Conventional Equal Channel Angular Pressing Research Articles

Design, Finite Element Analysis and Optimization of Helical Angular Pressing (HAP) Method as a Novel SPD Technique

Severe Plastic Deformation (SPD) processes improve the mechanical properties of materials by obtaining Ultra Fine Grained (UFG) materials, orienting the grains and reforming the grains. Helical Angular Pressing (HAP) is a newly proposed Severe Plastic Deformation (SPD) method. In order to improve the efficiency of the HAP method, its die geometry should be optimized first. In this context, four parameters (helical diameter, helical pitch, helical height and channel radius) were determined for the die channel geometry, each with four levels according to the literature. Then, thanks to Taguchi L16 combinations, 16 Finite Element Analyses (FEA) were carried out using Deform 3D software instead of 256 simulations, and effective strain values and maximum pressing load values were obtained. Later on, using the SPSS 16 software, Taguchi optimization was carried out to obtain the optimum HAP die channel geometries by minimizing the press load and maximizing the effective strain values. Next, the Finite Element Analysis (FEA) was repeated with these determined optimum die channel parameters. Finally, the efficiency of this novel HAP method was compared with conventional Equal Channel Angular Pressing (ECAP) and Twist Extrusion (TE) methods. As a result, HAP method provides effective strain values equivalent to 10 number of passes after processing with ECAP. And it is approximately 4 times higher than that achieved by TE processing. As a result of the Taguchi optimization, it is concluded that the values in the combination of diameter (d)=60 mm, height (h)=50 mm, radius (r)=4 and pitch (p)=1.25 are the optimum die geometry. In conclusion, these results indicate that the proposed novel HAP method is an efficient and applicable SPD technique.

Grain refinement effect on fatigue life of two grades of commercially pure titanium

The fatigue life and fatigue limit of commercially pure Ti grade 2 and 4 in coarse-grained and ultrafine-grained states were experimentally determined. Ultrafine structures were prepared by Conform severe plastic deformation method and by conventional Equal channel angular pressing, respectively. The differences in the improvement of fatigue life and the influence of both procedures on the fatigue limit based on 107 cycles to fracture are discussed in terms of grain refinement, microstructure, differences in fatigue damage mechanism and influence of surface roughness on the initiation of fatigue cracks. Improvement in fatigue life was observed for both materials, however, the improvement of the fatigue limit was found only for Ti grade 2.

A Novel Method for the Determination of High Temperature FLCs of ECAP-Processed Aluminum AA5083 Sheet Metal

In this study, investigations into the deformation behavior of aluminum AA5083 at elevated temperatures were carried out on a newly developed test rig. The test rig was developed jointly with ZwickRoell GmbH & Co. KG (Germany) and is based on a Nakajima test carried out with heated dies. In this way, statements can be made about the lightweight potential of the alloy. Additionally, equal-channel angular pressing (ECAP) was performed to process the aluminum sheet metal. The conventional ECAP process is mainly used for bulk material in laboratory use and therefore is often not suitable for many industrial applications, especially for large series. The use of sheet metal allows a significant increase in the areas of application. It is documented in conventional ECAP that grain refinement is achieved by the severe plastic deformation. At room temperature this primarily increases the mechanical strength. Formability is improved in fine-grained materials, especially at elevated temperatures, which is related to diffusion-controlled deformation mechanisms and grain boundary sliding. The advantages of ECAP for sheet materials are thus also in lightweight construction and can even optimize the use of the AA5083 alloy. ECAP-route C was used for the process to provide the most homogeneous microstructure possible (180° rotation around the ECAP-axis after the first pass). Nakajima specimens were taken from the processed sheet materials to determine the Forming Limit Curve (FLC) compared to the reference material (four different specimen geometries). FLCs under elevated temperatures (250 °C, 375 °C) were performed on the novel Nakajima test bench. A special feature of the test rig is the rapid heating to avoid microstructural changes. Microscopic examinations were performed after the deformation to study the deformation mechanisms. Differences of the forming and fracture mechanisms between the reference alloy and the ECAP material were found.

Properties inhomogeneity of AM60 magnesium alloy processed by cyclic extrusion compression angular pressing followed by extrusion

A new severe plastic deformation (SPD) technique for improvement of the metallurgical properties of the magnesium alloys is presented. In this process, a cyclic extrusion compression angular pressing (CECAP) process is followed by an extrusion step in the outlet playing the role of additional back pressure. Therefore, more uniform and enhanced mechanical properties are expected in comparison with equal channel angular pressing (ECAP). In order to evaluate the effectiveness and capabilities of this new method, an AM60 magnesium alloy was processed. Finite element results exhibited a significant increase in strain values as well as uniform strain distribution for the new method. In addition, ~110% increase in compressive stress was observed in new method compared to the conventional ECAP. Experimental results revealed a noticeable increase in the hardness and strength of the specimens processed by the new technique as a result of the formation of finer grains and more homogeneous microstructure with good distribution of refined β-phase along the boundaries. It may be concluded that the new process is very promising for future magnesium alloy products.

Deformation Behavior of Al/Cu Clad Composite During Twist Channel Angular Pressing.

The research and development of modern metallic materials goes hand in hand with increasing their lifetime via optimized deformation processing. The presented work deals with preparation of an Al/Cu clad composite with implemented reinforcing Cu wires by the method of twist channel angular pressing (TCAP). Single and double pass extrusion of the clad composite was simulated numerically and carried out experimentally. This work is unique as no such study has been presented so far. Detailed monitoring of the deformation behavior during both the passes was enabled by superimposed grids and sensors. Both the sets of results revealed that already the single pass imparted significant effective strain (higher than e.g., conventional equal channel angular pressing (ECAP)), especially to the Al matrix, and resulted in notable deformation strengthening of both the Al and Cu composite components, which was confirmed by the increased punch load and decreased plastic flow velocity (second pass compared to first pass). Processing via the second pass also resulted in homogenization of the imposed strain and residual stress across the composite cross-section. However, the investigated parameters featured slight variations in dependence on the monitored location across the cross-section.

Numerical Analysis of Conventional and Modified Equal Channel Angular Pressing

While conventional equal channel angular pressing (ECAP) has been widely investigated as the prominent severe plastic deformation method, no detailed work has been carried out on the modified ECAP techniques. So, this work deals with the numerical characterization of 7075 aluminum billet processed by conventional and modified ECAP methods. It has been found that T-shaped ECAP is the best technique to choose from the effective plastic strain point of view. Also, the highest plastic strain distribution uniformity and concomitant least required pressing load belong to the cross-ECAP condition. Moreover, conventional ECAP process should be selected if the minimum temperature rise and damage have been considered. Eventually, shear plane mode of oblique, V-shape, and X-shape is attained for the conventional, T-shaped, and cross-ECAP conditions, respectively.

Fast recrystallization and phase transformation in ECAP deformed Ti–6Al–4V alloy induced by pulsed electric current

Ultrafine-grained Ti–6Al–4V alloy with high mechanical properties in both strength and elongation was prepared by equal channel angular pressing and following pulsed electric current treatment. The mechanical properties of Ti–6Al–4V alloy were investigated by tensile tests at room temperature. Elongation of the samples treated by pulsed electric current and annealing was considerably increased by 66.5% and 20.8%, respectively. The plasticity of ECAP deformed Ti–6Al–4V alloy was significantly improved by pulsed electric current while the strength still remained relatively high. Comparing with conventional equal channel angular pressing and following annealing process, uniform fully recrystallization microstructure with fine grains, increasing proportion of beta phase and decreasing dislocation density was obtained at a relatively low temperature during a short time with the help of pulsed electric current. This study proves that the pulsed electric current provoked a fast recrystallization and phase transformation process of a titanium alloy produced by equal channel angular pressing.

Improvement of strength and ductility of an EZ magnesium alloy by applying two different ECAP concepts to processable initial states

The commercial magnesium alloy EZ33A was processed by Equal Channel Angular Pressing (ECAP). Two different tools were used: a conventional one with two channels and one intersection (90°), and a so-called double ECAP (D-ECAP) tool with two intersections (90° and 120°). Four passes were conducted at temperatures subsequently lowered from 350 °C down to 240 °C using route Bc.The as-cast, pre-deformed material and both ECAP conditions were investigated. The microstructure was revealed by means of optical microscopy, scanning and transmission electron microscopy (SEM, TEM), and X-ray diffraction. Mechanical properties were studied by Vickers hardness measurements as well as by compressive and tensile tests.The microstructure investigations show a significant grain refinement as well as fragmentation and redistribution of the hard intermetallic (Mg,Zn)12RE phase by ECAP. This effect is even more pronounced in the material processed by D-ECAP where this phase is two times finer compared to the size after conventional ECAP. Additionally, small Zn-Zr particles of a few nanometers size within grains or subgrains were observed.Microstructure changes evoked by the ECAP processing significantly affect the mechanical properties. This is especially the case after 4 passes in the D-ECAP tool where hardness (90 HV2) is almost 70% higher than in the as-cast condition (54 HV2) and the tensile yield strength is enhanced by nearly 300% (82 MPa up to 327 MPa). Hence, the D-ECAP tool is more efficient than the conventional one in improving mechanical properties.

Analytical and Experimental Investigation of Process Loads on Incremental Severe Plastic Deformation

From the processing point of view, friction is a major problem in the severe plastic deformation (SPD) using equal channel angular pressing (ECAP) process. Incremental ECAP can be used in order to optimize frictional effects during SPD. A new incremental ECAP has been proposed recently. This new process called as equal channel angular swaging (ECAS) combines the conventional ECAP and the incremental bulk metal forming method rotary swaging. ECAS tool system consists of two dies with an angled channel that contains two shear zones. During ECAS process, two forming tool halves, which are concentrically arranged around the workpiece, perform high frequency radial movements with short strokes, while samples are pushed through these. The oscillation direction nearly coincides with the shearing direction in the workpiece. The most important advantages in comparison to conventional ECAP are a significant reduction in the forces in material feeding direction plus the potential to be extended to continuous processing. In the current study, the mechanics of the ECAS process is investigated using slip line field approach. An analytical model is developed to predict process loads. The proposed model is validated using experiments and FE simulations.

Effects of aluminum and copper cover tube casing on the ECAP process of AM30 magnesium alloy

ABSTRACTAluminum (Al) and copper (Cu) thin tube casings were employed to facilitate the equal channel angular pressing (ECAP) process of wrought AM30 magnesium (Mg) alloy. We covered the Mg rods (diameter, 14 mm) with pure copper (Mg/Cu) and Al-1050 alloy (Mg/Al) sheaths in the form of tubes (thickness, 2.5 mm). We then performed the ECAP processes at 200, 250, and 275°C using the conventional ECAP of AM30 alloy and covered tube casing (CTC) methods with a single pass. We assessed the effect of CTC on ECAP temperature, grain refinement, uniformity of structure, hardness distribution, and strength. The results of Mg/Cu and Mg/Al bimetal sample tests showed that there was a significant decrease in the process temperature when compared with the conventional ECAP of AM30. The sheath resolved the segmented material flow that occurred in a conventional ECAP of material at 250°C, and transformed it to a uniform flow in CTC bimetal samples. Grain sizes of the CTC samples decreased by 20% compared with the conventional ECAP of AM30 samples. Furthermore, grain uniformity, strain distribution homogeneity, tensile yield strength (TYS), and elongation increased. However, we observed a similar trend of deformation twinning in compression test results for the ECAP and CTC methods, and there was no significant variation in material yield asymmetry between the ECAP and CTC samples.

Development of a novel severe plastic deformation method: friction stir equal channel angular pressing

In this research, a novel severe plastic deformation (SPD) method has been proposed which imposes a higher amount of the plastic shear strain during the modified equal channel angular pressing (ECAP) process. The deformation behavior of this novel process was analyzed through the finite element method, and the numerical simulations were validated by experimental data. The results showed that this process can impose higher effective strain during only one pass in comparison with the conventional ECAP even at high numbers of passes. According to the mean stress analyses of the process, it is obtained that this novel method leads to produce products with lower possibility of crack growth in comparison with the common method. At the second pass, the final product of the friction stir equal channel angular pressing (FS-ECAP) process exhibits better strain homogeneity at its surface along the length in comparison with that of the first FS-ECAP pass.

Study of a modified ECAP die for producing nanostructured Al6060 alloy using 3D finite element simulation

ABSTRACTUsing Finite Element Method (FEM) simulations is possible to study the homogeneity of deformation in the Equal Channel Angular Pressing (ECAP) process. In this work an investigation about the influence of a modified die on strain distribution in an ecaped Al6060 alloy was carried out. Due to that, tensile stress occurs in the vicinity of upper surface of the specimen in the severe plastic deformation zone, which increases the cracking and fracture tendency of the specimen and impedes further ECAP processing, the conventional ECAP die was modified to eliminate the tensile stress and enhance the compressive stress in the severe plastic deformation zone and reducing the cracking and fracture tendency of the specimen. Finite element analysis demonstrated that the stress state changes from tensile to strongly compressive when using the modified die. The aim of this study is to evaluate the advantages/disadvantages of the modified ECAP die and processing conditions.

Deformation of Pure Aluminum Along the Groove Path of ECAP‐Conform Process

Combining of rotary extrusion and equal channel angular pressing (ECAP) leads to the ECAP‐Conform process, which is one of the few successful continuous severe plastic deformation processes. Sample before reaching the ECAP die is influenced by three main deformations of rolling, bending, and forging, which can affect the microstructure and mechanical properties of the material. The effects of these steps on the microstructure and properties of AA1100 alloy are studied based on the simulation and experimental investigations. It is found that these steps significantly affect the material and they should be considered for evaluation of properties compared with the conventional ECAP.

Influence of twist extrusion process on consolidation of pure aluminum powder in tubes by equal channel angular pressing and torsion

In comparison with the conventional equal channel angular pressing (ECAP) process, a comprehensive study of influence of twist extrusion (TE) process on consolidating pure aluminum powder in tubes (PITs) by equal channel angular pressing and torsion (ECAPT) was conducted via three-dimensional (3D) finite element simulation, experimental investigation and theoretical analysis. Simulation results revealed that during the consolidation of aluminum powder particles by ECAPT, TE process played a significant role of back pressure. Due to the torsional shear and high hydrostatic pressure exerted by twist channel, both the magnitude and homogeneity of the effective strain were increased markedly. After one pass of ECAPT process using a square channel with an inner angle of 90° and a twist slope angle of 36.5° at 200 °C, commercial pure aluminum powder particles were successfully consolidated to nearly full density. Simulation and experimental results showed good agreement. In the microstructure observations, grains were greatly refined. At the same time, porosities were effectively eliminated by shrinking in size and breaking into small ones. Microhardness test indicated that strain distribution of ECAPT-processed billet was more homogeneous with respect to the ECAP-processed one. All these improvements may be attributed to the extreme intense shear strain induced during ECAPT and the increase in self-diffusion coefficient of aluminum due to the back pressure exerted by TE process.

Grain refinement in technically pure aluminium plates using incremental ECAP processing

Ultrafine grained materials are capable of superplastic elongation at strain rates approximately two orders of magnitude faster than those currently employed for commercial superplastic forming operations. However, such operations require the material in the form of thin sheets. Therefore, in this work, a new approach to produce ultrafine grained plate samples using a modified equal channel angular pressing (ECAP) method, namely incremental ECAP, was proposed. Unlike conventional ECAP, incremental ECAP works in small steps in which deformation and feeding are associated with two different tools acting asynchronously. Eight passes were applied to technically pure aluminium, with the sample rotation by 90° around the Z axis, which resulted in two full rotations and accumulated strain equal to 9.2. It was demonstrated that grain refinement under these conditions occurs very efficiently. Eight passes resulted in grain size reduction to below 500nm and very high fraction of high angle grain boundaries of about 80%. This was attributed to the activation of different slip systems in consecutive passes (thanks to sample rotation) and the lack of redundant strain, which results in early establishment of equiaxial grain structure. These two features confirm incremental ECAP to be one of the most effective severe plastic deformation methods in terms of grain size refinement and high angle grain boundaries formation.

Improvement of ECAP process by imposing ultrasonic vibrations

In a few last decades, equal-channel angular pressing (ECAP) has been one of the most prominent procedures for fabrication of ultrafine-grained (UFG) structures among various severe plastic deformation (SPD) techniques. The objective of this paper is to experimentally investigate the influence of longitudinal ultrasonic vibrations on the ECAP process. A robust experimental ECAP system was designed and manufactured, in which the punch can be excited by ultrasonic vibrations. ECAP experiments were carried out with and without ultrasonic vibration on pure Al. The microstructure of the specimens formed with ultrasonic-assisted ECAP and conventional ECAP were studied. The results of this study showed that superimposing ultrasonic vibrations on the ECAP process could improve the grain refinement efficiency. The grains of the specimens after conventional ECAP process were refined to 45 μm, while by applying ultrasonic vibration with amplitudes of 2.5 and 5 μm, the grains were refined to 28.2 and 22 μm , respectively. Using higher vibration amplitudes caused more refinement of the grains. The homogeneity of the microstructure after four passes of ECAP was also improved by 26.7 % while using ultrasonic vibration with amplitude of 2.5 μm. Higher vibration amplitudes made a more homogenous structure. The yield strength and ultimate tensile strength of the specimens after one pass of ECAP were higher in comparison with the conventional ECAP.

Incremental ECAP as a novel tool for producing ultrafine grained aluminium plates

Conventional equal channel angular pressing is an efficient technique to obtain bulk ultrafine grained materials (UFG) with extraordinary mechanical properties in the form of rods. In this work, an incremental method of ECAP process which allows to obtain thick sheets with UFG structure is presented. Using this method square plates (62 × 62 mm) were obtained. In this case, a combined route – A+ specific B – with 90 degree rotation along plate normal after each pass keeping other planes in the same positions relatively to the channel – has been applied. The efficiency of this methods was proved for technically pure 1050 aluminium. It was processed by incremental ECAP using 8 passes of A+B route. To characterize microstructure visible light microscopy and transmission electron microscopy were used. Mechanical properties were measured by microhardness test. The results obtained showed that the microstructure and mechanical properties of 1050 aluminium alloy processed by incremental ECAP are comparable to conventional ECAP. However, the new processing method broaden the potential applications of UFG materials.

Development of Homogeneity in an Al-6061 Alloy Processed by ECAP and ECAP-Conform

Equal-channel angular pressing (ECAP) has been established as an effective method to achieve ultrafine-grained materials and ECAP combined with the Conform process (ECAP-Conform) is considered a promising candidate to realize continuous processing by ECAP. This paper describes experiments conducted on samples of an Al-6061 alloy in order to evaluate the homogeneity development of the alloy processed by ECAP and ECAP-Conform. The samples of the Al-6061 alloy were processed by ECAP and ECAP-Conform at room temperature up to 4 passes via route BC. The microhardness measurements were recorded both in the cross-sectional planes and along the longitudinal directions of the samples. The results show the alloy obtained significant strengthening using both processes. There was reasonable plastic isotropy after 4 passes of ECAP-Conform in both the cross-sectional plane and the longitudinal direction and the alloy showed a homogeneous microhardness distribution in the cross-sectional plane after 4 passes of conventional ECAP.

Evaluating a New Core‐Sheath Procedure for Processing Hard Metals by Equal‐Channel Angular Pressing

A new design of billet, based on a core–sheath configuration, was used for the processing of Ni, Fe, and a NiTi alloy by equal‐channel angular pressing (ECAP) at room temperature. This configuration involves inserting metal cores within Fe sheaths prior to processing and it is designed especially for use with hard‐to‐deform materials. Billets were processed through one or two ECAP passes at room temperature and the microhardness values were recorded across the transverse directions within the cores to evaluate the flow process. As in conventional ECAP, the hardness increased significantly after the first pass and there were regions of lower hardness along the bottom surfaces of each core. The gradient of hardness decreased with increasing core diameter but the average microhardness values remained unchanged. Three‐dimensional finite element simulations were used to evaluate the flow behavior after one pass of ECAP using different core metals. These simulations show the lower areas of the cores undergo less deformation than the upper areas and the homogeneity increases with increasing levels of friction at the core–sheath interface.

Comparison of the monotonic and cyclic mechanical properties of ultrafine-grained low carbon steels processed by continuous and conventional equal channel angular pressing

In the current study the mechanical properties of ultra-fine grained low carbon steel processed by conventional equal channel angular pressing and a continuous equal channel angular pressing-Conform process were investigated. Both monotonic and cyclic properties were determined for the steel in either condition and found to be very similar. Microstructural analyses employing electron backscatter diffraction were used for comparison of the low carbon steels processed by either technique. Both steels feature very similar grain sizes and misorientation angle distributions. With respect to fatigue life the low carbon steel investigated shows properties similar to ultra-fine grained interstitial-free steel processed by conventional equal channel angular pressing, and thus, the general fatigue behavior can be addressed following the same routines as proposed for interstitial-free steel. In conclusion, the continuously processed material exhibits very promising properties, and thus, equal channel angular pressing-Conform is a promising tool for production of ultra-fine grained steels in a large quantity.