Ultra-fine grained bulk CP-Ti processed by multi-pass ECAP at warm deformation region

In order to refine the grain size of commercially pure titanium (CP-Ti) to a submicrometer scale, equal channel angular pressing (ECAP) was attempted at a temperature range of 200–300 °C. The experiments revealed that, 250 °C was the minimum temperature at which ten passes of ECAP could be performed in a 105° die without the cracking of billets. An ultrafine-grained (UFG) microstructure with a mean grain size of 183 nm was achieved after 10 passes. The processed CP-Ti displayed high tensile strength of 892 MPa and high elongation to failure of 20.5%. The enhancement in mechanical properties is explained in terms of grain refinement and dislocation density increasing. The high ductility of UFG pure Ti with the absence of strain hardening behavior is attributed to its enhanced strain rate sensitivity.     

Finite element analysis of rotary-die equal channel angular pressing

In this paper, the finite element method (FEM) was applied to analyze the plastic flow and strain hardening behavior of pure copper, subjected to rotary-die equal channel angular pressing (RD-ECAP) up to four passes. The die was rotated 90° counter clockwise between the passes in the simulation. The effective strain distribution and load–stroke curves were investigated. The load was increased with the number of rotary-die equal channel angular pressing passes. The results show that, plastic deformation becomes inhomogeneous with the number of passes due to an end effect, which was not found seriously in conventional equal channel angular pressing (ECAP). Especially, decreasing corner gap with increasing the number of passes was observed and explained by the strain hardening effect.     

ECAP process capability in producing a power transmission bimetallic rod

In recent years, bimetallic rods have been considered by researchers due to the industrial applications in power transmission systems. In this paper, an Al-Steel rod is produced by equal channel angular pressing (ECAP) process. First, severe plastic deformation is applied to Al-Steel rod by ECAP process, and then some experiments such as microhardness measurement, interface strength evaluation, scanning electron microscope (SEM), and microstructure analysis have been accomplished to assess the capability of ECAP process in producing a power transmission bimetallic rod. Then, to evaluate significant parameters on strain distribution and pressing force, the FEM has been utilized. After verification of the numerical method, the effect of several parameters such as diameter, location, peripheral materials, and die angle on the applied strain and homogeneity are studied. The results indicate that the steel and aluminum hardness are increased about 59 and 61% after four passes ECAP, respectively. Also, the average grain size of steel core is reduced about 79% at the same conditions after four passes. In addition, the images received from SEM show that the interfaces between steel and aluminum have been improved significantly.     

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

Abstract

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.     

Thermophysical Properties of Aluminum 1060 Fabricated by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) has the advantage of enabling an ultrafine grain size. Aluminum 1060 is used as a power plant material because of its favorable electrical properties. However, the weak strength of aluminum limits its application. In this study, the thermal conductivity and electrical conductivity of Al 1060 made by ECAP was investigated. ECAP was conducted through the die having a channel angle of 90° and a corner angle of 20° at a temperature of 473 K with a strain rate of 2 mm · s⁻¹. The specimen was then processed with 1 to 8 passes by the route Bc method with 90° rotation. In the case of eight passes, the grain size was reduced to as small as 300 nm. As a result of the ECAP, the tensile strength was raised from 75 MPa to 134 MPa, while the electrical conductivity did not show a significant difference after eight passes. The thermal conductivity gradually decreased with ECAP passes, because of the decreased grain size by ECAP.     

The development of hardness homogeneity in aluminum and an aluminum alloy processed by ECAP

Equal-channel angular pressing (ECAP) is an effective fabrication process for obtaining ultrafine-grained materials. This paper examines the development of homogeneity in materials processed by ECAP with emphasis on samples of pure aluminum and an Al-6061 alloy processed by ECAP for up to 8 passes at room temperature. The Vickers microhardness was recorded on the polished cross-sectional planes of each as-pressed billet and the results are plotted in the form of contour maps to provide a pictorial depiction of the hardness distributions throughout the cross-sections. The factors influencing the homogeneity are examined, including the die corner angle within the ECAP die and the number of imposed passes. It is shown that good homogeneity may be achieved through ECAP processing when the number of passes in ECAP is reasonably high.     

Microstructure and mechanical properties of ultrafine grain ZK60 alloy processed by equal channel angular pressing

The microstructure evolution and tensile properties of ZK60 magnesium alloy after equal channel angular pressing (ECAP) have been investigated. The results show that the two-step ECAP process is more effective in grain refinement than the single-step ECAP process due to the lower deformation temperature, a mean grain size of ~0.8 μm was obtained after two-step ECAP process at 513 K for four passes and 453 K for four passes. The EBSD examination reveals that ZK60 alloy after two-step ECAP process exhibits a more homogeneous grain size and misorientation distribution than single-step ECAP process. Both alloys after ECAP process present similar strong {0002} texture. The tensile strength of two-step ECAP alloy has also been improved compared with the single-step ECAP alloy. The strengthening effect was mainly ascribed to grain refinement.     

Texture and microstructure evolution in ultrafine-grained AZ31 processed by EX-ECAP

Extruded AZ31 alloy was processed by equal channel angular pressing (ECAP) up to 12 passes at 180 °C following route B_c, i.e. rotating the sample 90° between individual passes. Microstructure evolution was investigated using EBSD and TEM, as a function of strain imposed by ECAP. The first ECAP pass resulted in the formation of a new texture component which relates to the bimodal grain structure observed in this specimen. The grains larger than 10 μm show the orientation changes corresponding to the ECAP shear, which is characterised by the rotation of the basal poles by approximately 40° from the initial orientation. The fine grains with the average size of 1 μm maintain the initial orientation. The character of the bimodal grain structure and the distinct texture components between large and small grains remained unchanged up to 4 ECAP passes. Further ECAP pressing to 8 and 12 passes leads to a grain refinement through the whole sample volume and the orientation changes of all grains corresponding to the ECAP shear.     

Avoiding cracks and inhomogeneities in billets processed by ECAP

Although equal-channel angular pressing (ECAP) is now an established technique for producing bulk ultrafine-grained metallic materials, processing difficulties may arise because of the occurrence of cracking or inhomogeneities. This problem is examined with reference to experimental data for aluminum and magnesium alloys and a Pb–Sb alloy. It is shown that effective procedures are available for avoiding the development of inhomogeneities and the cracking of billets during ECAP: these procedures include introducing a pre-deformation of the as-cast material prior to ECAP, decreasing the strain produced in each ECAP pass by using dies with angles higher than 90°, and controlling the rotation of the billets between sequential passes.     

Microstructural evolution in an aluminum solid solution alloy processed by ECAP

Samples of an Al-1% Mg solid solution alloy were processed by equal-channel angular pressing (ECAP) at room temperature for totals of 1-12 passes and the microstructures of the processed samples were examined using orientation imaging microscopy. The results demonstrate the alloy achieves a reasonably stable microstructure after 6 passes through the ECAP die with an ultimate equilibrium grain size of ∼700 nm. Measurements show both the fraction of high-angle boundaries and the average boundary misorientation increase with increasing numbers of passes up to 6 passes but thereafter there is only a minor additional increase up to 12 passes.     

Deformation behavior of consecutive workpieces in equal channel angular pressing of solid dies

In this study, consecutive workpiece equal channel angular pressing (ECAP) in solid-dies, where the second workpiece is successively deformed without splitting and reassembling the die after the first workpiece processing, is employed to reduce the processing time in ECAP. The plastic deformation behavior of the two workpieces was investigated in terms of strain homogeneity, load, and defects using the finite element method (FEM). The experimental deformations of the consecutive workpiece during ECAP were compared with the FEM results, and it was found that the deformation was more heterogeneous in the second workpiece when compared with the first workpiece. The primary reason behind these findings is that the deformed geometry of the second workpiece was a back slant type and the first deformed workpiece provided back pressure to the second workpiece. Furthermore, the folding defect was less pronounced in the second workpiece because of the back slant head shape. Despite the less homogeneity in strain, the ECAP of the consecutive workpieces is an effective process for less defective materials and increases process efficiency.     

Effect of equal channel angular pressing on fracture toughness of Al-7075

In this paper, influence of equal channel angular pressing (ECAP) on the fracture behavior of Al-7075 alloy is experimentally investigated. The specimens are successfully processed by ECAP methodology up to four passes using different routes. Transmission electron microscope (TEM) images showed that after four passes of ECAP, the average grain size is refined from 40 μm to less than about 500 nm. The percentage increase in yield strength, ultimate strength and microhardness of the specimens after four ECAP passes was 230, 90 and 110 respectively. Standard tests on the disk-shaped compact DC(T) specimens showed that fracture toughness is decreased up to 8% at the first ECAP pass while after four passes, this parameter roused to 17% higher than that of annealed condition. Furthermore, scanning electron microscope (SEM) micrographs demonstrated that ductile fracture mechanism with large dimples occurred in the annealed samples, changed to limited ductile fracture with fine dimples after ECAP process. This research provides new insights into the effect of ECAP and grain refinement on the fracture behavior of materials.     

铸态AZ81镁合金ECAP态组织与性能研究

采用自制的90°模具,经Bc路径在温度为300℃下研究对比了铸态及不同道次的等通道挤压(ECAP)态AZ81镁合金微观组织和力学性能.结果表明ECAP随着挤压道次的增加,AZ81镁合金显微组织和力学性能发生显著变化.当挤压到4道次,平均晶粒尺寸由原来铸态的145um细化为9.6um,拉伸断口韧窝明显增多;抗拉强度从180 MPa提高到306 MPa,延伸率和硬度分别达到15.8%和142HL.分析表明,AZ81镁合金在高温挤压过程中Mg17Al12相粒子被破碎,并部分溶入基体,$-Mg基体与%-Mg17Al12相互相阻碍其晶粒长大,获得细小晶粒组织.     

Grain refinement in as cast Al–Mg–Mn alloy during high temperature equal channel angular pressing

Abstract

An as cast Al–Mg–Mn alloy with coarse equiaxed grain structure was processed by equal channel angular pressing (ECAP) at 350°C up to eight passes. Systematic studies were made on the microstructural evolution during ECAP by optical microscopy, electron backscattered diffraction and TEM. Equal channel angular pressing led to a considerable grain refinement, resulting in an average cell size of about 1 μm and a fraction of high angle boundaries of 75% after eight pressing passes. Deformation bands were not developed during the ECAP process, and a reasonably equiaxed substructure was obtained even after one pass. The main mechanism of grain refinement was attributed to the continuous dynamic recrystallisation based on the motion of deformation induced dislocations. Discontinuous recrystallisation at grain boundaries and triple junctions also contributed to the refinement, which played an important role especially at high strain of eight passes.     

Influence of equal channel angular pressing in an acute angle die with a back pressure notch on grain refinement,torsion and mechanical properties of aluminium

Severe plastic deformation improves the strength of a metal by strain hardening. Of the various severe plastic deformation processes, equal channel angular pressing proves to be the right candidate for bulk metal processing. Extensive works were carried out on equal channel angular pressing with channel angle ranging from 90° to 120 ° with or without back pressure on the exit channel. Numerical analyses suggest that reducing the channel angle below 90° would enhance the magnitude of strain imparted and, with prediction of a lesser strain homogeneity in such cases. Hence an acute angled equal channel angular pressing die with a back‐pressure notch sunken into the roof of the exit channel was designed, fabricated and was used for processing pure aluminium. Various mechanical properties of the processed materials were tested and acute angle processing imparted superior tensile strength to the work pieces in a single pass that would require several passes in a conventional equal channel angular pressing die. Substantial improvement in grain refinement and torsional properties was identified.     

Microstructure and mechanical properties of equal channel angular pressed Mg–Y–RE–Zr alloy

The microstructure and mechanical properties of equal channel angular pressed (ECAP) Mg–Y–RE–Zr alloy (WE43) are examined. Results show that after ECAP, the average grain size remarkably decreases from ～50?µm at initial state to ～1.5?µm through ECAP for four passes and the homogeneity of microstructure also improves gradually. Meanwhile the secondary-phase β-Mg₅RE morphology has obvious transformation from plate-like to spherical. Moreover, the initial random texture is converted to the strong (0002) basal texture. The ultimate tensile strength and yield strength increase in all passes. However, the ductility exhibits a tendency of increase from 1 to 4 passes then decrease from 4 to 12 passes. The variation in strength and ductility is attributed to the effect of specific microstructure evolution.     

Effect of combining plane-strain compression with equal channel angular pressing on mechanical properties and texture development in an Al alloy

Commercial purity aluminum (1050) was processed via equal channel angular pressing (ECAP) to one, two, and four passes using route B_c in a 90° channel die, and subsequently compressed in plane strain in two different loading directions, and to two different strain levels. One of the plane-strain-loading directions is parallel to the ECAP forward direction, while the other is perpendicular to it. The flow response in plane-strain compression of the ECAP processed samples revealed an anisotropic behavior, one loading direction systematically gave higher flow stresses. A strain path change parameter was calculated for the two deformation schemes, to justify this anisotropic behavior. Texture evolution, of the plane-strain-compressed samples, was measured, and a transition to the rolling texture was always evidenced. The evolution of the main ideal rolling-texture components obtained from such a combination of deformation schemes, ECAP and plane-strain compression, is presented.     

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5%Cr alloy processed by severe plastic deformation

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5% alloy subjected to equal channel angular pressing (ECAP) by route A and cold rolling with and without aging treatment were investigated. The lamellar grains in thickness of 100 nm were obtained after eight ECAP passes. They were not further pancake shaped, but fragmentary and obtained less sharp boundaries with more dislocations in addition to cold rolling. After aging at 450 °C for 1 h, high density of dislocations and some coarse grains were observable after ECAP and the additional cold rolling, respectively. The tensile tests show that tensile strength arrived at 460 MPa and 484 MPa after four and eight passes of ECAP, respectively, the corresponding tensile strength increased to 570 MPa and 579 MPa after the additional cold rolling. However, the electrical conductivity was not more than 35% IACS. It was proved that four passes of ECAP followed by 90% cold rolling and aging at 450 °C for 1 h offered a short process for Cu-0.5%Cr alloy to balance the paradox of high strength and electrical conductivity, under which the tensile strength 554 MPa, elongation to failure 22% and electrical conductivity 84% of IACS could be obtained. The high strength was explained by precipitation strengthening and fine grain strengthening.     

T-shaped equi-channel angular pressing of Pb–Sn eutectic and its tensile properties

Equi-channel angular pressing (ECAP) of a Pb–Sn eutectic alloy up to six passes in a T-shaped die, rather than a conventional L-shaped die, was studied for grain refinement. The effect of ECAP on the hardness and tensile properties was studied. Microstructure predominately changed in the early part of the ECAP process and became equiaxed and uniformly distributed in both the longitudinal and the transverse sections after four passes. There occurred substantial softening over the first two passes—hardness of 10 Hv, yield strength of 14.2 MPa and tensile strength of 16.3 MPa in the as-cast condition decreased upon two passes to 6 Hv, 9.7 MPa and 13.0 MPa, respectively. The ductility (% elongation) increased drastically from <50% in the as-cast condition to 150% upon two passes, and further increased to 230% after four passes. Various tensile properties and concurrent microstructural evolution were used to develop a mutual relationship among them.     

An investigation on the effects of equal channel angular pressing on the mixed‐mode fracture toughness and mechanical properties of 6063 aluminium alloy

In this study, effects of equal channel angular pressing (ECAP) on the mixed‐mode fracture toughness of Al‐6063 were investigated. The ECAP process continued up to 5 passes without failure. Grain refinement was obvious after 5 passes of the ECAP process. The average grain size reduced from 45μm to less than 1μm, and textural studies shows aligning the grains in known directions. After 4 passes, yield and ultimate strengths increase respectively from 100 and 209 MPa to 300 and 375 MPa and reduction in elongation was also observed. The microhardness improved after the process. The fracture toughness for different orientations was measured. For pure mode I (opening mode), its value decreased after the first pass from 18.4 to 15.71  ; however, it increased to about 18.8  after the fifth pass. For mixed‐mode loading condition, different orientations were investigated. The results revealed different fracture toughness reductions after the first passes of the process for specimens with different orientations. The fracture surfaces were studied by using scanning electron microscope, and refined equiaxed dimples were observed after the ECAP process.