ECAPed Samples Research Articles

Effect of Strain Rate Sensitivity and Strain Hardening Exponent of Materials on Plastic Strain Distribution and Damage Accumulation During Equal Channel Angular Pressing

Flow pattern and plastic strain distribution inside deformed sample are two important factors governing the microstructural uniformity of equal channel angular pressing (ECAP) processed materials. In the present study, the effects of strain hardening exponent (n) and strain rate sensitivity (m) on the characteristics of the ECAP process were investigated by the aid of finite element simulation. Investigated parameters are plastic strain distribution and accumulated damage. In addition, contour maps were generated to demonstrate mutual effects of n and m coefficients on the uniformity of plastic strain and maximum damage developed on ECAPed samples. Results showed that the effect of m and n values on plastic strain is more pronounced at downside regions of sample compared with upper regions. Also, at a constant strain rate sensitivity, the plastic strain is increased with decreasing strain hardening exponent due to the small corner gap formed in outer region of the intersecting area of two channels. Increasing strain rate sensitivity at constant strain hardening rate is accompanied by the formation of severely deformed area near downside of sample which leads to non-uniform strain distribution.

Microstructural, mechanical and acoustic emission-assisted wear characterization of equal channel angular pressed (ECAP) low stacking fault energy brass

Abstract Cu-37wt.%Zn brass samples have been ECAP processed using 1, 2, and 3 passes and then characterized using TEM, compression and tensile tests, indentation, scratching, wear with simultaneous monitoring acoustic emission and vibration acceleration. Mechanical tests showed higher mechanical strength, hardness, wear resistance as well as other characteristics of the ECAPed samples. TEM study demonstrated the microstructural evolution of samples after 1-, 2–3 pass ECAP. Structurally inhomogeneous microstructure composed of primary twin stacks and twin-free zones has been obtained after 1-pass ECAP. Further ECAP on these samples allowed revealing two deformation processes such as microtwinning in the twin-free zone and dislocation glide along the primary twin boundaries. The latter increased the inter-twin misorientation and transformed them into misoriented band structures. Wear test results revealed intense adhesion transfer and reduced wear on samples after ECAP. Acoustic emission and vibration acceleration signals have been obtained during wear and then used to characterize the wear mechanism. Primary twinning and microtwinning in the as-received and 1-pass ECAP samples, respectively, was identified by the AE signal median frequency peaks. On the contrary, the median frequency drops corresponded to the subsurface fracture development in 2- and 3-pass ECAP samples.

Austenite stability and mechanical properties of a low-alloyed ECAPed TRIP-aided steel

Equal channel angular pressing (ECAP) and post-ECAP heat treatment were conducted on a Fe-1.38Mn-0.67Si-0.56Al-0.014 Nb-0.18 C transformation-induced plasticity (TRIP) aided steel. The microstructure of unECAPed TRIP sample was mainly composed of polygonal ferrite, bainite, retained austenite (RA) and lath martensite, while lath martensite was not observed in ECAPed TRIP samples. The stability of retained austenite (RA) for unECAPed TRIP sample was mainly influenced by the carbon content in RA, while for ECAPed TRIP steel, it was dominated by the size of RA. Comparing the mechanical properties of the unECAPed samples with the ECAPed samples, the ultimate tensile strength (UTS) changed slightly, but the total elongation (TEL) increased from 25.6% to 39.8%. The 4 passes ECAPed TRIP sample exhibited excellent mechanical properties with the product of tensile strength and total elongation (PSE) of 29.4 GPa %, which was a consequence of TRIP effect and cooperative deformation of ferrite, bainite and austenite.

Workability Limits of Magnesium Alloy AZ31B Subjected to Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is an important severe plastic deformation process to produce ultrafine grained microstructures in metals and alloys. Magnesium and its alloys generally possess poor workability at temperatures below 250 °C. This investigation examines the influence of different passes and processing routes of ECAP on improving the workability of Mg alloy AZ31B. ECAP was carried out for three passes using a die of angle 120° using processing routes Bc and C. The operating temperature was 523 K for the first pass and 423 K for the subsequent two passes. The resultant microstructure and mechanical properties were determined. Workability of the alloy at 423 K (150 °C) was determined using upsetting experiments on cylindrical specimens machined from the annealed and ECAPed samples. Workability limit diagrams have been constructed for the various processed conditions. The workability data generated were also analyzed using five different workability criteria (also referred to as ductile fracture models) and the material constants for these five models were evaluated. Specimens processed by two passes through route C (pass 2C) exhibits better workability compared to other passes since the workability limit line after this pass shows maximum safe working area and lies above the other workability lines. Among the five different workability criteria investigated, the Freudenthal workability criterion is more suitable for prediction of failure in this alloy.

Effect of ECAP on Mechanical and Micro-Structural Properties Of Al7075-Ni Alloy

This research work is mainly focused on to study microstructure and mechanical properties of nickel reinforced aluminum 7075 alloy composites by equal-channel angular pressing (ECAP) process and ultrafine grained (UFG) of nickel reinforced aluminum 7075 alloy composites. The composites were prepared using liquid metallurgy technique. The content of nickel in the composition was varied from 2 to 8% (by weight) in steps of 2%. The ECAP processing was carried out using die with an intersecting channel angle of 120°. X-Ray Diffraction Technique (XRD) was used to confirm the percentage of reinforcement of in the composites. This study shows that severe plastic deformation has significantly improved the mechanical properties of nickel reinforced aluminium 7075 alloy composites compared to an alloy. Hardness test confirms that there is an increase in hardness for ECAPed samples at 8wt. % Ni and is 11% increase as compared to ECAPed pure Al7075 alloy and 40% compared to Non ECAPed 8wt. % Ni sample.

Influence of ECAP Processing on Fatigue Crack Nucleation on ZK60A Magnesium Alloy

Low-cycle fatigue tests were conducted on ZK60A magnesium alloy that were processed by equal-channel angular pressing (ECAP) method. The ECAP processing was carried out on a hot-extruded ZK60A alloy at a die temperature of 473K. Total pass number was four and the processing route was Route Bc. One of the ECAPed sample was annealed at 573K to induce grain coarsening. The low-cycle fatigue tests were conducted under a constant plastic strain amplitude of εpl=2×10-3, in air at room temperature. A hysteresis loop shape during the low-cycle fatigue tests depended on the sample: a tension-compression asymmetric shape was recorded in the as-drawn specimen having the tensile axis parallel to the extruction direction, while a symetric shape was seen in case of the tensile axis perpendicular to the extrusion direction. Deformation twinning during fatigue was most probably attribute to the asymmetric hysteresis loop shape. Because the asymmetric hysteresis loop was absent in the ECAPed specimen, it is possible that grain refinement suppressed the deformation twinning in the fatigue test. In the as-drawin specimen having the tensile axis parallel to the extrusion direction, a small crack was observed near a deformation twin. By contrast, a fatigue crack in the as-ECAPed specimen was generated along a shear band that was inclined to the tensile axis at 45°. After the ECAPed specimen was annealed at 573K, an intense shear banding and a subsequent crack nucleation were moderated. Accordingly, it can be said that the low-temperature annealing on the ECAPed ZK60A magnesium alloy reduced the fatigue crack nucleation sites.

Fabrication of an Ultra-Fine Grained Pure Titanium with High Strength and Good Ductility via ECAP plus Cold Rolling

Microstructure evolutions and mechanical properties of a commercially pure titanium (CP-Ti, grade 2) during multi-pass rotary-die equal-channel angular pressing (RD-ECAP) and cold rolling (CR) were systematically investigated in this work, to achieve comprehensive property for faster industrial applications. The obtained results showed that the grain size of CP-Ti decreased from 80 μm of as-received stage to 500 nm and 310 nm after four passes and eight passes of ECAP, respectively. Moreover, abundant dislocations were observed in ECAP samples. After subsequent cold rolling, the grain size of ECAPed CP-Ti was further refined to 120 nm and 90 nm, suggesting a good refining effect by combination of ECAP and CR. XRD (X-ray diffractometer) analysis and TEM (transmission electron microscope) observations indicated that the dislocation density increased remarkably after subsequent CR processing. Room temperature tensile tests showed that CP-Ti after ECAP + CR exhibited the best combination of strength and ductility, with ultimate tensile strength and fracture strain reaching 920 MPa and 20%. The high strength of this deformed CP-Ti originated mainly from refined grains and high density of dislocations, while the good ductility could be attributed to the improved homogeneity of UFG (ultra-fine grained) microstructure. Thus, a high strength and ductility ultra-fine grained CP-Ti was successfully prepared via ECAP plus CR.

Mechanical properties of ultrafine-grained AX41 magnesium alloy at room and elevated temperatures

Mechanical properties of ultra-fine grained AX41 magnesium alloy were investigated at ambient and elevated temperatures. The study focuses on the effect of the grain size, dislocation density and crystallographic texture on the strength and formability. Commercial AX41 magnesium alloy was processed by hot extrusion followed by eight passes of equal-channel angular pressing at temperatures of 220 and 250 °C. Material was tested in tension in the direction parallel to the ECAP processing at temperatures up to 200 °C. In this temperature range, the ultra-fine grained structure is thermally stable. The strength of the material at room temperature is significantly affected by texture. In particular, basal texture component formed in ECAP samples is tilted by 40° from the processing direction and therefore facilitates plastic deformation by basal slip. In contrast, the texture of extruded material is not suitable for basal slip deformed in the same direction. The effect of texture on strength can outweigh the effect of reduced grain size and increased dislocation density in ultrafine-grained AX41 alloy. At elevated temperatures, starting from 100 °C, the deformation behaviour is controlled simultaneously by dislocation slip and grain boundary sliding (GBS). Mechanical properties of the as-cast coarse grained material are virtually independent of the temperature. On the other hand, the reduced grain size of UFG material caused the progressive decrease of the proof stress and, simultaneously, considerably improves the ductility. The study systematically shows that the effect of microstructural features on mechanical properties of coarse grained and UFG AX41 alloy strongly depends on the dominant mechanism of plastic deformation.

Diffusional bonds in laminated composites produced by ECAP

Abstract The microstructure, diffusional and mechanical bonding behavior and microhardness distribution of laminated composites fabricated by ECAP process were investigated. Al-Cu and Cu-Ni laminated composites were produced by ECAP process up to 4 passes at room temperature and high temperature (300 °C). The results of microstructure characterization by SEM and shear strength test revealed that the joints between the layers of 4-pass ECAPed samples were considerably stronger than those of 1-pass ECAPed samples due to tolerating higher values of plastic deformations during ECAP. Furthermore, shear strength data showed that increasing ECAP temperature caused a notable increase in shear strength of the specimens. The reason lies in the formation of diffusional joint between the interface of both Al/Cu and Cu/Ni layers at high temperature. The shear bonding strength of ECAPed Cu/Ni/Cu composite at high temperature was remarkably higher than that of ECAPed Cu/Al/Cu composite.

Microstructure and homogeneity of semi-solid 7075 aluminum tubes processed by parallel tubular channel angular pressing

Semi-solid processing is a new developing technology for the fabrication of intricate parts at low temperatures in comparison with conventional casting routes. In this research, a parallel tubular channel angular pressing (PTCAP) was used as a pre strain-inducing process, and the influence of the number of PTCAP passes and semi-solid heating parameters on the microstructural characteristics of Al7075 tubes was investigated. The results demonstrated that PTCAP process could successfully be used as a best pre-straining method for tubular samples showing semi-solid microstructures. As the temperature is increased, the solid particle size first decreased, then increased, and gradually became more spherical. The appropriate condition for the subsequent semi-solid forming process was gained at reheating temperature of 620 oC. The suitability of this temperature was confirmed by the uniform distribution of grains. The grain size and shape factor both increased along with increasing the holding time. The distribution of the solid particles was strongly dependent upon the holding time and became uniform as the holding time increased. Comparison of the grain size and shape factor between ECAPed and PTCAPed samples revealed a high capacity of the PTCAP process as a strain-inducing stage. Also the two-pass PTCAP samples exhibited higher hardness than one-pass treated samples in the semi-solid state.

Effects of solution treatment and sheath on mechanical properties of Al7075 processed by ECAP

Al7075 as a hard-to-work alloy is processed difficultly by Equal channel angular pressing (ECAP) at room temperature. In this paper, experiments were conducted at several heat treatment conditions and also with a new developing strategy using sheath copper to process this alloy at room temperature. Mechanical properties were evaluated by tensile and micro hardness tests. The results demonstrated that the ultimate and yield strength of ECAPed aged samples improved. Tensile test of 4 pass processed samples with copper sheath indicated an increase in the strength in comparison with samples without sheath. The hardness test results showed more uniform distribution of hardness in their cross section for copper sheath casing samples. It was found that by increasing the copper sheath thickness, the hardness variation decreased while the average hardness increased. By considering the time limitation for the process, only solid solution samples without sheath could be successfully ECAPed in 2 passes and samples with sheath could be ECAPed only in one pass.

Deformation Heterogeneity Study of a 6061-T6 Aluminum Alloy Processed by Equal Channel Angular Pressing

Among the severe plastic deformation techniques, the equal channel angular pressing (ECAP) has drastically improved the mechanical properties of the processed alloys. However, information regarding friction phenomenon, which modifies the deformation at the surface and the heterogeneity microstrain state produced by the process itself, is still scarce. In the present work, the deformation heterogeneity and the friction effect, at the surface in the bulk material of the 6061-T6 aluminum alloy processed by ECAP, is presented and discussed. The residual stress (RS) measurements were performed by means of X-Ray diffraction. By means of synchrotron diffraction, volumetric sections of the ECAPed samples were characterized. Finite element analysis showed a good agreement with the experimentally obtained residual stress and microhardness mapping results. The study also showed that the highest deformation zones were located at the outer parts of the deformed samples (top and bottom), while the inner zone showed strain oscillations of up to 49±2 MPa.

WITHDRAWN: Microstructure and Mechanical Properties of Fe-canned Pure Mg after a Single ECAP at Room Temperature [Materials Science & Engineering A 700 (2017) 163–167

Pure Mg (99.99%) bar, which was cladded by a drilled pure Fe coat, was subjected to equal channel angular pressing (ECAP) at room temperature through a die with a crossing angle of 90° between two channels. Then an ECAPed pure Mg sample was successfully prepared without obvious cracks. Evolutions of microstructure and mechanical properties for deformed pure Mg were investigated in detail. After one-pass ECAP, grains are obviously refined compared with the initial one and inhomogeneous microstructure is arranged along the shearing direction. (0001), (10-10) and (10-11) textures were formed, which were inclined by about 40° from normal direction towards extruded direction (ND-ED) due to the dramatic shearing deformation. At the same time, tensile properties including yield strength (YS) and ultimate tensile strength (UTS) are highly improved as a result of hard working,whereas uniform elongation (UE) is decreased.

Finite Element Simulation of Pure Aluminum Processed by ECAP Using New Die Design

In the present work, a new die is designed for ECAP and the performance is analyzed using finite element modeling Deform 3D commercially available software. Channel angle (ϕ) 900 and corner angle (ψ) 200 has been considered for the study. Analysis is done for both the circular and the square specimen of Φ 25 mm and 22.15 mm × 22.15 mm × 80mm. The present work focuses on effective strain up to three passes using finite element analysis for both the dies in Route A and C and it is compared to the experimentally validated results. From the ECAP samples, tensile test and Vickers micro hardness measurement were validated. The recently designed die reduces the effect of friction in the process; it increases the hardness of the material and the grain refinement. The mechanical property was enhanced much in the new die design as compared to the existing conventional die.

Formation and Corrosion Resistance of Micro-Arc Oxidation Coating on Equal-Channel Angular Pressed AZ91D Mg Alloy

A commercial AZ91D Mg alloy, after bulk grain refinement by various passes of equal-channel angular pressing (ECAP), was selected for micro-arc oxidation (MAO) in silicate electrolyte, corrosion testing in 3.5 wt % NaCl solution and morphology analyses. The results showed that a large number of ECAP passes resulted in the homogeneous ultrafine-grained (UFG) Mg substrate with broken second-phases. The high-energy defects in the ECAPed samples lowered the anodizing potential of the MAO process, but the partial discharge was severe for those samples below eight passes. Increasing the ECAP pass, the compactness and thickness of the MAO coating first decreased and then increased. Due to the compact coating and the existence of Mg2SiO4, the coated alloy with 16 ECAP passes has a lower corrosion rate and a larger Rt value. Besides the well-known strengthening-toughening effect, grain refinement via multi-pass ECAP can improve surface protection of the MAO coating on the UFG Mg alloy.

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.

Bulk Ultrafine-Grained Interstitial-Free Steel Processed by Equal-Channel Angular Pressing Followed by Flash Annealing

Interstitial-free steel workpieces are deformed by equal-channel angular pressing (ECAP) for equivalent strain εvm = 3 and εvm = 21 followed by flash annealing. Microstructures are analyzed by optical microscopy, scanning electron microscopy and transmission electron microscopy. Mechanical properties are evaluated by hardness testing. Yield strength of materials is calculated from hardness values. Flash annealing (at 675 °C) of ECAPed samples for εvm = 3 and εvm = 21 results in abnormal subgrain growth and abnormal grain growth, respectively. Flash annealing at 700 °C of ECAPed (at εvm = 3) IF steel converts abnormally grown subgrains to grains which serve as nuclei for recrystallization and that result in bimodal grain size distribution. Bimodal grain size distribution is also produced when ECAPed IF steel for εvm = 21 is flash annealed at 675 °C due to abnormal grain growth or secondary recrystallization. Flash annealing of IF steel samples ECAPed for low εvm, in the temperature range 600-675 °C, decreases the hardness continuously with increase in the annealing temperature but it increases at high εvm. The former is due to annihilation of defects but the later is caused by ordering of nonequilibrium boundaries. The hardening and strengthening behaviors are similar.

Microstructural development during equal channel angular pressing of as-cast AZ91 alloy

Equal channel angular pressing (ECAP) was successfully applied to a typical as-cast AZ91 alloy with very coarse initial grains without the need for a prior thermomechanical treatment. A two-step ECAP tests were carried out in which the first pass was conducted at 623K to overcome cracking, and the next passes were performed at lower temperature to reduce grain growth. In order to evaluate the influence of ECAP temperature on the evolution of microstructure and mechanical properties, ECAP processing was carried out at different temperatures of 593K, 563K, and 533K at the second step. According to microstructural investigations, simultaneous occurrence of dynamic recrystallization (DRX) and dynamic precipitation during this two-step ECAP processing led to a noticeable grain refinement and formation of a homogeneous microstructure. It was demonstrated that lower ECAP temperatures accelerate dynamic precipitation and DRX resulting in more rapid formation of fine and uniform microstructures. The tensile properties of ECAPed samples were evaluated at room temperature, and it was proved that ECAP processing can simultaneously improve both ductility and strength of the alloy. It has been indicated that a combination of DRX ratio, and dynamic precipitation during ECAP plays a decisive role in improving the mechanical properties.

Microstructural evolution and fracture mechanism of a new Al–Zn–Mg–Cu–Zr alloy processed by equal-channel angular pressing

Equal-channel angular pressing (ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained (UFG) materials. A new Al–Zn–Mg–Cu–Zr alloy was subjected to ECAP experiment in Route BC (i.e ., rotated 90° in the same sense between each pass). The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope (OM), X-ray diffraction (XRD), tensile test (at room temperature), and scanning electron microscope (SEM). The results show that the main strengthening phase of the alloy is MgZn2, whose content increases apparently after ECAP, the dislocation density increases by one order of magnitude, the hardness value of the 1 pass ECAPed sample increases by 53 %, the ultimate tensile strength (UTS) increases by 29 %, and the true strain increases by 15.4 %. But the further increase in the strength with the passes increasing would cost a slight drop in the true strain. The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.

Metallurgical and Mechanical Properties of Mild Steel Processed by Equal Channel Angular Pressing (ECAP)

In the present work the annealed mild steel was processed by equal channel angular pressing (ECAP) at different temperatures of 200, 250, 300 and 350 °C. The mild steel of 60 mm height and 12 mm diameter was ECAPed for two passes through 120° die channel and 20° corner angle. The microstructure was observed through an optical microscope, the fractions of ferrite, pearlite and grain size measurement were carried out. Mechanical testing such as Vickers hardness and tensile test were conducted for ECAPed samples and the properties were compared with base metal. Inter-critical annealing was carried out to get the better combination of strength and ductility.