Combination Of Equal Channel Angular Pressing Research Articles

Influence of ultrafine-grained structure parameters on the annealing-induced hardening and deformation-induced softening effects in pure Al

This work investigates the influence of parameters of initial ultrafine-grained (UFG) structure in commercially pure (CP) Al on annealing-induced hardening (AIH) and deformation-induced softening (DIS) effects. UFG structures were formed via processing CP Al by various methods of severe plastic deformation (high pressure torsion (HPT), equal channel angular pressing (ECAP) and combination of ECAP and cold rolling (CR)). AIH and DIS effects are observed in all the studied UFG structures. However, HPT Al demonstrates large increase of strength due to annealing and drastic gain of ductility after subsequent additional deformation whereas in ECAP Al and ECAP + CR Al both effects are much less pronounced. Microstructure characterization by X-ray diffraction (XRD) analysis, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) was performed for HPT Al and ECAP + CR Al in the three studied states: before and after annealing and after annealing and subsequent additional deformation. Analysis of microstructure evolution during annealing and subsequent additional deformation shows that the key microstructure parameter which is responsible for AIH and DIS effect is the change of dislocation density in grain interior in ECAP + CR Al, whereas in HPT Al the effects are related to the change of dislocation density at/near grain boundaries. In addition, outstanding combination of high strength (∼210 MPa), high electrical conductivity (∼62 %IACS) with sufficiently good ductility (7–10 %) and thermal stability (up to 150°С, at least) was achieved for ECAP + CR Al after annealing at 150 °C, 1h.

Enhancing mechanical property and corrosion resistance of Mg–Zn-Nd alloy wire by a combination of SPD techniques, extrusion and hot drawing

Poor formability and corrosion resistance are the limitations that restrict the widespread applications of biodegradable magnesium alloys as surgical staples. In this study fine-grained Mg–2Zn-0.5Nd (ZN20) alloy wire with a diameter of 0.23 mm was fabricated by a combination of equal-channel angular pressing (ECAP), friction stir processing (FSP), extrusion and hot drawing. ECAP could be beneficial to the subsequent deformation by texture weakening, and FSP could improve the corrosion resistance by decreasing the number of second phases. A typical microstructure with similar diameter of matrix grains and second phase particles was observed in ZN20 alloy wire after combined processing of ECAP, extrusion and hot drawing. The strength of ZN20 alloy wire after combined processing of FSP, extrusion and hot drawing was increased from 292 MPa to 392 MPa due to the grain boundary strengthening, precipitates strengthening and texture strengthening. It was beneficial to the ductility by promoting shear band nucleation and inhibiting its prolongation when the diameter of matrix grains and second phase particles was similar, and the ductility was increased by 3.5 times. The immersion test showed that the corrosion rate could be decreased by nearly 31% after combined processing of FSP, extrusion and hot drawing. Grain refinement could improve the corrosion resistance by stabilizing the corrosion product layer, and the smaller amount of second phase also had a positive influence on the corrosion resistance by avoiding the galvanic corrosion.

Microstructure, mechanical properties and wear resistance of an Al–Mg–Si alloy produced by equal channel angular pressing

Microstructure, mechanical properties and wear resistance in an ultrafine-grained Al–Mg–Si alloy fabricated utilizing a combination of equal channel angular pressing (ECAP) and dynamic aging were investigated in this paper. The results indicated that the grain size of the ECAP alloy was significantly refined, i.e., to ~239 nm after three ECAP passes. Meanwhile, the yield and tensile strength of the ECAPed material reached 340 MPa and 445 MPa, respectively, while maintaining a significant uniform elongation of 14%. Wear resistance results demonstrated that the wear rate, wear depth and width of the ECAPed material decreased in comparison with the solution-treated (SST) and peak-aged (T6) conditions under a load range of 5–25 N. The adhesive wear that occurs in the undeformed specimens at 10 N does not appear in the ECAPed specimen at the same load, indicating that the ECAPed specimen delay the appearance of more serious wear mechanisms under certain loads. The cooperative interaction of high density nano-scale β" precipitates and dislocations resulted in a combination of super-high strength and good work hardening ability which suppressed the extension of cracks between the friction layer and the plastic deformation zone. As a consequence, the combination of ECAP and dynamic aging brings a significant improvement for antifriction performance of the 6061 aluminum alloy.

Decade of Twist Channel Angular Pressing: A Review.

The methods of severe plastic deformation (SPD) have gained attention within the last decades primarily owing to their ability to substantially refine the grains within metallic materials and, therefore, significantly enhance the properties. Among one of the most efficient SPD methods is the equal channel angular pressing (ECAP)-based twist channel angular pressing (TCAP) method, combining channel twist and channel bending within a single die. This unique die affects the processed material with three independent strain paths during a single pass, which supports the development of substructure and efficiently refines the grains. This review is intended to summarize the characteristics of the TCAP method and its main features documented within the last decade, since its development in 2010. The article is supplemented with a brief characterization of other known SPD methods based on the combination of ECAP and twist extrusion (TE) within a single die.

The influence of Cryo-ECAP and aging on the microstructure and mechanical behavior of AA6061 Al alloy

The combination of Equal-Channel Angular Pressing (ECAP) with cryogenic processing temperatures can be an efficient method to obtain very refined microstructures. However, there is a lack of research on the combination of these processes and the effects they have on microstructure and mechanical properties, particularly in precipitation hardened aluminum alloys. The present study describes the effects of cryogenic ECAP-processing and subsequent heat treatments on the microstructure and mechanical properties of AA6061 Al alloy. Samples in the solutionized state were processed by ECAP at 173 K (Cryo) and at room temperature (RT) up to an equivalent strain of 4.2. After Cryo-ECAP, the microstructure was very refined, with an average grain size close to 0.5 μm and strain concentrated within microscopic shear bands. EBSD analysis after Cryo-ECAP shows new fine equiaxed grains with a higher proportion of low-angle grain boundaries. The temperature of 173 K was effective in suppressing partially precipitation during ECAP, and made the process possible without extensive cracking. However, recovery mechanisms were not fully hindered, which undermined the strengthening effect of Cryo-ECAP. The yield stress was higher after RT-ECAP, while uniform elongation was improved by Cryo-ECAP plus T6 treatment, a result attributed to the higher fraction of low-angle grain boundaries observed in the microstructure. Finally, it was demonstrated that cryogenic processing is not in itself a guarantee of improvements in strength and ductility, in comparison with RT processing. Both recovery and precipitation processes dictated the feasibility of the process, the final microstructure and the mechanical response of the ECAP-processed AA6061 Al alloy.

An investigation of the limits of grain refinement after processing by a combination of severe plastic deformation techniques: A comparison of Al and Mg alloys

An Al-7075 aluminum alloy and a ZK60 magnesium alloy were processed by a combination of equal-channel angular pressing (ECAP) for 4 passes and high-pressure torsion (HPT) through total numbers of up to 20 turns. Processing by ECAP and HPT were performed at 473K and room temperature, respectively. Mechanical testing showed an increase in the hardness value of the Al-7075 alloy after a combination of ECAP and HPT whereas in the ZK60 alloy the hardness was reduced. Microstructural images of the Al-7075 alloy revealed very significant grain refinement after a combination of ECAP + HPT compared to the individual processing techniques. By contrast, and consistent with the hardness measurements, the average grain size of the ZK60 alloy was larger after processing by the two-step SPD technique. These results are examined and an explanation is presented based on the available microstructural evidence.

Research Progress of Ultrafine-Grained Pure Titanium Produced by Equal-Channel Angular Pressing

Recently, fabrication techniques of ultrafine-grained (UFG) pure titanium have been investigated to achieve enhanced performance. This paper reveals the process and properties of bulk ultrafine-grained pure titanium by equal-channel angular pressing (ECAP), with the influence of experimental parameters. Special attention is given to the deformation mechanisms via dislocation slip and twinning during ECAP. It is demonstrated that the change of microstructure in UFG Ti leads to significant enhancement of mechanical properties. Some mixed results about corrosion resistance of UFG Ti indicate the further investigations are necessary. Special emphasis is placed on the combination of ECAP and other treatments for improving overall properties. It is shown that significant enhancement has been made in UFG commercial-purity Ti after ECAP plus thermal-mechanical treatment, suggesting promising prospects of ECAP process for titanium alloys in various industries.

3D FEM simulations and experimental validation of plastic deformation of pure aluminum deformed by ECAP and combination of ECAP and direct extrusion

Rigid-viscoplastic 3D finite element simulations (3D FEM) of the equal channel angular pressing (ECAP), the combination of ECAP + extrusion with different extrusion ratios, and direct extrusion of pure aluminum were performed and analyzed. The 3D FEM simulations were carried out to investigate the load–displacement behavior, the plastic deformation characteristics and the effective plastic strain homogeneity of Al-1080 deformed by different forming processes. The simulation results were validated by microstructure observations, microhardness distribution maps and the correlation between the effective plastic strain and the microhardness values. The 3D FEM simulations were performed successfully with a good agreement with the experimental results. The load–displacement curves and the peak load values of the 3D FEM simulations and the experimental results were close from each other. The microhardness distribution maps were in a good conformity with the effective plastic strain contours and verifying the 3D FEM simulations results. The ECAP workpiece has a higher degree of deformation homogeneity than the other deformation processes. The microhardness values were calculated based on the average effective plastic strain. The predicted microhardness values fitted the experimental results well. The microstructure observations in the longitudinal and transverse directions support the 3D FEM effective plastic strain and microhardness distributions result in different forming processes.

Microstructure and Mechanical Properties of 6013 Aluminium Alloy Processed by a Combination of ECAP and Preaging Treatment

Microstructure and mechanical properties of a 6013 Al-Mg-Si-Cu aluminum alloy processed by a combination of equal channel angular pressing (ECAP) and preaging treatment were comparatively investigated using quantitative X-ray diffraction (XRD) measurements, transmission electron microscopy (TEM) and tensile tests. In addition, the precipitation sequences were obtained by thermodynamic calculations using the FactSage software package. Average grain sizes measured by XRD are in the range 211–501 nm while the average dislocation density is in the range 0.35-1.0 × 1014 m-2 in the deformed alloy. TEM analysis reveals that fine needle β′′ precipitates with an average length of 4-10 nm are uniformly dispersed in the preaging ECAPed alloy. The local dislocation density in this sample is as high as 2.2×1017 m-2. The strength is significantly increased in the preaging-ECAPed samples as compared to that of the undeformed counterparts. The highest yield strength among the preaging ECAPed alloys is 322 MPa. This value is about 1.25 times higher than that (258 MPa) of the static peak-aging sample. The high strength in the preaging ECAPed alloy is suggested to be related to grain size strengthening and dislocation strengthening, as well as precipitation strengthening contributed from both preaging treatment and ECAP deformation.

Effect of various kinds of severe plastic deformation on the structure and electromechanical properties of precipitation-strengthened CuCrZr alloy

The effect of various kinds of severe plastic deformation (equal-channel angular pressing and quasi-hydrostatic extrusion at 77 and 300 K) on the structural formation of precipitation-strengthened CuCrZr alloy has been studied. A combination of experimental methods has been used. Sputtering by deuterium ions was used as the tool for the layer-by-layer study of the alloy structure. The difference between the sputtering yields of the matrix (copper) and precipitates (Cr and Zr) allowed us to visualize the alloy structure to a total depth of 0.5−1 μm. The effect of severe plastic deformation on the precipitate distribution is considered. It has been shown that the main peculiarity of the microstructure is related to the high density of precipitates enriched in chromium, which completely determine the surface roughness. Their distribution is not related to the grain size. The combination of equal-channel angular pressing and quasi-hydrostatic extrusion was shown to lead to the increase in the microhardness of the CuCrZr alloy to 2300 MPa in the case of low-temperature quasi-hydrostatic extrusion (at 77 K) and to the retained high conductivity. It has been proved that the high anisotropy of precipitate shape, microhardness, and sputtering yield of the CuCrZr alloy is determined by equal-channel angular pressing.

Effect Of Severe Plastic Deformation On Microstructure Evolution Of Pure Aluminium

AbstractProcesses of severe plastic deformation (SPD) are defined as a group of metalworking techniques in which a very large plastic strain is imposed on a bulk material in order to make an ultra-fine grained metal. The present study attempts to apply Equal-Channel Angular Pressing (ECAP), Hydrostatic Extrusion (HE) and combination of ECAP and HE to 99.5% pure aluminium. ECAP process was realized at room temperature for 16 passes through route Bc using a die having an angle of 90°. Hydrostatic extrusion process was performed with cumulative strain of 2.68 to attain finally wire diameter of d = 3 mm. The microstructure of the samples was investigated by means of transmission and scanning electron microscopy. Additionally, the microhardness was measured and statistical analysis of the grains and subgrains was performed. Based on Kikuchi diffraction patterns misorientation was determined. The measured grain/subgrain size show, that regardless the mode of deformation process (ECAP, HE or combination of ECAP and HE processes), grain size is maintained at a similar level – equal to d = 0.55-0.59μm. A combination of ECAP and HE has achieved better properties than either single process and show to be a promising procedure for manufacturing bulk UFG aluminium.

Microstructural saturation, hardness stability and superplasticity in ultrafine-grained metals processed by a combination of severe plastic deformation techniques

A commercial Al-7075 aluminum alloy was used to investigate the significance of the saturation hardness and saturation microstructure after processing by high-pressure torsion (HPT) through up to 20 turns or a combination of equal-channel angular pressing (ECAP) for 4 or 8 passes and HPT. The results show additional grain refinement by initially processing the material by ECAP to produce an ultrafine grain size before conducting the HPT. Thus, the grain size immediately prior to the HPT processing controls the saturation microstructure and hardness. Microstructural images reveal a significant grain refinement from elongated grains in the samples prior to processing with an average grain diameter of ~8 μm to equiaxed grains with an average grain size of ~200 nm after processing by a combination of ECAP for 8 passes and HPT through 20 turns. This grain refinement leads to an improvement in the mechanical properties of the Al-7075 alloy. Vickers microhardness tests show a significant increase in the microhardness values of the Al-7075 alloy from Hv≈102 in the annealed samples to Hv≈270 after processing by a combination of ECAP for 8 passes and HPT through 20 turns. Specimens processed by a combination of ECAP and HPT also exhibit excellent superplastic properties with elongations up to >1000% at 673 K.

An examination of the saturation microstructures achieved in ultrafine-grained metals processed by high-pressure torsion

Experiments were conducted on two commercial alloys, a Cu–0.1%Zr alloy and an Al-7075 aluminum alloy, to investigate the significance of the saturation microstructure which is achieved after processing by high-pressure torsion (HPT). Samples were processed by HPT and also by a combination of equal-channel angular pressing (ECAP) followed by HPT. The results show that the saturation conditions are dependent upon the grain size in the material immediately prior to the HPT processing. Additional grain refinement may be achieved in HPT by initially processing the material to produce an ultrafine-grain size before conducting the processing by HPT.

An Investigation of Mechanical Properties and Microstructural Evolution in an Aluminum Alloy Processed by Severe Plastic Deformation

Processing by a combination of equal-channel angular pressing (ECAP) and high-pressuretorsion (HPT) was performed on disks of an Al-7075 alloy. The alloy was annealed at 753 K, processedby ECAP for totals of 4 passes and then processed by HPT under a pressure of 6.0 GPa up to amaximum of 20 turns. Measurements of Vickers microhardness showed reasonable hardnesshomogeneity after processing through 20 turns. It is demonstrated that the results from mechanicaltesting and microstructural analysis are consistent with the hardness measurements.

Microstructure and Mechanical Properties of AA5483 after Combination of ECAP and Hydrostatic Extrusion SPD Processes

Abstract Al-Mg alloys of the 5xxx series are strain hardenable and have moderately high strength, excellent corrosion resistance even in salt water, and very high toughness even at cryogenic temperatures to near absolute zero, which makes them attractive for a variety of applications, e.g. in systems exploited at temperatures as low as -270°C, and marine applications. The present study is concerned with the effect of a combination of 2 processes, which generate serve plastic deformation (SPD), equal channel angular pressing (ECAP) and hydrostatic extrusion (HE), on the microstructure and mechanical properties of an alloy that contain Al and Mg. The alloy was subjected to multi-pass ECAP followed by cumulative HE with a total true strain of 5.9. The microstructure of SPD samples was evaluated by transmission and scanning electron microscopy. The mechanical properties were determined by tensile tests and microhardness measurements. The combination of the two processes gave a uniform nanostructure with an average grain size of 70nm. The grain refinement taking place during the SPD processing resulted in the increase of the mechanical strength by 165% (YS) with respect to that of the material in the as- received state. The experiments have shown that the combination of HE and ECAP permits producing homogeneous nanocrystalline materials of large volumes.

Effect of Severe Plastic Deformation on Microstructure and Properties of Polycrystalline Aluminium Al99.5

Abstract Polycrystalline aluminium Al99.5 was deformed through the combination of equal-channel angular pressing (ECAP) by B route (4, 8 and 16 passes) and then by the hydrostatic extrusion (HE) using the cumulative way of deformation, just to the achieving the final wire diameter d = 3 mm. The microstructure of samples was investigated by means light microscopy (LM). Additionally the microhardness measurement and the tensile test were performed to determine the level of aluminium hardening. The texture was determined by using the Brucker Advance D8 equipment. The aim of the research was to determine the influence of severe plastic deformation exerted in the process of equal-channel angular pressing (ECAP) and hydrostatic extrusion (HE) on the microstructure and properties of polycrystalline aluminium Al99.5. The microstructure observations both after the HE process and the combination of ECAP + HE revealed the elongated to the extrusion direction grains and numerous bands and shear bands. The bands and shear bands most clearly revealed at the perpendicular section. The performed investigations showed that with the increase of the deformation the aluminium level hardening increase. The highest properties of tensile strength - UTS = 218 MPa and microhardness level HV0.1 = 46 were obtained after 8 ECAP + HE.

Microstructural evolution in a Cu–Zr alloy processed by a combination of ECAP and HPT

A Cu–0.1% Zr alloy was processed by equal-channel angular pressing (ECAP) for up to 8 passes and the samples processed through 4 and 8 passes were then sectioned into disks and further processed by high-pressure torsion (HPT) for 5 turns. Measurements were taken for the microhardness distributions on cross-sectional planes of the ECAP billets and on the HPT disks and the microstructures were examined using transmission electron microscopy and electron back-scatter diffraction. The results demonstrate that a combination of ECAP and HPT leads to additional grain refinement, higher hardness values and a larger fraction of boundaries having high angles of misorientation. The minimum average grain sizes recorded in these experiments were ∼280 and ∼260nm at the center and edge of a disk, respectively, after processing through 8 passes of ECAP and 5 turns of HPT. The results contrast with an earlier report using high-purity Cu where a combination of ECAP and HPT gave a mixture of ultrafine and coarse grains due to the occurrence of dynamic recrystallization during the torsional straining.

Service properties of ultrafine-grained Ti–6Al–4V alloy at elevated temperature

This study deals with investigation of mechanical properties and fatigue behavior of the ultra-fine grained (UFG) alloy Ti–6Al–4V at elevated temperatures. UFG samples were produced by means of combination of equal-channel angular pressing and thermomechanical treatments. Studies of the temperature dependence of mechanical properties of the UFG alloy demonstrated their thermal stability upto 175–350 °C. It was revealed that 100-hour creep rupture strength at 300 °C increased from 750 MPa in the conventional state to 890 MPa in the UFG state. The alloy demonstrates stability of the UFG structure at 300 and 370 °C in the conditions of long-term tests. The fatigue tests were conducted with axial loading applied on a sample at 175 °C, the asymmetry factor of the cycle was 0.1. The fatigue endurance limit of the UFG alloy was almost 50 % higher than that of the CG alloy.

Microstructure Evolution and Mechanical Properties of Al-1080 Processed by a Combination of Equal Channel Angular Pressing and High Pressure Torsion

Equal channel angular pressing (ECAP) and high pressure torsion (HPT) are the most promising severe plastic deformation (SPD) methods. Both methods impose very high strains, leading to extreme work hardening and microstructural refinement. In this paper, billets of Al-1080 were successfully processed by ECAP conducted for up to 10 passes, HPT at an applied pressure of 8 GPa for 5 revolutions, and a combination of ECAP and HPT (ECAP + HPT) at room temperature. The effects of the different SPD processes (ECAP, HPT, and ECAP + HPT) on the evolution of the microstructure and mechanical properties of Al-1080 were investigated. The HPT and ECAP + HPT processes were observed to produce finer grain sizes with greater fractions of high angle grain boundaries (HAGBs) than the ECAP alone. Although the grain sizes after HPT and ECAP + HPT were similar, the ECAP + HPT sample had more dislocations than the HPT sample. HPT after ECAP enhanced the mechanical properties (hardness, tensile strength, and ductility) of the ECAP-processed Al-1080, showing larger dimple size in the tensile fracture surfaces.

Homogenization of ECAPed Al 2024 alloy through age-hardening

Mechanical properties of aluminum alloys can be improved by obtaining ultra-fine grained structures via severe plastic deformation methods such as equal channel angular pressing (ECAP). In practice, however, the final structure may not be as homogeneous as desired. Thus, elimination of the inhomogeneity of ECAPed samples is a challenging task. In the case of age-hardenable alloys, a combination of ECAP and aging might provide new means of obtaining microstructural homogeneity. In this study, the effect of post-ECAP aging on the microstructural homogeneity of 2024 Al–Cu–Mg alloy was investigated. Following solutionization and rapid cooling, some samples were aged at 190°C for various times. Another group of samples were similarly aged after one-pass ECAP through a 120° die. Throughout the aging of the samples, maps of microhardness variation were acquired in order to monitor the precipitation behavior. It was observed that considerable homogenization in the microstructure of the ECAPed samples was reached, especially right after peak aging. The homogenization level was characterized with the hardness inhomogeneity index. EBSD and TEM investigations were performed to observe variations in the homogeneity of the microstructure.