This study presents a comprehensive evaluation of the effects of multi-channel spiral twist extrusion (MCSTE) processing on the mechanical properties and structural evolution of AA5083. The ...structural evolution and texture developed were mapped by electron backscatter diffraction (EBSD) for three successive passes and compared with an as-annealed plate. An evaluation of the hardness and tensile properties was presented and correlated with the EBSD findings. The displayed EBSD results revealed that grain refinement was strongly associated with the presence of a high density of low-angle grain boundaries (LAGBs) after one pass, which developed into fine grains of less than 20 μm and high-angle grain boundaries (HAGBs) after three MCSTE passes. The three pass processing led to a 65% reduction in grain size. This reduction in grain size was coupled with an enhancement in the hardness and tensile properties. Additionally, the crystallographic texture study represented a slightly random texture due to the presence of intermetallic particles in AA5083. This study demonstrates the efficacy of MCSTE as a grain refinement tool.
In this article, the effect of twist extrusion (TE) on the fatigue behavior of the AA1050 aluminum alloy is investigated. For this purpose, samples of AA1050 are TE processed for 1, 2 and 4 passes. ...Tensile testing and rotational bending fatigue testing were performed on samples extracted from the surface of the TE specimens. As well, the correlation between microstructure, tensile properties and fatigue response are discussed. The un-deformed AA1050 sample showed a yield strength (YS) of 26.6MPa and ultimate tensile strength (UTS) of 46.1MPa and resisted the 38MPa bending stress for 373,000cycles. While the YS and UTS increased after TE, the fatigue life of TE processed specimens reduced compared with the un-deformed sample. Indeed, the fatigue life reduced to 335,168, 299,798 and 259,260cycles after 1, 2 and 4 passes of TE, respectively. Reducing fatigue life was attributed to smaller strength ratio, i.e., UTS/YS, achieved after TE processing. Analyzing the fracture surface of the TE samples showed that the cracks were initiated from preferential locations and moved towards center leading to ultimate ductile fracture at the center. The area of ductile fracture was found to be reduced in TE processed specimens while the widths of striations were increased.
•Effect of twist extrusion (TE) on the fatigue behavior of the AA1050 aluminum alloy.•Samples of AA1050 are TE processed for 1, 2 and 4 passes.•Tensile testing and rotational bending fatigue testing were performed.•Fracture surface of the samples were analyzed.
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•A tandem process of the simple shear extrusion and twist extrusion was proposed.•Deformation heterogeneity was investigated using the finite element method.•The tandem process ...produces more homogeneous and larger deformation than extrusion.
Recently, simple shear extrusion (SSE) and twist extrusion (TE) are introduced to fabricate ultrafine grained bulk rod metallic materials. The SSE and TE processes generate significant deformation inhomogeneity, with higher and lower strains in the center, respectively, which easily causes mechanical instability of the materials. In this study, to overcome this deformation inhomogeneity problem in SSE and TE, a tandem process of SSE and TE (TST) is suggested. The finite element method is applied for plastic deformation behavior during the TST process. The results demonstrate that the TST process can produce relatively homogeneously deformed materials. In particular, the effects of back pressure and processing order on the plastic deformation behaviors in the TST process are systematically analyzed.
The results of studies of porosity, microhardness, microstructure, phase composition, and distribution of alloying elements in samples of VT6 and VT8 titanium alloys are presented. They were ...synthesized from a mixture of powder components with various modes and subjected to severe plastic deformation by torsion under high pressure with multiple regimes. The effects of sintering time and the regimes of subsequent severe plastic deformation on the microhardness, and it is dispersion through the cross-section of the samples were identified. It was shown that, regardless of the sintering regimes, the microhardness of the samples across the cross-section and does not depend on the processing regimes. Consequently, this serves as an indication of a saturation effect of fragmentation and hardening. The analysis of the porosity of the initial samples concerning both the sintering time and the samples subjected to high pressure torsion was conducted. It was demonstrated that irrespective of the initial value of porosity, severe plastic deformation enables the complete elimination of porosity across the entire cross-section of the samples. It was concluded that the formation of new phases does not occur in the samples of the studied titanium alloys during the process of the severe plastic deformation. It was shown that the samples after sintering obtain a significant chemical heterogeneity, which is effectively eliminated in the process of deformation. The beneficial role of the generated in the samples vortex flows, which facilitate efficient mass transfer was confirmed after adding slowly diffusing chemical elements into the composition of the powder mixture. Considering the physical similarity of the processes which occur in a thin deformable layer of samples during the severe plastic deformation by twist extrusion and high pressure torsion, conclusions on the effectiveness of using twist extrusion to homogenize structural and chemical inhomogeneities in bulk billets of the sintered titanium alloys were drawn.
The severe plastic deformation modification of reduced activation ferritic/martensitic (RAFM) steel was performed by sequential extrusion-twist-extrusion (SETE) at 873 K. Mechanical properties and ...microstructures were investigated by Vickers hardness and nanoindentation tests, metallography (OM), and electron backscatter diffraction (EBSD) for revealing the microstructures evolutions. The results have shown that SETE deformation can synchronously and effectively enhance the strength and plasticity, determining by the synergism fine-grain strengthening and dislocation strengthening through dynamic recrystallization and shear deformation. However, temperature (600 K) has little effect on the strength and microstructures (grain refinement and uniformity, dislocation density). The calculated standard deviations of grain size for RAFM samples are 5.3, 4.9, 2.8, and 2.2, respectively. The maximum values of fitted ellipse aspect ratio (R) for RAFM samples are 9.79, 8.88, 5.47, and 5.90, and their fractions of R< 3 are 82, 82, 88, and 83%. SETE deformation could enhance the plasticity through the improvement of the synergism grain refinement and uniformity.
► The influence of process parameters in TE was systematically analyzed using the finite element method. ► BP combined with a frictionless condition provides the best stress state distribution in ...terms of uniformity. ► The results provide a basis for reasonable decision of processing conditions for TE.
Twist extrusion (TE), a promising severe plastic deformation (SPD) technique for grain refinement down to ultrafine/nanocrystalline microstructures, was introduced as an attempt to provide large plastic deformation conditions similar to those in high pressure torsion while allowing large workpiece dimensions for industrial applications. As a relatively new SPD technique, TE requires in-depth investigation of its plastic deformation characteristics. The present study investigates the influence of process parameters such as backward pressure and friction on the loading history, the stress/strain states, and the final shape of processed workpieces using the finite element method. The results provide a basis for reasonable decision of processing conditions and also identify prerequisites for studies in formability and fracture of metals subjected to TE.
In this research, the effect of per pass applied strain on the mechanical and electrical properties of commercial pure copper in twist extrusion process was investigated. For this, two dies with ...different twist angles of 37° and 56° (called dies A and B, respectively) were manufactured to perform the process in 8 passes. Finite element simulation was used to find the average per pass applied strain in the investigated dies. Compressive testing and hardness testing were used to assess the mechanical properties of the samples processed up to different passes. Also, the optical micrographs accompanying with SEM images were prepared from the samples to explain the effect of the applied strain on the grain refinement and the consequent mechanical properties. Comparison of the samples processed in dies A and B with the same accumulated strain showed that reducing per pass applied strain causes the improvement in the mechanical properties of the samples. The results also showed that the electrical resistance of the samples changes in proportion to the changes in the mechanical properties.
Graphical Abstract
Practically, the helical products used as a mechanical part to satisfy the needs of mechanical strength and artistic appearance. In addition, during recent 5 years it used to produce an ultra-fine ...grain metal structure. However, there are very little works regarding this type of extrusion so far. This work proposed a new formulation for helical deformation zone to produce general helical polygonal shapes through a streamlined die that are usually made by hot extrusion through taper die. The general die surface was represented analytically. The velocity and strain rate fields are derived depending on the volume constancy and the velocity boundary conditions. The upper bound forming pressure was obtained for various frictional conditions, area reduction, helix angle, and die length. The results show that the axis of the product does not rotate through the helical extrusion. The peak value of the strain rate is located close to the die outlet and decreases as the helix angle increases. The optimum die length becomes high as the helix angle increases. The forming pressure increases with increasing helix angle, area reduction, factor of friction, while decreases when the number of sides increases. The theoretical results were verified with previous work of zero twist and showed completely compatible. A finite element solution was done using hardening material model to verify the analytical results and metal flow and to examine the strain and stress fields in the product.
We propose an experimental method for investigating the kinematics of metal flow in twist extrusion (TE). The method is based on a theoretical model of the velocity field. The parameters of this ...model are determined to satisfy the observed flow-line for characteristic points of the specimen. The model incorporates two physical constraints: (1) metal flow is limited by the surface of the die; (2) metal volume remains constant. The advantage of this method is that it takes into account the actual rheology of the metal and friction conditions.
We show that TE forms a vortex-like flow that stretches metal particles. The stretching increases with subsequent TE passes. The equivalent strain increases from 0.3 to 0.5 in the paraxial zone of the specimen to 2.0–2.5 at the periphery.
We analyze different sources of inaccuracy of the method and show that its error in estimating the equivalent strain is of the order of 0.1, which is perfectly acceptable when investigating severe plastic deformations.
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•Innovative twist extrusion was achieved by embedding a direct extrusion channel after the twist zone.•Finite element analysis showed that the direct extrusion channel decreased ...sample deformation heterogeneity.•All data indicated that absence of sufficient back pressure led to distortion and elongation of samples.•The best microstructure was achieved by combining twist extrusion and direct extrusion channel.
Twist extrusion (TE) is a relatively new severe plastic deformation technique in which radial deformation is heterogeneously distributed in the sample. In this research, in order to achieve favorable properties, a direct extrusion (DE) channel was embedded after the twist zone at the bottom of the TE die. The plastic deformation behavior of aluminum alloy 6063 (AA6063) was investigated in the TE process, with and without the DE channel. AA6063 successfully underwent TE under the conditions designed using the finite element analysis. According to the simulation results, a very heterogeneous distribution of the equivalent plastic strain (PEEQ) was observed in TE, while the TE+DE simulation exhibited more homogeneous PEEQ in the central and lateral regions. Microstructural evolution analysis using scanning electron microscope and Vickers microhardness evaluations showed that utilizing the DE channel increased the hardness and provided a more homogenous microstructure. Moreover, tensile testing results indicated an increase in strength and enhanced mechanical properties of the TE+DE processed AA6063.
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