Equal Channel Angular Pressing Samples Research Articles

The Microstructural Refinement of the A356 Alloy Using Semi-Solid and Severe Plastic-Deformation Processing

Improving the engineering properties of A356 alloy is an appealing option for the automotive industry. This study aimed at refining and redistributing Si particles and the eutectic phase by applying T6 heat treatment to a semi-solid A356 alloy, followed by severe plastic deformation (SPD). Using a cooling-slope technique, the as-cast and rheocast samples were subjected to heat treatment prior to being processed using equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) at room temperature. The results show that the brittle Si particles were effectively fragmented and redistributed in the homogenous microstructure. The grain size reduced from 170 μm to 23 μm in the as-cast sample after combining heat treatment and the cooling-slope. This was followed by the ECAP sample after six passes through route A (where the sample is not rotated between each pass), while it reduced to 160 nm after five turns of the HPT process in a heat-treated cooling-slope sample. The hardness of the heat-treated cooling-slope casting samples increased with the ECAP process; there was an increase from 61 HV to 134 HV for the as-cast alloy after six passes through route A. The hardness of the heat-treated cooling-slope sample improved with the HPT process to 211 HV after five turns.

Fabrication of ultrafine-grained Cu-Mn alloy with uniform microstructure and high mechanical properties

Homogenization, random orientation, and high strength are the research goals of target materials. In this study, the bulk ultrafine-grained (UFG) Cu-5Mn alloy target materials were prepared by two typical severe plastic deformation methods, equal channel angular pressing (ECAP) and auxiliary-cooling multi-pass friction stir processing (MPFSP), and their structure-property relationships were comparatively investigated. Compared to the ECAP sample with extremely heterogeneous microstructure, the MPFSP sample exhibited finer and more uniform equiaxed microstructure with weaker texture and higher tensile strength of 614 MPa, which was consistent with the requirements of an ideal target material. This study provides a new perspective on the optimization of target materials.

Effect of Plastic Deformation on the Structure and Mechanical Properties of the Zn-4Ag-1Cu Zinc Alloy.

It is known that zinc biodegradable alloys are a promising material for producing biomedical implants for orthopedics and vascular stents. Among them, the Zn-Ag-Cu zinc alloy is of special interest due to the antibacterial and antimicrobial properties of Ag and Cu. To improve the mechanical properties of the Zn-4Ag-1Cu zinc alloy, the effect of equal-channel angular pressing (ECAP) on the microstructure and strength has been investigated. The ECAP conditions for the Zn-4Ag-1Cu alloy were chosen by modeling in the Deform 3 D program (temperature and strain rate). The microstructure was analyzed using transmission electron microscopy, scanning electron microscopy and X-ray diffraction analysis. The study of strength was carried out by measuring the microhardness and tensile tests of small samples with a gauge dimension of 0.8 × 1 × 4 mm3. The microstructure after ECAP was characterized by equiaxed grains ranging in a size from 1.5 µm to 4 µm with particles in a size from 200 nm to 1 µm uniformly distributed along the boundaries. The ECAP samples showed a high strength of 348 MPa and good ductility of up to 30%, demonstrating their great potential as promising materials for producing medical stents.

Effect of deformation methods on microstructure, texture, and properties of a Cu–Mg alloy

The effect of cold working by drawing, rolling, or equal channel angular pressing (ECAP) on the microstructure, the texture, the mechanical properties, and the electrical conductivity of a Cu-0.25%Mg alloy was investigated. The plastic deformation led to the development of continuous dynamic recrystallization that was accompanied by strain-induced low-angle boundary formation and their transformation into high-angle boundaries with straining. The elongated grains evolved after drawing. Sheet rolling provided pancaked ultrafine grain formation assisted by the development of microshear bands. After ECAP almost equiaxed ultrafine grains formed readily inside the deformation microbands. The rapid kinetic of grain refinement assisted by geometric dynamic recrystallization during cold rolling and drawing led to the formation of ultrafine grains with transverse sizes of about 0.20 μm and 0.43 μm, respectively, while the grain size in the ECAP samples was 0.88 μm after total strain of 4. The deformation microstructures led to the significant strengthening resulting in the ultimate tensile strength of about 670 MPa after drawing or rolling to total strain of 4 and 625 MPa after ECAP to total strain of 9.2. Elongation slightly decreased from 21% to 19% after ECAP and dramatically degraded to 6–8% after drawing or rolling. A decrease in elongation was accompanied by a linear increase in the fraction of specific texture components. Electrical conductivity gradually decreased by about 6–10% IACS with straining regardless of deformation method. The strengthening mechanisms and the conductivity variation during deformation are discussed.

Microstructure evolution and corrosion properties of ECAPed Mg–Pb-9.2Al-0.8B alloys

Effect of grain refinement on corrosion behavior of Mg–Pb-9.2Al-0.8B alloy by equal-channel angular pressing (ECAP). By measuring open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS), the corrosion behavior of as-cast and ECAP samples in 3.5 wt % NaCl solution were compared and analyzed. The results showed that sample obtained fine crystal after ECAP, and grain refining reduced the corrosion resistance of the alloy. In the polarization test, the Icorr value was the largest, and the type changed from local corrosion to uniform corrosion. Two factors weaken the corrosion resistance: The first is that β-Mg17Al12 phase is homogenized by the tissue and disappears, thus losing the barrier of corrosion propagation, resulting in reduced corrosion resistance. The second is that Mg + Pb eutectic phase produced by thermal deformation is the first to be corroded. As a result, the corrosion resistance of the alloy decreases after ECAP.

Shear enhancement of mechanical and microstructural properties of synthetic graphite and ultra‐high molecular weight polyethylene carbon composites

AbstractUltra‐high molecular weight polyethylene (UHMWPE) has a variety of industrial and clinical applications due to its superb mechanical properties including ductility, tensile strength, and work‐to‐failure. The versatility of UHMWPE is hindered by the difficulty in processing the polymer into a well consolidated material. This study presents on the effects of shear imparted by equal channel angular pressing (ECAP) on UHMWPE composites containing Nano27 Synthetic Graphite (N27SG). Ductility and work‐to‐failure improvements up to ~60–80% are obtained in sheared N27SG‐UHMWPE composites as compared to non‐sheared N27SG‐UHMWPE controls of the same composition. Microscopy reveals increased fusion at particle boundaries and smaller voids in the sheared materials. Micro‐computed tomography results indicate different distribution of N27SG particulates in ECAP samples as compared to CM indicating enhanced grain boundary interactions. Tradeoffs are not avoided as ECAP samples were lower in conductivity as compared to compression molded (CM) billets of the same weight percent. However, ECAP samples were able to be doped with more N27SG allowing for an ~170% increase in conductivity over CM samples of the same work‐to‐failure. This work shows that ECAP is a viable processing method for obtaining stronger, more ductile conductive composite materials.

Optimization of electrical process parameters of WEDM on ECAP Al7075 alloys considering Radial Overcut (ROC) as output response

The aim and objective of the present experimental work is to find out the predicted value of Radial overcut (ROC) while processing of Al7075 alloy through Equal Channel Angular Pressing (ECAP) with channel angel 90 degree and edge angle 20 degree with chosen process route C and alongwith suitable back pressure and subsequently machining that ECAP sample by Wire cut electric discharge machining (WEDM). Response Surface Methodology is applied in present study to predict the ROC in WEDM process for previously ECAP Al7075 alloy. Pulse off time (Toff), pulse on time (Ton), peak current (IP) and servo voltage (SV) are taken as input electrical parameters of process to study the ROC. The experiment was designed to perform based on Central Composite Design (CCD) method. After performing 31 experimental runs a mathematical model was being evolved for finding out the correlation and significance of electrical parameters on ROC. The coefficients were obtained by performing analysis through ANOVA at 95% confidence level.Observation shows that Ton and IP has got significant impact on ROC. The forecasted results based on mathematical model generated are found to be in a reasonably good degree of accuracy with the experimental result. Optimum value of radial overcut is obtained experimentally as 26.075 µm against Ton 7 µs, Toff 54 µs, for IP value 100 A and SV 25 V respectively.

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.

Effects of severe plastic deformation on the microstructures, mechanical properties, and corrosion behavior of U-5.5Nb alloy

Equal-channel angular pressing (ECAP) and mechanical machining were employed to introduce large plastic shear strain into bulk and the surface layer of a U-5.5wt.%Nb (U-5.5Nb) alloy, respectively. Applying ECAP, the U-5.5Nb alloy exhibited a single yield feature on the stress-strain curve in comparison to the “double yield” feature in the water quenched (WQ) counterpart. The difference is attributed to the characteristics of severe plastic deformation (SPD) structures obtained by ECAP. Mechanical machining resulted in a further severe microstructure refinement of the SPD surface layer with nano-grains/subgrains, which is accompanied with a dramatic increase of both the hardness and the elastic modulus of the surface layer. It is further proposed that the suppression of the shape memory effect (SME) in the nanostructured U-5.5Nb alloy may be responsible for the enhanced elastic modulus. The results of corrosion rate and pitting susceptibility showed a microstructure dependency, where the ECAP sample exhibited a better pitting resistance than that of the WQ counterpart.

Bio-corrosion impacts on mechanical integrity of ZM21 Mg for orthopaedic implant application processed by equal channel angular pressing

The mechanical integrity of rolled ZM21 Mg was improved by equal channel angular pressing (ECAP) to function as a potential biodegradable bone screw implant. Electron backscattered diffraction (EBSD) revealed deformed grains of 45 µm observed in rolled ZM21 Mg. They were transformed to equiaxed fine grains of 5.4 µm after 4th pass ECAP. The yield strength of rolled and ECAPed ZM21 Mg alloys were comparable. In contrast, 4th pass ZM21 Mg exhibited relatively higher elongation when compared to rolled sample. The mechanical properties of rolled and ECAPed ZM21 Mg were dependant on both grain refinement and crystallographic texture. The rolled and 4th pass ECAPed tensile samples exhibited nonlinear deterioration of mechanical properties when tested after 7, 14, 21 and 28 days immersion in Hank’s solution. The evaluation signifies that regardless their processing condition, ZM21 Mg alloys are suitable for surgical areas that requires high mechanical strength. In addition, the 4th pass ECAP samples were viable to MG-63 cells proving themselves to be promising candidates for future in vivo studies.

Characterization of CRYO AND RT ECAPed Aluminium 6063 Followed by Aging Using CHARPY IMPACT TEST

Equal Channel Angular Pressing (ECAP) is one of the severe plastic deformation techniques that have attracted much attention from the material community in present days. This technique has ability to produce ultra fine-grained microstructures, without a significant change in geometry. Present work describes the effect of CRYO treatment on impact strength of post ECAP aging for aluminium 6063 alloy studied using Charpy impact test. For conducting ECAP process, a channel having angle of 1080 is used. For ECAP purpose, samples having dimensions of 9.5mm X 9.5mm X 100mm chosen and they were given, solution treatment at 5200C for 120 minutes. These solution treated samples divided into two groups. One set of samples were given by CRYO treatment by dipping in liquid nitrogen for 20 minutes and ECAP processes carried out and obtained CRYO ECAP samples. Another set of solution treated samples subjected directly to ECAP operation and obtained RT ECAP samples. These two sets of samples are again, reduced to Micro Vickers and Charpy Impact test dimensions and aged at 1800C for different timings. Micro Vickers hardness tests and Impact tests are conducted on these two sets of samples. The obtained results are correlated with Macro and Micro examinations.

Correlation between shear punch and tensile measurements for an AZ31 Mg alloy processed by equal-channel angular pressing

An AZ31 magnesium alloy was extruded and then processed by equal-channel angular pressing (ECAP) at 200 °C for 1, 2 and 4 passes. The grain structure was refined from 20.2 to 1.6 ?m after 4 passes. The shear punch testing (SPT) technique and uniaxial tensile tests were employed to evaluate the mechanical properties of the extruded and ECAP samples. The 4 pass ECAP alloy showed lower yield stress and higher ductility compared to the as-extruded condition, indicating that texture softening overcame the strengthening effects of grain refinement. The same trends in strength and ductility were also observed in shear punch testing. Three different linear correlations between the shear data and tensile data were established for ductility, yield stress, and ultimate strength. It is shown that SPT is a useful method for evaluating the mechanical properties of small quantities of fine-grained materials processed by ECAP

On the low-cycle fatigue response of CoCrNiFeMn high entropy alloy with ultra-fine grain structure

High Entropy Alloys (HEAs) are a new class of multi-component alloys with excellent tensile strength-ductility combination. Their yield strength levels, however, are still low as compared to other high strength materials. Here, Equal Channel Angular Pressing (ECAP) was employed to improve the yield strength of the most well-known HEA, CoCrFeMnNi, through microstructural refinement. The cyclic response of both coarse and ultrafine grained CoCrFeMnNi was investigated during strain-controlled low cycle fatigue tests under fully reversed push-pull loading at room temperature. The microstructural evolution during cyclic loading was compared to the microstructure under quasi-static monotonic loading. Very high yield strength levels around 1 GPa were obtained after ECAP. In addition, ECAP samples demonstrated a superior fatigue life at relatively low strain amplitudes while coarse grained samples exhibited a better fatigue life at the highest strain amplitude considered. X-ray diffraction, electron backscattered diffraction and transmission electron microscopy were performed to reveal underlying mechanisms for the superior fatigue life and the overall transient behavior upon cycling. The fatigue life and hardening behavior were governed by the refined grain size, high density dislocation walls, and the annihilation of existing dislocations resulting in the formation of cell structures in the ECAP samples. The lower fatigue life of the ECAP samples at the highest strain amplitude is attributed to the higher stress amplitudes and cyclic softening due to accelerated dislocation annihilation. Finally, the formation of dislocation cell structures and high-density dislocation walls simultaneously is rationalized by the effect of applied stress on the partial dislocation separation.

Influence of equal-channel angular pressing on the corrosion fatigue behaviour of an Al-Mg-Si aluminium alloy for automotive conductors

The influence of equal channel angular pressing (ECAP) on the corrosion fatigue behaviour of an Al-Mg-Si alloy was studied. Preliminary fatigue tests in air showed an increase in fatigue lifetime for ECAP samples, as compared to as-received samples, related to the ECAP-induced grain refinement. After pre-corrosion, the fatigue lifetime was lower for ECAP samples than for as-received samples, because the fragmentation of coarse intermetallics during ECAP led to an increase in the density of corrosion defects. Corrosion fatigue tests demonstrated a synergy between cyclic mechanical loading and corrosion processes for all samples; a deleterious effect of ECAP was also noted.

Influence of Ball Burnishing Process on Equal Channel Angular Pressed Mg-Zn-Si Alloy on the Evolution of Microstructure and Corrosion Properties

In the present study, Mg-4Zn-1Si alloy was subjected to equal channel angular pressing (ECAP) up to 4 passes at 300 °C, followed by ball burnishing using 0.3 mm depth of press, 300 mm/min feed and 1 pass successfully. The effect of ECAP and ECAP + ball burnishing process on microstructure, mechanical properties (tensile and hardness) and corrosion behavior was systematically investigated. After 4 pass ECAP, initial coarse grains (210 μm) were refined and average grain size is 6 μm and after ball burnishing, the grain size is found to be 3.3 μm. Microstructure evolution is discussed using optical images, scanning electron microscope images and transmission electron microscope images. For ECAP samples, maximum strength and hardness was recorded at 3 pass. Both strength and hardness decreased for 4 pass ECAP processed samples, even though grain size decreased, this is because of texture modification in the material. ECAP 4 pass + ball burnished samples exhibited 48.5% enhancement of microhardness as compared to 4 pass ECAP samples. Corrosion resistance of the samples decreased with increase in the number of ECAP passes, this is due to strain-induced grain refinement with more crystalline defects in samples. Combined process of ECAP and ball burnishing effectively reduces the Icorr and this consequently reduces corrosion rate of the Mg–4Zn-1Si alloy.

Effect of Equal Channel Angular Extrusion on the Thermal Conductivity of an AX52 Magnesium Alloy

An AX52 magnesium alloy (nominal composition Mg-5Al-2Ca in w.%) was submitted to equal channel angular pressing (ECAP) using processing route A; 1–8 passes through the ECAP tool were applied. The thermal conductivity of the ECAP samples was measured using a flash method in the temperature interval from room temperature up to 350 °C. The microstructure and texture of the samples were studied by light and electron microscopy. The severe plastic deformation, realized by the ECAP, influences the thermal properties of the alloy. The possible microstructural parameters determining the thermal conductivity were analyzed. New dislocations, the grain, phase boundaries, and texture of the samples may perceptibly change the thermal properties.

Controlling Corrosion Resistance of a Biodegradable Mg–Y–Zn Alloy with LPSO Phases via Multi-pass ECAP Process

Mg-RE (rear earth) alloys with long period stacking (LPSO) structures have great potential in biomedical applications. The present work focused on the microstructure and corrosion behaviors of Mg98.5Y1Zn0.5 alloys with 18R LPSO structure after equal channel angular pressing (ECAP). The results showed that the ECAP process changed the grain size and the distribution of LPSO particles thus controlled the total corrosion rates of Mg98.5Y1Zn0.5 alloys. During the ECAP process from 0p to 12p, the grain size reduced from 160–180 μm (as-cast) to 6–8 μm (12p). The LPSO structures became kinked (4p), then started to be broken into smaller pieces (8p), and at last comminuted to fine particles and redistributed uniformly inside the matrix (12p). The improvement in the corrosion resistance for ECAP samples was obtained from 0p to 8p, with the corrosion rate reduced from 3.24 mm/year (0p) to 2.35 mm/year (8p) in simulated body fluid, and the 12p ECAP alloy exhibited the highest corrosion rate of 4.54 mm/year.

Effects of microstructure on the torsional properties of biodegradable WE43 Mg alloy

Torsional properties are important performance parameters for bone screw applications, but they are seldom studied, especially for newly developed biodegradable Mg alloys. In this study, WE43 Mg alloy with different microstructures was achieved by equal channel angular pressing (ECAP) and heat treatment, and their torsional properties were studied. In addition, tensile properties were also tested as a comparison. The results indicated that grain refinement led to higher torsional strength and ductility, while the second phases improved the torsional strength but reduced the ductility. The texture was strengthened after ECAP, as a result the tensile strength increased, but the torsional strength did not increase and even decreased, especially for 2-pass ECAP sample with a typical basal fiber texture. The basal plane orientation deviation from the extrusion direction after 4-pass ECAP resulted in higher torsional strength and lower torsional ductility, but lower tensile strength and higher tensile ductility were obtained. This implied that a strong fiber texture would reduce the torsional strength but improve the torsional ductility, which was different from its effect on tensile properties.

Parameter optimization of extrusion-Bc ECA technology and its effect on microstructure and properties of 7075 aluminum alloy

Equal-Channel Angular Pressing (ECAP) was carried out on 7075 aluminum alloy with a process route of Bc mode, thus, achieving the aims of refining crystal grains and improving alloy plasticity. To save cost and optimize the ECAP process, DEFORM finite element simulation of the ECAP extrusion process was conducted to determine the ratio of die shear Angle to extrusion. The results show that the mold optimum process parameters are 135° for the shear angle (Φ) and λ = 2 the extrusion ratio. The deformation and processing stability of the alloy at the same time met the requirements. From the simulation and experimental results of the ECAP sample, the grain size of 7075 aluminum alloy after Bc-ECAP was obviously refined from 17.311 to 9.310 μm, and the grain shape more round. The equiaxed property of the grain was also improved, and the tissue distribution more uniform. Even though the strength of 7075 aluminum alloy slightly decreased, its plasticity increased significantly from 9.9 to 18.6%.

Al3(Sc, Zr) precipitation in deformed Al-Mg-Mn-Sc-Zr alloy: Effect of annealing temperature and dislocation density

The changes of Al3(Sc, Zr) morphology in deformed Al-Mg-Mn-Sc-Zr alloy were studied. Two experiment conditions were designed: different temperature and different dislocation density. Different dislocation density was obtained by different deformation method (traditional hot extrusion and equal channel angular pressing (ECAP)). It is calculated that the ECAP introduced a large amount of dislocations into the alloy and these dislocations accelerated the recrystallization making the interfaces move drastically. It is found that annealing the extruded sample at for 1 h does not cause the loss of coherency of the Al3(Sc, Zr) particles whether under 450 °C or 550 °C. However, annealing the ECAP sample at 450 °C causes a small amount of the particles loss of coherency. The main reason is that the grain boundary cut through the particle. Annealing the ECAP sample at 550 °C would cause most of the particles to lose coherency, and there are three main types of incoherency.