Room Temperature Equal Channel Angular Pressing Research Articles

Investigation of slip systems activity and grain boundary sliding in fine-grained superplastic zinc alloy

Zn alloys are desirable candidates for biodegradable materials due to their great biocompatibility and sufficient mechanical properties. Nevertheless, the most popular strengthening method by grain refinement after cold processing is usually ineffective in Zn alloys. Besides highly anisotropic deformation through a dislocation slip, grain boundary sliding (GBS) plays an important role in total deformation in fine-grained Zn alloys at room temperature (RT). Herein, Zn–0.5Cu (wt. %) alloy is fabricated by RT equal channel angular pressing, and its deformation mechanisms in tension were systematically analyzed at strain rates from 10–4 s−1 to 100 s−1. GBS contribution in total deformation was measured using surface markers and atomic force microscopy. In addition, dislocation slip activity was evaluated via electron-backscattered diffraction-based slip trace analysis. As a result, investigated alloy presents the GBS contribution in a total deformation at RT from 35% at the strain rate 100 s−1 to 70% at 10–4 s−1. Simultaneously, the number of slip-deformed grains decreased from 97.5% to 8%. Moreover, the basal slip system was dominant at all strain rates, while the prismatic and the pyramidal < c + a > slip systems were activated at the higher strain rates. The results presented here for the first time clearly show the complexity of deformation mechanisms in fine-grained Zn–0.5Cu, at significantly different strain rate conditions.

The effect of thermal and strain-induced aging on the mechanical behavior of room temperature ECAP processing of WE43 magnesium alloy

The WE43 magnesium alloy, in case of improved toughness, can be an appealing material for biomedical applications. The effects of equal-channel angular pressing (ECAP) and post-deformation aging (PDA) on the mechanical behavior of the WE43 alloy were investigated in this study. ECAP of WE43 magnesium alloy at room temperature is extremely challenging because of the insufficient number of slip systems. An optimized core–sheath configuration is proposed, which applies fully compressive stress on the WE43 alloy as the core, resulting in ECAP of the WE43 alloy at room temperature. Unprecedented strain-induced precipitation of both Mg41Nd5 and Mg24Y5 was observed owing to stored mechanical energy and temperature raise in the adiabatic shear bands during ECAP at room temperature. Moreover, the formation of oriented needle-like Mg3(Y, Nd) precipitates and partial recrystallization simultaneously increased the strength to 410 MPa and the strain to fracture to 11.4% after PDA. A combination of bimodal grain size distribution and a high volume fraction of precipitates increased the toughness to 38.96 MJ/m3 after ECAP and PDA.

Achieving high strength, excellent ductility, and suitable biodegradability in a Zn-0.1Mg alloy using room-temperature ECAP

High alloying elements effectively strengthen zinc alloys, but these elements also usually decrease the ductility and corrosion resistance of such alloys. In the present study, energy-saving and efficient rotary-die equal-channel angular pressing (ECAP) was successfully applied to a zinc alloy with a low Mg content (0.1 wt%) at room temperature (RT), which facilitated the formation of a microstructure with a fine grain size (1.14 ± 0.22 µm), weak texture, and dynamically precipitated nano-sized Mg-Zn precipitates at the grain interior. The Zn-0.1Mg alloy formed via RT-ECAP exhibited an outstanding performance, with a high ultimate tensile strength of 383 MPa, excellent ductility of 45.6 %, and a suitable biodegradation rate of 0.014 mm/y in Hank’s solution. This alloy is thus a promising candidate for various biodegradable medical applications.

Optimization of Al 6063 Button Head Rivet FEM Analysis Subjected to CRYO ECAP and RT ECAP

The severe plastic deformation technique that has attracted much attention from the material community in recent years is Equal Channel Angular Pressing (ECAP). By using this technique, ultrafine-grained microstructures can be produced without a significant change in the geometry of the material. In the present research, an aluminum 6063 sample was tensile tested after the ECAP process to know the properties of the material. ECAP is performed for two sets of specimens in which the channel angle is 108. One set of samples is at room temperature, and the other set is at -197oC, i.e., dipped in liquid nitrogen for 20 minutes. Tensile properties of the obtained samples are tested once more. The tensile test properties of samples, i.e., before processing and after Room Temperature (RT) and CRYO ECAP, are tabulated and saved for simulation. A rivet with American Society for Testing and Materials (ASTM) dimensions is designed using a design modeller in Analysis of Systems (ANSYS), and the properties obtained from the tensile tests are assigned to the rivet. One end of the rivet is constrained with a fixed support, and the other end is loaded with 35 kN in the downward direction. The process is repeated for three different sets of samples. The developed stresses in the three rivets are tabulated and correlated, and the results are drawn in the present investigation, which showed good correlation.

Cryogenic and Room Temperature ECAP Consolidation of Blended Elemental Powders of Aluminum and Copper

The effect of temperature was investigated on the consolidation of blended elemental powders of aluminum and copper by equal channel angular pressing (ECAP). Aluminum and Copper powders (1:1% vol.) were blended and consolidated in a 90° ECAP die at room (RT) and cryogenic temperatures (CT - ~77 K). ECAP samples were pressed until 4 passes at room temperature in route Bc. As a reference, a sample was obtained by conventional uniaxial pressing. The obtained results indicated a much denser (>99.5%) and harder structure by cryogenic ECAP. The hardness after one pass at CT was comparable with 4 passes at room temperature. Tensile tests performed at CT for materials with similar chemical composition showed a simultaneous increase in strength and ductility at CT, corroborating the results obtained by ECAP. The partial suppression of dynamic recovery and the activation and the transition between deformation mechanisms at CT, as well as stacking fault energies (SFE) of such metals, played an important role in these results. Copper presented a much higher capability of strain hardening than aluminum, due to its lower SFE and much lower homologous temperature. X-ray diffraction indicated a strong correlation between the variation of average microstrain and the variation of hardness on both metals. The results of this study demonstrated the great potential of the application of very low temperatures for the obtaining of deformation metal-metal composites.

Achieving ultra-fine grains and high strength of Mg–9Li alloy via room-temperature ECAP and post rolling

Ultra-fine grains (UFG’s) and high strength was successfully achieved in Mg–9Li alloy via room temperature (RT) equal channel angular pressing (ECAP) and post rolling. The solid solution (SS) treatment of the alloy was performed before ECAP to achieve the refined needle-like α-Mg phase and excellent RT plastic deformation ability. The SS-treated alloy was ECAP processed continuously for 8 passes at room temperature without any cracks. Low temperature effectively inhibits dynamic recovery and recrystallization during the multi-pass ECAP process, reaching ultra-fine grains of about 1 μm and ultimate tensile strength (UTS) values of 187 MPa of the alloy. Post RT rolling of the ECAP-processed alloy further refines the grains into ultra-fine grains ranging between 500 and 700 nm, which endows the alloy with an excellent UTS value of 206 MPa and decent elongation to failure (Ef) of 21%. The ultra-fine grains with certain intragranular dislocation, leading to grain boundary and dislocation strengthening was a major contributory factor to the obtained high strength. Texture strengthening from the formation of strong basal textures of the α-Mg phase also improved the strength.

Achieving nanoscale Al2Cu dispersoids in wrought Al-4.5wt.%Cu alloy by semi-solid isothermal treatment and post room-temperature ECAP

Al2Cu phase is the main strengthening phase of high-strength wrought Al-Cu based alloys. In this paper, a novel composite process coupling the semi-solid isothermal treatment and post room-temperature (RT) equal channel angular pressing (ECAP) is proposed to refine Al2Cu particles in a conventionally extruded Al-4.5wt.%Cu alloy. The results show that, after the optimized semi-solid treatment (610℃/10 min + 20℃ water quenching) the initial microscale Al2Cu particles transformed into lamellar eutectic at grain boundaries with a thickness of 70 ± 9 nm. The following ECAP broke the lamellar eutectic into nanoscale Al2Cu dispersoids, which significantly enhanced the tensile strength. As a result, the alloy subjected to the composite process exhibited the highest RT ultimate tensile strength(UTS) of 460 MPa and yield strength(YS) of 447 MPa compared with the initial extruded and direct ECAPed alloys.

Analysis of microstructural evolution and compressive properties for pure Mg after room-temperature ECAP

Pure Magnesium (Mg) bars prepared by hot extrusion were further processed by equal channel angular pressing (ECAP) with route BC at room temperature. Microstructural evolution and mechanical properties of ECAP-processed pure Mg samples were investigated. With increasing ECAP pass, grains are further refined and microstructure becomes homogeneous due to accumulated strains. Texture evolution indicates dynamic recrystallization (DRX) took place and non-basal slipping systems were activated during ECAP. After four-pass ECAP, compressive mechanical properties were improved due to grain refinement and stress–strain curve showed a steady-state flow without obvious work hardening.

Analysis of microstructure and properties of commercially cast Mg after a single room-temperature ECAP

An as-cast pure Mg (99.99%) bar canned with a drilled Fe coat was subjected to equal channel angular pressing (ECAP) at room temperature through a die with a crossing angle of 90° between two channels. Then an ECAP-processed sample without obvious cracks was prepared successfully. Microstructural evolutions and mechanical properties of the deformed Mg were investigated in detail. After processing by one-pass ECAP, grains were significantly refined and an inhomogeneous microstructure was arranged along the shearing direction. (0001), (10–10) and (10–11) textures were formed, which were inclined by ∼40° from the normal direction (ND) towards the extruded direction (ED) due to the drastic shearing deformation. Tensile properties including yield strength (YS) and ultimate tensile strength (UTS) were improved significantly, whereas uniform elongation (UE) decreased as a result of hard working.

Mechanical properties and microstructure evolution of ultra-high strength Al-Zn-Mg-Cu alloy processed by room temperature ECAP with post aging

Ultra-high strength Al-Zn-Mg-Cu alloy extrusion bars were processed by equal channel angular pressing (ECAP) at room temperature (RT). Post aging treatment was used to determine the optimum time of aging. ECAPed sample was divided into two types: near the upper channel (P1) and lower channel (P2). Micro-hardness and tensile tests showed that ECAPed sample reached peak aging state at 8 h, which greatly shortened the time to T6 state. The mechanical properties of ECAPed samples were also better than traditional T6 samples. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were used to study the phase transformation from extrusion bars to ECAPed samples. AlZnMgCu phase and Al2CuMg phase containing Zn can be found in ECAPed sample. Meanwhile, the coarsening phase Al7Cu2Fe decreased significantly. Optical microscopy (OM) and transmission electron microscopy (TEM) were used to analyze the microstructure evolution such as shear bands and grain size during ECAP process. In P1, the shear bands with width ranging from 90 to 300 µm can be found. These shear bands were divided into many thinner shear bands and became intragranular deformation bands gradually in P2. Compared with P2, the average grain size in P1 decreased greatly and the precipitate η′ phase became finer and denser. Grain boundary strengthening and precipitation strengthening in P1 were much better than P2. The diameter of the channel should not exceed 20 mm when it used to press ultra-high strength Al-Zn-Mg-Cu alloy and the 3/4 parts near the top channel of product should be used to avoid unrefined grains.

Effect of Microstructure and Mechanical Properties of Al–Mg Alloy Processed by ECAP at Room Temperature and Cryo Temperature

This research primarily focuses on improving the strength of Al 5083 alloy by both the ECAP and Cryo ECAP methodology. Equal Channel Angular Pressing (ECAP) is one of the best technologies that enable the direct transformation of conventional macro grained metals into sub-micron, ultra-fine and nano grained materials. Fine grain size increases the strength and the fracture toughness of the material and provides the potential for super plastic deformation at moderate temperatures and at high strain rates. The microstructure evolution in Al 5083, subjected to Room Temperature ECAP and Cryo ECAP were analysed. ECAP was carried out using an optimized die with Channel angle ‘ϕ’ = 90°and corner angle ‘Ψ’ = 20° through processing route A and C up to four passes. The results were thoroughly studied using TEM, SEM, and optical microscopic images. Initially the annealed sample had the grain size of 80 µm with the equi-axed grains. In Room Temperature, the hardness values and the mechanical strength were found to be increased from 88 to 410 HV and 306 to 453 MPa after four passes in route A and in route C the strength increased from 390 to 416 MPa after four ECAP passes. Moreover, in Cryo Condition, the sample was processed up to four ECAP passes at route A and route C. The hardness of 153 HV was obtained after four passes in route C and 164 HV obtained after four passes on route A. Additionally, fracture behaviour using SEM, grain size using TEM and crystallite size by X-ray diffraction studies were analyzed. It was observed that the Cryo ECAP showed marginal improvements in mechanical properties relative to the RT ECAP in case of Al 5083.

Microstructure and mechanical properties of 7005 aluminum alloy processed by room temperature ECAP and subsequent annealing

A coarse-grained microstructure of the extruded 7005 aluminum alloy was processed by equal channel angular pressing (ECAP) via route BC at room temperature. Microstructural evolution of the alloy processed by ECAP with different passes and subsequent annealing treatment were analyzed by using optical microscope, transmission electron microscope and electron backscatter diffraction. The results revealed that grains were refined gradually, and the low angle boundaries were progressively transformed to high angle boundaries by an increasing ECAP passes. After 7 ECAP passes, the average grain size decreased to ∼0.87 μm, and the fraction of high angle boundaries increased to ∼65.5%. Furthermore, the results of tensile testing indicated that the yield strength was remarkably increased from ∼170 MPa before ECAP to ∼389 MPa after 7 ECAP passes, and the corresponding tensile strength increased to ∼400 MPa after 7 ECAP passes, maintaining an appropriate elongation of ∼13%. After annealing treatment at 150 °C for 1 h, the samples processed by 7 ECAP passes obtained large elongation of ∼16%, and still maintained a high yield strength of ∼337 MPa and tensile strength of ∼350 MPa, which may be attributed to the recovery effects.

Microstructure evolution and mechanical behavior of a binary Al–7Mg alloy processed by equal-channel angular pressing

Achieving high strength and uniform deformation simultaneously in Al alloys processed by severe plastic deformation (SPD) remains a challenging task as these alloys usually possess high strength but very limited uniform deformability, i.e.<∼4%. In the present work, however, high strength (∼507MPa) and large uniform elongation (∼11%) were achieved simultaneously in a binary Al alloy by using room-temperature equal-channel angular pressing (ECAP) and a high solute Mg content. Detailed characterization by electron backscattered diffraction (EBSD), conventional transmission electron microscopy (TEM) and delicate ASTAR-TEM orientation imaging has been carried out to reveal the microstructure evolution. It was found that it was difficult to form well-developed substructures in Al–7 Mg deformed by 1 pass or 2 passes of ECAP, in contrast to the pure Al and dilute Al–Mg alloys deformed under similar conditions, where well-aligned subgrains and cells are frequently formed. As a result, a bimodal grain structure, i.e. ultrafine/fine grains with mean sizes of<∼500nm were developed accompanied by micron-sized grains having a high dislocation density after 3 passes. The high strength is due to a combination of strengthening by the high density of dislocations, ultrafine grains and high solute Mg content. The high uniform elongation is due primarily to the enhanced work hardening resulted from the high solute Mg content and the bimodal grain structure, while the dynamic strain aging effect is supposed also to contribute to the high ductility. Most importantly, the present work revealed that inhomogeneous deformation during SPD introduced by high solid-solution contents can be utilized as a strategy to generate desirable bimodal grain structure, gaining both a high strength and high uniform ductility.

Evaluating the Room Temperature ECAP Processing of a NiTi Alloy via Simulation and Experiments

The NiTi alloys are generally considered hard‐to‐deform materials when processing by equal‐channel angular pressing (ECAP) at room temperature. Nevertheless, it is shown by experiment that a NiTi alloy may be successfully processed by ECAP for up to two passes using a core–sheath configuration. Three‐dimensional finite element simulations were used to more fully evaluate the flow behavior after the first and second pass of ECAP. The values of the microhardness were recorded across transverse directions within the cores and the results show that the imposed strain both decreases by comparison with the processing of conventional sheath‐free NiTi billet and increases by increasing the dimensions of the core. The lower areas of the cores undergo less deformation than the upper areas after successful ECAP processing but the imposed strain, and thus the microhardness values, become homogeneously distributed on the longitudinal planes after two passes of ECAP.

The effects of room temperature ECAP and subsequent aging on mechanical properties of 2024 Al alloy

Abstract Mechanical properties of the 2024 aluminum alloy, which was plastically deformed by equal channel angular pressing (ECAP) at room temperature and aged naturally and artificially at 70 °C and 100 °C for different times, were investigated in this research. Many of the short shear bands were observed on the microstructure after one pass of ECAP and led to fragmentation of grains. Hardness and yield stress of the sample aged naturally after deformation were considerably improved due to increase of dislocation density calculated by XRD data analysis and their interaction with solute atoms during ECAP. The ductility and work hardening exponent of the deformed samples were significantly reduced due to formation of shear bands within the microstructure. However aging the samples immediately after sever plastic deformation at 70 °C and 100 °C caused an additional improvement in hardness and yield stress relative to the samples aged naturally after deformation.

Room temperature equal-channel angular pressing of a magnesium alloy

Equal-channel angular pressing (ECAP) of magnesium alloy Mg–3Al–1Zn (wt.%) has been carried out at room temperature by applying a back-pressure three times larger than the yield stress in a 90° die. In a single pass, the initial grain size of ∼10μm originating from twin-roll casting was reduced down to ∼3μm. {101¯2} tensile twins were observed by orientation imaging up to ∼40% volume fraction in grains that remained relatively high after ECAP. Regions with small grain size did not show twinning. The small lattice curvatures indicated that dynamic recovery/recrystallization took place during testing. The 90° ECAP deformation field was approximated by two-stage simple shear due to a large dead metal zone appearing at the outer corner of the die. Using this strain path, the viscoplastic self-consistent (VPSC) model was employed to model the texture evolution in the version where a parameter (α) tunes the interaction equation between a grain and the homogeneous equivalent medium. The textures were reproduced in good accord with experiments only if the α parameter corresponded to the Tangent VPSC model. Twinning was simulated in a quantitative way by introducing the volume transfer scheme in the VPSC model without employing a criterion for selection of the six possible twin variants.

Predicting the critical pre-aging time in ECAP processing of age-hardenable aluminum alloys

Age-hardenable Al alloys may be successfully processed by equal channel angular pressing (ECAP) at room temperature, if the processing is carried out immediately after water quenching from the solution treatment temperature. It is important to estimate the critical time for any age-hardenable alloys, since after this time, ECAP processing will cause catastrophic cracking or segmentation at room temperature. In this study, ECAP processing was carried out on two age-hardenable Al alloys (2014 and 7075) at room temperature. The results demonstrated that the critical time could be predicted successfully by using tensile test curves related to different times after quenching. It is also shown that room temperature ECAP processing of these materials for more than a single pass is not possible and causes damage. However, a single pass will have significant effects on the strength of the material.

Microstructure and mechanical properties after annealing of equal-channel angular pressed interstitial-free steel

The evolution of microstructure, microtexture and mechanical properties during isothermal annealing of an ultrafine-grained interstitial-free steel after eight passes of route B C room temperature equal-channel angular pressing (ECAP) was studied. The microstructure and microtexture were characterized by electron back-scattering diffraction, and mechanical properties were assessed by shear punch and uniaxial tensile testing. Homogeneous coarsening via continuous recrystallization of the ECAP microstructure is accompanied by minor changes in the ∼63% high-angle boundary population and a sharpening of the original ECAP texture. This is followed by abnormal growth during the final stages of softening due to local growth advantages. Linear correlations between shear and tensile data were established for yield, ultimate strength and total elongation. After yield, the changes in uniaxial tensile behaviour from geometrical softening after ECAP to load drop, Lüders banding and continuous yielding after annealing is attributable to a coarsening of the microstructure.

The Influence of Texture and Grain Size on Compressive Deformation Behavior of Pure Mg through Equal-Channel Angular Processing

Multi-pass of equal channel angular pressing (ECAP) at a single temperature as low as room temperature from 200 °C were measured using electronic back scatter diffraction (EBSD). The effect of texture and grain size on mechanical properties was investigated to realize the strengthening and large plastic deformation mechanism. A room temperature ECAP with multi-pass procedure is effective to product high strength and large plastic Mg, as a result of submicron grain structure and texture strengthening.

Contribution of Twins to the Strengthening of Commercial Purity Titanium after Equal-Channel Angular Pressing

Room temperature equal-channel angular pressing (ECAP) was employed on commercial purity titanium in the present work. Mechanical twining was observed in ~90% grains while the grains were not significantly refined (~10 μm) after ECAP. TEM observations showed that the twins observed under OM are usually composed of a serial of parallel twin bands with a width of ~1 μm. Microhardness and tensile tests showed that such a coarse-grained microstructure combined with a high fraction of mechanical twins has a microhardness of ~ 240 Hv, yield strength of ~ 730 MPa, tensile strength of ~ 740 MPa and elongation to failure of ~ 16%. This yield strength is much higher than 620-640 MPa, the yield strength of ultrafine-grained titanium by 8~12 passes of ECAP at 450 oC with a grain size of 200-300 nm, and is close to ~ 790 MPa, the yield strength of commercial Ti-6Al-4V alloys.