plastic strain and intrinsic back-pressure on the processed billet. The plastic deformation behaviors of commercially pure aluminum during ECAEE-SC process were investigated using finite element analysis DEFORM-3D simulation software. The material flow, the load history, the distribution of effective strain and mean stress in the billet were analyzed in comparison with conventional equal channel angular extrusion (ECAE) process. In addition, single-pass ECAEE-SC was experimentally conducted on commercially pure aluminum at room temperature for validation, and the evolution of microstructure and microhardness of as-processed material was discussed. It was shown that during the process, the material is in the ideal hydrostatic stress state and the load requirement for ECAEE-SC is much more than that for ECAE. After a single-pass ECAEE-SC, an average strain of 3.51 was accumulated in the billet with homogeneous distribution. Moreover, the microstructure was significantly refined and composed of equiaxed ultrafine grains with sub-micron size. Considerable improvement in the average microhardness of aluminum was also found, which was homogenized and increased from HV 36.61 to HV 70.20, denoting 91.75% improvement compared with that of the as-cast billet.

Severe plastic deformation of AA 5083 and copper bimetallic metal

The purpose of the present study is to investigate the effect of Cu casing and wall thickness of the drilled copper bars on uniform distribution of imposed stain in terms of structural homogeneity and distribution of micro-hardness in the severely deformed AA 5083 after equal channel angular extrusion (ECAE). In this study, AA 5083 cylindrical inserts of 6 mm, 8 mm and 10 mm diameter with 100 mm length are tightly inserted in the 16 mm square copper bars having the respective diameter holes. The square cross sectioned AA 5083 billets of 16 mm × 16 mm and 100 mm length are also considered as feedstock. The longitudinal surfaces of the bimetallic metals are polished and annealed at 530 °C for 1 h and then processed by ECAE up to four passes in route A (same sense after every pass without any rotation) at room temperature using a die with square cross-sectioned channels having channel intersection angle (ϕ) 105° and outer corner angle (Ψ) 30°. The initial grain size of 60 µm has been greatly refined and the ultrafine grains of the sizes in the range of 400–700 nm are formed in the extruded AA 5083 inserts after the four passes. The microhardness of extruded AA 5083 significantly increased from 69 to 134 VHN, 132, 176 and 157 respectively for the square billets without Cu casing and cylindrical inserts with the diameters of 6, 8 and 10 mm covered with Cu casing after the four passes. The variations in the microhardness measurements at different regions on the sectioned surfaces are also investigated in this study. The requirement of pressing force is very significantly reduced by using copper casing which is having more ductile nature and the frictional forces between the copper and steel die are very less as compared to the Aluminium and steel. The chances of formation of dead metal zone are avoided by filling the corner gap by cooper metal during the ECAE process. The uniform distribution of strain imposed on the severely deformed billets develops the homogeneous ultrafine grain structure and significantly improves the micro-hardness of the processed material.

Microstructural Refinement and Performance Improvement of Cast n-Type Bi2Te2.79Se0.21 Ingot by Equal Channel Angular Extrusion

How to form a uniform fine-grained structure in n-type polycrystalline Bi2Te3 based alloys to stabilize and improve the thermoelectric properties is the burning issue to be solved. In the present work, equal channel angular extrusion (ECAE) method was used to extrude the cast ingot directly at various temperatures to obtain the BiTeSe polycrystalline bulk alloys with uniform microstructure. The initial lamellae coarse grains (hundreds microns to several millimeters) were efficiently and uniformly refined to a minimum of 4.07 μm at 703 K, which fully demonstrates the feasibility of grain refinement by ECAE for cast n-type BiTeSe ingot. The average grain size of the extruded billets rapidly increased from 5.35 to 29.55 μm with the increase of extrusion temperature from 703 to 823 K. Meanwhile, the behavior of abnormal grain growth became more evident as the extrusion temperature increased because the growth rate increased more rapidly than the rate of nucleation. As the extrusion temperature increased, the Vickers hardness decreased gradually due to grain coarsening. BiTeSe alloys extruded at 703 K achieved the maximum Vickers hardness of 59.8 HV0.05, which was nearly three times higher than that of the initial cast ingot. All extruded BiTeSe billets possessed the much higher dimensionless figure of merit (ZT), compared with the initial cast ingot due to the simultaneously optimization of electrical and thermal transport performances caused by ECAE process. Finally, the specimen extruded at 823 K achieved the maximum ZT of 0.685 at 383 K.

Equal channel angular extrusion: An effective method to refine the microstructure of cast n-type Bi2Te3 based ingot to co-optimize thermoelectric and mechanical properties

Although the mechanical strength of n-type polycrystalline Bi2Te3 based alloys prepared by conventional powder metallurgy technology is good, its thermoelectric properties have poor repeatability and contamination is introduced. In this work, n-type polycrystalline Bi2Te3 based alloys with uniform microstructure were fabricated by applying equal channel angular extrusion (ECAE) method to extrude the cast ingot directly for four passes at 783 K. The initial lamellae coarse grains with hundreds of microns were broken down efficiently and refined uniformly to only 10–20 μm. And the Vickers hardness was increased by 2.3 times due to the refined grains. On the other hand, it is noteworthy that the ECAE process is also an ideal method to improve the thermoelectric properties of cast ingot by boosting electrical transport properties due to the donor like effect induced by heavy deformation and reducing thermal transport properties due to the enhanced phonon scattering. In order to further optimize the thermoelectric performance, BiCl3 doping was used to precisely tune the carrier concentration to the best range. The intrinsic excitation temperature of Bi2Te3 based alloys gradually shifted from low temperature (below 303 K) to high temperature (463 K) owing to the increased carrier concentration. Finally, the extruded Bi2Te3 based alloy doped with 0.064 wt % BiCl3 obtained the maximum dimensionless figure of merit (ZT) of 0.68 at 423 K, which was far higher than the nearly zero of the initial cast ingot.

Dynamic Strength of AZ31B-4E and AMX602 Magnesium Alloys Under Shock Loading

Free surface velocity histories for two magnesium (Mg) alloys are obtained from planar shock compression experiments. Symmetric plate impacts at velocities of approximately 400, 600, 800, and 1000 m/s are reported, where axisymmetric cylindrical specimens (flat-faced discs) are launched in single stage light gas guns. The studied specimens have been produced from an equal channel angular extrusion process for Mg AZ31B-4E and from a hot extrusion of consolidated powder prepared via a spinning water atomization process for Mg AMX602. The present studies focus on the region of the velocity profiles spanning the Hugoniot elastic limit through the plastic rise up to the Hugoniot state, as opposed to wave reflection, release and spall studied previously in these materials. A semi-analytical method is invoked to extract inelastic constitutive response information from particle velocity histories. The only parameters entering the procedure are fundamental thermoelastic properties—notably including elastic constants up to order three—and the ratio of plastic work to energy storage of defects generated in the crystal lattice. Plastic shock velocities are not available from the present data; these are estimated from the initial bulk modulus, its pressure derivative, and known shock velocities in conventional Mg AZ31B. Shear stress, plastic strain, plastic strain rate, temperature, and dislocation density are computed outcomes. Results demonstrate similar trends in extracted behaviors for the two alloys, whereby maximum strength in the plastic shock front increases with increasing impact velocity in each material. Strain rate sensitivity appears to be greater in AZ31B-4E than AMX602. Flow stress on the Hugoniot is calculated as 295 to 336 MPa for AZ31B-4E and 163 to 293 MPa for AMX602. Maximum flow stress in the plastic rise, as extracted from tests with maximum impact velocity, is on the order of 700 MPa for each alloy.

Experimental investigation and numerical simulation of mechanical properties and thermal stability of tin alloy processed by equal channel angular extrusion (ECAE)

In this study, experimental investigation and numerical simulation of the compressive stiffness, effective plastic stress-strain behaviour, the hardness and thermal stability of tin alloy parts subjected to equal channel angular extrusion (ECAE) process were investigated. The numerical simulation was carried out using Automatic Dynamic Incremental Non-linear Analysis (ADINA) and the results were compared with the experiment. The as-received and extruded Sn alloy samples were subjected to metallographic examination using scanning electron and optical microscopy. The external fracture that was observed during ECAE did not show at the interior parts on the optical image. The results of compressive and hardness tests showed that stiffness, modulus, and hardness values increased with the number of extrusions. However, the maximum compressive stress and strain also increased marginally after the second ECAE pass. The thermal properties and transformations of the sample were studied with differential scanning calorimetry (DSC). The effective strain of the samples was simulated and observed to increase with each extrusion pass. The severe plastic deformation brought about by ECAE processing increased dislocation density (work hardening) in the affected parts accounting for an increase in the modulus of the alloy. ECAE processing is, therefore, a potential tool for enhancing the mechanical properties of tin alloy.

Micro Deep Drawability of the Superplastic Zn–22Al Alloy at a High Strain Rate and Room Temperature

Abstract This study aimed to investigate the micro deep drawability of the Zn–22Al alloy at room temperature in which it shows superplastic properties. To this goal, first the two-step equal channel angular extrusion (ECAE) process was carried out to obtain an ultra-fine-grained structure (UFG). Upon achieving the grain size of 200 nm, the formability of the alloy at room temperature and at a high strain rate was investigated both experimentally and numerically. Micro deep drawing experiments were performed at different deep drawing ratios (1.66, 1.84, 2.0, and 2.25) and for different sheet thicknesses (0.2, 0.4, and 0.6 mm). The finite element model of the micro deep drawing was also established to assess and compare the thickness variation in deep drawn parts. Results showed that the superplastic Zn–22Al alloy has a great potential in microforming applications. It was also noted that the limiting drawing ratio can be obtained as high as 2.25 in the room temperature condition.

Study the Effect of Casting Method on the Mechanical Properties of ZA-27 Alloy Formed by Equal Channel Angular Extrusion

In this study the effect of casting technique or method of ZA-27 alloy and die angle of equal channel angular extrusion (ECAE) process on the mechanical properties of alloy after forming was studied. Two casting methods, New Rheocast (NRC) and Gravity Die Cast (GDC) were employed to produce the alloy. Four dies of ECAE with different angles (90°, 105°, 120° and 135°) were used in this process at (100° C). Test specimen was manufactured with circular cross section (12mm in diameter and 85mm in length). The results show that the (NRC) method and 90° angle of die in (ECAE) gave the best of compression strength and hardness due to refinement of microstructure more than other angles.The load in (ECAE) process strongly depends on angle of die and specimen product by (NRC) required higher load.

Microhardness evolution of pure titanium deformed by equal channel angular extrusion

Microhardness homogeneity was assessed on commercial pure titanium processed by equal channel angular extrusion (ECAE). The operation was performed with die channel angle of 90° and processing temperature of 450 °C by route BC up to six passes. The Vickers microhardness measurements were investigated on both cross-sectional and longitudinal planes of the annealed, one-, two-, four-, and six-pass ECAEed titanium. It was found that the application of the process and the addition of pass numbers lead to the improvement of hardness magnitude. It was shown that there are some areas of microhardness heterogeneity in surrounding and bottom regions of the one-pass and two-pass specimens at the cross-sectional plane which is slightly disappeared by adding the pass numbers. Furthermore, there is a suitable amount of hardness homogeneity in the longitudinal plane, irrespective of the specimen condition. It can be concluded that a desirable homogeneity of hardness can be attained after imposing six passes of ECAE process on both cross-sectional and longitudinal planes of titanium.

ALTERNATIVE STUDY OF A BEVEL PUNCH-ASSISTED ECAE SCHEME

It is a common practice in pressure forming to make an Equal Channel Angular Extrusion (ECAE) of a workpiece through a die with channel intersection angle 2θ = 90° using a standard punch of brick or cylindrical shape with 2θ0 = 90°. However Nejadseyfi et al (2015) have applied a beveled 2θ0-punch to the process of ECAE through a standard angular die of Segal geometry with 2θ = 90° and 2θ0 ≠ 2θ. The scope of the article is focused on an alternative numerical study of Nejadseyfi-ECAE-Scheme using techniques of Computational Fluid Dynamics (CFD). A finite-difference method was applied to the numerical solution of the boundary value problem for the Navier-Stokes equations in the form of a vorticity transfer equation. The complex of 2D plots for CFD-derived fields of flow lines and flow velocities and 3D plots for spatial distributions of flow velocities and tangential stresses were firstly derived for Nejadseyfi-ECAE-Scheme during viscous flow of polymer workpiece models through angular die with 2θ = 90° for the different punch inclination angles 30° ≤ 2θ0 ≤ 150°. It was found that Nejadseyfi-ECAE-Scheme provides enhancement of the rotary modes of intensive deformations during ECAE. Results provide visualization of velocity gradients and macroscopic rotation and the illustration of Nejadseyfi et al’s ideas from an alternative CFD-based viewpoint.

Mg–3Zn–0.5Zr/HA nanocomposites fabricated by high shear solidification and equal channel angular extrusion

ABSTRACTMagnesium alloy matrix and hydroxyapatite (HA) nanoparticle reinforced composites for biomedical applications were fabricated by combined high shear solidification and equal channel angular extrusion (ECAE). The high shear treatment was performed immediately prior to casting at 680°C using a rotor–stator mechanism. The as-cast composite ingots were processed by ECAE at 300°C to various strains. The high shear treatment effectively reduced HA particle agglomeration and produced a fine grain structure for all HA contents. ECAE processing resulted in further grain refinement and an improved HA particle distribution, with the formation of a desirable HA dispersion. The composites with 3–5 wt-% HA displayed an optimum combination of strength and ductility, with a yield strength of 150–210 MPa and compressive reductions of 9∼13% before fracture.