Equal Channel Angular Pressing Deformation Research Articles

Effect of equal channel angular pressing on microstructure and mechanical properties of a Cu-Cr-Ni-Si-Co alloy

The microstructural and properties of a Cu-Cr-Ni-Co-Si alloy produced by equal channel angular pressing (ECAP) were systematically investigated. After the fourth-pass ECAP deformation, the average grain size was refined from 30 μm (solid solution state) to below 3 μm, resulting in a fine and regularly shaped equiaxed crystalline microstructure. The distribution of grain boundaries became more uniform. During ECAP deformation, the volume fraction of Copper texture {001} <100> decreased, while that of the Brass {011} <211> increased, and the Shear {123} <634> remained nearly constant. An increase in the number of ECAP deformation passes facilitated dynamic recrystallization, leading to an increase in the fraction of the recrystallized texture. After thermomechanical treatment (first-pass ECAP +450 °C aged/120 min + 80 % cold-deformation +450 °C aged/30 min), the alloy exhibited good mechanical properties, with a tensile strength of 546 MPa, a yield strength of 475 MPa, an elongation of 18.2 %, and an electrical conductivity of 52.8 %IACS. The main strengthening mechanisms included precipitation strengthening, dislocation strengthening and grain boundary strengthening, with the precipitation strengthening accounting for 45.6 % of the yield strength.

Enhanced yield stress and reduced elastic modulus of metastable β Ti–Nb alloys deformed by equal channel angular pressing attributed to the Synergistic effect of deformation mechanisms

This work aims to obtain Ti–Nb alloys with a high yield stress, good plasticity, and low elastic modulus. To this end, metastable β Ti–Nb alloys were subjected to multipass equal channel angular pressing (ECAP) deformation at room temperature, and a thorough investigation of their microstructure evolution, deformation mechanisms, and strengthening/toughening mechanisms was conducted through X-ray diffraction, transmission electron microscopy, electron backscatter diffraction, and tensile tests. In the initial deformation stages, multiple deformation mechanisms are observed, including dislocation slip, {332} <113> twinning, stress-induced martensite (SIM) α″-phase, {112} <111> twinning, and stress-induced ω-phase. However, as the strain accumulates, the ω-phase disappears, the volume fraction of the SIM α″-phase gradually decreases, and the dominant deformation mechanism changes to dislocation slip and {332} <113> twinning. The ECAP deformation results in a complex-network microstructure and the precipitation of the nanoscale SIM α″-phase, which leads to the twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects. As a consequence, the Ti–Nb alloy simultaneously exhibits a high yield stress and a good plasticity. Furthermore, the high-density dislocations and interfaces generated by the ECAP deformation reduce the stability of the β-phase, and the introduced nanopores cause a decrease in density, resulting in a decrease in the elastic modulus of the alloy.

Optimization of ECAP parameters of ZX30 alloy using feature engineering assisted machine learning and response surface approaches

The precise control of equal channel angular pressing (ECAP) deformation parameters is crucial for producing ultrafine grains in structural ZX30-Mg alloy biodegradable components. To address this challenge, this study aims to conduct a comprehensive analysis of the effects of various ECAP parameters on the microstructure, corrosion, and mechanical properties of ZX30 alloy. ZX30 was utilized through a maximum of 4 passes along routes A, Bc, and C, using die angles of 90ᵒ and 120ᵒ, by utilizing machine learning (ML), artificial neural networks (ANNW), response surface methodology (RSM), and simulated annealing (SA) techniques. Experimental investigations revealed the significance of the number of passes in reducing grain size by up to 1.9 µm, consequently enhancing both mechanical and corrosion resistance properties, notably in route Bc. The corrosion rate was enhanced by 97.6 % while the corrosion resistance was increased by 254 % compared to the as-annealed condition. RSM and simulated annealing optimization results closely aligned with experimental findings. The evaluation of each extrusion parameter revealed that the correlation coefficient, as determined by the optimized Gaussian Process Regression model, ranged from 94 % to 97 % for all evaluated responses, and near to unity via ANNW. The overall distribution of mechanical and corrosion measures showed a significant correlation with the number of passes, with route A, Bc, and die angle following closely behind. Interestingly, route Bc had the main impact on the yield strength, followed by the number of passes and die angle. Thus, the combination of statistically and mathematically selected techniques effectively promotes the attainment of optimal properties. Furthermore, the Simulated Annealing (SA) algorithm demonstrated its capability to provide optimal solutions for ECAP deformation parameters. This study presents a promising avenue for improving the accuracy of ECAP-induced structural optimization in ZX30 alloy.

Mechanical properties and microstructure of Al–Mg (5052) alloy processed by equal-channel angular pressing (ECAP) with variation of ECAP routes and heat treatment

Equal-Channel Angular Pressing (ECAP) has become an effective technique of severe plastic deformation designed to produce ultrafine grain metals with improved mechanical properties, such as a good combination of strength and ductility. A report on the effect of ECAP routes on the mechanical and microstructure of commercial 5052 aluminum alloy needs also to be included. This work has been undertaken, in order to obtain the results. In this work, several deformation routes were used to process the Al – Mg (5052) alloy, namely A, Ba, Bc and C. Deformation route A involved repeatedly pushing the sample into the ECAP die without rotation, route Ba was performed by rotating the sample through 90° in alternate directions between each pass, route Bc by rotating the sample 90° in the same sense between each pass and route C by rotating the sample 180° between passes. The addition of the pass number decreases the grain size of ECAP-processed samples when compared to the as-annealed sample. It also confirmed that the microstructure of the 8-pass samples shows a finer grain size than the as-annealed sample. Furthermore, the Bc route (samples rotated in the same sense by 90° between each pass) has been proven to be the most effective deformation route, in order to obtain equiaxed ultrafine grain structure when compared to other deformation routes. This phenomenon takes place due to the continuous deformation in all cubic planes. The restoration after the 4-pass number will lead to the rapid evolution of sub-grains to high-angle grain boundaries, forming equiaxed grains. The characterization of the hardness number also shows that the addition of the ECAP pass number increases the hardness number of 5052 aluminum alloy, where samples processed with the Bc route indicate the highest hardness number at 168.4 HB. Moreover, a similar phenomenon also suggests that the tensile strength of all ECAP deformation routes has comparable values. The effect of heat treatment for samples with the Bc route also shows that 200 °C annealed samples have the highest hardness number and tensile strength when compared to other samples.

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.

Evolution of microstructure, macrotexture and mechanical properties of high strength biomedical TA4 pure titanium during multi-pass ECAP

The application of equal-channel angular pressing (ECAP) to TA4 pure titanium (Ti) results in a fine-grained microstructure. This technique presents an substitute for alloying, delivering enhanced mechanical properties without reducing biocompatibility and corrosion resistance. This study employs scanning electron microscopy (SEM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM) to explore the microstructure evolution and the toughening mechanism of TA4 pure Ti after deformation. ECAP performed at 573 K endows TA4 pure Ti with a uniformly fine-grained microstructure, leading to a significant enhancement in its mechanical properties, exemplified by a yield strength of ∼731.9 ± 2.7 MPa and an elongation of ∼30.8± 1.3 %. While the {0001} basal slip primarily governs the ECAP deformation, the non-basal slip plays an increasingly important role with the increase of passes. The increase of yield strength can be attributed to grain refinement and the modification of the {0001} basal texture. Meanwhile, the improvement of plasticity is related to the strengthening of the {101‾ 0} prismatic texture. These findings offer fresh insights and methodologies for the design and manufacture of high-performance biomedical pure Ti.

Study on the effect of the ECAP deformation on the organization and properties of the extruded Mg-Sn-Al alloys

In order to refine the grain and the second phase size of the Mg-Sn-Al alloys further, as well as enhance the alloy's strength-ductility performance match, the alloy was deformed by equal-channel angular pressing (ECAP) technique after conventional extrusion. After ECAP (180℃), the microstructures and mechanical properties of the alloy were observed. The results show that the average grain size of the alloy reduced from 23.3 μm to 1.25 μm, and the percentage of the high-angle grain boundaries rise to 71 %. The texture of the ECAPed alloy on TD direction shows a typical fiber (10 1¯ 0) < 11 2¯ 0>, with an intensity of 12.016. The mechanical properties of the ECAPed alloy were tested after aging at 240℃ for 192 h, and the results show that the ultimate tensile strength of the aging alloy was 415 MPa, the yield strength was 324 MPa and the elongation was 10.5 %.

Simultaneously enhancing mechanical properties and electrical conductivity of Cu-0.5%Cr alloy as 5G connector material

With the rapid development of the 5 G communication, materials such as the high-speed backplane connector and the integrated circuit lead frame require higher strength and electrical conductivity. Copper alloys have been widely concerned due to their excellent electrical conductivity, thermal conductivity and good strength. A new method of preparing the Cu-0.5%Cr alloy by equal channel angular pressing (ECAP), deep cryogenic treatment (DCT) and aging treatment (AT) was proposed. The electrical conductivity, mechanical properties and microstructure of the Cu-0.5%Cr alloy were investigated, and the precipitation kinetics was analyzed. The results show that ECAP deformation and DCT treatment make the grains elongate and refine along the deformation shear direction. After four ECAP passes and DCT (12 h), the lamellar grains with the thickness of 200–300 nm were obtained, and the dislocation density was evidently increased. After the subsequent AT treatment, the fine Cr phase disperses uniformly at the grain boundaries and within the grains, and distributes on the matrix and along the dislocation lines. Compared with the solid solution, the results showed that after four passes of ECAP + DCT (12 h) + AT (425 ℃ × 1 h), the microhardness increased from 60.5 HV to 210 HV, the electrical conductivity changed from 27.9 % IACS to 69 % IACS, the strength improved from 262 MPa to 587 MPa, the elongation to failure decreased from 44.2 % to 21.9 %. The electrical conductivity was enhanced due to the second phase charge analysis showed that the scattering effect on electrons is weakened. The improvement of strength could be attributed to grain refinement and increase of dislocation density. Based on the Avrami empirical equation of precipitation kinetics analysis, the electrical conductivity equation and the phase change kinetics equation were established, and the relationship between aging time and electrical conductivity was established.

Effects of Zn Addition on Microstructural Evolution, Mechanical Properties, and Corrosion Resistance of Al‐6Mg Alloy Subjected to Equal Channel Angular Pressing Processing at 200 °C

The evolution of microstructure, mechanical properties, and corrosion performance of Al‐6Mg and Al‐6Mg–1Zn alloys processed using equal channel angular pressing (ECAP) at 200 °C is systematically investigated. Microstructural analysis reveals that different T and β phases are generated in the two studied alloys, resulting in different grain refinement processes. The average size of T phase in Al‐6Mg–1Zn alloy increases first and then decreases, and the distribution of T phase inside grains becomes denser with increasing ECAP deformation. The continuity of T phase at the grain boundary increases from 0 to 2 passes and decreases from 2 to 4 passes. In contrast, the β phase in Al‐6Mg alloy mainly locates at grain boundaries and becomes coarser and more continuous from 0 to 4 passes. The fracture strength of Al‐6Mg–1Zn alloy after 4‐pass ECAP reaches 391 MPa with a fracture elongation of 28%, which is superior to that of 4‐pass ECAP Al‐6Mg alloy. The 4‐pass ECAP Al‐6Mg–1Zn alloy has a higher corrosion resistance compared to the Al‐6Mg alloy under the same deformation condition. The low corrosion susceptibility in 4‐pass ECAP Al‐6Mg–1Zn alloy is attributed to sparse distribution of the T phase along the grain boundary.

Microstructure and properties evolution of Cu-Ti-Cr-Mg alloy during equal channel angular pressing at room temperature and cryogenic temperature

A Cu-2.5Ti-0.4Cr-0.1Mg (wt%) alloy was prepared in a vacuum medium frequency induction furnace. The evolution of the microstructure and mechanical properties of the samples deformed by equal channel angular pressing (ECAP) at different temperatures was investigated by hardness tests, tensile tests, optical metallography observation, X-ray diffraction and electron back-scattered diffraction. The cryogenic-temperature-deformed (CDed) samples have a little higher hardness than room-temperature-deformed (RDed) samples at any given ECAP pass. After 8 ECAP passes, the yield strength of CDed and RDed samples is close to each other, with the value of 812 ± 17 MPa and 793 ± 25 MPa, respectively. ECAP deformation significantly refines the grain size of the alloy due to the dislocation subdivision and twin fragmentation, and the average grain sizes of RDed and CDed samples after 8 passes are about 0.32 µm and 0.37 µm, respectively. Calculation results show that dislocation strengthening plays a key role in increasing the strength of ECAPed samples.

Effect of equal-channel angular pressing on structure and properties of Fe-Mn-С alloys for biomedical applications

In this work two Fe - Mn - C alloys with different Mn contents were treated by equal-channel angular pressing (ECAP) in order to study the possibility of obtaining alloys with an increased degradation rate for the manufacture of biodegradable implants. Special attention was paid to the obtaining an ultrafine-grained alloys structure in a fully austenitic state and studying its effect on the corrosion rate, mechanical properties and biocompatibility in vitro. The X-ray analysis showed the formation of an austenitic structure in both alloys with the structural elements sizes of 100–250 nm after ECAP. For Fe-27Mn-C alloy ECAP resulted in significant increase in strength while maintaining satisfactory plasticity. The Fe-36Mn-C alloy samples destruction under tension occurs in the elastic region, which is associated with the α-Mn precipitation in the structure during ECAP deformation. The studied alloys were found to be hemocompatible. Reduced proliferation was noted on the Fe-36Mn-C alloy samples, indicating a non-specific biocidal effect of Mn. The alloys corrosion rates by weight loss method and potentiodynamic polarization analysis were studied. An increased corrosion rate of alloys after ECAP in comparison with the one of the course-grained counterpart, significantly exceeds the rate of corrosion of annealed iron.

Effects of equal channel angular pressing and heat treatments on the microstructures and mechanical properties of selective laser melted and cast AlSi10Mg alloys

This study investigated the impact of the equal channel angular pressing (ECAP) combined with heat treatments on the microstructure and mechanical properties of AlSi10Mg alloys fabricated via selective laser melting (SLM) and gravity casting. Special attention was directed towards determining the effect of post-fabrication heat treatments on the microstructural evolution of AlSi10Mg alloy fabricated using two different routes. Three initial alloy conditions were considered prior to ECAP deformation: (1) as-cast in solution treated (T4) condition, (2) SLM in T4 condition, (3) SLM subjected to low-temperature annealing. Light microscopy, transmission electron microscopy, X-ray diffraction line broadening analysis, and electron backscattered diffraction analysis were used to characterize the microstructures before and after ECAP. The results indicated that SLM followed by low-temperature annealing led to superior mechanical properties, relative to the two other conditions. Microscopic analyses revealed that the partial-cellular structure contributed to strong work hardening. This behavior enhanced the material’s strength because of the enhanced accumulation of geometrically necessary dislocations during ECAP deformation.

3D FEM simulation on Deformation and Strain analysis for grain refinement of Mg Alloy passed through ECAP

Equal Channel Angular Pressing (ECAP) is a cutting-edge Severe Plastic Deformation (SPD) process for grain refining of materials up to ultra-fine or nanostructured standards, resulting in superior mechanical properties. To consider the effect of each processing parameter on the end results, computer simulation is one of the better alternatives to real ECAP deformation. The alloys used in this study are AZ61 magnesium alloy, which is a difficult material to work with in automotive applications. The ECAP process is subjected to 3D FEM simulation using ANSYS software in order to better understand the process/die design parameters. 90° channel angles and corner angles 20° i.e the best combination suggested by experimental studies were used in the simulation. For a single ECAP pass, the ECAP phase was simulated. Extrusion load, established stresses, effective strain, and temperature variation on the processed material were all noted in the results. The minimum channel angle produces the highest temperature profile on the material, developing maximum stress and strain at the deformation zone, according to the observed results. Furthermore, the results obtained using such computational techniques show that the shear strain decreases as the channel and corner angle increase.

On the possibility to reduce ECAP deformation temperature in magnesium: Deformation behaviour, dynamic recrystallization and mechanical properties

This work investigates the effect of temperature on the dynamic recrystallization (DRX) behaviour and its consequence on the microstructure, texture, and mechanical properties in pure magnesium during equal channel angular pressing (ECAP) by route-A up to eight passes ( ε E f f = 9.3 ) . The ECAP temperature was reduced in steps for gradual grain refinement. Thereby the 8th pass could be conducted successfully at 200 °C , 150 °C and 27 °C , respectively. Irrespective of the 8th pass ECAP temperature, ~0.30 microstructure fraction was found to be DRXed. Continuous dynamic recovery and recrystallization (CDRR) predominantly occurred, resulting in the formation of fine grains with the necklace structure for all the conditions. However, distinctive and abnormally coarse CDRR grains evolved irrespective of the ECAP temperature. CDRR lead to the formation of Σ 13 a boundaries with [0002]- 30 ° axis-angle pair. Discontinuous DRX was also observed intermittently in the ECAP microstructures. The average grain size after the 8th pass ECAP at 200 °C , 150 °C and 27 °C was ~ 2.6 μ m , ~ 1.4 μ m and ~ 0.75 μ m μ m , respectively. The yield strength increases and the ultimate compressive strength (UCS) as well as strain to failure, decreases with grain refinement. The ambient temperature compressive strain hardening behaviour was initially sigmoidal, attributing to the evolution of { 10 1 ‾ 2 } 1 ‾ 011 extension twins. Sigmoidal flow behaviour reduces gradually as the grain size decreases with ECAP. No sigmoidality indicate slip-dominated deformation after 8th pass ECAP at 150 ° C and 27 ° C . • Strategic reduction in ECAP deformation temperature in Mg is possible to obtain ultrafine grains. • ~0.30 microstructure-fraction recrystallized after effective-strain of 9.3 regardless of ECAP temperature. • Continuous dynamic recovery & recrystallization occurred, forming fine and coarse grains. • Discontinuous dynamic recrystallization increases as the ECAP temperature reduced. • Yield strength increase, ultimate strength and ductility decrease with grain refinement.

SIMULTANEOUSLY ENHANCING MECHANICAL PROPERTIES AND ELECTRICAL CONDUCTIVITY OF CU-CR ALLOY PROCESSED BY ECAP AND DCT

Mechanical properties and electrical conductivity of Cu-0.5%Cr alloy were simultaneously enhanced by combing the equal channel angular pressing (ECAP) and deep cryogenic treatment (DCT). The effect of DCT on the microstructure and properties of Cu-0.5%Cr alloy prepared by ECAP was investigated. The results show that the grains were elongated and refined along the deformation shear direction, and the dislocation density increased significantly by ECAP deformation. After the subsequent DCT, the grains were further refined, and at the same time, the dislocation density was further increased. With the increase of passes of ECAP, the microhardness and tensile strength of Cu-0.5%Cr alloy increased significantly, but the elongation to failure and electrical conductivity decreased slightly. After the DCT, the microhardness, electrical conductivity, tensile strength and elongation to failure of the Cu-0.5%Cr alloy were improved. After the ECAP (four passes) and DCT (12 h), the tensile strength, elongation to failure and electrical conductivity reached 483 MPa, 17.6% and 29%IACS respectively. The improvement of tensile properties could be attributed to the increase of dislocation density and grain refinement. The electrical conductivity was improved by the DCT due to the decrease of vacancy concentration.

Impact of Equal Channel Angular Pressing on Mechanical Behavior and Corrosion Resistance of Hot-Rolled Ti-2Fe-0.1B Alloy.

In the present study, the unique bimodal grain size distribution microstructure with the ultrafine substrate and embedded macro grains was fabricated by a traditional hot-rolling process in a novel low-cost Ti-2Fe-0.1B titanium alloy, which possesses a good combination of strength (around 663 MPa) and ductility (around 30%) without any post heat treatment. Meanwhile, the mechanical behavior and corrosion resistance of hot-rolled Ti-2Fe-0.1B alloy after equal channel angular pressing (ECAP) deformation were studied. Results indicated that the average grain size decreased to 0.24 μm after 4 passes ECAP deformation, which led to the enhancement of tensile strength to around 854 MPa and good ductility to around 15%. In addition, corrosion resistance was also improved after ECAP due to the rapid self-repairing and thicker passivation film. Our study revealed that the novel low-cost titanium alloy after hot-rolling and ECAP could be used instead of Ti-6Al-4V in some industrial applications due to similar mechanical behavior and better corrosion resistance.

Effect of ECAP Deformation on Microstructure and Properties of Pure Magnesium

In this paper, the effect of the deformation of equal-channel angular pressing (ECAP) on the microstructure and the mechanical properties at room temperature was studied under the extrusion temperature of 350°C and extrusion path of BC. The results show that the grain size of pure magnesium is obviously refined with the increase of the number of extrusion passes. The yield strength, tensile strength and elongation of the as-cast sample are 20MPa, 55MPa and 14.7% respectively. The yield strength and tensile strength of the 3-pass extrusion sample can be increased by 350% and 170%, respectively. The tensile strength and yield strength of the 4-pass extrusion sample are reduced compared with the 3-pass extrusion sample, but the elongation is further increased. The grain refinement of alloy ECAP process is mainly a combination of mechanical shear and dynamic recrystallization.

Deformation analysis of Al Alloy AA2024 through equal channel angular pressing for aircraft structures

ABSTRACT Equal Channel Angular Pressing (ECAP) is one of the most innovative Severe Plastic Deformation (SPD) methods used for grain refinement of materials up to ultra-fined or Nano structured level which leads to superior mechanical properties. Computer simulation is one of the best alternative of actual ECAP deformation to know the influence of each processing parameters on end results. In the present work, AA2024 alloys is used, which is a demanding material in aircraft structure and automotive applications. To understand the process/die design parameter, 3D FEM simulation is done on ECAP process using DEFORM-3D software. Simulation was done on different channel angles such as 90º, 105º, 120º and 135º and corner angles such as 0º, 10º, 20º and 30º. The ECAP process was simulated for a single ECAP pass. The results concern to the extrusion load, developed stresses, effectivestrain and temperature variation on the processed material were noted obtained. From the observed results, it was found that the minimum channel angle produces the maximum temperature profile on the material, develop maximum stress and strain at deformation zone. Additionally, the outcome acquired by such computational technique illustrate that the shear strain decrease with increase in channel and corner angle.

Investigation wavy interface forming and stretching in severe plastic deformed copper/steel bimetallic rod

Bimetallic copper-clad steel rod was prepared via three successive passing the samples through equal-channel angular pressing (ECAP) die with route Bc. The core steel tensile properties and copper/steel interface microstructures were investigated after each passes. It is observed the yield strength of steel core increased from about 200 MPa to 840 MPa and equiaxed grains with the size lower than the one-third of the initial size were formed. Only, during the third passing of ECAP deformation, the copper/steel interface was changed to waveforms in some angular positions. The shear strain and mating surface stretch were modeled to explain this phenomenon.

Investigation of joint interface and cracking mechanism of thick cladding of copper on aluminum by equal channel angular pressing (ECAP)

Joint interface and cracking mechanism during thick cladding of copper on aluminum have been investigated. For this purpose, deformation of Al-Cu bimetallic inserts during equal channel angular pressing (ECAP) is investigated using finite element method (FEM). FEM results show that both metals undergo similar straining during ECAP. However, the values of maximum principal stresses that may cause cracking are significantly higher in the casing tube which continues to more significant increase by increasing number of ECAP passes. Therefore, it is concluded that cracking is likely to occur in the copper casing if ECAP deformation of the composite exceeds two passes. This is in agreement with the experimental results in which cracking is observed in the fourth pass of ECAP. Cracking in the copper casing at 45 degrees with respect to the joint interface is attributed to the existence of tensile maximum principal stresses caused by severe shear stresses at the interface. Shear bond strength between the aluminum core and the copper casing in the deformed composite increases up to 3 passes and reduces in the fourth pass. The increase is preliminary attributed to increasing the joint fraction between aluminum and copper substrates and the reduction in the fourth pass is correlated to formation of cracks on the copper substrate. Estimation of shear friction factor (m) between aluminum and copper at the joint interface indicates that it is around 0.21 independent from the number of ECAP passes. Indeed, the number of ECAP passes can change the joint surface fraction, however, it is not effective on the nature of the joint. Indeed, m smaller than 1 indicates that a solid metallurgical bonding has not formed over the joint and mechanical bonding is mostly responsible for the joint strength. In addition, as m is not a function of number of passes, it is concluded that the type of bonding at the interface is not affected by number of ECAP passes.