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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In this research, the feasibility of making aluminum–copper bimetallic bar by twist extrusion followed by forward extrusion is addressed. In this consecutive process, twist extrusion was used in ...several passes and its effect was investigated on the bond strength between aluminum and copper as well as the mechanical properties of the produced bimetallic bars. When forward extrusion was the only applied process, the compressive yield and shear bond strength of produced bimetallic bars were 184MPa and 5.4MPa, respectively. Applying four twist extrusion passes followed by one forward extrusion pass increased these values such that the compressive yield and shear bond strength were increased by about 64% and 200%, respectively. The hardness was also significantly increased by the utilization of this procedure. Microstructures of copper and aluminum in the produced bars showed that by applying and repetition of the twist extrusion, the grain size was reduced. The Mechanical locking was the main factor in bond formation. Reducing the gap between the metal plates at the interface and increasing the joint fraction improved the shear bond strength.
In this study, inhomogeneity in the distribution of effective strain, microstructure and mechanical properties of AA1050 during twist extrusion (TE) are investigated. The samples are deformed up to 8 ...passes without rotation between passes. It is found that flow stress of the material increases by the number of passes. The observed percentage of the increase is more significant after two passes deformation. By increasing the number of passes to 4, smaller enhancement in flow stress occurs. As the number of passes increases to 8, a pronounced enhancement in strength is observed and fraction of high angle grain boundaries significantly increases. Microstructural analysis indicates that regardless of the number of passes, no development of cells and subgrains is observed in the central region of the specimens. In contrast, distinguished cell structure forms at the surface even by applying the first 2 passes of TE. In addition, inhomogeneity in strain, microstructure and mechanical properties are more significant at higher number of passes.
Researchers have recently interested in devising integrated severe plastic deformation (SPD) techniques that can create ultra-fine grained (UFG) metal in one pass. This paper proposes a novel ...integrated severe plastic technique called multi-angular twist channel extrusion (MATE). This technique was created the aim of retaining strain uniformity while applying a significant strain in a single pass. The input parameters such as annealing temperature, type of lubricant and ram speed, were optimized in this study in relation to the Vickers hardness, hardness inhomogeneity and ultimate tensile strength of the extruded material. Experiments were carried out based on full factorial design, and the TOPSIS approach was used to find the best combination of input parameters. The analysis of variance is used to determine the amount of contribution of input parameters on the mechanical properties. Finite element analysis was performed with the identified optimum parameter of annealing temperature = 550 °C, type of lubricant = MoS2 and ram speed = 3 mm/sec. The average effective strain of 2.72 is obtained by in the MATE process. Experimental studies revealed that the strength and hardness of copper alloy was increased by 69.8 % and 80.5 % respectively. Scanning electron microscope image revealed the grain refinement by MATE process in the copper alloy.
In the present paper, the effect of twist extrusion (TE) on the variations of hardness and tensile properties in commercial pure copper is investigated. It is found that hardness, yield and ultimate ...tensile strength of the alloy increased by increasing distance from the center of the sample after one pass TE. Similar consequences are observed when the second pass of deformation is considered. This is attributed to inhomogeneity of deformation and the higher strain imposed on the material at the peripheral regions. It should be noted that the inhomogeneity is increased at the second pass when route A of deformation is utilized and reduces by utilization of route D. This has as a well-established effect on the development of microstructure throughout the cross section of the samples. In fact, it is found that the microstructure at the peripheral regions is more significantly deformed leading to higher dislocation density and extensive subgrain formation. In addition, it is found that at the second pass using route A, inhomogeneity of deformation and microstructure increases. However, less inhomogeneity is observed when route D is utilized which is in line with the hardness and tensile test results. In the end, it is concluded that depending on the aim of the SPD process, if more homogeneous deformation and microstructure is required, route D is recommended and route A should be utilized in case if maximum inhomogeneity is desirable.
Processing by twist extrusion was used to produce copper billets with a hexagonal cross-section. A special feature of the billets is their gradient microstructure owing to a specific strain pattern: ...an undeformed core and a deformed outer sheath. The initial sample with a 40 mm diameter was processed at room temperature by four twist extrusion passes through a twist die having a hexagonal cross-section and a small twist-line slope angle β = 40° with a back-pressure of 100 MPa. The results showed that the processed sample had an undeformed core 20 mm in diameter and a deformed outer sheath with a gradient microstructure in which the average grain size decreased gradually from 50 μm to 0.5 μm towards the periphery along a radius direction. The microstructure gradient represented the various stages of the grain refinement process corresponding to increasing shear strain. The texture revealed two different shear deformation modes whose shear planes were perpendicular and parallel to the extrusion axis. The measured Vickers hardness showed good agreement with the microstructure. In the deformation zone, the classical Hall-Petch relation between the hardness and the grain size of the various characteristic areas formed by twist extrusion was found.
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•Hexagonal shaped twist extrusion produced an undeformed core and a highly deformed external zone.•Gradient microstructure was identified from 50 to 0.5 μm grain size.•The shear mode was identified from the measured texture showing a transition between two shears.•The Hall-Petch relation was valid within the gradient deformed part of the sample.
Twisted variable channel angular pressing (TV-CAP) is a novel method. While it combines the advantages of equal channel angular pressing (ECAP), twist extrusion and direct extrusions, also it ...eliminates the disadvantages of these methods. Finite element analysis was also carried out in order to examine the design parameters, material flow and examine the effective strain values. Hardness and tensile tests were performed to examine the effect of TV-CAP on the mechanical properties of AA6082. In addition, optic microscope, SEM and TEM images were taken respectively and XRD, EDS and EBSD analyses were accomplished in order to investigate the microstructural analysis. As a result of this study, it has been observed that the material has hardened approximately 3 times compared to the annealed material and became 1.5 times stronger in terms of ultimate tensile strength. It was also concluded that, this new method is more efficient than twist extrusion and multi-pass equal channel angular pressing processes.
The effect of process parameters such as forming load, temperature and the number of passes on AA6061-T6 alloy subjected to severe plastic deformation by twist extrusion process has been assessed. ...Full factorial design was used to plan the experiments. Analysis of variance was applied to investigate the influence of process parameters and their interactions. An empirical relationship has been formulated using response surface methodology to optimize the forming characteristics. The empirical relationship indicates that the number of passes was found to be the most significant factor affecting the output parameters such as tensile strength and hardness. The experimental outcomes such as tensile strength and micro hardness indicated that there is a considerable increase in the tensile strength and hardness.
Commercially pure copper sample was subjected to severe plastic deformation (SPD) processing via applying twist extrusion (TE) and equal channel angular pressing (ECAP) at room temperature. It was ...found that in the same accumulated strain (~2.4), TE decreased the mean grain size more than ECAP did. Moreover, the microstructure produced by TE was more homogeneous than that obtained by ECAP. The results of the tensile test showed that the strength properties of the TEed sample were higher than those of the ECAPed one. However, in the same strain value the ductility of the ECAPed specimen was higher than that of the TEed sample.
•In the same accumulated strain TE decreases grain size more than ECAP does.•Microstructure produced by TE is more homogeneous than that obtained by ECAP.•The strength of TEed sample is more than that of ECAPed one.•In the same imposed stain ductility of ECAPed sample is higher than TEed one.
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