Equal Channel Angular Pressing Process Research Articles

Effect of equal-channel angular pressing on microstructure, aging kinetics and impact behavior in a 7075 aluminum alloy

Among the precipitation hardenable 7xxx series aluminum alloys, AA7075 alloys (one of the most important engineering alloys) due to their low density (lightweight), high toughness and strength, and enhanced fatigue behavior have been used over the years in aerospace, aircraft, automotive, construction and marine applications. In the present study, the influence of the artificial aging through conventional heat treatment (i.e., precipitation hardening) and the thermomechanical treatment (equal-channel angular pressing (ECAP) + post-ECAP aging) on the quasi-static tensile, impact toughness and precipitation behavior as well as on the microstructure of an AA7075 alloy is investigated systematically. The results indicate that the ECAP process as well as post-ECAP aging result in considerably increased strength and hardness of the AA7075 alloys because of the superimposed effects of grain boundary strengthening (Hall-Petch relation), strain hardening (by means of the increased dislocation density) and precipitation hardening (due to the fine precipitates formed in Al matrix). Multi-pass ECAP processing has been found to result in a considerable decrease of the impact toughness (from 15.3 J·cm−2 to 7.6 J·cm−2) associated with the failure mode (i.e., ductile-to-brittle transition) of the AA7075 alloys, whereas the artificial peak aging leads to a marked improvement (∼67 %) in the impact toughness in ECAPed conditions. Moreover, the ECAP process noticeably accelerates the precipitation kinetics of AA7075 alloys: The peak aging time in the ECAPed alloy is reduced significantly – from 30 h to 4 h. The results of the present study provide a deeper understanding of the combination of ECAP and heat treatment, and their effect on the fracture mode and toughness under impact loading, the aging kinetics and the microstructural evolution of an AA7075 alloy.

Excellent strength-ductility synergy properties of Mg–Sn–Zn–Zr alloy mediated by a novel differential thermal ECAP (DT-ECAP)

The application of structural magnesium (Mg) alloys in engineering industry is usually impeded by the challenge of strength-ductility synergy. In this study, a considerable ductility (elongation, ∼27–33 %) and high ultimate tensile strength (UTS, ∼340–370 MPa) Mg–Sn–Zn–Zr alloy was developed by a combination of aging, extrusion and novel differential thermal equal-channel angular pressing (DT-ECAP) process. Both dislocation slip and (double) cross-slip are primary deformation mechanisms of the alloy. Furthermore, jogs or kinks induced by the interaction between high density of dislocations were also observed in the alloy before and after tensile test, indicating good deformability. More importantly, based on the two-beam bright-filed TEM under three g conditions, multiple slip systems containing pyramidal <c + a>, prismatic and basal <a> dislocations were activated to accommodate both c-axis and a-axis strains of the alloy, leading to superior work-hardening effect and thus superb ductility. On the other hand, the DT-ECAP process was in favor of grain refinement and ultrafine second phases with ∼54–63 nm. Therefore, the principal strengthening mechanisms of the DT-ECAPed alloys were grain boundary strengthening, precipitation strengthening and dislocation strengthening. The contributions of the three strengthening mechanisms to TYSs of second pass (2P) and forth pass (4P) alloys are ∼77 MPa and ∼66 MPa, ∼30 MPa and ∼27 MPa, ∼34 MPa and ∼27 MPa, respectively. The current work develops a novel DT-ECAP process for preparing a new Mg–Sn–Zn–Zr alloy with strength-ductility synergy and provides a strategy to break the strength-ductility tradeoff dilemma of rare-earth-free Mg alloy.

On some Features of the Grain and Subgrain Size in a Cu-Cr-Zr Alloy After ECAP Processing and Aging

A Cu-1Cr-0.1Zr alloy has been subjected to ECAP processing via route Bc and aging at 250-800°C. Electron BackScatter diffraction (EBSD), Transmission Electron Microscopy (TEM) and X-Ray Diffraction Line Profile Analysis (XRDLPA) techniques have been used to unveil some peculiarities of the grain and subgrain structure with a special emphasis on the comparison of the grain size estimated by the three techniques. For the alloy ECAP processed and aged up to 16 passes, the grain size (from EBSD, 0.2 &amp;lt; d &amp;lt; 5 μm), subgrain size (from TEM, d ~ 0.75 μm) and “apparent” average crystallite size (from XRDLPA, d &amp;lt; 0.25 μm) are manifestly different. The results were compared to the published data and analyzed based on the fundamental aspects of these techniques.

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.

Effect of microstructural and texture evolution of ECAP-processed Mg-Zn-Zr alloy on the corrosion and wear behaviours for bone repair applications

Mg-Zn-Zr alloys show great potential for replacing the currently used materials in biodegradable applications. They exhibit similar mechanical properties to that of human bones, while possessing favorable biodegradable properties that can be engineered to allow the complete, safe degradation of the alloy in the human body around the time the bones fully heal, without the need for a removal surgery. Literature confirms that grain refinement through processing via severe plastic deformation (SPD) techniques enhances both corrosion and wear behavior of Mg alloys; thus, in this study Mg-3Zn-0.6 Zr (ZK30) billets were ECAP-processed for up to 4-passes of route Bc to investigate their wear and corrosion behaviors improvement in relation to their microstructural and texture evolutions. Electron back-scatter diffraction (EBSD) was used to study microstructural and texture evolution of the billets, their electrochemical behavior was investigated using a body simulated fluid as a corrosive agent, and wear tests with load, velocity and distance parameters were carried out to investigate the improvements resulting from the produced ultrafine-grained structure and crystallographic texture. EBSD revealed that 4-pass ECAP processing yielded a grain size reduction of 92.7%. Accordingly, this ultrafine-grained structure reduced the corrosion rate by 94%, improved the corrosion resistance by 726%, and notably improved the billets’ wear behavior, compared to the as-annealed condition. Therefore, this in-depth analysis confirms the promising potential of ZK30 alloy for industrial use in bone applications.

Atomistic modeling of idealized equal channel angular pressing process

Severe plastic deformation (SPD) processes are forming techniques that impose large plastic strains to achieve ultra-fine grained and nanocrystalline microstructures. The refined microstructure results in a significant increase in strength and in many cases without a considerable loss in ductility. Despite their long existence, a comprehensive understanding of the deformation and grain refinement mechanisms during SPD is still lacking. Atomistic simulations that are regularly used to obtain insights into material behavior have rarely been used to study SPD processes. In this work, we use large scale atomistic simulations of the molecular statics/dynamics kind to model the equal channel angular pressing (ECAP) process, a specific SPD process. Three different materials—Al, Ni and Cu—are used to model high, medium and low stacking fault energy materials. Large simulation cells are used to facilitate grain refinement at the nanoscale. The simulations are carefully analyzed in terms of stress–strain behavior, dislocation activity and grain refinement. All samples show the formation of deformation twins at the nanoscale, which generally detwin at increased strains via dislocation twin interactions. A significant number of stair-rod dislocations form via dislocation–dislocation interactions and are present at low angle grain boundaries in the early stages of deformation. Such stair-rod dislocations also result in the formation of stacking fault tetrahedra which are present in significant numbers in all samples. Finally, difficulties in studying grain refinement at very large strains in atomistic simulations are discussed.

The microstructure and mechanical properties of Mg-Sn-based alloy processed by differential-thermal equal channel angular pressing

Numerous studies of equal channel angular pressing (ECAP) considered the sample and mould temperatures as a whole, ignoring their different control effects during ECAP deformation. In this paper, the microstructure and mechanical properties of Mg-Sn-Zn-Zr (TZK) alloys were investigated after ECAP deformation at different mould and sample temperatures. The results revealed that higher mould temperatures controlled the actual deformation temperatures and lower sample temperatures prevented grain growth during preheating. After ECAP deformation at mould temperature of 300 °C and sample temperature of room temperature, the alloy consisted of abundant dynamical recrystallisation grains, with an elongation of 30% and a strength of 251.49 MPa. This study would provide a novel idea for the optimisation of the ECAP process.

Effect of ECAP process on deformability, microstructure and conductivity of AA5083 under thermal effect

An alternate method of alloying is to use extreme plastic deformation on commercially available AA5083 to generate an ultrafinegrained microstructure. The objective of this approach is to improve mechanical characteristics without sacrificing corrosion resistance and biocompatibility. Anisotropy in mechanical properties is introduced by plastic deformation leading to the production of a distinct texture. This is a crucial concept to understand in order to build and model structural devices and components from a perspective based approach. The ultrafine-grained structure of AA5083, which was obtained by equal channel angular pressing, is examined in this work. Ex-situ and indirect in-situ thermal studies are used to supplement this investigation while the material is heat treated at different annealing temperatures. The results show that the elastic properties undergo very small change during the annealing process, in contrast to other parameters as thermal expansion, internal friction, or hardness. The strong relationship between the elastic anisotropy and texture highlights the importance and possibilities of using texture into the design and customization of mechanical characteristics. Pure deforms plastically in order to improve mechanical qualities while maintaining biocompatibility and corrosion resistance. Analysis of the materials elastic inhomogeneity and crunchiness in detail. In comparison to other characteristics like as inner conflict thermal enlargement or hardness, the results demonstrate that elastic properties barely marginally change during annealing. The microstructure fragmentation had no influence on the conductivity of the AA5083, which oscillated at 18 MS/m after the ECAP procedure. According to the findings, all deformed specimens strain hardening exponent and capacity were lower than they were in their as-received state. Investigated was the effect of size of grains on the strain hardening comportment of the ECAPed AA5083.

Residual stress, fatigue behavior, and mechanical properties of equal-channel angular pressed commercial pure titanium

Residual stresses, fatigue behavior, and mechanical properties of equal channel angular pressing (ECAP) commercial pure titanium (CP–Ti) are investigated in this study. Residual stresses can significantly affect the performance and reliability of CP-Ti components under cyclic loading conditions. The study focuses on understanding the relationship between ECAP processing, residual stresses, and fatigue behavior in CP-Ti. The ECAP process was employed to produce CP-Ti grade 2 samples, and their fatigue behavior was characterized. The results revealed a significant increment in residual stresses, fatigue strength, microhardness, and tensile strength by ECAP processing on the CP-Ti. The measured fatigue limit of the processed CP-Ti was found to be higher than that of coarse-grained CP-Ti and approaches the fatigue limit of the Ti–6Al–4V alloy. Residual stresses resulting from non-conventional machining processes and surface treatments are known to affect the fatigue life of titanium alloys. Compressive residual stresses have been shown to inhibit the growth rate of fatigue cracks and improve fatigue life. Understanding the effect of residual stresses on the fatigue behavior and mechanical properties of ECAP-processed CP-Ti is crucial to optimizing the design and ensuring the long-term durability of CP-Ti components in engineering applications.

Strengthening of Mechanical Properties and Electrical Conductivity Study on 6061 Al Alloy after ECAP Process

Strengthening of Mechanical Properties and Electrical Conductivity Study on 6061 Al Alloy after ECAP Process

Microstructure evolution and mechanical properties of Mg–Mn–RE alloy processed by equal channel angular pressing

Equal Channel Angular Pressing (ECAP) has been used to successfully produce ultrafine-grained ME21 alloy with a good strength-ductility synergy. The microstructure of the as-cast ME21 alloy and its evolution during the ECAP processing were characterized using a combination of optical microscopy (OM) and scanning electron microscopy (SEM). Fracture surfaces after tensile test were also characterized using SEM. Chemical analysis and phase identification were done by energy dispersive spectroscopy (EDS) and X-ray diffraction analysis, respectively. The combination of these techniques enabled the interpretation of the mechanical behavior during the various processing stages of the alloys. The ECAP process was performed up to 16 passes, producing a uniform ultra-fine grain (1 µm) ME21 alloy resulting from full dynamic recrystallization. At room temperature, the yield strength after 16 ECAP passes (191.4 MPa) was 251% higher than that of the as-cast ME21 alloy, accompanied by a good elongation of 8.1%. The hardness increased to 60.7HV which is about 52% higher than that of the as-cast alloy. These improvement in mechanical properties is due to the ultra-fine grains with high angle grain boundaries (HAGBs) and the precipitate strengthening effects of the uniformly dispersed fine precipitates of Mg12Ce and Mn formed as a result of the intense shear during the ECAP process.

Investigation of the Effects of Various Severe Plastic Deformation Techniques on the Microstructure of Laser Powder Bed Fusion AlSi10Mg Alloy

In this paper, we present a complete characterization of the microstructural changes that occur in an LPBF AlSi10Mg alloy subjected to various post-processing methods, including equal-channel angular pressing (ECAP), KoBo extrusion, and multi-axial forging. Kikuchi transmission diffraction and transmission electron microscopy were used to examine the microstructures. Our findings revealed that multi-axis forging produced an extremely fine subgrain structure. KoBo extrusion resulted in a practically dislocation-free microstructure. ECAP processing at temperatures between 100 °C and 200 °C generated moderate grain refinement, with subgrain diameters averaging from 300 nm to 700 nm. The obtained data highlighted the potential of severe plastic deformation as a versatile method for tailoring the microstructure of the AlSi10Mg alloy. The ability to precisely control grain size and dislocation density using specific SPD methods allows for the development of novel materials with ultrafine-grained microstructures that offer the potential for enhanced mechanical and functional properties.

Processing of the Ti25Ta25Nb3Sn Experimental Alloy Using ECAP Process for Biomedical Applications

The development of titanium-β alloys for biomedical applications is associated with the addition of alloying elements or the use of processing techniques to obtain suitable bulk properties. The Ti25Ta25Nb3Sn alloy has been highlighted for its mechanical properties and biocompatibility. To further enhance the properties of titanium alloys for biomedical applications, equal channel angular pressing (ECAP) was used due to its capability of refining the microstructure of the alloy, leading to improved mechanical properties without significant changes in Young’s modulus. This study aims to evaluate the impact of ECAP on the microstructure of the Ti-25Sn-25Nb-3Nb alloy and investigate the correlation between the microstructure, mechanical properties, and corrosive behavior. Grain refinement was achieved after four ECAP passes, with an average grain diameter of 395 nm and a non-homogeneous structure, and microhardness was slightly increased from 193 to 212 HV after four ECAP passes. The thermomechanical aspects of the ECAP processing have led to the formation of a metastable α″ phase during the first two passes, while after four passes, the structure was composed only of the β phase. The corrosion resistance of the alloy was increased after four passes, presenting the best results in terms of the improvement of passivation corrosion density.

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

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

Impact of ECAP processing on dislocation density and subgrain size in a ti6al4V alloy prepared by direct energy deposition

Ti6Al4V alloy billets were additively manufactured by direct energy deposition and then equal channel angularly pressed (ECAPed) at 700 °C. The originally prepared α′ martensite microstructure was completely converted to an equiaxed fine grain structure during ECAP processing. The α′ martensite decomposed into α + β dual phase structure. The dislocation density in the deposited and ECAPed samples was measured by X-ray profile analysis in samples of two orientations. The dislocation density estimated in the deposition plane was found to be higher than that estimated perpendicularly. This difference is probably a consequence of the internal stresses generated in the samples during the deposition process. A similar anisotropy in dislocation density and crystallite size was found in the ECAPed samples. Lattice constants were measured for the α′ martensite and α phase of the ECAPed alloy. The crystallite size distribution was found to be moderately different for samples cut parallel and perpendicular to the extrusion direction.

Effect of the Equal Channel Angular Pressing on the Microstructure and Phase Composition of a 7xxx Series Al-Zn-Mg-Zr Alloy.

A supersaturated Al-4.8%Zn-1.2%Mg-0.14%Zr (wt%) alloy was processed by the equal-channel angular pressing (ECAP) technique at room temperature in order to obtain an ultrafine-grained (UFG) microstructure having an average grain size of about 260 nm. The hardness and microstructural characteristics, such as the phase composition and precipitations of this UFG microstructure were studied using depth-sensing indentation (DSI), transmission electron microscopy (TEM), as well as non-isothermal scanning of differential scanning calorimetry (DSC), and compared to the properties of the un-deformed sample. Emphasis was placed on the effect of the UFG microstructure on the subsequent thermal processes in DSC measurements. It has been shown that the ECAP process resulted in not only an ultrafine-grained but also a strongly precipitated microstructure, leading to a hardness (2115 MPa) two and a half times higher than the initial hardness of the freshly quenched sample. Because of the significant changes in microstructure, ECAP has also a strong effect on the dissolution (endothermic) and precipitation (exothermic) processes during DSC measurements, where the dissolution and precipitation processes were quantitatively characterized by using experimentally determined specific enthalpies, ΔH and activation energies, Q.

Improving Mechanical Properties, Corrosion Resistance and Biocompatibility of Zn-1Mg-0.3Y Alloys Through Equal Channel Angular Pressing

This paper discusses refining the microstructure of Zn–Mg–Y alloy via equal channel angular pressing (ECAP), leading to enhanced mechanical properties of the Zn alloy. Following ECAP, the strength and elongation of the Zn–Mg–Y alloy increased from 227 MPa and 3% in the as-cast state to 350 MPa and 23%. The increase in strength is primarily attributed to the reduction in grain size, the refinement of the lamellar eutectic Mg2Zn11 phase, and the granular YZn12 phase. Additionally, the nanoscale precipitates generated during ECAP-induced deformation can also contribute positively to strengthening. Beyond strength enhancement, the refinement of the second phase can mitigate stress concentration at the Zn/Mg2Zn11 and Zn/YZn12 interfaces, thereby enhancing the deformability of the Zn alloy. Electrochemical and immersion experiments demonstrate an enhanced corrosion resistance of the Zn–Mg–Y alloy after ECAP processing. This improvement can be primarily attributed to the increased uniformity of the microstructure after refinement, which inhibits the occurrence of localized corrosion. Regarding biocompatibility, Zn–Mg–Y alloys in both the cast and ECAP states exhibited cell viabilities exceeding 100% in MC3T3 cell cultures using 50% and 25% extracts, outperforming the control group of Ti. In summary, the Zn–Mg–Y alloy prepared through ECAP significantly enhances mechanical properties, corrosion resistance, and biocompatibility. These findings open new avenues for advancing the development of improved degradable Zn alloys.

Developing a Zn alloy with high strength and uniform elongation as a biomedical device

The equal channel angular pressing (ECAP) process was used to develop a Zn-1Mg alloy with a tensile strength of 440 MPa and uniform elongation of 11%. The uniform elongation of the ECAPed Zn-1Mg alloy is higher than that of other Zn alloys with strengths over 400 MPa. The microstructure of the ECAPed Zn-1Mg alloy evolved through dynamic recrystallization (DRX), resulting in a refined grain structure. Additionally, the lamellar eutectic structure was fragmented into sub-micrometer particles (∼0.9 μm). The high strength of the Zn-1Mg alloy is due to both grain boundary strengthening and second phase strengthening. The high uniform elongation is attributed to the presence of plate-shaped precipitates with a high density of 1014m−2. The in-vitro results indicate that ECAPed Zn-1Mg alloy has high cell viability (>100%). Meanwhile, the Zn-1Mg alloy processed by ECAP exhibited better ALP activity and alizarin red results than pure Zn. These results demonstrate that Zn-1Mg alloy is beneficial to the proliferation and differentiation of osteoblasts, and also promote blood vascular formation. The good osteogenic and angiogenic properties of the alloy are attributed to the release of Mg2+ and Zn2+ during the degradation process, which play a critical role in biochemical reactions in the human body. Therefore, the high uniform elongation and good biological properties make Zn-Mg based alloys a promising material for expanding applications in the orthopedic field.

Revealing the strengthening contribution of stacking faults, dislocations and grain boundaries in severely deformed LPBF AlSi10Mg alloy

In this study, microstructural features direct metal laser melted (DMLM) aluminium–silicon-magnesium (AlSi10Mg) are investigated using advanced transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The focus is on post-processing by ECAP (Equal Channel Angular Pressing) and its effects on grain refinement, stacking fault formation and dislocation accumulation. In addition, the strength enhancing role of stacking faults is for the first time quantified. The results show that ECAP can increase the yield strength from 294 to 396 MPa, while the elongation increases from 2.4% to 6%. These results show that ECAP processing offers a new approach for producing AlSi10Mg products with improved strength and ductility.

Grain growth activation energy of ECAP-processed Mg-Ce alloy: Effect of deformation temperature

In the present work, the grain growth activation energy, Q was evaluated in a Mg-0.3Ce (wt%) alloy after equal-channel angular pressing (ECAP) processing via route Bc for 4 passes at 300 and 350 °C and followed by isochronal annealing at 150, 250, 350, and 450 °C for 2 h. The results demonstrated that Q depends strongly on the deformation processing. The Q value was equal to 111.4 ± 5.7 kJ/mol for the sample ECAP-processed at 300 °C. While the sample ECAP-processed at 350 °C shows the presence of two different Q values depending on the annealing temperature, QI = 26.5 ± 3.4 kJ/mol in the low-temperature range (150–350 °C) and QII = 120.7 kJ/mol in the high-temperature range (350–450 °C). This behaviour was attributed to the resulting deformation microstructure and the occurrence of dynamic grain growth during ECAP processing at 350 °C.