Multi-pass Equal Channel Angular Extrusion Research Articles

A Study of Microstructure Evolution for Mg Alloy Subjecting to Multi-Pass Equal Channel Angular Extrusion

A Study of Microstructure Evolution for Mg Alloy Subjecting to Multi-Pass Equal Channel Angular Extrusion

Decoupling Seebeck coefficient and resistivity, and simultaneously optimizing thermoelectric and mechanical performances for n-type BiTeSe alloy by multi-pass equal channel angular extrusion

Equal channel angular extrusion (ECAE) has become a new process for both preparing ultrafine grained uniform microstructure and minimizing contamination. In the present work, the BiTeSe polycrystalline bulk alloys with uniform microstructure was obtained by applying ECAE method to extruding the cast ingot directly. The lamellae coarse grains (hundreds microns to several millimeters) of initial cast ingot were efficiently and uniformly refined to about 18 ~ 24.7 μm. Experiments combining with numerical simulation confirmed that the uniformity of the grain size distribution was remarkably improved by increasing the number of extrusion pass owing to the continuous refinement of grains in the unrefined region and the retainment of grains in the refined region. The Vickers Hardness was doubled at 4th pass in this connection. On the other hand, it is inspiring that applying ECAE to the initial cast ingot not only decoupled the Seebeck coefficient and resistivity, but also simultaneously optimized the electrical and thermal transport performances. For this reason, the dimensionless figure of merit (ZT) increased rapidly with the increase of the number of extrusion pass. Finally, BiTeSe billet extruded for 4 passes achieved the maximum ZT, which was far higher than that of the initial state.

Repeated equal-channel angular extrusion of polypropylene: Processing routes and back-pressure influence

Multi-pass equal channel angular extrusion (ECAE) process of polypropylene was investigated at room temperature using a 90° die-angle tooling outfitted with a back-pressure. The process was repeated until eight times using two different extrusion orientation routes: route A where the sample orientation is kept constant between each extrusion and route C where the sample is rotated by 180°. The crystalline textures were examined by WAXS measurements and the changes on the mechanical response were observed by full-field strain measurements during tensile tests. The use of a back-pressure turns the deformation behavior, along the flow direction of the ECAE products, from highly heterogeneous (characterized by a peculiar periodic shear-banding behavior) to roughly homogeneous and leads to completely different plastic processes in the crystalline phase. The textural differences subsequent to the multi-pass processing and the use of a back-pressure are the source of significant differences in tensile response along the flow direction. The observations show that the polypropylene processed via route C reaches more easily a saturation state than that obtained via route A with a strong beneficial influence of a back-pressure.

Strong ductile bulk tungsten

Tungsten has long faced the problem of limited to no ductility in bulk polycrystalline form, due in part to the low energy needed for intergranular fracture. This limited ductility can be overcome through processing by dramatically reducing the cross sectional area following a conventional temperature step-down method that improves ductility through elongation of grain boundaries and development of a {110} fiber texture along the length of the material. While this technology is over 100 years old, little progress has been made to improve the ductility of bulk material. In the current investigation plastically deformed bulk tungsten was observed to have a room temperature tensile ductility between 17% and 23% total elongation at failure in bend specimens, and a flexural yield strength near ~ 3GPa. This improvement in ductility following multipass equal channel angular extrusion processing appears to be caused by a similarity in microstructure and texture to that of ductile tungsten wire. The onset temperature for transition to noticeable ductility is seen to decrease dramatically with the level of plastic strain. The results indicate that severe plastic deformation processing at low homologous temperatures may be an effective way to improve the ductility and toughness of bulk tungsten and other brittle crystalline metals.

An Analysis on the Deformation of Pure Copper during Multi-pass Equal Channel Angular Extrusion

Nanomaterials are produced by subjecting materials to severe plastic deformation (SPD) which has widely emerged as a technique for grain refinement in Al, Cu, Ti, Mg alloys with improved mechanical properties. Equal Channel Angular Pressing (ECAP) is one of the attractive SPD techniques because it offers potential for high strain rate super plasticity by effective grain refinement from macro gained structure to the level of sub-micron or nano-scale. The aim of this paper was to study the deformation homogeneity of pure copper during multi-pass equal channel angular extrusion. The Finite Element Modeling of ECAP is done in metal forming software FORGE. The experiment is performed in cold working conditions though route C with channel angle Φ = 90° and having different friction conditions. The evolution of equivalent strain is analysed for the deformed billet under different processing parameters upto 5 passes. Also, variation in extrusion force, energy and stresses are studied for the considered conditions. It is established through simulations that number of passes and friction plays significant role in strain homogeneity and changes in vonmises stresses. The study helps in developing ultra-fine grain materials for automobile and aerospace applications.

High-cycle fatigue behavior of severe plastically deformed binary Zn–60Al alloy by equal-channel angular extrusion

High-cycle fatigue properties, mainly the fatigue strength and fatigue life, of two-phase Zn–60Al alloy subjected to severe plastic deformation (SPD) via multi-pass equal-channel angular extrusion (ECAE) using two different routes, route-A and route-BC, were studied. The effect of ECAE processing parameters on the fatigue behavior of the alloy was investigated, and the stress amplitude versus number of cycles to failure (S–N) curves of the alloy were determined in the as-cast and multi-pass ECAE-processed conditions. The results showed that the fatigue performance of the alloy improved significantly through multi-pass ECAE. The fatigue endurance limit of the as-cast alloy reached to 146MPa from 79MPa. On the other hand, the fatigue properties of the ECAE-processed alloy were affected by ECAE parameters, and showed sensitivity to number of cycles and stress levels. Correlation of fatigue data showed that Basquin's law can be used to express the fatigue behavior of the multi-pass ECAE-processed alloy. Also, the ECAE processing changed the nature of fracture characteristics of the as-cast Zn–60Al alloy.

Microstructure and Mechanical Properties of 6061 Aluminum Alloy Processed by Multi-Pass ECAE at Room Temperature

In order to investigate effect of equal channel angular extrusion (ECAE) on microstructure and mechanical properties of annealed and solution-aged 6061 aluminum alloys, continuous ECAE process was carried out by physical test and finite element methods. The results show that the grains are refined with the increase of deformation; the metal flow lines cross and shear each other to form the clear boundaries. The solution-aged Al alloy does not show a monotonic increase in surface hardness with increasing passes as the annealed Al alloy does, but reaches a maximum value after the second pass and decreases successively during next two passes, which is closely related with the dislocation multiplication, recombination and annihilation. For the annealed and solution-aged Al-6061, the peak load reaches a maximum value in the second pass and fluctuates during the additional passes, which is caused by both material properties and frictions. The simulation shows that the peak load increases slowly with increasing passes, which is not in agreement with the measured value. Therefore the finite element mode using a single constitutive equation is not suitable for simulating multi-pass ECAE processing. The constitutive relations need to amend accordingly due to great changes of the mechanical properties between different passes.

Grain Refinement Efficiency in Equal Channel Angular Extrusion of FCC Metals Inferred from Crystal Plasticity Simulations of Slip Activities

Equal channel angular extrusion (ECAE) is a relatively new technique to produce ultrafine-grained materials by severe plastic deformation. Its efficiency of grain refinement varies with the processing route, i.e. the billet rotation () about its longitudinal axis between successive passes. The influence of processing route can not be fully explained by existing theories that consider only the macroscopic deformation features. In this study, the mesoscopic deformation behavior during multi-pass ECAE of face-centered cubic (FCC) metals was simulated using a visco-plasticity self-consistent (VPSC) polycrystal model and assuming simple shear deformation in each pass. It is shown that the slip activities vary significantly at the transitions between successive passes, depending on the die angle and processing route. The efficiencies of grain refinement in the different cases can be well correlated to the contribution of slip systems newly activated in a subsequent pass. The grain refinement is more efficient when such contributions are higher, such as in route B ( = 90) with a 90 die or route A ( = 0) with a 120 die. These crystal plasticity simulations provide insights into the efficiency of grain refinement during severe plastic deformation with strain path changes.

Enhancing room temperature mechanical properties of Mg–9Al–Zn alloy by multi-pass equal channel angular extrusion

Influence of equal channel angular extrusion on room temperature mechanical properties of cast Mg–9Al–Zn alloy was investigated. The results show that room temperature mechanical properties of Mg–9Al–Zn alloy, such as yield strength, ultimate tensile strength and elongation, can be improved heavily by equal channel angular extrusion. Processing routes, processing temperature and extrusion passes have important influence on room temperature mechanical properties of processed Mg–9Al–Zn alloy by equal channel angular extrusion. The optimum room temperature mechanical properties such as yield strength of 209 MPa, ultimate tensile strength of 339 MPa and elongation of 14.1%, can be obtained when Mg–9Al–Zn alloy was processed by equal channel angular extrusion for 6 passes at route B C at 498 K. Large bulk materials of Mg–9Al–Zn alloy with average grain size of 4 μm and high mechanical properties can be prepared.

Enhancement of Tensile Ductility of Severe Plastically Deformed Two-Phase Zn-12Al Alloy by Equal Channel Angular Extrusion

Tensile properties (mainly the ductility and fracture mode) of two-phase Zn-12Al alloy subjected to severe plastic deformation (SPD) via multi-pass equal-channel angular extrusion (ECAE) following route-Bc were investigated. As a result of ECAE processing, elongation to failure (as a ductility) of the alloy increased substantially and continuously with increasing the number of ECAE passes. However, the majority of the tensile strains are obtained in the state of plastic instability and therefore the uniform strains achieved along the gage length are very limited for this alloy. On the other hand, the strength of the alloy increased with increasing the number of passes up to 2, above which it decreased. The alloy sample after four ECAE passes exhibited 168% total elongation to failure at room temperature, which was 26 times higher than that of the as-cast one. This result indicates that multi-pass ECAE is effective on improving the tensile ductility of binary Zn-Al alloys. The fracture mode of the as-cast alloy samples completely changed after multi-pass ECAE and the brittle fracture behavior of the as-cast alloy was transformed into the ductile mode after processing.

Microstructural Evolution and Mechanical Response of Equal-Channel Angular Extrusion-Processed Al-40Zn-2Cu Alloy

Microstructural evolution, tensile properties, and impact toughness of an aluminum-zinc-copper (Al-40Zn-2Cu) alloy subjected to repetitive equal-channel angular extrusion (ECAE) up to four passes following either route A or route BC were investigated. The experimental results reveal that the ECAE eliminated as-cast dendritic microstructure along with casting defects such as microporosities almost completely. The ECAE-processed samples consisted of mostly elongated microconstituents via route A and equiaxed microconstituents via route BC. The high stresses imposed in ECAE lead to the fragmentation of the copper-rich θ phase into smaller particles with significant fragmentation occurring in the first pass and additional breaking in the subsequent passes in both routes. The ECAE processing simultaneously increased both the strength and ductility of the alloy as compared to the as-cast state, regardless of the processing route and number of passes. The deformation behavior of as-cast Al-40Zn-2Cu alloy has changed from brittle to ductile mode after ECAE due to the microstructural refinement, deformation-induced homogenization, and reduction of porosities. The limited impact toughness of as-cast alloy was significantly improved by multipass ECAE, especially in route A.

Finite Element Analysis of Plastic Strain Distribution in Multipass ECAE Process of High Density Polyethylene

Equal channel angular extrusion (ECAE) is a relatively novel forming process to modify microstructure via severe plastic deformation without modification of the sample cross section. In this study, an optimized design of die geometry is presented, which improves homogeneity of the plastic deformation and decreases the pressing force required for extrusion. Then, a typical semicrystalline polymer (high density polyethylene) was subjected to multipass ECAE using two different processing routes: route A where the sample orientation is kept constant between passes and route C where the sample is rotated by 180 deg. Compression tests at room temperature and under different strain rates were used to identify the material parameters of a phenomenological elastic-viscoplastic model. Two-dimensional finite element analysis of ECAE process was carried out, thus allowing to check out the homogeneity of the plastic strain distribution. The effects of die geometry, number of passes, processing route, and friction coefficient on the plastic strain distribution were studied. The simulations were performed for three channel angles (i.e., 90 deg, 120 deg, and 135 deg), considering different corner angles. According to simulation results, recommendations on the angular extrusion of the polymer are provided for improving die and process performance.

Mechanical and wear properties of ultrafine-grained pure Ti produced by multi-pass equal-channel angular extrusion

In this study, pure grade 2 Ti was processed via equal-channel angular extrusion (ECAE) for 8 and 12 passes following route-E at 300 °C. After processing, the microstructural evolution, tensile properties and wear behavior were investigated. ECAE-processed Ti exhibited a significant improvement in strength values with a slight decrease in ductility. However, the wear test results surprisingly showed that the strengthening of titanium by ECAE processing does not lead to the improvement of wear resistance at least for the pressures and sliding distances used in this study. This finding was mainly attributed to the tribochemical reaction leading to oxidative wear with the abrasive effect in Ti. Three distinct regions were formed on the subsurface of CG and UFG Ti after sliding wear, which are the tribolayer including titanium oxide with smeared wear material at the top, a deformed region having material structure oriented along the sliding direction in the middle, and the original unaffected bulk material at the bottom.

Three-dimensional finite element analysis of multi-pass equal-channel angular extrusion of aluminum AA1050 with split dies

Equal-channel angular pressing (ECAP) is an effective method to produce bulk nanostructured materials with high strength and toughness. Many experimental researches using a conventional solid die have been done so far, but few attempts on finite element analysis have been undertaken to exploit load predictions of the multi-pass ECAP because of difficulty involved with handling the boundary and processing conditions. In this study, split dies were newly designed to reduce the flash formation and the accuracy of finite element simulations of the multi-pass ECAP was improved by introducing better friction condition and saturated flow stress model considering the effect of routes and number of passes. Experiments with commercially available pure aluminum alloy (AA1050) of a square cross-section were carried out using the split dies newly designed for routes A, B C and C up to three passes. The forming simulation tool, CAMP form3D, was currently used to investigate the effect of routes and number of passes in terms of prediction of the forming load and deformation behavior. It was found out that predicted loads obtained from current numerical simulations were reasonably accurate compared to the measured load data for the three-pass ECAP.

Microstructural evolution and mechanical properties of Al–40 wt.%Zn alloy processed by equal-channel angular extrusion

The Al-based Al–40 wt.%Zn alloy was subjected to multi-pass equal-channel angular extrusion (ECAE) via route-A and route-B C. Before and after ECAE processing, microstructural evolution, the tensile properties, impact toughness and fracture behavior of the alloy were investigated. ECAE processing caused to elimination of the as-cast dendritic microstructure and formed a structure consisting of elongated, ribbon shaped α-phase via route-A and mostly equiaxed α-phase via route-B C. ECAE processing also caused plastic instability as necking at early onset of deformation. As a result of more effective mechanical mixing via route-B C, softening and necking occurred more apparently. The tensile and yield strength of the alloy increased just after first pass and then slightly decreased with increasing number of passes. On the other hand, its elongation to failure and impact toughness increased with increasing number of passes in both routes. The increase obtained via route-A is more pronounced in both properties. Fracture behavior of the as-cast alloy changed from brittle to ductile mode after multi-pass ECAE. Elimination of dendritic as-cast structure with reduction of porosities and deformation-induced homogenization by the effect of ECAE processing increased the ductility and impact toughness of the alloy and caused formation of a fracture surface consisting of micro-voids and dimples which indicates of ductile fracture. Attained experimental results indicate that multi-pass ECAE processing is very effective in improving the tensile elongation and impact toughness of binary Al–40 wt.%Zn alloy.

Evaluation of Reshaping Methods for Multi-Pass Equal Channel Angular Extrusion

Equal Channel Angular Extrusion is a widely adopted severe plastic deformation process capable of imparting large amounts of strain in a material via multiple passes through the die. In order to facilitate reinsertion of worked bars for multipass processing, reshaping is often required. Although this topic is rarely discussed in the literature, it is a significant step that can influence processing efficiency. This paper presents several reshaping options and makes recommendations for method selection based on the authors’ experiences with each.

Uniformity and continuity of effective strain in AZ91D processed by multi-pass equal channel angular extrusion

AZ91D magnesium alloy was processed by equal channel angular extrusion(ECAE). The influence of extrusion temperature, extrusion pass and extrusion route on the ultimate strength of the extruded billet was analyzed. The process of multi-pass extrusion was simulated with the method of finite element analysis, and the continuity and uniformity of effective strain in multi-pass extrusion were investigated. The results show that extrusion pass plays the most important role in improving the ultimate strength of AZ91D magnesium alloy, the extrusion route is the second, and the extrusion temperature is the last. From the numerical simulation, there exists the continuity of the accumulated deformation in multi-pass extrusion and the effective strain increases linearly. The tendency of the strain uniformity is different in multi-pass extrusion with extrusion routes. The results of experiment agree with those of numerical simulation.

3D finite element simulation of deformation behavior of CP-Ti and working load during multi-pass equal channel angular extrusion

In this paper, 3D FEM was applied to analyze the commercial pure Ti (CP-Ti) billet subjected to four-pass ECAE process at 400 °C with Bc route. The effective strain distribution and load–stroke curves within up to four-pass were described with friction conditions. The load was increased with the number of ECAE process. The propensity for cracks was predicted, which did correlate approximately to the experiment.

Multipass equal channel angular extrusion of MgB 2 powder in tubes

In the current study multipass equal channel angular extrusion (ECAE) is adopted for the first time to study the applicability of the process to compact magnesium boride (MgB 2) powder in tubes (PITs). The influence of number of ECAE passes on MgB 2 PITs was also analyzed in terms of microstructure, density and mechanical properties. MgB 2 PITs with iron tube were processed up to six ECAE passes. X-ray analysis of the compacts showed no other phases, other than MgO, in MgB 2 compacts even after large mechanical working and annealing. Simple shear stresses predominant in ECAE constantly rendered compaction of the hard brittle MgB 2 powders.

Study of deformation homogeneity in the multi-pass equal channel angular extrusion process

Abstract Ultra-fine grained and nanostructured materials have been widely investigated in the past decade due to the enhanced material properties such as improved tensile strength, hardness, toughness, fatigue life, and the optical and electrical related properties. The property improvement of the ultra-fine grained and nanostructured materials is usually achieved through severe plastic deformation (SPD). The SPD is currently an efficient technique for the production of bulk ultra-fine or nanostructured materials and it is realized via equal channel angular extrusion (ECAE) process. In this paper, the experimental research on ECAE process of conventionally used aluminum 6061 alloy is conducted and the deformation homogeneity in ECAE process is investigated. The aluminum samples are first treated with a pre-ECAE ageing heat treatment and then they are extruded in the ECAE die for up to 16 passes at room temperature without any rotation of the workpiece in each extrusion. To investigate the deformation homogeneity of the ECAE process, finite element simulation is conducted. The simulation results show that the materials on the outer side of the extrusion channel undergo severe plastic deformation compared to those on the inner side of the extrusion channel. To verify the simulation results, a series of Vickers microhardness measurement conducted on the polished cross-sections of the ECAE processed billets to map out the distribution of the hardness over the cross-section. The hardness distribution due to strain hardening is found to be inhomogeneous and its value increases significantly with the extrusion passes of ECAE process.