Number Of Equal-channel Angular Pressing Research Articles

Effect of number of ECAP passes on structure and mechanical properties of Al–Ca–Mn–Fe alloy

The effect of number of equal-channel angular pressing (ECAP) passes on the structure and mechanical properties of the as-cast 4% Ca–1.3% Fe–0.8% Mn–0.1% Zr–0.1% Sc Al alloy is studied. ECAP was carried out at room temperature, through BC path using an angle between the channels of 110°. The number of ECAP passes was N = 2, 3, and 4. The as-cast alloy consisted of the solid solution dendrites (Al) and the [(Al) + Al10CaFe2 + Al4Ca] eutectic, as well as of a small fraction of the Al6(Fe, Mn) particles. As a result of ECAP, the dendrites are elongated approximately at an angle of 30° relative to the direction of ECAP. After two passes of ECAP, the dislocation density increased, but with an increase in the number of passes, the dislocation density slightly decreased as a result of the rearrangement of the dislocation structure; besides calcium segregated from the eutectic. After ECAP, a significant hardening of the alloy was observed. The highest strength observed after two passes (the ultimate tensile strength of the as-cast alloy was 130 MPa, and after the second pass it was 305 MPa), and the lowest one was after four passes (the ultimate strength was 219 MPa). The relative elongation of the ECAP-processed samples did not depend on the number of passes and it was about 1%.

Preparing high-strength and osteogenesis-induced Mg-Gd alloy with ultra-fine microstructure by equal channel angular pressing

Mechanical strength and corrosion resistance are needed for Mg based BMs in the application of biomedical fields. In the present study, a high-strength biodegradable Mg-Gd alloys with an ultrafine microstructure successfully were prepared by equal channel angular pressing (ECAP). The high tensile strength of ECAPed Mg-Gd alloys was attributed to ultrafine DRX grains and fragmented secondary phases. During ECAP, the grain structure was refined by dynamic recrystallization (DRX), and the size of the DRX grains was approximately 300 nm. The secondary phase with lamellar structures was fragmented into fine particles of submicrometer size after ECAP process. As the number of ECAP passes increased, the distribution of the fragmented secondary phase has been changed into a uniform distribution. The corrosion rates calculated from the hydrogen evolution test demonstrated that the 8p-ECAP Mg-Gd alloy with an ultrafine microstructure possessed better corrosion resistance. Cell and osteogenesis induction experiments confirmed that Mg-Gd alloys processed by ECAP exhibited good biocompatibility. This study provides a new method for preparing high-strength Mg alloys with good corrosion resistance and biocompatibility.

Corrosion-fatigue resistance of ultrafine grain commercially pure titanium in simulated body fluid

Commercially pure titanium (CP-Ti) due to excellent biocompatibility and high specific strength is known as a metallic biomaterial and is widely utilized in medical applications as implant material. Because of low strength of CP-Ti as compared to other bio-metals, it has been proved in literatures that applying equal channel angular pressing (ECAP) process can be useful to enhancement of mechanical and metallurgical properties of CP-Ti by improvement of initial microstructure to ultrafine grained (UFG). Implant in human body is attacked from cyclic fatigue loads and corrosion, simultaneous. Hence, aim of this study is examination of corrosion-fatigue resistance of CP-Ti before and after introducing ECAP in simulated body fluid (SBF) as a saline solution close to blood plasma. In this study, multi-pass ECAP is conducted on CP-Ti at room temperature and then the axial fatigue test is performed in SBF environment with temperature 37 °C. The comparison of stress-cycle curves demonstrated that corrosion-fatigue resistance of ECAPed CP-Ti is extremely higher than initial annealed one. Moreover, it was observed that by increasing the pass number of ECAP, corrosion-fatigue resistance improves significantly. Furthermore, these results are compared to fatigue behavior of CP-Ti in air environment. The results show that corrosion-fatigue resistance of unECAPed and ECAPed CP-Ti in SBF is slightly lower than fatigue ones in air. According to the results of this experimental research, it is concluded that UFG CP-Ti has an awesome corrosion-fatigue resistance in human body and it is very suitable for utilizing as material of implants.

Grain refinement of Al–Zn–Mg alloy during equal channel angular pressing (ECAP)

Locally produced Al–Zn–Mg alloy was subjected to severe plastic deformation through Equal Channel Angular Pressing (ECAP) technique at temperatures of 150 °C and 200 °C. Rectangular thick-walled medium carbon steel die (σc = 450Mpa, σy = 176Mpa) with an L-shaped channel of uniform configuration to provide the pressing chamber was used. Four ECAP passes were imposed consecutively on set of samples for 150 °C and 200 °C temperatures, and characterized with optical microscopy, scanning electron microscopy (SEM) and x-ray diffraction (XRD). The phases were identified by X-ray diffraction (XRD) using monochromatic Cu Kα radiation, while vickers’ microhardness and tensile tests were performed for mechanical properties examination. Optical micrographs showed no tangible precipitation in the as cast samples with reduced grain width and deformation bands but at high temperatures of 150 °C and 200 °C, precipitation was promoted as a result of slipping systems activation. SEM images of the as-cast alloy exhibits dendrites of 250 ± 20 μm in size with η′ phase (MgZn2) precipitates in the inter-dendritic regions. For 150 °C ECAP temperature, a significant refinement was achieved as the passes increased with sub-grain development within the boundary and the precipitate observed has a grain size of 35 ± 15 μm, 25 ± 10 μm, 15 ± 8 μm and 8 ± 6 μm for first, second, third and fourth passes respectively. However, grain sizes of 85 ± 15 μm, 50 ± 10 μm, 30 ± 8 μm and 10 ± 5 μm for first, second, third and fourth passes were observed for 200 °C ECAP temperature. XRD results showed peaks for aluminum and other phases in as-cast condition with precipitates growth in the alloy after the first pass, identified as metastable η′ phase. As the number of ECAP passes increases, η′ peaks moved towards the equilibrium η phase confirming the transformation of η′ phase to stable η phase. The microhardness, Ultimate tensile strength (UTS) and the yield strength of Al–Zn–Mg alloy in different conditions of 150 °C and 200 °C respectively also increased with increase in the number of ECAP passes. This is due to increase in dislocation density, work hardening and grain refinement during ECAP process.

Effect of the deformation temperature on the deformation behavior of a Cu-Cr-Zr alloy

The mechanical properties and deformation behavior of a Cu-Cr-Zr alloy after solution treatment (ST) or aging (ST+AT) and equal channel angular pressing (ECAP) at elevated temperature were investigated. ECAP at elevated temperature led to strengthening and degradation of plasticity compared with the initial state. The deformation behavior of the alloy after 1 and 2 ECAP passes at 200 °C was almost the same. An increase in ECAP temperature promoted uniform strain and plasticity. An increase in the number of ECAP led to a gradual increase in strength. YS and UTS in ST+AT condition were higher than in ST samples regardless of the ECAP temperature and the number of passes. The maximum values of YS and UTS were obtained after 4 ECAP passes at 400 °C and achieved 525 MPa and 600 MPa in ST and 570 MPa and 650 MPa in ST+AT condition, respectively. The effect of deformation strain and ECAP temperature on work hardening rate and recovery were discussed in terms of the Voce equitation.

Characterization of the Gas Tungsten Arc Welding (GTAW) joint of Armco iron nanostructured by Equal-Channel Angular Pressing (ECAP)

• Ultrafine-grained Armco iron was obtained by severe plastic deformation and submitted to welding. • Gas Tungsten arc welding generates a gradient microstructure as a function of the heat input. • Hardness decreases after the welding process but still superior to the annealed material. • High heat inputs generate the formation of Widmanstätten ferrite. After Severe Plastic Deformation (SPD), the strength of the Armco iron sharply increases with the number of Equal-Channel Angular Pressing (ECAP) passes. So, the ultimate tensile stress (UTS) reached up to 800 MPa after eight passes, reflecting an increment of around four times than the as-received material strength. The original grain size of the annealed iron of about 70 μ m also experimented with drastic changes after ECAP, reaching grain sizes approaching to 300 nm. Samples were then welded by the Gas Tungsten Arc Welding (GTAW) process varying the voltage and current conditions. Metallographic analysis by Light Optical Microscopy (LOM) and Electron Backscatter Diffraction (EBSD), was carried out to analyze the weld penetration, Fusion Zone (FZ), and the size and microstructure morphology across the Heat Affected Zone (HAZ). Special attention was given to microstructure changes of the nanostructured base metal. A microstructural gradient was observed throughout the welded joint with hardness reduction concerning the nanostructured material but still superior to the material without ECAP. The temperature heterogeneity gave rise to different grain sizes and morphologies like Widmanstätten ferrite around the FZ, especially at high heat inputs.

The Effect of Equal Channel Angular Pressing on Coarsening Kinetics of AZ80–0.2Y–0.15Ca Alloy in Semisolid State

Semisolid samples of the AZ80–0.2Y–0.15Ca wt% (AZ80M) magnesium alloy are fabricated using equal channel angular pressing (ECAP) followed by semisolid isothermal heating treatment. The effect of the number of ECAP passes on the coarsening dynamics of the alloy at different semisolid temperatures is investigated. The results show that as the number of ECAP passes increases, the coarsening rate constant (K) shows a similar trend downward and then upward at different temperatures. And the K value of the sample after three passes of ECAP processing (3P) is the lowest, which is primarily attributed to the maximum proportion of high‐angle grain boundaries (HAGBs) and the most uniform grain size in the 3P sample. At high solid fractions, a high proportion of HAGBs hinders the coalescence of the adjacent solid grains. At low solid fractions, uniform and fine grains result in insufficient driving force for the Ostwald ripening process. These lead to the lowest K value in the 3P sample.

Effect of ECAP on the Microstructure and Mechanical Properties of a Rolled Mg-2Y-0.6Nd-0.6Zr Magnesium Alloy

A fine-grained Mg-2Y-0.6Nd-0.6Zr alloy was processed by bar-rolling and equal-channel angular pressing (ECAP). The effect of ECAP on the microstructure and mechanical properties of rolled Mg-2Y-0.6Nd-0.6Zr alloy was investigated by optical microscopy, scanning electron microscopy, electron backscattered diffraction and a room temperature tensile test. The results show that the Mg-2Y-0.6Nd-0.6Zr alloy obtained high strength and poor plasticity after rolling. As the number of ECAP passes increased, the grain size of the alloy gradually reduced and the texture of the basal plane gradually weakened. The ultimate tensile strength of the alloy first increased and then decreased, the yield strength gradually decreased, and the plasticity continuously increased. After four passes of ECAP, the average grain size decreased from 11.2 µm to 1.87 µm, and the alloy obtained excellent comprehensive mechanical properties. Its strength was slightly reduced compared to the as-rolled alloy, but the plasticity was greatly increased.

Experimental investigations of effects of SiC contents and severe plastic deformation on the microstructure and mechanical properties of SiCp/AZ61 magnesium metal matrix composites

The objective of this research is to investigate the effects of equal channel angular pressing (ECAP) plastic deformation processes on the evolution of microstructural distributions and mechanical properties of SiC particles reinforced magnesium metal matrix composites (Mg MMCs). Investigations of the combined effects of the number of ECAP passes and SiC particles weight percentages were considered. The microstructural analysis results demonstrated a uniform distribution of matrix grain sizes and SiC particles (SiCp) segregation along the matrix grain boundaries as the number of ECAP passes increased. As the number of ECAP passes increased the presence and size of secondary phases were reduced at the pure AZ61 magnesium ally and 2 wt% SiCp/AZ61 Mg MMC. In the case of 5 wt% SiCp/AZ61 Mg MMC, the brittle Mg2Si secondary phase was observed and detected throughout the whole ECAP processes. The corresponding mechanical properties experimental investigation results confirmed that the elastic modulus was reduced by 47.98% for pure AZ61, increased by 5.38% for 2 wt% SiCp/AZ61 Mg MMC and increased by 25.9% for 5 wt% SiCp/AZ61 Mg MMC. The ECAP deformed 2 wt% SiCp/AZ61 Mg MMC showed the highest performance of strain hardening rate, strength and ductility.

Solid-State Recycling of Aluminum Alloy (AA-6061) Chips via Hot Extrusion Followed by Equal Channel Angular Pressing (ECAP)

Aluminum alloy (AA-6061) chips were recycled using hot extrusion followed by equal channel angular pressing (ECAP) process at room temperature. AA-6061chips were cold compacted into billets, then extruded into rods under extrusion ratio of 5.2 at different extrusion temperatures (ET). Finally, the rods were processed through ECAP die with inner angle Φ of 90°, and outer arc angle Ψ of 32.8°, which impose strain ɛ of 1 per each pass up to different number of passes. The effects of the ECAP number of passes and extrusion temperature on the microstructure evolution and mechanical properties were fully investigated. Furthermore, the microstructure and the mechanical properties of the ECAPed samples were compared with those of the extruded samples. Grain refinement were noted after the ECAP process. Moreover, the ECAPed samples revealed higher mechanical properties than those of the extruded samples. The extrusion temperature (ET) and the number of the ECAP passes have an obvious effect on both the microstructure and mechanical properties of the solid state recycled chips samples.

Influence of ECAP as grain refinement technique on microstructure evolution, mechanical properties and corrosion behavior of pure aluminum

Pure aluminum samples were processed by equal channel angular pressing (ECAP) up to 10 passes at room temperature. The effects of the ECAP number of passes on the microstructure evolution, the mechanical properties, deformation homogeneity and corrosion behavior of the processed samples were fully investigated. The imposed strain resulted in an obvious reduction in the grain size from 390 µm before ECAP down to 1.8, 0.4, and 0.3 µm after ECAP up to 2, 4 and 10 passes, respectively. The microhardness, deformation homogeneity and tensile strength were increased while the elongation decreased with the increase of ECAP number of passes. Immersion tests, open circuit potential, Tafel polarization, cyclic polarization and potentiostatic measurements in 3.5% NaCl solution revealed an obvious improvement in the corrosion resistance of ECAP processed samples compared with the as-cast sample. The increase of the number of passes can be used successfully in producing ultra-fine grained (UFG) bulk pure aluminum sample with a high misorientation angle, reasonably high mechanical properties and corrosion resistance.

Evolution of structure and properties of Al–Sn composites under deformation

The effect of equal-channel angular pressing on the structure and mechanical properties of sintered Al–Sn composites with a different content of the second phase is investigated. It is established that the pressing results in a hard strengthening of the composite owing to grain structure refinement in the aluminum matrix. The strength of the processed composites is determined from the mixture rule. The shape of tin inclusions almost returns to the original one after each even number of equal-channel angular pressing by route C, while their thickness decreases with the number of pressing passes by route A. A decrease in the interlayer thickness leads to the additional refinement of grains in the aluminum matrix and causes the additional strengthening of Al–Sn composites.

The Effect of Severe Plastic Deformation Processing on Creep Properties of Metallic Materials

Processing by severe plastic deformation (SPD) may be defined as such metals forming procedure in which a very high strain is imposed on a bulk material. This paper investigates the effect of different equal channel angular pressing (ECAP) routes and number of ECAP passes on resulting microstructure, mechanical properties and creep behaviour of selected materials. The distinction between various ECAP routes (A, B and C) and the difference in number of ECAP passes applied may lead to variations both in the macroscopic distortions of the individual grains and in the capability to develop a reasonably homogeneous and equiaxed ultrafine-grained microstructure. Experimental materials were processed by ECAP at room temperature using a die with an internal angle of 90° between the two parts of the channel. The ECAP pressing was performed by different routes up to 12 ECAP passes. Tensile creep tests were conducted at temperatures 473 - 673 K and at different applied stresses on ECAP materials and, for comparison purposes, on their unpressed states. Microstructure of samples was characterized by scanning electron microscope (SEM) equipped with the electron backscatter diffraction (EBSD) unit. In conclusion, the ECAP processing route and number of applied ECAP passes could play an important role in creep behaviour and their effect may be different for particular materials. The highest differences in processing routes were revealed for materials especially at lower number of ECAP passes. However, a little apparent dependence of the creep properties was observed during subsequent pressing.

Effect of Equal-Channel Angular Pressing Passes on Corrosion Behavior of Ultrafine-Grained Pure Iron

A series of bulk ultrafine-grained (UFG) pure iron with grain size of 250-450 nm were fabricated by equal-channel angular pressing (ECAP) and annealing. Effects of ECAP passes on the corrosion behavior of the UFG pure iron were investigated. Results show that ECAP accelerates the acid corrosion rate of pure iron, but improves its anodic passivation property. The acid corrosion resistance of the UFG pure iron is restored through a large number of ECAP passes as well as through an annealing treatment. Annealing treatment is not good for the anodic passivation property of the UFG pure iron after a small number of ECAP passes. However, after a large number of ECAP passes (up to16), the corrosion resistance and anodic passivation property of UFG pure iron are less affected by annealing.

The Influence of ECAP Pass through Bc Route on Mechanical Properties of Aluminum Alloy 6061

Equal Channel Angular Pressing (ECAP) is one of Severe Plastic Deformation (SPD) methods used to produce ultra-fine grains. In this study, aluminum alloy 6061 in a rod shape as a result from casting process was used in the experiment. The rod samples were then subjected to ECAP, up to 3 passes, through Bc route. The die channel angle of the ECAP is 1200. The changes in the microstructure and mechanical properties of the samples deformed by 1-pass, 2-pass, and 3-pass of ECAP were investigated. The results show that as number of ECAP passes increase, the applied strain accumulated in the samples also increases and the grains change from equiaxed to elongated structure. The hardness is proportional to the number of ECAP passes, and the highest value is 107 HV for 3 passes with strain value of 2.0.

Ultrafine-grained Ti–Nb–Ta–Zr alloy produced by ECAP at room temperature

To ascertain the influence of severe plastic deformation (SPD) on a Ti–Nb–Ta–Zr (TNTZ) alloy, we studied the room temperature mechanical behavior and microstructural evolution of an ultrafine-grained (UFG) Ti–36Nb–2Ta–3Zr (wt%) alloy prepared via equal-channel angular pressing (ECAP) of the as-hot-extruded alloy. The tensile behavior, phase composition, grain size, preferred orientation, and dislocation density of the UFG alloy, processed under different conditions, were analyzed and discussed. Compared to the as-hot-extruded alloy, the ECAP-processed TNTZ alloy (3 passes) exhibited approximately 40 and 88 % increase in average ultimate strength and yield strength, respectively. Moreover, as the number of ECAP passes increased from 3 to 6, the TNTZ alloy exhibited not only the expected increase in ultimate and yield strength values, but also a slight increase in elongation. Our results suggest that the deformation mechanisms that govern the behavior of the as-hot-extruded coarse grained (CG) TNTZ alloy during ECAP involve a combination of stress-induced martensitic transformation and dislocation activity. In the case of the ECAP-processed UFG TNTZ alloy, the deformation mechanism is proposed to involve two components: first, dislocation activity induced by the strain field imposed during ECAP; and second, the formation of α″ martensite phase during the early stages of ECAP which eventually transforms into β phase during continued deformation. We propose that the deformation mechanism governing the room temperature behavior of the TNTZ alloy strongly depends on the grain size of the β phase.

Corrosion Behavior of Commercial Aluminum Alloy Processed by Equal Channel Angular Pressing

A commercial aluminum alloy was subjected to severe plastic deformation through equal channel angular pressing (ECAP). The alloy contains a low volume fraction ofα-AlFeSi located essentially at the grain boundaries. The corrosion behavior of the ECAP’ed alloy was investigated in NaCl solution using potentiodynamic polarization and immersion tests. The effects of scan rate and NaCl concentration on the alloy susceptibility to corrosion were also studied. The results obtained were compared with those of the nonpressed alloy. ECAP leads to an intensive grain refinement accompanied by an increased dislocation density. All electrochemical tests confirm that corrosion resistance of the alloy remarkably diminished with increasing the ECAP number of passes. This is presumably due to the breakdown of theα-AlFeSi after ECAP leading to higher number of galvanic cells and enhanced dissolution of the aluminum matrix.

Influence of the pre-homogenization treatment on the microstructure evolution and the mechanical properties of Al–Cu alloys processed by ECAP

Abstract Equal channel angular pressing (ECAP) is a material processing method that allows very high strains to be imposed, leading to extreme work hardening and microstructural refinement. Billets of nonhomogenized (ascast) and homogenized Al–2 and 3 wt.%Cu alloys were successfully processed by ECAP up to different number of passes at room temperature. The microstructure was evaluated into ultrafine grained (UFG) microstructure with high grain boundary misorientation angle in the case of Al–Cu homogenized and nonhomogenized alloys due to imposed strain resulted. It was observed that more homogenized microstructures with smaller grain sizes and higher values of high grain boundary misorientation angle were obtained in the case of homogenized alloys. Higher improvement in the tensile properties and the microhardness values was noted in the case of Al–Cu homogenized alloys. The elongation% and uniform elongation% were observed to decrease with increase of the number of passes for all of the Al–Cu alloys except in the case of Al–3%Cu homogenized alloy. In the case of Al–3 wt.%Cu alloy, the elongation% and uniform elongation% were decrease after the second pass then it increases with the addition of more passes. The microhardness distribution and the deformation homogeneity across the transverse direction of the billet were measured. The homogeneity of deformation was observed to increase with the increase of the ECAP number of passes and the copper content. Higher degree of the homogeneity of deformation was observed in the case of the homogenized alloys comparing to that in the case of the nonhomogenized alloys.

Microstructure Characteristics of Eutectoid Pearlitic Steel after Equal Channel Angular Pressing at Room Temperature

An ultrafine microduplex structure was successfully produced through equal channel angular pressing (ECAP) at ambient temperature. According to the morphological characteristics of cementite lamellas, the deformed pearlite consists of shear break lamella, locally thinned lamella and irregularly bent lamella. The proportion of locally thinned lamella and irregularly bent lamella has increased with the pass number of ECAP. In addition, the deformed pearlitic ferrite became a supersaturated solid solution of carbon due to the partial dissolution of cementite during ECAP.

Microstructure of Equal-Channel Angular Pressed Cu and Cu-Zr Samples Studied by Different Methods

Polycrystalline samples of technical-purity Cu (99.95 wt pct) and Cu with 0.18 wt pct Zr have been processed at room temperature by equal-channel angular pressing (ECAP). The microstructure evolution and its fragmentation after ECAP were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD), positron annihilation spectroscopy (PAS), and by X-ray diffraction (XRD) line-profile analysis. The first two techniques revealed an increase in the fraction of high-angle grain boundaries (HAGBs), with increasing strain reaching the value of 90 pct after eight ECAP passes. The increase was more pronounced for pure Cu samples. The following two kinds of defects were identified in ECAP specimens by PAS: (1) dislocations that represent the dominant kind of defects and (2) small vacancy clusters (so-called microvoids). A detailed XRD line-profile analysis was performed by the analysis of individual peaks and by total profile fitting. A slight increase in the dislocation density with the number of ECAP passes agreed with the PAS results. Variations in microstructural features obtained by TEM and EBSD can be related to the changes in the XRD line-broadening anisotropy and dislocation-correlation parameter.