In the current study, a comprehensive evaluation of AA5083 processed via the novel Multi-Channel Spiral Twist Extrusion (MCSTE) method was conducted. The induced stress-strain state and the ...deformation mechanism of multiple pass deformation via MCSTE dies with twist angle β (30°) and (40°) were analyzed using finite element analysis. Nanohardness measurements were carried out along the billet surfaces to validate the numerical model output. The micro-hardness, tensile-up-to-fracture, fracture behavior and microstructural properties were investigated. The numerical model and the empirical findings reveal that the increase in the mechanical properties of the billets processed via MCSTE die with a twist angle β (40°) was associated with a plastic strain of 0.9 (mm/mm) compared to 1.2 (mm/mm) for conventional twist extrusion dies of β (60°). For the MCSTE die with angle β (30°), the hardness and tensile properties increased as a function of increasing the number of passes, with an insignificant reduction in ductility. Processing via a die angle β (40°) was limited to one pass due to excessive strain hardening, which resulted in shear localization during the second pass. The detailed analysis presented herein validates the effectiveness of MCSTE processing as a severe plastic deformation tool with a favorable potential for industrial applications.
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This study aims to establish the effects of equal channel angular pressing (ECAP) processing on the corrosion behavior and hardness values of the AZ31 Mg alloy. The AZ31 billets were processed ...through ECAP successfully at 250 °C and their microstructural evolution was studied using optical and field emission scanning electron microscopy. The corrosion resistance of the AZ31 alloy was studied before and after processing through ECAP. The homogeneity of the hardness distribution was studied using both sections cut parallel and perpendicular to the extrusion direction. ECAP processing resulted in highly deformed central regions with elongated grains aligned parallel to the extrusion direction, whereas the peripheral regions showed an ultra-fine-grain recrystallized structure. After processing, small ultra-fine secondary particles were found to be homogeneously dispersed alongside the grain boundaries of the α-Mg matrix. Regarding the corrosion properties, measurements showed that ECAP processing through 1-P and 2-Bc resulted in decreasing their corrosion rate to 67.7% and 78.3%, respectively, of their as-annealed counterpart’s. The corrosion resistance of the ECAPed Mg alloy increased with the number of processing passes. This was due to the refinement of the grain size of the α-Mg matrix and secondary phases till ultra-fine size, caused by the accumulation of strain during processing. On the other hand, ECAP processing through 2-Bc resulted in increasing the Vickers hardness values by 132% and 71.8% at the peripheral and central areas, respectively, compared to the as-annealed counterpart.
Recently, several severe plastic deformation (SPD) techniques have been developed with the aim of incorporating grain refinement and strengthening metal forming technology into the industry without ...dimensional changes. Multi-channel spiral twist extrusion (MCSTE) was innovated and patented in an attempt to provide an effective, cost-saving SPD process that would attract the industrial uptake of the renowned twist extrusion (TE) method. The MCSTE process is based on the use of customized stacked disks that host non-circular cross-sectioned billets extruded through a die with a twist angle (β). Hence, an empirical study was conducted on AA1100 to investigate the influence of 4 successive MCSTE passes on the mechanical behavior and microstructural evolution of the extrudates compared to the as-received (AR) condition. Electron backscatter diffraction (EBSD) was employed for mapping the structural evolution, misorientation angles and the texture developed as a function of the processing passes. Additionally, hardness and tensile properties were evaluated and correlated with the EBSD findings. EBSD analysis revealed the formation of almost equiaxed grains after 1 pass, which were evolved into elongated grains aligned at approximately 45° relative to the extrusion direction after 2-passes. Moreover, MCSTE processing 1-pass produced a structure with 64% and 36% HAGB and LAGB, respectively, while 2-passes via MCSTE increased HAGBs to 80%. Processing 4-passes increased the amount of recovery depicted by the percentage of LABs within the grains, which was associated with a noticeable increase in the fraction of fine grains < 8 µm. MCSTE produced a very strong texture that increased in intensity with an increasing number of passes. The results demonstrated a significant increase of 73% and 40% in the average hardness and tensile strength, respectively, with an increasing number of passes up to 4, which was coupled with an insignificant 2% reduction in ductility. The displayed results validated the effectiveness of MCSTE as an SPD tool for grain refinement with a favorable potential for industrial applications.
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This study presents a comprehensive evaluation of Equal Channel Angular Pressing (ECAP) processing on the structural evolution and mechanical properties of AA2xxx aluminum alloy. Finite element ...analysis (FE) was used to study the deformation behavior of the AA2xxx billets during processing in addition investigate the strain homogeneity in the longitudinal and transverse direction. Billets of AA2011 aluminum alloy were processed successfully through ECAP up to 4-passes with rotating the sample 90° along its longitudinal axis in the same direction after each pass (route Bc) at 150 °C. The microstructural evolution and crystallographic texture were analyzed using the electron back-scatter diffraction (EBSD) and optical microscopy (OM). An evaluation of the hardness and tensile properties was presented and correlated with the EBSD findings and FE simulations. The FE analysis results were in good agreement with the experimental finding and microstructural evolution. Processing through 4-passes produced an ultrafine-grained structure (UFG) and a recrystallized fine grain dominated the structure coupled with a geometric grain subdivision which indicated by grain refining and very high density of substructures. This reduction in grain size was coupled with an enhancement in the hardness, tensile strength by 66.6%, and 52%, respectively compared to the as-annealed counterpart. Processing through 1-pass and 2-passes resulted in a strong texture with significant rotation for the texture components whereas 4-passes processing led to losing the symmetry of the texture with significant reduction in the texture intensity.
The hexagonal close-packed (HCP) crystal structure of Mg alloys lead to poor formability as well as other undesirable mechanical behaviors in an otherwise highly sought-after alloy for commercial ...use. This study investigates the evolution of microstructure, texture, corrosion and mechanical behaviors in Mg–Zn–Mn (ZM31) alloy after processing using Equal Channel Angular Pressing (ECAP). Dynamic recrystallization was evident in the ECAP-processed samples, correlated with a substantial fiber structure, and resulted in the attainment of notable grain refinement and high lattice strain. Average grain sizes of 2.2 and 2 μm were achieved via 2 and 4-Pass Bc processing, respectively. This significant refinement yielded lower corrosion rates through enhancement of the thickness, coherency, and stability of formed protective oxide layers. The corrosion rate in the NaCl medium was substantially enhanced by 99.5% after four passes via route Bc. The recrystallized fine structure was found to have contributed to yield strength, ultimate strength, and microhardness improvements. Deformation enhanced yield and ultimate strengths by 132% and 64%, respectively. The distinctive grain refinement mechanism exhibited through the current ECAP procedure has potential to pave the way for novel and impactful utilizations of ZM31 in industries that demand exceptional mechanical and corrosion performance.
The current study presents a detailed investigation for the equal channel angular pressing of pure copper through two regimes. The first was equal channel angular pressing (ECAP) processing at room ...temperature and the second was ECAP processing at 200 °C for up to 4-passes of route Bc. The grain structure and texture was investigated using electron back scattering diffraction (EBSD) across the whole sample cross-section and also the hardness and the tensile properties. The microstructure obtained after 1-pass at room temperature revealed finer equiaxed grains of about 3.89 µm down to submicrons with a high density of twin compared to the starting material. Additionally, a notable increase in the low angle grain boundaries (LAGBs) density was observed. This microstructure was found to be homogenous through the sample cross section. Further straining up to 2-passes showed a significant reduction of the average grain size to 2.97 µm with observable heterogeneous distribution of grains size. On the other hand, increasing the strain up to 4-passes enhanced the homogeneity of grain size distribution. The texture after 4-passes resembled the simple shear texture with about 7 times random. Conducting the ECAP processing at 200 °C resulted in a severely deformed microstructure with the highest fraction of submicron grains and high density of substructures was also observed. ECAP processing through 4-passes at room temperature experienced a significant increase in both hardness and tensile strength up to 180% and 124%, respectively.
Multi-channel Spiral Twist Extrusion (MCSTE) is introduced as a novel severe plastic deformation (SPD) technique for producing superior mechanical properties associated with ultrafine grained ...structure in bulk metals and alloys. The MCSTE design is based on inserting a uniform square cross-sectioned billet within stacked disks that guarantee shear strain accumulation. In an attempt to validate the technique and evaluate its plastic deformation characteristics, a series of experiments were conducted. The influence of the number of MCSTE passes on the mechanical properties and microstructural evolution of AA1100 alloy were investigated. Four passes of MCSTE, at a relatively low twisting angle of 30 deg, resulted in increasing the strength and hardness coupled with retention of ductility. Metallographic observations indicated a significant grain size reduction of 72 pct after 4 passes of MCSTE compared with the as-received (AR) condition. Moreover, the structural uniformity increased with the number of passes, which was reflected in the hardness distribution from the peripheries to the center of the extrudates. The current study showed that the MCSTE technique could be an effective, adaptable SPD die design with a promising potential for industrial applications compared to its counterparts.
Equal-channel angular pressing (ECAP) is among the most applicable severe plastic deformation processes used to fabricate ultrafine-grained materials with superior mechanical properties. In this ...work, a commercial purity aluminum has been processed via ECAP process up to four passes. The infl uence of ECAP routes (A and Bc) on the mechanical properties of the material and its grain size was investigated. Microstructural observations of the as-annealed and the rods processed via ECAP were undertaken using optical microscopy. Hardness profiles and contour maps of sections cut perpendicularly and parallel to the load direction were assessed to investigate the effect of ECAP processing on the hardness distribution across the deformed rods. Compressive properties of the rods were also examined. In addition, digital images correlation was used to display the stress distribution along the longitudinal section of the processed sample during the compression test. Experimental results showed that, 1-pass of ECAP results in an inhomogeneous distribution of strain hardening, which has lower values at the disc center, and increases gradually toward the center. The hardness values of the processed rod increase by 73 and 60.5% post ECAP processing at the rod periphery and center, respectively; on the other hand, ECAP processed rods via 4-A showed an increase in the yield and compressive strengths by 54 and 39%, respectively, compared to the as-annealed condition.
The disability of lower limbs is one of the major problems facing human lives. In order to restore the missing functionality and aesthetic feature of the amputee's locomotion, finding the optimal ...design of the human lower limb knee prosthesis is crucial. This paper focuses the design optimization of a four bar knee mechanism capable to reproduce the complex flexion/extension knee joint motion in the sagittal plane with variable instantaneous center of rotation positions. Thus an optimization approach with appropriate constraints is formulated in order to consider the degree of compatibility between the instantaneous center of rotation trajectories of the human reference knee joint and the four bar knee mechanism. To solve this high nonlinear optimization problem, an algorithm based on multi-objective modified imperialist competitive method is proposed where all the constraints are managed with the penalty method. The results obtained by the multi-objective modified imperialist competitive method showed the capability to reach a small tracking error. The obtained results prove the effectiveness of the proposed optimization approach for the optimal synthesis of the four bar knee mechanism, compared with other literature techniques.
Billets of pure Mg were processed using two ECAP dies with internal channel angle of 90° and 120° for 4-passes of route Bc at 225 °C. Finite element analysis was used to investigate the deformation ...behavior of Mg billets. Electron back-scatter diffraction was utilized to analyze the microstructural evolution and the crystallographic texture of the ECAPed billets. Vicker's microhardness and the tensile properties were studied. The finite element simulations showed that the 90°-die revealed a relative more homogenous distribution of the plastic strain compared with the 120°-die. From EBSD analysis, 1-pass condition of the 90°-die showed a bimodal structure that consisted of newly formed fine grains and heavily distorted large ones, whereas 120°-die counterpart revealed fewer areas with fine-grained structure. Accumulating the plastic strain up to 4-passes in the 90°-die and 120°-die resulted in significant refining of 0.88 μm and 1.89 μm, respectively compared to the as-annealed counterpart of 6.34 μm. The texture after 1-Pass and 2-Passes showed weakening in its intensity, which resembles the B fiber texture of ideal orientation {0 0 0 1} . Increasing the number of ECAP passes to 4-passes resulted in a significant strong texture with more than 26 times random with the intense {0001} poles. This was attributed to the grain refining that occurred after 1-Pass and 2-Passes, which allowed the activation of more slip systems upon the 4-Passes. On the other hand, ECAP processing resulted in a significant increase in the tensile strength, hardness, and ductility.
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