Equal Channel Angular Extrusion Passes Research Articles

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.

Manufacturing a curved profile with fine grains and high strength by differential velocity sideways extrusion

Abstract For structural and aerodynamic reasons, curved profiles are widely used in the transport industry for manufacturing lightweight structures. In the present work, a curved AA1050 bar with fine grains and high strength was manufactured by a novel forming technique, differential velocity sideways extrusion (DVSE). The evolution of grain structure and micro-texture during DVSE and the mechanical properties of the formed bar were studied, and the grain refinement mechanism was revealed. Due to the severe strains arising in the process, (greater than that for conventional one pass equal channel angular extrusion), significant grain refinement in the curved bar (grain size ∼3 μm) was achieved from the original billet (grain size ∼357 μm) in one extrusion operation. Coarse band-like structures containing subgrains with low angle boundaries in the shearing zone gradually transformed into fine shear band-like structures containing equiaxed (sub)grains with a mixture of low and high angle boundaries. The fine shear band-like structures inclined approximately along the shear intersection planes. Severe plastic deformation induced a high dislocation density that initiated subgrain walls with low angle boundaries, which gradually transformed into grain boundaries with high misorientation, indicating that refinement of AA1050 grains in the DVSE process is due mainly to continuous dynamic recrystallization (cDRX). Due to the appearance of greater effective strain on the inner bend of the extruded bar, the grain refinement degree and high angle boundary fraction of the material on the inner bend are slightly greater than those of the material on the outside. DVSE resulted in a weak C-type shear-texture component which can be determined by a proper rotation of the negative simple shear texture. Compared with the billet, significant increase of the hardness, yield strength and ultimate tensile strength by 134.8%, 354.0% and 116.8% respectively was achieved in the formed curved bar, although the elongation to fracture was decreased by 60.0%.

Processing, structure and thermal conductivity correlation in carbon fibre reinforced aluminium metal matrix composites

Al matrix composites reinforced with Cu-coated pitch-based carbon fibres (Al/Cu-CFs) were fabricated, using a novel combination of rheocasting and equal channel angular extrusion (ECAE) techniques, in order to exploit the thermal conductivity (K) of the material. Rheocasting allowed the introduction and dispersion of Cu-CFs within the Al3Mg matrix. The subsequent ECAE processing reduced the porosity of the composites from 3 to 0.03% and induced a high degree of fibre alignment within the matrix, although considerable damage to the fibres occurred during this processing step. After 6 ECAE passes, in which the billet orientation remained constant, the composite with the highest degree of fibre alignment show a thermal conductivity (K) improvement of ~20% with respect to the rheocast composite. The improvement is due to porosity reduction, improved fibre alignment and forced intimate contact of clean CF surfaces with the matrix.

Improvement of Strength and Energy Absorption Properties of Porous Aluminum Alloy with Aligned Unidirectional Pores Using Equal-Channel Angular Extrusion

Porous aluminum alloy with aligned unidirectional pores was fabricated by dipping A1050 tubes into A6061 semi-solid slurry. The porous aluminum alloy was processed through Equal-channel Angular Extrusion (ECAE) while preventing cracking and maintaining both the pore size and porosity by setting the insert material and loading back pressure. The specific compressive yield strength of the sample aged after 13 passes of ECAE was approximately 2.5 times higher than that of the solid-solutionized sample without ECAE. Both the energy absorption EV and energy absorption efficiency ηV after four passes of ECAE were approximately 1.2 times higher than that of the solid-solutionized sample without ECAE. The specific yield strength was improved via work hardening and precipitation following dynamic aging during ECAE. EV was improved by the application of high compressive stress at the beginning of the compression owing to work hardening via ECAE. ηV was improved by a steep increase of stress at low compressive strain and by a gradual increase of stress in the range up to 50 pct of compressive strain. The gradual increase of stress was caused by continuous shear fracture in the metallic part, which was due to the high dislocation density and existence of unidirectional pores parallel to the compressive direction in the structure.

Strength and electrical resistivity of heavily worked copper

Copper and its alloys are a topic of interest for various cryogenic conductor applications. Often, it is used as a supporting matrix for superconducting filaments requiring that it have good strength and high conductivity. One of the best methods to increase strength while preserving conductivity is work hardening. In this study, CDA101, CDA110, and C182 copper were processed by a severe plastic deformation (SPD) procedure called equal channel angular extrusion (ECAE). In this study we explore the relationships between the levels of plastic strain and annealing with tensile and hardness properties, grain size, and electrical resistivity. While C182 has the highest strength, it also has the lowest conductivity. CDA101 and CDA110 both retain over 95% of their conductivity in the fully worked state, while C182 has about 40% of the IACS value. Saturation of strength occurs around 3-4 ECAE passes. It is concluded that a lower amount of plastic strain via ECAE is best for creating a material with the highest combination of strength and conductivity, and is suitable for high strength high conductivity applications.

Effect of strain-path change on the anisotropic mechanical properties of a commercially pure aluminum

Samples of commercially pure aluminum were subjected to equal channel angular extrusion (ECAE) using a 90° square die by routes A and C, where the specimens are not rotated and are rotated 180° between extrusion passes, respectively. Qualitatively similar anisotropic responses under compressive loading along the three orthogonal directions of the ECAE billet are seen in both cases. The plastic anisotropy is related to the effect of strain-path change, namely that different slip activities are induced for specimens loaded along different directions with respect to the last ECAE pass. The anisotropic mechanical behavior is more evident in the sample deformed by route C. Considering the shear patterns imposed in each ECAE route, the characteristics of dislocations introduced in ECAE should affect the mechanical response in post-ECAE loading. It is suggested that during the ECAE process, dislocations on fewer slip systems are activated in route C than in route A, and therefore, a stronger plastic anisotropy results in this sample. The as-ECAE specimens were also heat treated to achieve a recovery-annealed state. The plastic anisotropy persists in the annealed specimens to slightly reduced extent, which can be ascribed to partial annihilation of preexisting dislocations.

Characteristics of friction welding within a short time for aluminum alloy deformed by ECAE process

Abstract In order to obtain high-strength materials, several plastic deformation processes such as ECAE (equal channel angular extrusion) process is effective. However, it is hard to produce a workpiece with elongate workpiece because the dimensions of dies for ECAE process influence the shape of the workpiece. Therefore, one of the best approaches for elongated shape is welding. The friction welding is the most appropriate method without distortion of deformed microstructure by ECAE. The aim of this study, in order to improve the joint efficiency, the friction welding for the aluminum alloy deformed by ECAE is carried out in very short welding time. The workpiece material was A6063-T5. The ECAE process was carried out at room temperature by means of the dedicated device that developed by one of authors, and the workpieces were deformed by ECAE repeatedly up to 3rd passes. After ECAE, the friction welding process was carried out In these process, the upset pressure was same as heating pressure. The heating time by friction was within 1 sec. The joint efficiencies of all pressure condition were over 70% from results of tensile tests, and the point of fracture was joint zone on all condition. The friction welding within a short time is beneficial for joining of materials deformed by multiple passes of ECAE.

Microstructure and Mechanical Properties of Nb Alloyed Steel Processed by Hot Equal Channel Angular Extrusion

A Nb alloyed low carbon steel was processed by hot equal channel angular extrusion (ECAE) and following transformation. The workpieces were heated up to the 960°C in the furnace for 10 min within the container block. Before extrusion, the die was preheated to 400oC. The workpiece was cooled in the die after ECAE process. 1 pass and 2 pass via route C were conducted at a speed of 32mm/s, the inter-pass time is about 2 sec. The sample of average ferrite grain size of about 2μm, a tensile strength of 800MPa, a total elongation about 20% is produced after 2 pass ECAE processed and subsequent cooling.

Substructural Alignment during ECAE Processing of an Al-0.1Mg Aluminium Alloy

An investigation has been carried out into the microstructures developed during the early stages of equal channel angular extrusion (ECAE) in a polycrystalline single-phase Al-0.13Mg alloy, with emphasis on the substructural alignment with respect to the die geometry and the crystallographic slip systems, which is essentially related to the grain refinement and texture development during deformation. The material was processed by ECAE at room temperature to three passes, via a 90° die. Microstructures were examined and characterized by EBSD. It was found that dislocation cell bands and microshear bands were respectively the most characteristic deformation structures of the first and second pass ECAE. Both formed across the whole specimen and to align approximately with the die shear plane, regardless of the orientation of individual grains. This confirmed that substructural alignment was in response to the direction of the maximum resolved shear stress rather than to the crystallographic slip systems. However, a significant fraction of material developed preferred orientations during deformation that allowed the coincidence between the crystallographic slip systems and the simple shear geometry to occur, which governed texture development in the material. The third pass deformation was characterized with the formation of a fibre structure with a significant fraction of high angle boundaries, being aligned at an angle to the extrusion direction, which was determined by the total shear strain applied.

Enhanced grain refinement of commercial pure copper using the ECAE of Al–Cu–Al tri-layer composite

Equal channel angular extrusion (ECAE) is a promising technique for production of ultrafine grained (UFG) materials of few hundred nanometers size. In this research, the grain refinement of copper strip is accelerated to ultrafine range by sandwiching it between two aluminum strips and then subjecting the three strips to ECAE process simultaneously. After passing the aluminum–copper–aluminum laminated billet through ECAE die up to 8 passes, tensile properties of the copper layer are evaluated. The optical, scanning and transmission electron microscopes, differential scanning calorimeter, and X-ray diffraction were used to characterize the microstructural changes. The results show that the yield stress of the middle layer (Cu) is increased significantly by about eight times after application of four consecutive passes of ECAE and then it is slightly decreased when more ECAE passes are applied. An ultrafine grain within the range of 150 to 200 nm is obtained in the Cu layer.

Mechanical Behavior Enhancement of AM60/Al2O3p Magnesium Metal–Matrix Nanocomposites by ECAE

The effect of equal channel angular extrusion (ECAE) on the mechanical behavior of AM60/Al2O3p magnesium metal–matrix nanocomposites was investigated. ECAE is a useful technique to produce bulk nanostructured materials through severe plastic deformation. The present magnesium metal–matrix composites (Mg MMCs) with 1 wt% nanosized Al2O3 particles for ECAE were fabricated using stir-casting method. The significantly enhanced mechanical behavior of AM60/Al2O3p magnesium metal–matrix nanocomposites at room temperature, for instance, yield strength (YS), ultimate tensile strength (UTS), and ductility, can be obtained after ECAE process. The AM60/Al2O3p MMC after 4 passes of ECAE exhibited greater YS, UTS, and ductility (+135%, +107%, and +245% increase, respectively) than those of as-cast AM60. Experimental results show that the AM60/1wt %Al2O3p MMC after 4 passes of ECAE exhibits the superior mechanical behavior.

Microhardness Characteristics of Al-6063 Alloy Processed by Equal Channel Angular Extrusion

In this study, annealed AL-6063 alloy was processed by the Equal Channel Angular Extrusion (ECAE) up to 6 passes at a temperature of 200°c following route A with a constant ram speed of 30 mm/min through a die angle of 90° between the die channels. The influence of ECAE processing on the evolution of microhardness in the material was studied using Vickers microhardness testing. The detailed analysis was carried out on the samples of as-received, one, two, three, four, five, and six pass conditions. The grain diameter reduced from 45μm to 2.8 μm after 6 passes of ECAE. The results indicated around 90% increase in Microhardness after 5 passes. Hardness of the inner surface where the billet was under compression was slightly higher than that of the mid-surface.

ECAE processed NiTi shape memory alloy

The current work evaluated the microstructures and martensitic transformation temperatures of NiTi shape memory alloy (SMA) deformed by equal channel angular extrusion (ECAE). The Ti-55.27wt.%Ni alloy was processed by 1 ECAE pass at 250 °C using a die with an intersection angle of 120°. After processing, samples were annealed at 300 °C, 400 °C and 500 °C for 1h to evaluate the microstructural changes. Microstructural characterization was performed by scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS) device, and Vickers hardness measurement. Martensitic transformations temperatures were analyzed by differential scanning calorimetry (DSC). Results show that the annealing treatments presented no significant change in the microstructure of the ECAE processed samples. Meanwhile, the DSC curves corresponding to the annealing treatments performed at 300 °C and 400 °C show two step martensitic transformation related to B2→R→B19'. For the annealing at 500 °C, the martensitic transformation temperatures returned to the ST condition, indicating a reduction of the processing defects.

Shape Recovery in Stainless FeMnSiCrNi(-Co) SMA Processed by ECAE

Stainless shape memory steel presents reasonable shape recovery but lower than the traditional NiTi shape memory alloys (SMA). However, recent results have shown that the shape recovery could be improved by decreasing the austenitic grain size. The present work describes the influence of the austenitic grain size on the shape recovery in stainless shape memory steel deformed by equal channel angular extrusion (ECAE) using a die intersection angle of 120o. Two alloys, FeMnSiCrNi and FeMnSiCrNiCo, were deformed by 1 ECAE pass and then they were compared in the deformed state; deformed and annealed in different temperatures for 1 h, resulting different grain sizes. Both alloys were evaluated by compression tests and the results shows an increase in total shape recovery related to grain size decrease. The best total shape recovery was 73% after a pre-strain of 4% for FeMnSiCrNi alloy.

Effect of Temperature and Extrusion Pass on the Consolidation of Magnesium Powders Using Equal Channel Angular Extrusion

The microstructure and characteristics of bulk magnesium consolidated from Mg powder by equal channel angular extrusion (ECAE) wereinvestigated. Cu cans filled with Mg powder, of about 74µm in diameter, were ECAE processed for one, two and four passes via the Bc route at473, 523 and 573K. The microstructure of ECAE-processed samples was observed by OM and SEM. The density of each sample wasdetermined using Archimedes’ principle. Microhardness and compression tests were conducted to investigate the mechanical properties of eachECAE-processed sample. The best consolidated condition between powders was achieved after four passes of ECAE at 573K. Density at 98.4%of the ideal density of bulk Mg was achieved, microhardness was about 49Hv, and compressive yield stress was about 100MPa.[doi:10.2320/matertrans.M2013006](Received January 7, 2013; Accepted February 4, 2013; Published March 15, 2013)Keywords: magnesium, powder metallurgy, equal channel angular extrusion, consolidation

The effects of equal channel angular extrusion on the mechanical and electrical properties of alumina dispersion-strengthened copper alloys

Two alloys of alumina dispersion-strengthened copper were subjected to 1-4 passes of equal channel angular extrusion (ECAE) by route BC. Microstructures before and after deformation were characterized by scanning electron microscopy, scanning ion microscopy and electron backscatter diffraction. Mechanical and electrical properties were evaluated using uniaxial tensile testing and the four point probe method, respectively. The initial microstructure consisted of cylindrical grains, elongated in the extrusion direction and highly textured in a <100>/<111> orientation. Following four ECAE passes, the average major axis of grains in both alloys decreased by over 50%, and the microstructure approached an equiaxed morphology. The texture decreased in intensity and shifted to a <112> orientation after one ECAE pass, followed by a transition to a <101> orientation by the fourth pass. Flow stress of AL-25 and AL-60 increased only 48MPa (10%) and 24MPa (5%), respectively, while the conductivity of both alloys remained essentially unchanged. A combination of Hall–Petch strengthening and texture softening are used to explain the observed changes in mechanical behavior.

Directionality of slip traces and banded structures in fcc materials processed by equal-channel angular extrusion

A statistical analysis of the directionality of slip traces in face-centered cubic crystals processed by a single pass of equal-channel angular extrusion was conducted based on crystal plasticity simulations. The slip traces are found to orient along various directions on each of the inspection planes, indicating a strong grain-orientation dependency. The slip traces depict preferred alignment directions that coincide with those of banded structures found in the literature and can be traced to the macroscopic deformation mode.

Effects of equal channel angular extrusion on the microstructure and high-temperature mechanical properties of ZA85 magnesium alloy

This study examined the microstructure and high-temperature tensile properties of the Mg–8wt.%Zn–5wt.%Al (ZA85) alloy that was subjected to equal channel angular extrusion (ECAE) with various passes at 180–250°C. The original grain size and precipitate size of the as-cast specimen were 150 and 100μm, respectively. The average grain size was reduced to 4μm by dynamic recrystallization and the precipitate size was reduced to 1μm after six ECAE passes at 180°C. However, the average grain size of the ECAE-processed specimens at 250°C increased from 14μm after two passes to 20μm after four passes owing to the grain growth effect. In tensile tests at 200°C, the ultimate tensile strength (UTS) and yield strength (YS) of the specimens processed with six ECAE passes at 180°C improved to 249MPa and 162MPa, respectively, compared with 105MPa (UTS) and 74MPa (YS) for the as-cast specimens. Furthermore, elongation increased from 5.1% to 28.5%. This significant improvement in the high-temperature tensile properties of the ZA85 alloy was attributed to the refined grains and the well-distributed fine Mg32(Al, Zn)49 (τ-phase) precipitates.

Microstructural evolution and mechanical properties of niobium processed by equal channel angular extrusion up to 24 passes

We have systematically investigated the microstructural evolution of niobium (Nb) subjected to severe plastic deformation via equal channel angular extrusion (ECAE) up to 24 passes. The starting Nb billet material consists of a centimeter-scale grain size with a columnar structure. We have found that the grain size reduction of the Nb is almost saturated at ∼300nm after eight passes of ECAE. However, the population of high-angle grain boundaries continues to increase with further ECAE, and no saturation appears to have been reached at 24 passes. We have evaluated the mechanical properties of the samples with different number of ECAE passes over a wide range of strain rates, from quasi-static to high strain rates. We have used strain-rate jump tests to examine the strain-rate sensitivity (SRS) of the processed samples and found that the SRS of the ECAE-processed Nb is ∼0.012, which is a factor of three smaller than that of the coarse-grained counterpart. The activation volume derived for plastic deformation indicates that the double-kink formation of screw dislocations is still the predominant deformation mechanism in the ECAE-processed Nb. Quasi-static true stress–strain curves exhibit elastic–nearly perfectly plastic behavior. The quasi-static yield strength is also nearly saturated after eight passes of ECAE. High-strain-rate compressive true stress–strain curves show uniform flow softening. However, the dynamic peak stress keeps rising with an increased number of ECAE passes, suggesting a strong grain boundary contribution to dynamic strengthening. Scanning electron microscopy of post-loaded surfaces displays a morphology of diffuse shear bands accompanying highly compressed grains. In our report, we demonstrate that grain boundaries of severely deformed metals play different roles at low, quasi-static vs. high-strain rates of mechanical loading. The difference is primarily determined by the strength of grain boundaries acting as dislocation barriers at different loading rates. This discovery is significant for the understanding of the effect of the microstructure as a function of the applied loading rate.

Evolution of Microstructure and Crystallographic Texture in AA2014 Aluminium Alloy during Equal Channel Angular Extrusion

Present work addresses the evolution of texture and microstructure of equal channel angular extrusion (ECAE) processed AA 2014 Al alloy upto four passes at room temperature by adopting route BC. TEM is used to assess the microstructural changes during each ECAE pass. Texture measurements on samples of each pass were carried out by XRD technique. The evolution of texture components after each ECAE pass are analyzed and the changes are discussed with respect to the initial texture.