Equal Channel Angular Pressing Passes Research Articles

Strain‐Induced Dissolution and Precipitation of Secondary Phases and Synergetic Stengthening Mechanisms of Al–Zn–Mg–Cu Alloy during ECAP

The evolution of secondary phase of 7A60 aluminum alloy before and after equal channel angular pressing (ECAP) deformation and the resultant variation of mechanical properties are studied by means of X‐ray diffractometer (XRD), transmission electron microscopy (TEM), optical microscope (OM), and Instron testing machine. The results show that grains are refined to submicron level after ECAP (from 9.86 µm to about 1 µm). As the strain increases, the main secondary phase (MgZn2) dissolves into the aluminum matrix to form a supersaturated solid solution. Part of the solute atoms diffuses along the vacancies and dislocations under the combined effect of interface energy, strain energy, and grain boundary energy. In addition, grain boundary segregation occurs and further leads to relatively coarse secondary phase. With the increase of temperature, discontinuous precipitation (DP), which occurs from the grain boundary to the grain internal, dominates the formation process of secondary phases. The phase transformation brings about significant precipitation strengthening, resultantly, enhances strength, and ductility are achieved for 7A60 aluminum alloy via ECAP. Moreover, the precipitation strengthening effect, which is closely related with the dissolution and DP, first enhances and then attenuates with the increase of ECAP passes. Dislocation strengthening and Hall‐Petch strengthening aggravate monotonically with the ECAP passes but play less important roles in the overall stress responses.

Ultra-fine grained Mg-Zn-Ca-Mn alloy with simultaneously improved strength and ductility processed by equal channel angular pressing

The influence of equal channel angular pressing (ECAP) on the microstructure, texture evolution and mechanical properties of extruded Mg-5.0Zn-0.5Ca-0.3Mn (weight percent) alloy has been systematically investigated in the current study. A typical ultra-fine grained (UFG) structure is obtained in the as-ECAPed alloy for 4 passes, due to a completed recrystallization process. With the increasing ECAP pass, the conventional basal texture can be gradually changed to an asymmetric non-basal texture with its basal plane inclined to normal and transverse directions ∼45°, which is related to the typical shear mode, leading to an obvious increase of Schmid factor for the activation of basal slip system. The room-temperature tensile yield strength, microhardness and ductility of extruded alloy are simultaneously improved by successive ECAP processing, which is derived from the grain refinement and texture modification.

Effect of equal channel angular pressing (ECAP) on the evolution of texture, microstructure and mechanical properties in the Al-Cu-Li alloy AA2195

In this study, one of the severe plastic deformation (SPD) techniques, Equal Channel Angular Pressing (ECAP) has been successfully applied to the Al-Cu-Li alloy AA2195 at 250 °C and the development of microstructure, texture and mechanical properties has been studied. A systematic analysis has been carried out by using EBSD and TEM to understand the microstructural features, and the nature of different precipitates presence in the alloy AA2195. Microstructural features indicate considerable grain refinement leading to an average grain size of 2.8 ± 0.7 μm after 4 ECAP passes. Continuous dynamic recrystallization (CDRX) has been identified as the mechanism that leads to the formation of fine grain structure in the alloy AA2195 during the warm ECAP process. TEM results confirm the distribution of strengthening precipitates δ′(Al3Li), β(Al3Zr) and T1(Al2CuLi) in the alloy. The overall texture has become weak after ECAP processing and has been simulated using Visco-plastic self-consistent simulation (VPSC). The evaluation of mechanical properties indicates a substantial increment in hardness, strength properties with a minor reduction of ductility after 4 passes. Low mechanical property anisotropy is expected in the processed AA2195 alloy due to its weak texture.

Fatigue Life Improvement of Copper Processed by Equal Channel Angular Pressing

In this paper, the high cycle fatigue life of ultra-fine grained copper, purity 99.7%, processed by equal channel angular pressing (ECAP) has been considered. To produce the ECAPed specimens, the associated die set was designed and manufactured. Mechanical properties of the ECAPed material were evaluated by standard tensile tests. Moreover, the high cycle fatigue life was assessed using a cantilever rotating bending machine at room temperature at 50 Hz frequency. Based on the obtained results, the estimated S-N diagram was constructed. The experimental results showed that the tensile strength of the pure copper has been remarkably increased using equal channel angular pressing. In addition, the fatigue life at high stress amplitudes was significantly improved. For instance, the fatigue life at stress amplitude equals 180 MPa increases approximately ten times. However, an insignificant increase in the fatigue limit endurance was observed in the long life regime in excess of ten million cycles. Furthermore, the fatigue life was not affected by the number of ECAP pass.

Ecap Consolidation and Heat Treatment of Blended Elemental Powders of Iron, Chromium, Nickel and Manganese

Equal channel angular pressing (ECAP) is one of the severe plastic deformation processes that can also be used for metallic powder consolidation. Consolidation of blended elemental powders of iron, chromium, nickel, and manganese (Fe-25Cr-20Ni-2Mn wt. %) was performed at room temperature in a Φ = 120° die by 1 and 2 passes. SEM micrographs indicated that single pass ECAP consolidated sample presented close to full densification. Additional pass of ECAP led to hardness increase and to an apparent better mixing between the different particles. SEM/EDX analysis made before and after heat treatment of the samples showed that effective diffusion only took place after heat treatment and especially in the sample subjected to 2 ECAP passes. Results indicate that alloying by ECAP consolidation and posterior heat treatment is feasible, especially for systems that cannot be processed by conventional means, as well as mechanical alloying.

Microstructure and mechanical properties of severely deformed Al-Mg-Sc-Zr alloy and their evolution during annealing

The ultrafine-grained structure developed here after severe plastic deformation of Al-Mg and Al-Mg-Sc-Zr by equal channel angular pressing (ECAP) and cold rolling (CR) is presented to consist of dense dislocation walls and cell structure of dimension of ~ 300 nm. Detailed characterization by traditional transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and X-ray diffraction (XRD) has been carried out to reveal microstructure evolution during deformation and annealing. A unique bimodal grain structure, which consists of ultrafine grains (less than 150 nm) and fine grains (in the range of 200–500 nm) having high dislocation density, was developed after 16 ECAP passes and CR. It was also found that microstructure inhomogeneity exits even after high ECAP passes and annealing at high temperature (280 °C) for 1 h. High yield strength (YS) of ~ 550 MPa and tensile strength (TS) of ~ 560 MPa were obtained after 16 ECAP passes and CR, however, the corresponding elongation dropped to ~ 8.2%. Subsequent optimum annealing was found to be 240 °C × 1 h, by which comprehensive mechanical properties were maintained (~ 481 MPa for YS, ~ 512 MPa for TS and ~ 13.7% for elongation) in Al-Mg-Sc-Zr (16 ECAP passes). The reasons of inhomogeneous microstructure and the origins of high strength, i.e. high solute Mg content, dense dislocations, ultrafine grains and nanoscale Al3(Sc, Zr) particles are discussed.

Microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy during equal channel angular pressing

The homogenized Mg-13Gd-4Y-2Zn-0.6Zr alloy was subjected to different equal channel angular pressing (ECAP) passes to investigate the effect of long period-stacking order (LPSO) phase on microstructure evolution and mechanical properties. The heterogeneous bimodal microstructure can be obtained due to the inhibition effect of intragranular 14H-LPSO phase on dislocation slip and lattice rotation at early stage. The intragranular 14H-LPSO phase was kinked and broken, which facilitate the transformation from LAGBs to HAGBs and subdivision of the deformed grains. Furthermore, the interdendritic 14H-LPSO phase was crushed and broken with further ECAP passes, which contribute to the dynamic recrystallization (DRX) process at grain boundaries via particle-stimulated nucleation (PSN) mechanism. The microstructure after 3p-ECAP demonstrates finer randomly oriented dynamic recrystallization (DRX) grains, broken 14H-LPSO phase at grain boundaries and precipitated intragranular lamellar 14H-LPSO phase. In addition, the alloy after 3p-ECAP exhibits the ultimate tensile strength of 361 MPa, tensile yield strength of 197 MPa and fracture elongation of 9.3%. The elevated temperature ultimate tensile strength after 3p-ECAP exceeds 300 MPa at test temperature of 300 ℃ and strain rate of 0.001/0.003 s−1, which can be ascribed to the broken 14H-LPSO phase at grain boundaries and precipitated lamellar 14H-LPSO phase within DRX grains.

Effect of ECAP on structural, mechanical and functional characteristics of the austenitic Cr-Ni-Ti steels

In this study, equal-channel angular pressing (ECAP) of austenitic Cr-Ni-Ti stainless steel was carried out. Effect of ECAP on the evolution of the microstructure and mechanical and service properties of the Cr-Ni-Ti steel was investigated. The microstructure in the completely austenitic state processed by 6 passes of ECAP at 200 °C was obtained and examined by optical and transmission electron microscopy. Mechanical properties were determined by the Vickers micro-hardness measurements and tensile testing. Fracture toughness was evaluated and tribological properties of Cr-Ni-Ti stainless steel processed by ECAP were studied. It was revealed that submicrocrystalline structure with an average size of structural elements of 100 nm produced by ECAP significantly increased the strength properties of Cr-Ni-Ti stainless steel than that in the quenched state. After ECAP the ultimate tensile strength increased by 1.7 times, the fatigue limit by 1,5 times than that in the initial state. It was revealed that Cr-Ni-Ti steel after ECAP demonstrates 2.9 times higher fracture toughness than that in the quenched state. It is established that ECAP does not significantly affect the coefficient of friction and mass wear.

Mechanical behaviour of the St. 20 Steel after equal chanel angular pressing

The mechanical properties of low-carbon (0.2% C) St. 20 steel with conventional and ultrafine-grained (UFG) structures have been studied. The UFG structure of 340-448 nm in grain size was prepared by the method of equal-channel angular pressing (ECAP) for different numbers of passes (N = 4, 8 and 12) and subsequent annealing at 400 and 450°C. The study included static tension, impact bending at room and lower temperatures, fatigue tests, and the examination of the development of plastic deformation zones by replicas. It was established that an increase in the number of ECAP passes increases strength, but decreases plasticity and impact toughness, decreases strain hardening coefficient, and increases yield strength to the level of ultimate tensile strength. The ECAP for 8 passes leads to an increase in fatigue strength by 25%. Annealing does not substantially change mechanical properties. The optimum set of properties is characteristic of the steel after ECAP for 8 passes and annealing at 400°C. The shear instability revealed in the UFG steel upon static loading as the formation of a network of localized deformation bands inclined at an angle of ~ 55° to the loading axis of the specimen depends on the number of passes.

Adaptive neuro-fuzzy and regression models for predicting microhardness and electrical conductivity of solid-state recycled EN AW 6082

In the last few years, there is a demand for developing new technologies in order to increase scrap reuse potential and CO2 emission savings. In this paper, aluminum was recycled from chips obtained by machining without any remelting in order to reduce environmental pollution and to increase material yield during the process. This process is called solid-state recycling (SSR) or direct recycling. SSR process consists of chips cleaning, cold pre-compaction, and hot direct extrusion followed by equal channel angular pressing (ECAP) at different temperatures. Influence of direct extrusion temperature, ECAP temperature, and number of ECAP passes on electrical conductivity and microhardness of the recycled EN AW 6082 aluminum chips was investigated. Microhardness and electrical conductivity of the recycled samples were comparable with commercially produced EN AW 6082. Experiments were planned utilizing design of experiments approach. Both adaptive neuro-fuzzy interference system (ANFIS) and regression models were developed and compared to describe the influence of input SSR process parameters on electrical conductivity and microhardness. Density and metallographic analysis of the recycled samples were also performed.

Solid particle erosion wear behavior of severe plastically deformed AA7075 alloys

Abstract In this study, severe plastic deformation (SPD) and wear behavior of AA 7075 allosy widely used in aerospace, automotive and defence industries, has been investigated. The equal channel angular pressing (ECAP) process was applied to achieve an ultra-fine grain structure of homogenized AA 7075 materials. Solid particle abrasion behavior was impressed into homogenized and ECAP' ed materials via a variable particle impingement angle (PIA) and acceleration pressure. Microstructure and wear behavior of the tested materials were investigated using scanning electron microscopy (SEM) and a surface profilometer. In the studies conducted, it was observed that an increase in the number of ECAP passes with the effect of SPD, reduced the solid particle wear behavior.

Enhancement of Mechanical and Electrical Properties in Al 6101 Alloy by Severe Shear Strain under Hydrostatic Pressure

Samples of commercially received aluminum AA6101 alloy are homogenized, quenched, and subjected to 2, 4, and 8 passes of Equal Channel Angular Pressing (ECAP) with 200 MPa of applied backpressure. Tensile strength of the alloy's samples increases with the accumulated strain to the double value of 400 MPa after 8 ECAP passes, while electrical conductivity slightly decreases from 51.3 to 48.2%IACS. Aging at 130 °C for 72 h is used to restore conductivity with very small loss of strength. Moreover, the increase in conductivity is directly proportional to the number of ECAP passes and conductivity exceeds those values measured for the as‐received and solution treated states. Strong inhomogeneity of the microstructure and formation of a network of differently oriented shear bands during severe plastic deformation is observed, which is beneficial for simultaneous enhancement of mechanical and electrical properties.

Development of High-Performance SiCp/Al-Si Composites by Equal Channel Angular Pressing

Relatively low compactness and unsatisfactory uniformity of reinforced particles severely restrict the performance and widespread industry applications of the powder metallurgy (PM) metal matrix composites (MMCs). Here, we developed a combined processing route of PM and equal channel angular pressing (ECAP) to enhance the mechanical properties and wear resistance of the SiCp/Al-Si composite. The results indicate that ECAP significantly refined the matrix grains, eliminated pores and promoted the uniformity of the reinforcement particles. After 8p-ECAP, the SiCp/Al-Si composite consisted of ultrafine Al matrix grains (600 nm) modified by uniformly-dispersed Si and SiCp particles, and the composite relative density approached 100%. The hardness and wear resistance of the 8p-ECAP SiCp/Al-Si composite were markedly improved compared to the PM composite. More ECAP passes continued a trend of improvement for the wear resistance and hardness. Moreover, while abrasion and delamination dominated the wear of PM composites, less severe adhesive wear and fatigue mechanisms played more important roles in the wear of PM-ECAP composites. This study demonstrates a new approach to designing wear-resistant Al-MMCs and is readily applicable to other Al-MMCs.

Mechanical and microstructural variations in ECAP of Ti–6Al–4V alloy with equiaxed microstructure

The aim of this study is to investigate mechanical and microstructural variations of Ti–6Al–4V acquired through various equal channel angular pressing (ECAP) cycles. The ECAP of Ti–6Al–4V alloy with the first equiaxed microstructure was carried out by an isothermal warm and isothermal die method. ECA pressing carried out on cylindrical samples at 650 °C. Mechanical and microstructural investigations were performed concerning Ti–6Al–4V in the first state after 2, 4, and 8 passes. Optical microscopy (OM) investigation shows that alpha grain size increases and beta grain size decreases with the pass numbers increasing. Beta phase content initially decreases in the first two ECAP passes. The results show that more equiaxed alpha grains are achieved after four ECAP passes. Results of X-ray diffraction (XRD) analysis show that crystallite size decreases with the number of passes increasing. After two ECAP passes, a vivid increase in mechanical strength is observed; however, the increment dramatically slows down by the increasing number of passes.

Mechanical properties of an Al-Zn-Mg alloy processed by ECAP and heat treatments

An investigation was conducted to study the influence of equal-channel angular pressing (ECAP) and post-ECAP aging at 393 K for 20 h on the microstructures and tensile properties of a supersaturated Al-Zn-Mg alloy together with the effect of pre-ECAP heat treatments on the mechanical properties of the alloy after ECAP and after post-ECAP heat treatments. The results show that during ECAP processing for up to 4 passes for the supersaturated Al alloy there is a simultaneous occurrence of grain refinement, increases in the dislocation density and dynamic aging precipitation forming large numbers of fine spherical well-distributed precipitates which enhance the yield strength but decrease the ductility. During post-ECAP aging, there is a limited dislocation recovery with slight grain growth and the precipitate sizes increase together with the formation of a few larger platelet precipitates and the transformation of G.P. zones to η′ and η′ to η leading to a strength reduction after 4 passes of ECAP. The precipitates in the ECAP-processed alloy with pre-ECAP in the supersaturated state formed through dynamic aging precipitation are higher in their volume fraction, smaller in their size and more homogeneously distributed in the Al matrix than those in the alloy with pre-ECAP in the peak aging state which mainly come from the fragmented η′ existing in the matrix before ECAP. The strengths of the alloy both after ECAP processing and after post-ECAP heat treatments with pre-ECAP in the supersaturation state are higher than with pre-ECAP in the peak aging state.

Effect of equal-channel angular pressing and post-aging on impact toughness of Al-Li alloys

Overcoming the toughness inadequacy of Al-Li alloys is in urgent need for developing new low-density and high-performance aerospace aluminum alloys. In this research, continuous equal-channel angular pressing (ECAP) and post-aging were developed to significantly enhance the impact toughness of 1420 Al-Li alloy. The effects of the processes on microstructure evolution, impact absorbed energy and fracture surfaces of 1420 alloy were investigated. The results demonstrated that the impact toughness of ultrafine-grained (UFG) 1420 alloy after 8 ECAP passes at 573 K reached up to 26.6 J/cm2 at room temperature and increased sixfold compared with that of the coarse-grained sample, but the post-aging reduced the beneficial effect. The remarkable improvement after the warm ECAP was mainly due to the UFG microstructure, certain amount of dislocations, and the fine precipitates with uniform distribution, thereby making UFG 1420 alloys more attractive in aerospace applications.

Surface Properties and Erosion–Corrosion Behavior of Nanostructured Pure Titanium in Simulated Body Fluid

Titanium and its alloys are used in several industries, especially in medical and dental applications. In the present study, the surface properties of nanostructured commercially pure titanium (CP-Ti) and its erosion–corrosion (E–C) behavior in simulated body fluid were studied. Equal-channel angular pressing (ECAP) was performed at a high temperature (400 °C) to produce nanostructured grain samples of CP-Ti. Then, the effects of ECAP passes on the E–C resistance under various conditions were investigated via weight loss measurements. Optical microscopy and transmission electron microscopy observations were performed to investigate the microstructural changes of the material. The surface roughness of the CP-Ti samples was evaluated using an optical profiling system. Mathematical equations of the modified Finnie model were employed for the analytical analysis of the E–C behavior. Additionally, computational fluid dynamics was utilized to model the E–C behavior of CP-Ti. Overall, the results showed that the ECAP process improved the E–C resistance of CP-Ti. A difference of 12 pct was observed between the experimental and numerical results of E–C resistance, which is acceptable for practical applications

Exploration of equal channel angular pressing routes for efficiently achieving ultrafine microstructure in magnesium

This research explored the equal channel angular pressing (ECAP) routes for efficient microstructure refinement of pure magnesium. The samples were processed for a series of numbers of ECAP passes through three different routes (i.e. A, Bc, and C routes). The utilized ECAP mold had a large channel angle of 142° and the processing temperature was 200 °C. The microstructure and texture of the processed samples were characterized using optical microscope and x-ray diffraction technique. The results show that tension twinning deformation mechanism during an ECAP pass led to the formation of profuse twins in magnesium and the twinning/detwinning dominated microstructure refinement mechanisms. After 8 ECAP passes, both Bc and C routes reduced the length and width of twins to ~ 13 µm and ~ 3 µm respectively. Bc and C routes can refine the microstructure of magnesium more efficiently than A route. Among the three studied routes, Bc route achieved the most homogeneous microstructure with uniformly distributed twins, while both A and C routes resulted in heterogeneous microstructure.

Research on Grain Refinement Mechanism of 6061 Aluminum Alloy Processed by Combined SPD Methods of ECAP and MAC.

Equal channel angular pressing (ECAP) and multi-axial compression deformation (MAC) are severe plastic deformation (SPD) processes that produce bulk nanostructured materials with ultrafine grains. The grains could be observably refined by multi-pass of ECAP and MAC. This research proposed new routes of cyclic equal channel compression (CECC), which combines ECAP and MAC to increase the mechanical properties of 6061 aluminum alloy. The tests, which are conducted through electron backscattered diffraction (EBSD) and transmission electron microscope (TEM), were performed on the grain size, recrystallization distribution, misorientation distributions, dislocations, and secondary phase distributions of CECC-processed 6061 aluminum alloys on the purpose of exploring the mechanism of grain refinement. MEM is the short form for the CECC processing route of MAC + ECAP + MAC, which is one ECAP pass between two MAC passes. The tests results showed that the average grain size could reach to as much as 1.1 μm after two MEM deformation circles named MEM-MEM, with the non-annealing average grain size being 21 μm and recrystallization annealed average grain size being 28 μm. The dislocation cells, which could be transformed into sub-grains with the increase of the strain, were formed by the slip and the accumulation of dislocations. The secondary phase was Mg2Si, which could prevent the refined grains from growing up again by pinning at the grain boundaries. Above all, the dislocation proliferation and secondary phases will both lead to the grain refinement.

Three-dimensional microstructural analysis of fragmentation behavior of platelet Al3Ti particles in Al-Al3Ti composite deformed by equal-channel angular pressing

The fragmentation of platelet Al3Ti particles in an Al-Al3Ti composite by equal-channel angular pressing (ECAP) is investigated using three-dimensional (3D) microstructural evaluation and crystallography. The Al-Al3Ti composite comprises coarse platelet Al3Ti particles in an α-Al matrix. The ECAP of this composite is performed for up to 4 passes under processing routes A, Bc, and C. Route Bc produces the smallest Al3Ti particle fragments in comparison with the fragments produced under routes A and C. This is because that route Bc produces the largest number of shearing directions and shearing planes. Platelet Al3Ti particle fragments in the specimen deformed by ECAP under route A are homogeneously distributed along the deformation axis. In contrast, in the specimens deformed by four ECAP passes under routes Bc and C, the Al3Ti particle fragments are gathered into several groups. The fragment groups have a length similar to the initial length of the platelet Al3Ti particles. These spatial distributions of particle fragments can be explained by material flow of α-Al matrix during ECAP. Moreover, from 3D microstructural evaluation and crystallographic analysis of the Al3Ti particle fragments, it is found that the Al3Ti particles are preferentially fragmented on the twin boundary plane of {112}Al3Ti. Therefore, it is concluded that fragmentation of a platelet Al3Ti particle by ECAP occurs along the twin boundary plane after twin deformation.