Twist Extrusion Research Articles

Investigation of direct extrusion channel effects on twist extrusion using experimental and finite element analysis

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.

Multi-channel Spiral Twist Extrusion (MCSTE): A Novel Severe Plastic Deformation Technique for Grain Refinement

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.

Densification Optimized Design for CuZnAl Sintered Powders by Different Twist Angle During Twist Extrusion Process by Numerical Method

As a new type of severe plastic deformation method (SPD), deformation of twist extrusion (TE) is mainly determined by the twist angle α and the helix angle β. And when the length of the spiral channel is constant, the twist angle α is indirectly decided to the helix angle β. The numerical simulation model of CuZnAl powder material was established by the finite element software Deform-3D and the influence of the different twist angle α on its densification behavior was simulated in the paper. The results show that spiral channel in TE die structure is a strong shear plastic deformation area and can produce high hydrostatic pressure, and then promotes material density of the powder porous materials. Moreover, the larger twist angle is favorable for densification of the sintered powder material but the densification of the material is not exactly proportional to the twist angleα, and it is the optimized design for TE die because of the minimal uniformity coefficient and the best relative density distribution for the twist angle 270°, too.

The Occurrence of Ideal Plastic State in CP Titanium Processed by Twist Extrusion

This paper deals with the analysis of strength and plastic characteristics of commercially pure (CP) titanium as a function of equivalent plastic strain accumulated during Twist Extrusion (TE) process. It is shown experimentally that multipass TE leads to the saturation of the following characteristics of the material: yield stress, reduction in area, elongation to failure, and uniform elongation. This fact indicates the occurrence of an ideal plastic state in the processed material. The threshold value of accumulated plastic strain for ideal plastic behavior of CP titanium during TE is defined. The strain state and mechanical properties of CP titanium billets processed by TE are studied. An explanation for the hardening on the axis of a billet during TE is offered. The analysis of deformation modes on the billet axis during TE and High Pressure Torsion is carried out. It is shown that the differences in strain state on the axis are caused by the difference in symmetry of these processes.

Fatigue Behaviors of Materials Processed by Planar Twist Extrusion

Since the last decade, the fabrication of ultrafine grain and nanostructure metals and alloys has attracted much attention in the field of materials engineering. The present study aimed at experimentally investigating the fatigue properties that are of great importance in dynamic structures before and after the planar twist extrusion process for both commercially pure copper and 6061 aluminum alloy. The results indicated that the yield strength, tensile strength, hardness, and fatigue endurance of copper increased by about 398, 122, 198, and 183 pct, respectively, while they improved by about 429, 212, 227, and 148 pct, respectively, in aluminum alloy as compared to the initial conditions. The stress-strain curves displayed sizable reduction of strain hardening. Furthermore, grain-size correction factors based on the empirical results were introduced to include the effect of the grain-size effect on both low and high-cycle fatigue strengths of the material.

Assessment of Gas Saturation of Titanium Alloys Synthesized From Powders Using Twist Extrusion

The gas saturation of semi-finished titanium alloys produced from metal powder using the technique comprising cold pressing, vacuum sintering, and subsequent severe plastic deformation by twist extrusion is analyzed. The main sources are considered and the quantitative analysis of pollution of sintered alloys with nitrogen and oxygen impurities contained in the powder particles on their surface and in the pore spaces of the billet is conducted. It is established that the quality of the starting titanium powder has the biggest impact on the pollution of alloys. It is shown that the use of titanium powders with low content of impurities allows keeping the oxygen and nitrogen content of synthesized semi-finished products at the level meeting the requirements of the reference documentation for VT1-0 titanium and heat-resistant titanium alloys. It is shown that the share of impurities entering the synthesized alloy from (i) the oxides on the powder particle surface and (ii) the air filling the closed pore space of the billet is insignificant.

Microstructural evolution and fatigue properties of severely deformed AA1050 aluminum alloy

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.

Thermophysical Properties and Temperature of the Start of Titanium Recrystallization in Different Structural States

The results of measurements of the thermal diffusivity, thermal conductivity, and heat capacity of VT1-0-grade titanium samples in as-cast, deformed submicrocrystalline, and sintered states are presented. It has been established that the decrease in the thermal conductivity and thermal diffusivity of titanium in the submicrocrystalline and sintered states is associated with the increase in the quantity of defects in the material volume, whereas the increase in the temperature of polymorphic transformation of titanium is connected with the dissolution of oxygen in its lattice. The results of investigation of the coefficient of thermal linear expansion of titanium in the macrocrystalline and submicrocrystalline states are presented. The decrease in the coefficient of thermal linear expansion of titanium of submicrocrystalline structure has been established, which may point to the decrease in its melting temperature. It is shown that annealing of samples in a submicrocrystalline state leads to the growth of the temperature coefficient of linear expansion, bringing its value closer to the temperature coefficient of linear expansion of titanium in the equilibrium state. Studies by the method of back reflection photography in a KROS chamber made it possible to estimate the temperature of the start of VT1-0-grade titanium recrystallization after intense plastic deformation by the twist extrusion method. The decrease in the temperature of the start of recrystallization for titanium in the deformed submicrocrystalline state has been established. Based on the trends revealed, optimum regimes of thermal treatment of VT1-0-grade titanium for removing internal stresses and preserving the submicrocrystalline structure have been established.

Twist Extrusion as a Potent Tool for Obtaining Advanced Engineering Materials: A Review

Twist extrusion (TE) is one of the most popular techniques of severe plastic deformation, aiming at imparting to a material a tailored microstructure and the associated property improvement. The article provides a survey of the literature on the mechanics of TE and the effect it has on the structure, texture, and the attendant properties of various materials, including metals and alloys, powder materials, and polymers. Special emphasis is placed on vortex flow during TE and its hitherto unexplored potential for producing micro‐ and macrostructures that promise superior properties of the materials. In particular, the possibility of creating novel hybrid materials with chiral inner architecture is demonstrated. The survey is concluded by a presentation of examples of practical applications of TE.

Stress and strain distribution in twist extrusion of AA6063 aluminum alloy

Twist extrusion is one of the common methods in the area of severe plastic deformation. By passing the sample through a twist channel grain refinement will occur. In this article, the twist extrusion process is modeled by ABAQUS finite element software. Three different approaches are used for prediction of strain field distribution for higher passes of TE. The FE results are compared with the experimental results of twist extruded AA6063 aluminum alloy specimens. A sensitivity analysis has been implemented to choose the proper element size and friction coefficient during simulation. The microstructures of TE samples have been observed by SEM microscopy and analyzed by Pixcaviator software. Comparing the results of the microstructure study and FE shows that importing the material properties and deformation field from the previous pass to the current pass is the best way to simulate a multi-pass twist extrusion process. The plastic strain distributions show that the effective plastic strain is higher at the corner of the samples than at the center of it. The FE results show that the maximum Von-Mises stress increases at the corner elements by increasing the extrusion passes from 42 MPa at pass #1 to 110 MPa at pass #7. Most of this increase occurs in the first three passes.

Producing of ultrafine grained composites with a large uniform elongation by twist extrusion: Mathematical simulation

The conditions of production of a composite material of the ultrafine grained shell–coarse-grained core type are determined by mathematical simulation of twist extrusion. A combination of regions with ultrafine grained and coarse-grained structures in the sample volume leads to a substantial increase in strength of the sample at a retained large uniform elongation.

Monotonic and dynamic mechanical properties of PTCAE aluminum

Abstract This paper is motivated by the aim of obtaining monotonic and dynamic mechanical properties of pure aluminum within planar twist channel angular extrusion (PTCAE) process. Hence, PTCAE die which is the fine integrated of equal channel angular extrusion and planar twist extrusion was designed and manufactured. It is found that exceptional grain refinement of material using PTCAE process leads to 71%, 137% and 62% improvements in tensile strength, hardness and fatigue endurance after the first pass and 92%, 170% and 78% enhancements through the subsequent pass, respectively as compared to the annealed condition. Also, this enhancement is caught up with expense of tensile ductility and work hardening under cyclic deformation. Besides, process affects the fatigue strength performance and decreases it from 62 to 10 by increasing the pass number. Additionally, increment of tensile strength has the most essential role on fatigue strength growth. Referring to the numerical findings, material with the plastic strain of 1.64 and strain distribution of 0.40 was obtained after the single pass. So, with respect to the achieved advances, the aforementioned method is promising for future industrial applications.

非線形ねじり押出法による結晶粒超微細化

非線形ねじり押出法による結晶粒超微細化

Application of Response Surface Methodology in optimizing the process parameters of Twist Extrusion process for AA6061-T6 aluminum alloy

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.

Effect of the Strain Kind on the Texture and Microstructure of Low-Alloyed Steel

Crystallographic texture and microstructure of low-alloyed steel after twist extrusion (TE) and subsequent cold rolling along and across the TE axis were studied. The double axial cylindrical texture with axes 110 and 100 parallel to the TE axis and the vortex-like microstructure are formed in the steel during the TE. The subsequent rolling of extruded steel along the TE axis promotes the forming of typical steel rolling texture as well as the microstructure with elongated grains in rolling direction. Typical steel rolling texture as well as the equiaxed microstructure is formed in extruded steel after rolling in the direction transverse to the TE axis. The mechanisms of formation of the texture are discussed.

Inhomogeneity in strain, microstructure and mechanical properties of AA1050 alloy during twist extrusion

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.

Analysing the Twist Extrusion of Porous Blanks Using Modified Theories of Plasticity for Porous Bodies

Features of the twist extrusion of blanks containing pores and plane cracks are considered. The effect of flat cracks on the porosity distribution and rate of local loosening during deformation is analyzed. The analysis is conducted using a modified theory of plasticity for porous bodies and the finite-element method. It is established that the porosity distribution is sensitive to the concentration of flat defects. At a certain concentration of plane defects, the porosity distribution is inverted: the porosity is higher at the periphery than at the center. The effect of flat defects on the accumulated strain and, as a result, on the structure refinement is less significant. It is confirmed that using the counter-pressure allows suppressing the growth of defects, reducing the refinement efficiency.

Vortices in Noncompact Blanks During Twist Extrusion

The causes and consequences of the formation of multifractal vortices during severe plastic deformation of powder and porous bodies by twist extrusion are analyzed. It is demonstrated that the developed pore space in noncompact blanks leads to the formation of self-similar vortices at different scales. It is established that the multifractal vortices occurring during simple shear in twist extrusion, are responsible for the differences in the mechanisms of hardening of compact and noncompact materials. Being significantly increased (in comparison with the concentric streamlines during deformation of compacted materials), the integral deformation path intensifies the accommodation of particles of a mixture of powder components. In addition, the vortices cause intensive mixing and mass transfer at both micro and macro scales. The intensive mass transfer leads to chemical and structural homogenization and elimination of porosity.

Деформация сдвигом методом кручения, осадки и прессования

Integrated process of metal deformation by Torsion, Upsetting and Press Forming serves to produce submicrocrystalline structure of large weight metal stocks. The performed work demonstrated efficiency of shear deformation with twist torsion. The most efficient is the use of indirect twist torsion allowing preparation of the stock metal structure for subsequent conventional conversion with the minimum time and economic costs. As compared to the known methods of nonmonotonic deformation, such as high pressure torsion, equal channel angular extrusion and twist extrusion, twist torsion allows solid stock processing. The new trend in the deformation domain will be particularly vital for extra strong metal production for aircraft engineering, space technologies, automotive industry, shipbuilding, bridge engineering and other industries. The developed process allowed comparing of the conventional upsetting and extrusion with shear deformation and determining its efficiency.

Modeling and Characterization of Texture Evolution in Twist Extrusion

Twist extrusion (TE) is a severe plastic deformation method with a potential for commercialization. Deformation during the TE process is non-uniform and non-monotonic, which is expected to result in significant and non-trivial microstructural changes in metallic materials. In this study, texture evolution during TE of pre-textured copper was investigated. Experimental characterization of textures after various numbers of passes demonstrated that TE can be used for producing uniformly weak textures in pre-textured copper. Crystal plasticity simulations were found to run into the problem known as strain reversal texture. In particular, crystal plasticity simulations predicted the return of initial texture upon strain reversal in the first pass of TE, whereas the experimental texture was not reversed and had components related to simple shear. Grain refinement, imperfect strain reversal, and material asymmetry are proposed to be responsible for the occurrence of strain reversal texture in TE. Effects of the non-random initial texture on the microstructure and texture evolution are also discussed.