Equal Channel Angular Processing Research Articles

Modeling and optimization of equivalent plastic strain in equal-channel angular rolling using response surface methodology

The mechanical properties of metallic strips can be improved by producing an ultra-fine-grained microstructure. The equal-channel angular rolling process is a severe plastic deformation technique suitable for such a purpose. In this article, the effect of the equal-channel angular rolling parameters on the equivalent plastic strain is investigated and their optimum values are reported. The analysis is focused on the following parameters: thickness ratio ( K), die channel angle ( ϕ), die outer corner angle ( ψ), fillet radius ( r), friction coefficient between strip and rolls ( µ), and friction factor between strip and die ( m). Using a combination of the finite element modeling and the response surface methodology with central composite design, a simple and efficient quadratic model is developed to predict the equivalent plastic strain dependence on the equal-channel angular rolling process parameters. The analysis of variance is applied to assess the validity of the model and find the significant parameters. The results show that the die channel angle is the most significant parameter, while the friction coefficient between strip and rolls has no considerable effect on equivalent plastic strain. Moreover, the following optimum values of the parameters are obtained: K = 0.96, ϕ = 90.10°, ψ = 21.21°, r = 2.31 mm, µ = 0.20, and m = 0.19. An increase of about 14.86% in the equivalent plastic strain can be achieved by adopting these values for the process parameters.

Effect of Tensile Twinning on Low Temperature Shear Formability of Mg-3Al-1Zn Alloy

Mg-3Al-1Zn (AZ31) alloy samples with different starting textures have been processed using Equal Channel Angular Processing (ECAP) at 150°C and 200°C. The common temperature limit for ECAP of wrought AZ31 alloys has been reduced from 200°C to 150°C by suppressing tensile twinning activity. Twinning activity was reduced by either changing the starting texture or increasing the temperature. A crystal plasticity model was utilized to gain a better insight into the operating deformation mechanisms during ECAP. Suppression of tensile twinning and pronounced prismatic slip activity resulted in a crack-free, homogeneous deformation at 150°C. In addition, twinning, when exists, was shown to have a significant effect on the promotion of DRX and shear band formation.

Large-scale manufacturing of aluminum alloy plate extruded from subsize billet by new porthole-equal channel angular processing technique

To manufacture plate by the combination of equal channel angular processing (ECAP) and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing (P-ECAP), was studied. Extrusion of AL6005A plate used for the bullet train plate was investigated by finite element method. The relevant porthole dies involving ECAP technique in channels were designed. Dimensional changes in the scrap part of the extrudate obtained after extrusion from the P-ECAP die, with different channel angles, were predicted. Effects of the channel angle and extrusion speed on the maximum temperature of the workpiece and other field variables were evaluated. At the channel angle of 160° of P-ECAP dies, the extrudate exhibited the optimal performance and the least amount of extrudate scrap was obtained. The optimal extrusion speed was 3–5 mm/s. Moreover, with the increase in ram speed from 1 to 9 mm/s, the peak extrusion load increased by about 49% and the maximum temperature was increased by about 70 °C. The effective strain exhibited ascending trend in the corner of the ECAP deformation zone. In the solder seam and the side of die bearing of extrudate, the maximum principal stresses were tensile stress.

Mechanical properties and precipitate behavior of Mg–9Al–1Zn alloy processed by equal-channel angular pressing and aging

Magnesium alloy processed by equal channel angular processing (ECAP) usually had a good ductility, but often inadequate strength. Herein, an approach was developed to simultaneously achieve high strength and good ductility in the Mg–9Al–1Zn alloy. This approach involved pre-solution treatment, ECAP and subsequent aging. The pre-solution accelerated the grain refinement and increased the strain hardening during the ECAP that improved the strength of the alloy. The spherical big precipitates and dispersed nanosized fine precipitates generated separately during the ECAP and the following aging process. As increasing the ECAP passes from 4 to 12, the strain hardening decreased but the fine structure became more equilibrium. Moreover, the aging hardening became more effective that resulted in a good ductility and a high strength in the Mg–9Al–1Zn alloy.

An Investigation into Optimized Ti-6Al-4V Titanium Alloy Equal Channel Angular Extrusion Process

The shear plastic deformation behavior of a material during equal channel angular (ECA) extrusion is governed primarily by the die geometry, the material properties, and the process conditions. This paper employs the rigid-plastic finite element (FE) to investigate the plastic deformation behavior of Ti-6Al-4V titanium alloy during ECA extrusion processing. Under various ECA extrusion conditions, the FE analysis investigates the damage factor distribution, the effective stress-strain distribution, and the die load at the exit. The relative influences of the internal angle between the two die channels, the friction factors, the titanium alloy temperature and the strain rate of billet are systematically examined. In addition, the Taguchi method is employed to optimize the ECA process parameters. The simulation results confirm the effectiveness of this robust design methodology in optimizing the ECA processing of the current Ti-6Al-4V titanium alloy.

Effect of Si addition on the microstructure and mechanical properties of ECAPed Mg–15Al alloy

In the paper, Si element was added in Mg–15Al alloy and processed by the equal channel angular processing (ECAP) for 4 passes using route Bc at 300°C. Microstructure characteristics of experimental alloys before and after ECAP were observed by OM, SEM, EDS and XRD. Tensile test (25, 150 and 200°C) was carried out by a WDW-100KN tensile testing machine. The results show that the grain size of as-cast Mg–15Al alloy was decreased with addition of 1wt% Si element, and new Mg2Si phase formed in the matrix. Meanwhile, network β-Mg17Al12 phases tend to form with the increasing amount of β. After processing by ECAP, the net structure of β-Mg17Al12 phases was disappeared and the morphology was modified. Moreover, the grain size of α-Mg matrix was decreased sharply, from 11.3μm (in Mg–15Al) to 5.98μm (in Mg–15Al–1Si), and Coarse Chinese script Mg2Si phase emerged in Mg–15Al–1Si alloy was broken into particle with dimension of ~3μm by ECAP simultaneously. As a result, the mechanical properties of Mg–15Al–1Si and Mg–15Al alloy were improved by ECAP and the increased amount of Mg–15Al–1Si alloy was greater than that of Mg–15Al, about 51.6MPa in room temperature tensile strength. The Mg2Si phases with high melting were fragmented by ECAP and distributed uniformly in matrix, thus, the mechanical properties of ECAPed Mg–15Al–1Si alloy were more excellent at high temperature, comparing with other experimental alloys.

Factors governing strength and ductility of metallic composites

Two commercial Zn–Al alloys, constituting a natural composite consisting of ductile fibres of face-centred cubic aluminium in the less ductile close-packed hexagonal Zn-rich matrix, variously subjected to warm rolling and warm equal channel angular processing, were investigated to examine the factors governing strength and ductility. Comparison with the published behaviour of an aluminium–copper alloy subjected to similar treatment suggested that the observed behaviour and the interpretation offered were general. When strong crystallographic orientation occurred — as in rolling — strength, and to a less extent ductility, largely depended on crystallographic orientation; ductility strongly depended on the processing route (rolling or equal channel angular processing), but the diffuse orientation characteristic of equal channel angular extrusion allowed the inverse Hall–Petch parameter (as a measure of filament thickness) to display a role in that case. High ductility of the rolled material correlated with orientation of a large number of grains of the close-packed hexagonal matrix phase for easy slip. Strengthening by reduction in size of the units of structure is likely to be available in metallic composites only when dislocation hardening substantially outweighs orientation softening.

Effect of Severe Plastic Deformation at Ambient Temperature on Microstructures and Mechanical Properties of Aluminum Alloy 2519

The effect of severe plastic deformation at ambient temperature on microstructures and mechanical properties of aluminum alloy 2519 was investigated by means of tensile test, micro-hardness test, optical microscopy and scanning electron microscopy. The results showed that tensile strength of as-queched 2519 alloy was greatly enhanced to nearly 550MPa (ultimate tensile strength, UTS) and 520MPa (yield strength, YS) by severe cold rolling or equal channel angular processing (ECAP) while the elongation decreased to 5%. The 2519 alloy could obtain quite well mechanical properties as much as 80 % and 12 passes cold rolling deformation. This indicated that pre-deformation by ECAP is effective in improving the mechanical properties of 2519 alloy by grain refinement, strain aging and high density dislocations.

Surface hardening of biocompatible ultrafine-grained niobium zirconium alloy by two-stage oxidation treatment

The present study reports on an optimized surface hardening process for biocompatible ultrafine-grained (UFG) niobium 2.3 wt% zirconium (NbZr) alloy, a promising candidate implant material. The as-received material of conventional grain size (CG) was processed using multipass equal channel angular processing at room temperature to obtain an UFG microstructure featuring high strength and ductility. Subsequent surface hardening was performed by a heat treatment leading to internal oxidation. Using a thermogravimetric system, the influence of temperatures, time, and partial pressure of oxygen ( $$ p_{{\text{O}}_2} $$ ) on the oxidation kinetics were investigated. Metallographic and microscopic analyses and hardness measurements were employed to evaluate maximum hardness, penetration-depth and scale formation under various conditions. Heat treatment at 620 °C for 6 h at a $$ p_{{\text{O}}_2} $$ of 0.2 hPa led to sufficiently rapid oxidation kinetics yielding a relatively high depth of penetration without formation of loose Nb2O5 on the surface, which was observed at higher $$ p_{{\text{O}}_2} $$ . As compared to CG material, improved hardness profiles were reached using the same heat treatment parameters, since the UFG structure significantly changes diffusion conditions and therefore oxidation kinetics. After a second heat treatment in high vacuum the high maximum hardness of 820 HV0.01 in the UFG material was reduced effectively and a less steep hardness gradient was achieved, both contributing to a less brittle behavior under mechanical loading. High-cycle fatigue tests performed on surface-hardened UFG NbZr samples showed a substantial improvement of fatigue life in tests conducted near the endurance limit. Especially when high fatigue and wear resistance are key issues for a given application, the internal oxidation process offers an effective way to further improve the properties of UFG NbZr.

Effect of Process Parameters on Microstructure and Mechanical Properties on Severe Plastic Deformation Process of Aa7075-T6 Aluminum Alloy

Severe plastic deformation is one of the emerging and promising techniques applied to bulk materials to produce fine grain structure with attractive properties. This study aims to investigate the effect of extrusion parameters like extrusion temperature, number of passes on the equal channel angular pressing and twist extrusion forming behavior of AA7075-T6 Aluminum alloy by hot extrusion process. AA7075-T6 samples of 70x28x18 mm cross sections extruded by equal channel angular pressing and twist extrusion process was subjected to microstructure analysis, hardness and tensile tests in order to determine their mechanical properties. As a result of the experiments, it was determined that twist extrusion leads to more grain refinement at high temperatures with more number of passes compared to equal channel angular pressing. SEM micrographs show that there is severe orientation of the grains facilitated by the extrusion process which enhances the strength. The dense banding of the grains had effected in marginal hardness enhancement in the matrix of the specimens processed by twist extrusion and equal channel angular extrusion process.

Effect of Equal Channel Angular Pressing on Microstructure and Properties of AZ61-4Si Magnesium Alloy

The microstructure and mechanical properties of AZ61-4Si magnesium alloy before and after equal channel angular processing (ECAP) were studied. Results show that the matrix α-Mg and divorced eutectic β-Mg17Al12are refined and chinese script type Mg2Si phases are broken to dispersed particles after ECAP. The mechanical properties of the alloy after ECAP are significantly improved. After 4 passes of ECAP, the yield strength is increased from 50MPa to 109 MPa, tensile strength from 129MPa to 237MPa, elongation from 6% to 22%, and hardness from 61.2HBS to71.5HBS. The modification mechanism for microstructure and mechanical properties of the experimental alloy by ECAP was analyzed.

Underwater friction stir welding of ultrafine grained 2017 aluminum alloy

2017 aluminum alloy plates with an ultrafine grained (UFG) structure were produced by equal channel angular processing (ECAP) and then were joined by underwater friction stir welding (underwater FSW). X-ray diffractometer (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) and microhardness tester were adopted to investigate the microstructural and mechanical characteristics of the FSW joint. The results indicate that an ultrafine grained microstructure with the mean grain size of ∼0.7 μm is obtained in the weld nugget by using water cooling. However, The FSW joint exhibits softening compared with the ultrafine grained based material and the heat affected zone (HAZ) has the lowest hardness owing to the coarsening of the strengthening precipitates.

Effect of grain size on prismatic slip in Mg–3Al–1Zn alloy

The grain size of Mg–3Al–1Zn magnesium alloy was systematically varied from 33 μm down to 350 nm, while keeping the crystallographic texture nearly constant, via multi-temperature equal-channel angular processing. Nearly the same texture allowed the activation of mostly prismatic slip in tension and thus evaluation of the effect of grain size on prismatic slip. The maximum tensile yield strength of 385 MPa and ultimate tensile strength of 455 MPa were achieved in materials with an average grain size of 350 nm, accompanied with 13% ductility.

Corrigendum to “Nano grained AZ31 alloy achieved by equal channel angular rolling process” [Mater. Sci. Eng. A 528 (2011) 6426–6431

Corrigendum to “Nano grained AZ31 alloy achieved by equal channel angular rolling process” [Mater. Sci. Eng. A 528 (2011) 6426–6431

Application of Separated Die Design to Production of Ecap Dies

Metal forming processes with principally shear stresses that very high plastic strains are obtained in one pass are defined as severe plastic deformation (SPD) processes. Strain values can additionally be increased with additional passes throughout the process. Equal channel angular processing (ECAP) is the most applied method among the SPD processes due to relative ease of die manufacturing. On the other hand, die failures like corner cracking are frequently observed due to high notch effect and therefore use of the dies is limited. In the presenting study multi element die design (separated die design) approach was applied to production of ECAP dies in order to eliminate die failures and 5083 Aluminum alloy specimen were deformed with several passes. Although some additional development for die arrangement and fixation are needed, corner cracking was never observed and dies could be used safely.

Application of Separated Die Design to Production of Ecap Dies

Metal forming processes with principally shear stresses that very high plastic strains are obtained in one pass are defined as severe plastic deformation (SPD) processes. Strain values can additionally be increased with additional passes throughout the process. Equal channel angular processing (ECAP) is the most applied method among the SPD processes due to relative ease of die manufacturing. On the other hand, die failures like corner cracking are frequently observed due to high notch effect and therefore use of the dies is limited. In the presenting study multi element die design (separated die design) approach was applied to production of ECAP dies in order to eliminate die failures and 5083 Aluminum alloy specimen were deformed with several passes. Although some additional development for die arrangement and fixation are needed, corner cracking was never observed and dies could be used safely.

Microstructural stability of ultrafine-grained niobium–zirconium alloy at elevated temperatures

The present study reports on microstructural evolution upon static annealing treatment and elevated-temperature low-cycle fatigue (LCF) of an ultrafine-grained (UFG) body-centered cubic (bcc) niobium–zirconium (NbZr) alloy, processed by equal channel angular processing (ECAP) at room temperature.UFG NbZr showed recovery and recrystallization at homologous temperatures, which are in the same range as those of another UFG bcc material, i.e. interstitial free (IF) steel. Unlike the UFG IF steel, the UFG NbZr featured a distinct plateau of decreased hardness due to recovery at temperatures below the recrystallization limit. This was attributed to the absence of dynamic recovery during ECAP due to the low homologous temperature of Th=0.11 (Th=0.16 for IF steel) at room temperature processing.Strain-controlled elevated-temperature LCF tests performed in vacuum revealed stable cyclic deformation response up to 600°C (Th=0.32). At higher temperatures, but still below the static recrystallization limit (≈900°C, Th=0.43), cyclic softening, rapid decrease of mean stress and premature failure were observed. As compared to the UFG IF steel, cyclic stability is preserved up to higher Th due to the stabilizing effect of solid solution alloying elements, i.e. mainly Zr.In the case of the UFG IF steel, localized grain coarsening at the crack tip caused premature failure upon elevated-temperature LCF below the static recrystallization temperature. The more stable microstructure in the UFG NbZr did not show any localized alterations in the vicinity of the crack tip, but instead slightly coarsened throughout the whole gauge length.In combination with the results obtained on the UFG IF steel in previous studies, a comprehensive summary of the microstructural evolution of UFG bcc materials at elevated temperatures is presented.

Microstructure Refinement During Severe Plastic Deformation (SPD) of FCC Materials: A Texture Based Study

FCC materials were subjected to large strain deformation by three techniques: equal channel angular pressing (ECAP), plane-strain machining and friction stir processing (FSP). Based on the orientation imaging mapping (OIM) analysis of the deformed regions, the most likely microstructure refinement mechanisms have been identified for each of the techniques and compared among one another.

Corrosion fatigue behavior of a biocompatible ultrafine-grained niobium alloy in simulated body fluid

The present study reports on the corrosion fatigue behavior of ultrafine-grained (UFG) Niobium 2 wt-% Zirconium (NbZr) alloy in simulated body fluid (SBF). The alloy was processed using multipass equal channel angular processing at room temperature, resulting in a favorable combination of high strength and ductility along with superior biocompatibility and excellent corrosion resistance. Electrochemical measurements revealed stable passive behavior in SBF saline solutions, similar to conventional Ti–6Al–4V alloy. High-cycle fatigue tests showed no alteration in the crack initiation behavior due to the SBF environment, and an absence of pitting and corrosion products. More severe test conditions were obtained in the fatigue crack growth experiments in saline environments. Crack growth rates in UFG NbZr were marginally increased in SBF as compared to laboratory air at a constant test frequency of 20 Hz. Upon a 100 fold decrease in the test frequency, slightly higher crack growth rates were observed only in the near-threshold region. Such excellent corrosion and corrosion fatigue properties of UFG NbZr recommend it as an attractive new material for biomedical implants.

Hot working and crystallographic texture analysis of magnesium AZ alloys

The hot working behaviour of magnesium AZ (e.g. AZ31; Al: 3%, Zn: 1%) alloys and their associated crystallographic texture evolution is reviewed. Under hot working conditions, the stress–strain curves show flow softening at all the temperatures and strain rates indicating dynamic recrystallisation (DRX) is predominant. The mean size of the recrystallised grains in all the alloys decreases as the value of Zener–Hollomon parameter Z increases. The hot working range of the alloys dwell between 200 and 500°C and the strain rates between 10−3 and 5 s−1. The hot working of AZ series alloy shows discontinuous DRX as the main mechanism. Equal channel angular processing shows continuous DRX. The constitutive equation development shows a linear relationship between the stress and the Z parameter. The activation energy for the alloys ranges from 112 to 169 kJ mol−1 and Z values range from 10 to 10 s−1. Textural examinations show basal texture as the predominant orientation.