Equal Channel Angular Pressing Samples Research Articles

Enhancing Strength and Maintaining Ductility of Mg-3%Li-1%Sc Alloy by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) has been conducted on as-cast Mg-3%Li-1%Sc alloy for four-passes to study the microstructure uniformity and tensile properties. After ECAP, the microstructure become muddled, contains about 65% of deformed coarse grains with abundant low angle grain boundaries and about 35% of recrystallized small grains. Meanwhile, a strong basal texture is formed in the ECAP sample. The texture type of the recrystallized grains and the deformed grains are the same, however, the texture strength of the recrystallized grains is much lower than the deformed ones. Tensile strength is improved effectively and the elongation is maintained after ECAP. The increment of strength results from the microstructure refinement and residual dislocations produced by ECAP, while the recovery of ductility may be attributed to a shear type texture formed in the alloy during ECAP.

Assessment of tensile strength using small punch test for transversely isotropic aluminum 2024 alloy produced by equal channel angular pressing

The microstructures of metallic materials become extremely refined and their mechanical strengths exhibit considerable anisotropy when subjected to severe plastic deformation by equal channel angular pressing (ECAP). The small punch (SP) testing method was employed as a substitute for the standard tension test to assess the anisotropic tensile strength of materials produced by ECAP. SP testing is a viable alternative to standard tension tests because ECAP samples are usually limited to approximately 10 mm in length in the transverse direction perpendicular to the extrusion (longitudinal) direction of the ECAP process and the dimensions of the SP test specimen are 10 mm × 10 mm × 0.5 mm. The SP tests were performed using specimens of over-aged aluminum 2024 alloy subjected to three ECAP passes at 150 °C and extracted by wire cutting along the longitudinal and transverse axes. The failure surfaces of SP specimens after testing showed that failure was caused by shear deformation and that ECAP-processed materials displayed anisotropic strength. Based on these results, a method is proposed to assess tensile strength along both the transverse and the longitudinal axes of ECAP materials exhibiting anisotropic strength. The validity of the proposed method was verified through a comparison of its performance evaluating plastic flow strength with measurements obtained by tension tests along the longitudinal axis.

Microstructural evolution during extrusion and ECAP of a spray-deposited Al–Zn–Mg–Cu–Sc–Zr alloy

The microstructural evolution of an Al–Zn–Mg–Cu–Sc–Zr alloy prepared by spray deposition via extrusion and equal-channel angular pressing (ECAP) was investigated in this study. Deformation route A for Al–11.5 wt% Zn–2 wt% Mg–1.5 wt% Cu–0.2 wt% Sc–0.15% Zr super-strength alloy was carried out at 573 K by ECAP. The microstructures of extruded and ECAP samples were investigated by means of Electron Backscatter Diffraction (EBSD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). A large amount of dislocation tangles were formed inside grains during ECAP, which further evolved into sub-boundaries and high angle grain boundaries. Microstructure analyses showed that the grain size was refined to 800 nm after 8 passes ECAP from earlier 3.5 μm of sprayed and extruded alloy. A few finer MgZn2 and Al3(Sc,Zr) were dispersed uniformly after ECAP. The textures of 8 passes ECAPed sample were dominated by the strong Cu orientation and relatively weak S orientation.

Improvement of mechanical properties of AL (A356) cast alloy processed by ECAP with different heat treatments

Severe plastic deformation (SPD) by equal channel angular pressing (ECAP) has been used as a reliable method to achieve an ultra-fine and homogenous microstructure in the bulk materials. In this research, study was conducted on the structures and mechanical properties of A356 (7%Si) Al alloy produced by severe plastic deformation through ECAP. Special attention was paid to the effect of heat-treatments such as annealing, solution, quenching and pre/post-aging on the properties of the materials. The heat treated as cast structure was successfully deformed in ECAP process. The yield strength, ultimate strength, and hardness of the ECAP samples were improved after pre/post-artificial aging. Mechanical properties improvement was achieved after ECAP process in the samples with the pre-aging treatment. The results show near 114% improvement of the ultimate tensile strength (UTS) and 166% elongation from the as-cast structure. From experimental work, it was also found that the acceleration of precipitation kinetics after ECAP process is not important factor to achieve improvement of mechanical properties, but distribution of Si particles with precipitates formed during T6 is important in high UTS achievement along with high elongation.

Deformed Microstructures and Mechanical Properties of CP-Ti Processed by Multi-Pass ECAP at Room Temperature

The deformed microstructures and mechanical properties of commercial pure titanium (CP-Ti) with an initial grain size of about 28 μm was investigated using equal channel angular pressing (ECAP). ECAP was conducted at room temperature adopting a die with a channel angle of 120° via route BC. Special attention was paid on the microstructure evolution and mechanical properties of the ECAP samples. Deformation twins were found in most grains after the first and second pass of ECAP. After four ECAP passes, the original grains were refined from 28 μm to about 250 nm, and the ultimate strength and microhardness were significantly enhanced to 773 MPa and 2486 MPa, respectively. Meanwhile good ductility of 16.8% elongation still remained.

Distributions of Hardness and Strain during Compression in Pure Aluminum Processed with Equal-Channel Angular Pressing and Subsequent Annealing

Single compression tests were conducted for two types of pure Al (99.99%): one processed using equal-channel angular pressing (ECAP) through route Bc for 8 passes and the other with the same ECAP but successively annealed at 573 K for 1 h. The distributions of the equivalent strain introduced by the compression were quantitatively examined by finite element analysis (FEA). Comparison was made between the ECAP samples and the ECAP-annealed samples with regard to the inhomogeneity and magnitude of the strain developed during the compression. Hardness variations with the equivalent strain were also compared with those obtained by earlier studies using ECAP and high-pressure torsion. Moreover, the hardness variation throughout the cross section after compression was well predicted using the FEA for both ECAP sample and ECAP-annealed sample. It is shown that the change in the strain path from ECAP to compression affects the hardness variation with respect to the equivalent strain. [doi:10.2320/matertrans.MD200819]

Work-piece length of the effect on stress and analysis of cracking-criterion under equal channel angular pressing

Finite-element method (FEM) and experimental investigation of 2024 Al subjected to equal-channel angular pressing (ECAP) has been carried out. The maximum equivalent normal stress and the maximum shear stress at an optionally given displacement of ECAP have been obtained through FEM for various given initial length of ECAP samples. The cracking criterion for the materials subjected to ECAP is further discussed with the help of experimental investigation. It is observed that at all given displacement of ECAP, the maximum equivalent normal stress is always less than the ultimate tensile strength of materials for all ECAPed samples with various initial length, while the maximum shear stress is always present at the angular channel zone of ECAP die, and its value decreases with the decrease of initial length of ECAPed samples. When the used initial length is small enough, the computed maximum shear stress becomes less than the shear strength of the materials, which is in very good agreement with the experimental observation that the frequency of sample cracking is decreased greatly. It is concluded that the non-cracking criterion of the materials subjected to ECAP could be expressed as "the maximum shear stress is less than the shear strength of materials". It is also suggested that a rational research should be involved in the actual measurement of stress-strain curve and the optimization in the configuration of ECAP die, the technology of materials pretreatment and the length of samples based on the above-motioned non-cracking criterion.

Effect of Equal Channel Angular Pressing on Microstructure and Mechanical Properties of Commercial Purity Aluminum

Commercial purity aluminum was deformed by equal channel angular pressing (ECAP) using steel dies producing two different shear strains of either 1.15 or 0.60 in each pass. Two sets of samples were selected for study, of which the first set consists of aluminum billets repeatedly deformed without changing orientation (process A) up to three passes using first die. The second set of samples was equal channel angular pressed (ECAPed) using the second die up to 10 passes adopting process Bc, where samples were rotated by 90 deg between successive passes. The flow patterns were revealed by optical metallography. Tensile strength and hardness were measured. The ECAPed samples were isochronally-annealed and recrystallization behavior was studied by microscopy and Vickers hardness measurements. Refinement of grain size, substructure, and texture was studied by transmission electron microscopy (TEM) and orientation imaging microscopy (OIM). The results show that flow patterns are complex and distinct from simple shear. Strain is higher at the outer surfaces, highest at the bottom surface, and intermediate in the middle of the billet. The work piece strain hardens significantly in first pass with an attendant drop in ductility. The degree of strengthening reduces in subsequent passes. The high defect density introduced during the initial passes leads to grain refinement to an ultrafine level and advantageously the material regains ductility. The refinement in microstructure obtained after two to three passes is stable up to 250 °C. The flow patterns are very similar to those obtained by physical modeling in our earlier studies using plasticine. Equiaxed ultrafine-grained structure (average grain size = 0.53 μm) was obtained after ECAP at an equivalent shear strain of 6.0.

Three-dimensional numerical simulations of multi-pass equal-channel angular pressing by a variation difference method and comparison with experiment

A variation-difference method (VDM) of solving continuum mechanics equations has been implemented for simulation of the equal-channel angular pressing (ECAP) process. Application of the developed DRAKON code (VNIIEF, Russia) for numerical study of multi-pass ECAP allowed processes of severe plastic deformation to be described in three-dimensional (3D) continuum approximation in the field of low strain rates and high-pressure levels in terms of contact interaction. The influence of ECAP processing parameters on stress–strain field distribution over the ECAP sample's cross-section is studied in 3D formulation. The model validation is performed by comparison of simulation results with various experimental data. Deformation histories provided by DRAKON were used together with a polycrystal plasticity model (viscoplastic self-consistent model) allowing simulation of texture evolution during ECAP with account to macro-parameters of the process. It is shown that the VDM-based model possesses good predictive capabilities for 3D simulation of severe plastic deformation processes involving strain-path changes.

Microstructure quantification and correlation with flow stress of ultrafine grained commercially pure Al fabricated by equal channel angular pressing (ECAP)

Commercial purity Al was severely deformed by equal channel angular pressing (ECAP) up to eight passes using route B C. The deformation microstructure was characterized quantitatively by electron-backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The microstructural homogeneity was investigated by EBSD at various locations from center to surface of the samples on a longitudinal section parallel to the pressing direction. Structural parameters including mean boundary spacing, boundary misorientation angle and fraction of high angle grain boundaries were measured and characterized through the section of the ECAP samples. EBSD scans revealed a homogeneous ultrafine grained microstructure after 8 passes. The analysis showed that the fraction of high angle grain boundaries was more than 70% at most locations of the sample section. Also, an average boundary spacing of 380 nm was obtained by the linear intercept method. TEM analysis was used for more detailed characterization of the microstructure, such as low angle boundaries with misorientation angles smaller than 2°. Using the structural parameters–flow stress relationship, the flow stress was estimated based on the EBSD and TEM/Kikuchi-line analyses and compared with measured values.

Mechanical behaviour and texture of annealed AZ31 Mg alloy deformed by ECAP

AZ31 Mg alloy samples were processed by equal channel angular pressing (ECAP) at 220°C for four passes. An average grain size of ∼1·9 μm with reasonable homogeneity was obtained. The ECAP process imparted large plastic shear strains and strong deformation textures to the material. Subsequent annealing of the equal channel angular pressed samples produced interesting mechanical behaviours. While yield strength increased and ductility decreased immediately after undergoing ECAP, annealing at temperatures <250°C restored ductility significantly at a small decrease in of yield strength. Annealing at temperatures >250°C reduced yield strength without additional improvement in ductility. It is believed that the combination of stress relief via dislocation elimination, refined microstructure and the retention of a strong ECAP texture at low annealing temperatures enhance ductility. High temperature annealing breaks down the ECAP texture resulting in no further improvement in ductility. The results show that the mechanical properties of the alloy can be positively influenced by annealing after ECAP to achieve a combination of strength and ductility.

Mechanical properties of equal channel angular pressed powder extrudates of a rapidly solidified hypereutectic Al-20 wt% Si alloy

The processing and mechanical properties of rapidly solidified and consolidated hypereutectic Al-20 wt% Si alloys were studied. A bulk form of rapidly solidified Al-20 wt% Si alloy was prepared by extruding gas atomized powders having a powder size of 106–145 μm. Powder extrudates were subsequently equal channel angular pressed up to eight repetitive route C passes to refine matrix microstructure and Si particles by imposing severe plastic deformation. The microstructures of the gas atomized powders, extrudates and equal channel angular pressed samples were investigated via a scanning electron microscope. The mechanical properties of the bulk samples were measured by compressive tests. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength of the Al-20 wt% Si alloy without deteriorating ductility in a range of experimental strain of up to 30%.

Grain refinement of commercially pure zirconium by ECAP and subsequent intermediate heat treatment

Microstructural evolution of commercially pure zirconium (Zr702) processed by equal channel angular pressing (ECAP) and subsequent intermediate heat treatment was investigated. ECAP was carried out at room temperature, and the sample was rotated 90° in the same sense in each pass. Also, intermediate heat treatment of the ECAP samples processed by was performed at 773 and 873 K for their recovery and recrystallization temperatures. When the samples were annealed at recrystallization temperature of 873 K, the mean grain size of these samples decreased from ∼40 to ∼3 μm by the further four passes of ECAP. However, when the samples were annealed at recovery temperature of 773 K, the mean grain size was found to be 0.2 μm after the same ECAP process. A difference in microstructural evolution with annealing processes indicated that the rate of formation of new grains for ultra-fine-grained Zr702 was accelerated due to the high fraction of subgrains into the matrix of Zr702 after recovery.

The effect of equal-channel angular pressing on the structure and mechanical behavior of Ti–6Al–4V alloy

Abstract The paper reports on the formation of ultrafine-grained structure in the Ti–6Al–4V alloy by equal-channel angular pressing (ECAP). ECAP processing with various regimes on die-sets with angles of channels intersection equal to 135° and 120° has been studied. Special attention is paid to the features of the processed microstructures and properties of the ECAP samples. It is shown that low-temperature deformation applied after ECAP contributes to additional strengthening of the alloy preserving sufficient ductility.

급속응고 Al-20 wt% Si 합금분말 압출재의 ECAP

In this paper processing and mechanical properties of Al-20 wt％ Si alloy was studied. A bulk form of Al-20Si alloy was prepared by gas atomizing powders having the powder size of 106-145 <TEX>${\mu}m$</TEX> and powder extrusion. The powder extrudate was subsequently equal channel angular pressed up to 8 passes in order to refine grain and Si particle. The microstructure of the gas atomized powders, powder extrudates and equal channel angular pressed samples were investigated using a scanning electron microscope and X-ray diffraction. The mechanical properties of the bulk sample were measured by compressive tests and a micro Victors hardness test. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength and hardness of the Al-2OSi alloy without deteriorating ductility in the range of experimental strain of 30％.

Microstructural Control of a Precipitate-Hardenable Al-Ag Alloy Using Severe Plastic Deformation

Departments of Aerospace & Mechanical Engineering and Materials ScienceUniversity of Southern California, Los Angeles, CA 90089-1453, USA, langdon@usc.eduKeywords: Al-Ag alloy, equal-channel angular pressing, precipitate particles, aging, metastablephaseAbstract. An Al-10.8wt%Ag alloy was subjected to aging treatment followed by Equal-ChannelAngular Pressing (ECAP) (designated process AE) or ECAP followed by aging treatment(designated process EA). Hardness measurements were undertaken with respect to the number ofECAP passes for process AE or with respect to aging time for process EA. Microstructures wereexamined by transmission electron microscopy (TEM) including X-ray mapping. It is shown thatage hardening is observed for the ECAP sample due to the precipitation of very fine particles withinthe small grains.IntroductionIt is well known that the process of equal-channel angular pressing (ECAP) is used to reduce thegrain size of metallic materials to the submicrometer range or the nanometer range [1-3]. However,it is not so well established that the ECAP process may also be used to control the morphology anddistribution of second phase particles in two-phase metallic materials. Thus, grain refinement andsecond-phase control are both feasible because severe strain is created through the process of ECAPbased on the principle that a sample is pressed through a channel bent into an L-shape within a dieand this pressing may be repeated without any change in the cross-section of the sample.Fragmentation not only of the grains but also of second-phase particles may occur due to theintroduction of severe strain in the material.Although many reports have now been published for grain refinement using the ECAP process[2,3], there are only a limited number of examples of the application of the ECAP process tosecond-phase control [4,5]. It was shown that the application of ECAP led to dissolution of 0'particles precipitated by aging of an Al-3.7wt%Cu alloy [4]. Supersaturation thus occurred in thealloy and subsequent aging gave rise to the formation of a stable 0-phase. The 0-phaseprecipitation was also recognized after aging of a severely deformed Al-3.7wt%Cu alloy usingECAP. An application of ECAP to an A1-0.9wt%Mg

High coercive states in Pr–Fe–B–Cu alloy processed by equal channel angular pressing

Using the method of severe plastic deformation (SPD), namely equal channel angular pressing (ECAP), the bulk billets with the microcrystalline structure were processed out of the low-plastic multiphase hard magnetic Pr 20Fe 73B 5.5Cu 1.5 alloy. Alloy coercivity increases due to grain refinement and uniform microstructure forming under SPD. As a result of three ECAP cycles at 600°C coercivity is more than 1500 kA/m. It is obvious that j H c changes at ECAP samples annealing depends upon the temperature and ECAP cycles number.