Subsequent Equal Channel Angular Pressing Research Articles

Impact of ECAP at 300 °C on the microstructure and mechanical properties of the quenched Zr–2.5%Nb alloy

We investigated the microstructure of the Zr–2.5%Nb zirconium alloy after subjecting it to equal-channel angular pressing (ECAP) and found that ECAP at 300 °C increases the strength by 140 to 180 %. Notably, unlike other studies, our alloy did not show complete dissolution of niobium particles, which may be due to the reduced diffusion rates at the lower deformation temperature of 300 °C. Pre-treatment involving quenching before severe plastic deformation was also studied, which developed a lamellar structure introducing additional boundaries that facilitated grain refinement during subsequent ECAP. The strength of the alloy was further enhanced by solid-solution hardening, achieved through the complete dissolution of the Nb particles into the matrix post-quenching. This process resulted in a 2.3-fold increase in yield strength after quenching plus ECAP compared to the initial coarse-grained state.

Overcoming the strength-ductility tradeoff of a 3D-printed Al-Si alloy by equal channel angular pressing

The integration of additive manufacturing and severe plastic deformation has produced an Al-Si alloy with superior mechanical properties. The novel processing pathway effectively avoids strength-ductility trade-off, resulting in an elongation increase of three times while maintaining a comparable yield strength to that of the original condition. The implementation of an intermediate annealing heat treatment (HT) before the subsequent equal channel angular pressing (ECAP) processing resulted in the most favorable combinations of strength and ductility. The ECAP process transformed the ultrafine interconnected eutectic network into ultrafine particles. This process also led to the formation of a heterogeneous grain size and the transformation of the 3-dimensional network of aluminides (Al2Cu) and Si-enriched precipitates into particles with varying sizes, ranging from 4 nm to 500 nm. In contrast, the ECAP processing without an intermediate annealing heat treatment led to a maximum yield strength increment of 22%. Notably, this enhancement in strength was achieved while preserving comparable levels of elongation to those observed in the as-built material. Hence, achieving the optimal combination of yield strength and ductility ratio demands a careful balance between various strengthening mechanisms, including subgrains and precipitates.

Изменение структуры, механических и коррозионных свойств сплава системы Mg–Zn–Zr, подвергнутого равноканальному угловому прессованию

Magnesium alloys are considered promising materials for the production of bioresorbable implants. Their main disadvantages are low strength and corrosion resistance in biological environment. In the work, the authors studied the effect of severe plastic deformation using the equal channel angular pressing (ECAP) method on the structure, mechanical properties, and corrosion resistance of the Mg–8.6Zn–1.2Zr magnesium alloy. It was identified that one ECAP cycle at 400 °C leads to a substantial hardening of the Mg–8.6Zn–1.2Zr alloy by ~10 %, up to 330 MPa. Structural studies showed that dynamic recrystallisation plays a significant role in the structure transformation. ECAP leads to the formation of a bimodal structure with large deformed grains with an average transverse size of 20±4 µm and recrystallised grains with an average transverse size of 6±2 µm. It was found that with a decrease in the strain temperature up to 250 °С, the process of deformation-induced decay of the supersaturated solid solution takes place. Electrical conductivity of a sample after ECAP at 400 °C amounted 29±2 % according to the International Annealed Copper Standard (IACS), while second ECAP cycles lead to an increase in the electrical conductivity up to 32±2 % IACS. Using the electrochemical corrosion method, the authors found that one ECAP cycle at 400 °C leads to a slight decrease in the corrosion resistance of the alloy under study compared to the initial state. The study showed that the corrosion current increases from 24 to 32 µA/cm2, while the subsequent ECAP cycle at 250 °С increases the corrosion current more than twice (up to 57 µA/cm2).

Investigation of Microstructure and Mechanical Properties of SLM-Fabricated AlSi10Mg Alloy Post-Processed Using Equal Channel Angular Pressing (ECAP).

With the aim of improving the excellent mechanical properties of the SLM-produced AlSi10Mg alloy, this research focuses on post-processing using ECAP (Equal Channel Angular Pressing). In our article, two different post-processing strategies were investigated: (1) low-temperature annealing (LTA) and subsequent ECAP processing at 150 °C; (2) no heat treatment and subsequent ECAP processing at 350 °C, 400 °C and 450 °C. The microstructure and mechanical properties of this alloy were analyzed at each stage of post-treatment. Metallographic observations, combined with SEM and EBSD studies, showed that the alloys produced by SLM have a unique cellular microstructure consisting of Si networks surrounding the Al-based matrix phase. Low-temperature annealing (LTA), followed by ECAP treatment, facilitated the microstructural evolution of the alloy with partial breakup of the Si network and observed nucleation of β-Si precipitates throughout the Al matrix. This resulted in a Vickers microhardness of 153 HV and a yield strength of 415 MPa. The main results show that post-processing of SLM-produced AlSi10Mg alloys using ECAP significantly affects the microstructural evolution and mechanical properties of the alloy.

Modeling of texture evolution in copper under equal channel angular pressing

Abstract Texture evolution was analyzed with the full-constraint Taylor model for an idealized perfectly plastic face-centered cubic material as well as for real, strain-hardening copper subjected to equal channel angular pressing (ECAP). For the idealized material, the stress in the plastically deformed part of the billet was shown to be uniform leading to complete filling of the die. Finite element simulations showed that plastic deformation is localized in a narrow shear zone and that the plastic strain and texture in the billet become uniform after ECAP. A simplified recipe for texture calculation akin to that proposed by Gholinia et al. was suggested: it reduces the deformation under ECAP to a combination of two rotations separated by tension-compression. For the case of copper, a strain hardening model based on dislocation density evolution was used. It was shown that due to significant strain hardening during the first ECAP pass, the flowing material does not fill the outside die corner and a strain and texture non-uniformity develops. A gradual decrease of the strain hardening in subsequent ECAP passes leads to a more uniform strain and texture across the billet. The simulated pole figures were shown to be in good agreement with the neutron diffraction data for copper deformed by ECAP (Routes A, Cr, Bγ and Bcr) suggesting that the model used provides a reliable modeling tool for simulating texture evolution under ECAP.

Optimizing microstructure and mechanical properties of biomedical Mg–Y–Zn–Mn alloy with LPSO phases by solution treatment plus equal-channel angular pressing

Long-period stacked ordered (LPSO) Mg–Y–Zn alloys have shown great medical prospects. To explore the impact of LPSO phase evolution on mechanical properties, a new biomedical Mg-2.2Y-1.1Zn-0.4Mn (wt.%) alloy prepared by solution treatment plus equal-channel angular pressing (ECAP) was systematically investigated. The results indicate that massive 18R LPSO networks along α-Mg grain boundaries are disintegrated during solution treatment of the as-cast alloy, whereas 14H lamellas are precipitated in α-Mg grains. Following a similar dispersion of 14H precipitated phases, the remnant 18R network phase was gradually extended, broken, and refined throughout the subsequent multi-pass ECAP process. The refined LPSO phases promote dynamic recrystallization (DRX) during the severe deformation process and improve mechanical properties of the obtained fine-grained alloy. After 773K solution treatment for 10h plus 693K ECAP for 12 passes, the biomedical alloy with co-existing 18R and 14H LSPO phases shows excellent mechanical properties with an ultimate tensile strength of 326.6 MPa and elongation of 14.5 percent.

Developing an industrial-scale ECAP Mg-Al-Zn alloy with multi-heterostructure for synchronously high strength and good ductility

Although equal channel angular pressing (ECAP) effectively improves the mechanical properties of Mg alloys, it suffers from several problems, like complexity, being time-consuming, and being feasible for small sample sizes, which limit its potential application in industrial fields. Herein, we developed a compact processing route that combined industrial-scale ECAP with partial pre-homogenization and post-aging processes (rather than the commonly used full pre-homogenization and post-aging processes) to improve the processing efficiency. Using this compact processing route, we obtained an industrial-scale AZ91 ECAP alloy with a superior combination of high strength and good ductility. A multi-heterostructure with a heterogeneous grain structure and heterogeneous precipitates characterized the microstructure of this alloy. The heterogeneous grain structure comprised coarse grains and fine grains, and the heterogeneous precipitates included precipitate-dense grains and precipitate-sparse/free grains. The optimal mechanical properties stemmed from the simultaneous effects from the heterogeneous grain structure, heterogeneous precipitates, grain refinement, fine and dense γ-phase particles, and basal plane texture component. The present result highlights the impact of the initial second phase morphology and size on the microstructure evolution during subsequent ECAP or conventional thermo-mechanical treatments, which provides a new approach to control the microstructure of Mg alloys.

Synergistic effect of broken Mg2Si and sub-micron Mg17Al12 induced by EX- ECAP on the strength and ductility of deformed Mg-4Al-1Si-1Gd alloy

In order to obtain higher synthetically mechanical properties, Mg-4Al-1Si-1Gd alloy was deformed by the combination of hot extrusion and equal channel angular pressing (ECAP). The results show that combined deformation process can further promote grain refinement of Mg-4Al-1Si-1Gd alloy, so that Mg2Si phase distributes more uniformly and induce the precipitation of Mg17Al12 particles. With the addition of subsequent ECAP, the grain size of the alloy was reduced from 10.68 ± 0.2 μm to 2.48 ± 0.1 μm. After the hot extrusion at 300 ℃ and two passes ECAP at 200 ℃, the short rod-like Mg2Si phase was broken and evenly distributed in the matrix. Remarkably, a large number of sub-microns Mg17Al12 precipitation particles along the grain boundaries were observed, and the average particle size was 0.43 ± 0.05 μm, which can inhibit grain growth to promote grain refinement. And Mg17Al12 precipitation particles can be able to prevent the dislocation from moving in view of the Orowan mechanism. At the same time, the broken Mg2Si particles with uniform distribution can enhance the elongation of alloy by reducing the crack source. Therefore, the optimum mechanical properties can be obtained. Specifically, the tensile strength is 293.8 MPa, the yield strength is 241.5 MPa and the elongation reaches 30.1%.

Texture Hardening Observed in Mg–Zn–Nd Alloy Processed by Equal-Channel Angular Pressing (ECAP)

The addition of Nd significantly improves the mechanical properties of magnesium alloys. However, only limited amounts of Nd or other rare earth (RE) elements should be used due to their high price. In this study, a low-alloyed Mg–1% Zn–1% Nd (ZN11) alloy was designed and processed by hot extrusion and subsequent equal-channel angular pressing (ECAP) in order to achieve a very fine-grained condition with enhanced strength. The microstructure, texture, and mechanical properties were thoroughly studied. The microstructure after 8 passes through ECAP was homogeneous and characterized by an average grain size of 1.5 µm. A large number of tiny secondary phase precipitates were identified as ordered Guinier–Preston (GP) zones. Detailed analysis of the Schmid factors revealed the effect of the texture on deformation mechanisms. ECAP processing more than doubled the achieved yield compression strength (YCS) of the ZN11 alloy. Significant strengthening by ECAP is caused by grain refinement and the formation of ordered Guinier–Preston zones and particles of a secondary γ-phase.

Microstructure, mechanical properties, and degradation of Mg-Ag alloy after equal-channel angular pressing.

Enhancing the strength of Mg-based biodegradable alloys without decreasing their corrosion resistance is a major engineering challenge. In addition, the growing demand for effective reduction of infections and inflammation after implant placement motivates the design of alloys with appropriate compositions or coatings. One promising alloying element is silver, whose antibacterial effect has long been known. Therefore, a Mg-4% Ag alloy was selected for this study. The alloy was investigated under three conditions: as-cast, after T4 treatment, and after T4 treatment with subsequent equal-channel angular pressing (ECAP) using a newly developed double-ECAP die, which offers an equivalent strain per pass of 1.6. The first pass through the double-ECAP die was conducted at 370 °C and the second at 330 °C using route BC. The microstructure of the as-cast Mg-4% Ag consisted of large grains (several hundred microns) and a dendritic structure with micron-sized Mg54Ag17 precipitates. T4 heat treatment caused dissolution of the dendrites and formation of a solid solution without changing the grain size. Consequently, the ultimate compressive strength (UCS) was increased by approximately 30%, and the compressive strain at fracture reached approximately 23%. The compressive yield strength (CYS) remained nearly constant at approximately 30 MPa. Subsequent ECAP led to strong grain refinement (from 350 μm to 38 μm after one pass and 15 μm after two passes) and further increases in the CYS and UCS, to 45 and 300 MPa after the first pass and 62 and 325 MPa after the second pass, respectively. The as-cast alloy exhibited a very high degradation rate in a simulated body fluid at approximately 36 °C. The degradation rate of the alloy after T4 treatment was much lower. Subsequent ECAP had no significant effect on the degradation properties. Thus, it can be concluded that grain refinement has little effect on the degradation rate.

Managing strength and ductility in AZ91 magnesium alloy through ECAP combined with prior and post aging treatment

In the present work, we firstly and comparatively investigated the microstructure evolution and mechanical properties of AZ91 alloy processed by equal channel angular pressing (ECAP) combined with prior and post aging treatment. Both processes induce homogenous microstructures consisting of fine grains modified by uniformly dispersed spherical precipitates. The prior aging treatment facilitates a well-developed dynamic recrystallized microstructure with low dislocation density, and finer and more precipitates, while both processes induce comparable grain size. Thus, the prior aging treatment benefits to the occurrence of dynamic recrystallization during subsequent ECAP processing. Furthermore, both the strength and ductility of AZ91 alloy are enhanced and flexibly managed through ECAP with a combination of prior or post aging treatment. The post aging treatment is of benefit to the improvement in yield strength, while the prior aging treatment facilitates the more significant ductility enhancement.

Investigation on ECAPed structural steel IS2062 and evaluation of strengthening mechanisms

The structural steel IS2062 was processed by equal channel angular pressing (ECAP) at room temperature with 120° channel angle die. The microstructural properties are evaluated and correlated with the mechanical properties of the ECAP processed material. Every subsequent ECAP passes the strength of the sample was improved and the results are attributed by the SPD process which generated higher dislocation density with refined grains. X-ray diffraction line profile analysis was used to determine the crystallite size, lattice strain and dislocation density. TEM analysis confirmed the dislocation structure in deformed samples. The ECAP processed sample exposed an increase in lattice strain and dislocation density with the number of passes and with a reduced crystallite size. Quantitative contributions of individual strengthening mechanisms for the overall yield strength of ECAP sample was analytically calculated. The results illustrate that the significant contribution comes from dislocation density followed by grain boundary strengthening.

Effect of equal channel angular pressing on in vitro degradation of LAE442 magnesium alloy

Effect of processing by equal channel angular pressing (ECAP) on the degradation behaviour of extruded LAE442 magnesium alloy was investigated in a 0.1M NaCl solution, Kirkland's biocorrosion medium (KBM) and Minimum Essential Medium (MEM), both with and without 10% of foetal bovine serum (FBS). Uniform degradation of as extruded and ECAP processed samples in NaCl solution was observed, nevertheless higher corrosion resistance was found in the latter material. The increase of corrosion resistance due to ECAP was observed also after 14-days immersion in all media used. Higher compactness of the corrosion layer formed on the samples after ECAP was responsible for the observed decrease of corrosion resistance, which was proven by scanning electron microscope investigation. Lower corrosion rate in media with FBS was observed and was explained by additional effect of protein incorporation on the corrosion layer stability. A cytotoxicity test using L929 cells was carried out to investigate possible effect of processing on the cell viability. Sufficient cytocompatibility of the extruded samples was observed with no adverse effects of the subsequent ECAP processing. In conclusion, this in vitro study proved that the degradation behaviour of the LAE442 alloy could be improved by subsequent ECAP processing and this material is a good candidate for future in vivo investigation.

Wear resistance and electroconductivity in a Cu–0.3Cr–0.5Zr alloy processed by ECAP

The ultrafine-grained microstructures and functional properties, including wear resistance for dry sliding and electrical conductivity, were investigated in a Cu–0.3 %Cr–0.5 %Zr alloy processed by equal-channel angular pressing (ECAP) at a temperature of 400 °C to total strains of 1, 2, and 4. Severe plastic deformation by ECAP to a total strain of ~1 led to a significant decrease in the wear resistance because of the rapid surface damage to both solution-treated (ST) and aged (AT) samples where a high density of dislocations was arranged in stochastic low-angle subboundaries by brittle fracture. Further deformation by subsequent ECAP passes promoted the subdivision of the shear bands by geometrically necessary boundaries. Correspondingly, the number of fine crystallites outlined by high-angle boundaries increased, and the wear rate decreased. After four ECAP passes, the wear rate decreased to the level of the initial state of the alloy and equaled 1.68 × 10−5 mm3/(N m) and 1.40 × 10−5 mm3/(N m) for ST and AT samples, respectively. The results demonstrate that the damage mechanism is the controlling factor for wear resistance of Cu–Cr–Zr bronze hardened by intense plastic straining.

Optimization of interpass annealing for a minimum recrystallized grain size and further grain refinement towards nanostructured AA6063 during equal channel angular pressing

Grain structure evolving during severe plastic deformation (SPD) and interpass annealing strongly influences grain refinement occurring during subsequent SPD. The aim of this research was to determine an optimum interpass annealing condition that could lead to the formation of a nanostructure of the AA6063 alloy during subsequent equal channel angular pressing (ECAP). Different interpass annealing temperatures and times as well as different prior ECAP passes were used to define an optimum annealing condition that led to a minimum grain size for further ECAP by route A. TEM confirmed the attainment of nano-scale grains with sizes around 500nm after six passes of ECAP. EBSD revealed the majority of grain boundaries being high-angle ones.

Texture and Lattice Distortion Study of an Al-6061-T6 Alloy Produced by ECAP

Equal channel angular pressing (ECAP) is a severe plastic deformation (SPD) technique that produces nanostructured materials. Based on a remarkable grain size reduction, this process has led to improve mechanical properties, such as yield strength, fatigue, UTS, etc. In this work the characterization of the microstructure of the aluminum 6061-T6 alloy; plastically deformed up to ¾ µ 6, by the ECAP process, following route Bc, is presented. For this purpose, the ECAP processed samples were characterized by means of X-ray diffraction (for texture and line pro fi le analysis) and transmission electron microscopy. The initial crystallographic texture vanished after one ECAP pass and a new, well de fi ned, shear texture C a was generated. For the subsequent ECAP passes, more shear components: A 1 a , B a and B a were also developed. From the orientation distribution function analysis, a shift (generally less than 15°) between some experimental maxima and the reported ideal shear texture positions was observed. From these results, it was found that the microstructure generated with this process was stabilized after the 5th ECAP pass. Finally, the micro-strain analyses, in addition to the texture and transmission electron microscopy, contributed to the understanding of the effec t of the physical and mechanical processes that were activated during the SPD-ECAP techniques

Enhanced creep properties of copper and its alloys processed by ECAP

This work describes the effect of equal channel angular pressing (ECAP) on the microstructure and creep properties of pure copper and its two binary alloys with addition of small amounts of Zr or Co. The ECAP pressing was performed at room temperature by route Bc up to 12 passes using a die with an internal angle of 90° between the two parts of the channel. Ultrafine-grained (UFG) microstructure formed through ECAP process has been studied by methods of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with the electron backscatter diffraction (EBSD) unit. Tensile creep tests were conducted in tension at temperature 673 K and at different applied stresses on ECAP material and, for comparison purposes, on unpressed coarse-grained states of materials under investigation too. It was found that both alloys processed by ECAP exhibited similar character of creep behaviour. Creep resistance was markedly improved after first two ECAP passes in comparison with creep behaviour of unpressed materials. The minimum creep rate of ECAP material may be up to two orders of magnitude lower than that of unpressed material. However, subsequent ECAP passes lead to a decline of creep life and the difference in the minimum creep rate for the ECAP material and unpressed state consistently decreases with increasing number of ECAP passes. Further, ECAP process led to significant improvements in fracture strain. The link between microstructural processes and creep behaviour of pressed copper and its selected alloys is examined in detail.

Microstructure stability of ultra-fine grained magnesium alloy AZ31 processed by extrusion and equal-channel angular pressing (EX–ECAP)

Thermal stability of the ultra-fine grained (UFG) microstructure of magnesium AZ31 alloy was investigated. UFG microstructure was achieved by a combined two-step severe plastic deformation process: the extrusion (EX) and subsequent equal-channel angular pressing (ECAP). This combined process leads to refined microstructure and enhanced microhardness. Specimens with UFG microstructure were annealed isochronally at temperatures 150–500°C for 1h. The evolution of microstructure, mechanical properties and dislocation density was studied by electron backscatter diffraction (EBSD), microhardness measurements and positron annihilation spectroscopy (PAS). The coarsening of the fine-grained structure at higher temperatures was accompanied by a gradual decrease of the microhardness and decrease of dislocation density. Mechanism of grain growth was studied by general equation for grain growth and Arrhenius equation. Activation energies for grain growth were calculated to be 115, 33 and 164kJ/mol in temperature ranges of 170–210°C, 210–400°C and 400–500°C (443–483K, 483–673K and 673–773K), respectively.

Microstructural and mechanical characteristics of EUROFER’97 processed by equal channel angular pressing

EUROFER’97 was processed by equal channel angular pressing (ECAP) at 823K for a total of 4 or 8 passes, using a die angle of 105°, and its microstructure and tensile behavior in temperature range 568–873K investigated. A single ECAP pass developed a deformation texture {110} 〈011〉 that was practically stable during subsequent ECAP passes. The materials processed by 1 or 2 passes exhibited a fine microstructure of recovered subgrains and tensile behavior very similar to that for the tempered material in the as-received condition. The materials processed using 4 or 8 passes exhibited nearly equiaxial submicron grained structures with a high density of high-angle grain boundaries. These materials became softer than the as-received material at a testing temperature of ∼823K. EUROFER ECAP processed under the present conditions exhibited hardening ratio somewhat higher than that of the as-received material.

Fabrication of High Performance PM Nanocrystalline Bulk AA2124

AA2124 nanopowders <100 nm in particle size and 20 nm internal structure produced by high energy ball milling of gas-atomized micronpowders ~45 μm in particle size and 700 nm internal structure were processed in to bulk rods. The micro- and nanopowders were hot compacted using uniaxial pressing for preliminary densification at 0.7T m of the alloy. Selected intact hot compacts (HCs) were promoted for warm severe plastic deformation via equal channel angular pressing (ECAP) at the minimum possible deforming temperature for final densification. Effect of the fabrication method of the consolidated powders was investigated. A combined processing via HC/ECAP produced bulk nanostructured rods 2.5 μm and 50-60 nm in grain size for the micro- and nanopowder consolidates, respectively. The powder properties controlled the degree of densification and mechanical behavior during the hot compaction stage, which influenced strongly the deformation behavior during subsequent ECAP. At the end of HC/ECAP one pass, the HC stage was responsible for about 83 and 95% of the total grain coarsening encountered for the micro- and nanopowder HCs, respectively. Throughout the various consolidation stages employed, the ball-milled (BM) nanopowder consolidates exhibited 2/3 the grain growth and displayed almost twice the hardness and compressive strength values of the gas-atomized micronpowder ones. Influence of BM and HC on the Al2O3 layer formed around the individual powder particles was also investigated.