Equal Channel Angular Pressing Technique Research Articles

Mechanical characteristics and crystallographic texture of AA5083 during Equal Channel Angular Pressing Technique

AA5083 bars processed by four pass ambient Equal Channel Angular Pressing were subjected to intersection annealing, where time and temperature were varied after each pass. The microstructures, texturing and compressive characteristics of the samples were meticulously examined. Due to the high annealing temperatures, both ultimate tensile strength and compressive stresses decreased with increasing grain size. However, intersection annealing at room temperature resulted in the best compressive yield strength. The deformation behavior of AA5083 billets was investigated using finite element analysis. Electron back scatter diffraction was employed to examine the texture of the Equal Channel Angular Pressed billet crystals. Extensive research was conducted on the tensile properties and Vickers microhardness. The finite element simulations revealed that the 900 die exhibited a significantly more uniform dispersion of plastic strain compared to the 1200 die. The renewal of additional slip mechanisms during the four Pass process was attributed to the grain refining that occurred after the 1-Pass and 2-Pass stages. Equal Channel Angular Pressing successfully produced a homogeneously ultra-fine grained microstructure. The increase in strength was attributed to grain refining and dislocation strengthening. Molecular dynamics simulations were employed to study the ECAPed approach of AA5083 providing insights into the deformation behavior and polycrystal formation.

Simulation of deformation behaviour of Aluminium 7075 during Equal Channel Angular Pressing (ECAP)

This paper presents a finite element simulation of equal channel angular pressing (ECAP) since it is one of the most common and successful severe plastic deformation techniques. This study reports the influence of the most significant factors influencing the ECAP technique. Through finite element simulation, the effect of the die geometry, workpiece geometry, and the pressing speed on the effective strain distributions, damage, and pressing loads, were investigated. The influence of the ECAP method on different material models is also presented. Additionally, the prospective expansion and future applications of ECAP are herein highlighted. From the results, the die geometry of a 90° channel imparts the highest strains during ECAP. Additionally, specimens of rectangular geometry are susceptible to cracking and damage as compared to circular samples. It was found that very high processing speeds (>7mm/sec) are undesirable during ECAP since they cause very high internal stresses to the structure of the workpieces. Besides, processing at room temperature can achieve homogeneous strain distribution with minimum sample damage.

Influence of Equal Channel Angular Extrusion on Mechanical Characteristics and Associated Microstructural Changes of Aluminum, Copper, Titanium and Magnesium Alloys and Their Metal Matrix Composites—A Review

Abstract A focus of the current industrial sector is motivated to develop a new class of advanced materials with superior characteristics compared to currently available conventional materials. In the recent past, light metals and alloys, such as aluminum, copper, titanium, and magnesium alloys and their metal matrix composites (MMCs) have been increasingly accepted in automotive, aerospace, and biomedical sectors. Moreover, for improving the physical and mechanical characteristics of these materials, the processing of materials with secondary metalworking techniques (severe plastic deformation [SPD], complete and partial heat treatment processes, cryogenic treatment, surface coatings, etc.) is essential. Out of several secondary metalworking techniques, the most efficient is the SPD technique with equal channel angular pressing (ECAP). ECAP is widely adopted to produce materials with significantly reduced grain size and excellent properties. The current review article aims to present the effect of ECAP on the physical and mechanical characteristics of aluminum, copper, titanium, and magnesium alloys, and their MMCs are discussed. Microstructural studies and their associated statistical parameters of these materials are discussed using several destructive and nondestructive techniques. Also, the use of in-situ methods, such as digital image correlation, infrared thermography, etc., is examined to study the deformation mechanisms in ECAP. This review article provides a new direction for researchers working in materials engineering and science fields to recognize the importance of the ECAP technique on mechanical characteristics and associated microstructural changes of majorly used alloys and MMCs.

Microstructure and Microhardness of Directionally Solidified Al-Si Alloys Subjected to an Equal-Channel Angular Pressing Process

The directional solidification technique allows the study of growth of the solid phase, as-cast structure and, finally, its mechanical characteristics as a consequence of thermal parameters. On the other hand, in the last decade, a process called equal-channel angular pressing (ECAP) has emerged as a widely-known technique in fabrication of ultrafine-grained metals and alloys. Applicability of the ECAP technique affords an excellent potential for changing, in a controlled and beneficial manner, the resulting properties of metals and alloys. For this paper, an experimental research has been conducted to study the effects of solidification parameter (cooling rate) on resulting microhardness in hypoeutectic Al-Si alloys, upon use of an ECAP procedure. The influence of cooling on the scale of the dendritic patterns is presented and discussed with recourse to equations. The resulting microhardness variation with position throughout the as-cast materials and cooling rate were characterized by experimental power laws. Results determined after the solidification experiments have revealed microhardness as a function of both cooling rate and position (P) of the as-cast materials to be dependent on alloy composition. In the ECAP process via route C with three passes, “as-solidified” microstructures have been found to be distorted and fragmented during the severe plastic deformation. This deformation imposed on the billets during the ECAP process facilitated obtaining a fine microstructure and high levels of microhardness were observed. However, even with the ECAP process, it was shown that microhardness is strongly dependent of the cooling rates.

Effect of Die Design parameters on materials processed by Equal Channel Angular Pressing

Equal Channel Angular Pressing technique is used for grain refinement in bulk materials, where the material is passed through the die in which the two channels intersect at some angle, that result in finer grains. There are number of die design parameters which affects the production of ultra-fine grains. This paper presents the effect of die design parameters such as channel angle, corner angle, several passes and route followed for processing of the material for grain refinement. The results of different parameters are compared, and it was observed that the optimum values for producing maximum shear strain is for channel angle 90° and it reduces with the increase in channel angle. About 20° corner angles is found to suitable for filling the corner gap, around 4 to 6 passes, and route Bc leads to the ultrafine grained structure of homogeneous equiaxed grains separated by high angle grain boundaries in the materials. The sample of Al-TiO2 was prepared and its microstructure and mechanical properties were tested after equal channel angular pressing.

Effect of processing parameters on equal-channel angular pressing of aluminum alloys: An overview

Equal-channel angular pressing (ECAP) is one of the emerging Severe plastic deformation (SDP) technique that makes ultra-fine grains (UFG) microstructure to improve the properties of different materials and composites. The uniqueness of the ECAP technique is that it can refine the grain size without changing the cross-section. Many factors like processing temperature, number of ECAP passes, die channel angle and processing route affects the results obtained from ECAP technique. This review is mainly focused on the mechanical and microstructural properties of aluminium alloys generated after ECAP Process along with number of passes. It is observed as the number of passes increased the hardness and tensile strength of the alloy increase and ductility of the material is reduced. The maximum percentage of grain refining is obtained in the first two or three passes after that no significant changes were observed because the effect of temperature is more than the effect number of passes on the grain size.

Structuration of Refractory Metals Tantalum and Niobium Using Modified Equal Channel Angular Pressing Technique

In the present work, we use a modified Equal Channel Angular Pressing technique for structure and properties change of Tantalum and Niobium at room temperature. The main advantage of this modified technique is the possibility to produce relatively large samples with ultrafine-grained microstructure in all volume of the workpiece by reduced deformation load up to 25% via friction decrease, and also to prevent the punch fracture under high compression stress during pressing. The various microstructures and properties were produced in metals by using different von Mises strain levels up to ƐvM = 13.8. The changes in microstructure were studied by using SEM and TEM techniques. The change of mechanical properties was measured by using various tension and hardness testing setups. We can conclude that during processing the ultrafine-grained microstructure in as-cast Nb and Ta was formed. The uniaxial tensile strength, Vickers hardness, and plasticity of Nb and Ta significantly increased as compared to coarse-grained counterparts. We believe that the relatively large workpieces of pure bulk Ta and Nb metals with improved microstructure and exploitation properties are suitable materials for the modern industry.

Corrosion Behavior of AA6012 Aluminum Alloy Processed by ECAP and Cryogenic Treatment

In this work, the corrosion behavior of an AA6012 aluminum alloy, submitted to a T6 strengthening treatment (solubilization and aging), and later to a severe plastic deformation, through equal channel angular pressing (ECAP) was studied. Some of these samples were submitted to a cryogenic treatment before the ECAP process. The analysis of corrosion behavior of the AA6012 samples was carried out at room temperature by means of electrochemical characterization in 0.1 M Cl− deaerated and aerated solution at pH 2. For this purpose, Tafel plots and electrochemical impedance spectroscopy tests were performed. The evolution of the microstructure was studied by means of SEM and TEM observations. The experimental results show that the cryogenic treatment does not influence the corrosion behavior of the studied alloy submitted to T6 treatment. Moreover, it was found that the ECAP technique does not induce a marked deterioration of the analyzed samples in terms of corrosion resistance.

Experimental Investigation of Microstructure and Mechanical Properties of Al 5052 Processed by Equal Channel Angular Pressing Technique

Experimental Investigation of Microstructure and Mechanical Properties of Al 5052 Processed by Equal Channel Angular Pressing Technique

Microstructure Changes and Improvement in the Mechanical Properties of As‐Cast AlSi7MgCu0.5 Alloy Induced by the Heat Treatment and ECAP Technique at Room Temperature

The changes in the microstructure and improvement in the mechanical properties of as‐cast AlSi7MgCu0.5 alloy induced by the heat treatment and technique of equal channel angular pressing (ECAP) were investigated. The heat treatment of as‐cast alloy performed before the ECAP technique was required to increase the plasticity of the alloy. Therefore, the samples of analysed alloys were solution annealed at optimized temperature of 823 K for 4 hours to dissolve the particles of intermetallic π(Al8FeMg3Si6) phase and to spheroidize the Si particles. Subsequently, water quenching and artificial ageing at optimized temperature of 573 K for 5 hours was used to obtain an overaged alloy state. The microstructure of alloy was consisted of α(Al) solid solution, eutectic Si particles, and intermetallic β(Mg2Si), Q‐Al4Mg5Si4Cu, α‐Al12(Fe,Mn)3Si, and/or α‐Al15(Fe,Mn)3Si2 phase particles. The crystal structure of present phases was confirmed by hard X‐ray diffraction at Deutsches Elektronen‐Synchrotron (DESY) in Hamburg and by the selected area electron diffraction (SAED) performed inside the transmission electron microscope (TEM). The heat‐treated alloy was processed by ECAP at room temperature following route A. Repetitive ECAP of alloy homogenized the heterogeneous as‐cast microstructure and formed the ultrafine subgrain microstructure with elongated subgrains of 0.2 µm in width and 0.65 µm in length and the high dislocation density. Microstructural changes in alloy induced by both heat treatment and ECAP led to the high strain hardening of the alloy that appeared in an improvement in strength, ductility, and microhardness of alloy in comparison with as‐cast alloy state.

Gentamicin-Eluting Titanium Dioxide Nanotubes Grown on the Ultrafine-Grained Titanium.

Titanium (Ti)-based materials is the most appropriate choices for the applications as orthopedic and dental implants. In this regard, ultrafine-grained (UFG) titanium with an enhanced mechanical properties and surface energy has attracted more attention. Titanium dioxide (TiO2) nanotubes grown on the titanium could enhance bone bonding, cellular response and are good reservoirs for loading drugs and antibacterial agents. This article investigates gentamicin loading into and release from the TiO2 nanotubes, grown on the UFG compared to coarse-grained (CG) titanium substrate surfaces. Equal Channel Angular Pressing (ECAP) was employed to produce the UFG structure titanium. TiO2 nanotubes were grown by the anodizing technique on both UFG and CG titanium substrate surfaces. Scanning electron microscopy (SEM) imaging confirmed TiO2 nanotube growth on the surface. The UV-vis spectroscopy analysis results show that the amount of gentamicin load-release in the anodized UFG titanium sample is higher than that of CG one which can be explained in terms of thicker TiO2 nanotube arrays layer formed on UFG sample. Moreover, the anodized UFG titanium samples released the drug in a longer time than CG (1day for the UFG titanium vs. 3h for the CG one). Regarding wettability analysis, anodized UFG titanium sample showed more enhanced hydrophilicity than CG counterpart. Therefore, the significantly smaller grain size of pure titanium provided by the ECAP technique coupled with appropriate subsequent anodization treatment not only offers a good combination of biocompatibility and adequate mechanical properties but also it provides a delayed release condition for gentamicin.

Finite element analysis of die offsetin two-turn incremental ECAP

Severe plastic deformation (SPD) is the process used to produce ultra fine grain(UFG), metals are characterised by improved mechanical properties which make them suitable for advanced structural applications. Apart from various SPD techniques, two turn incremental equal channel angular pressing (ECAP), S-shape channel discussed in this paper to double the effective strain in a single press. Unfortunately, processed UFG metals are rarely used in industrial applications due to lack of advancement in ECAP technique. Analysis of ECAP technique by changing die geometry and process parameter helps to produce defect free UFG metals. ECAP channel continuously pressed a very long billet in which repetitions accumulate large plastic strain. Two turn ECAP is useful to increase the productivity. However, any changes in channel angle, corner angle as well as offset length are cause for variation in mechanical properties of metals. In order to check the die suitability of two-turn ECAP with variation of effective strain, punch load, a FEA simulation is carried out and the suitable tool geometry and process kinematics are established. Die channel sat two different offset length are used to study the flow behaviour of metal through 900 channel angel. The mode of material flow is the same as in the well established classical L-shape ECAP process following route C pass, while continuous character and improved productivity suggest that new S-shape ECAP process might be suitable for grain refinement of metals on an industrial scale.

Influence of incremental ECAP on the microstructure and tensile behaviour of commercial purity titanium

Severe plastic deformation (SPD) is an effective method for producing ultrafine grained (UFG) structures in metals. UFG materials are characterized by an average grain size of <1 µm and mostly high angle grain boundaries. These materials exhibit exceptional improvements in strength, superplastic behaviour and in some cases enhanced biocompatibility. Among various SPD methods available, equal channel angular pressing (ECAP) is the most effective method for obtaining bulk UFG billets. Lately, the interest is towards industrialization of the ECAP technique to enable processing of very long or continuous billets. Incremental ECAP (I-ECAP) developed at University of Strathclyde, offers such possibility. The present work details the processing of commercial purity titanium (CP-Ti), using I-ECAP process, with the objective of improving its strength characteristics. CP-Ti billets were successfully processed for up to four passes at 300 °C using an I-ECAP die with a channel angle of 90°. Electron backscatter diffraction (EBSD) technique was used to characterize the microstructure after first and fourth pass of the process. Analysis of the first pass sample revealed heterogeneous structure with a mixture of elongated and refined equi-axed grains. Moreover, existence of {101 2} tensile twinning in the microstructure was also observed. Remarkable refinement was achieved after fourth pass and ultrafine-grain (UFG) structure was successfully achieved. Room temperature tensile tests carried out on unprocessed and UFG material, display the improvement in strength. The yield strength of the processed material was increased from 308 to 671 MPa and the ultimate tensile strength from 549 to 730 MPa. However, strain-hardening ability of the material was greatly reduced because of processing. Consequently, the material suffers loss in ductility, from 31.9% elongation to failure in the unprocessed form to 21.1% in UFG form. Finally, fracture morphology of the unprocessed and processed CP-Ti displays characteristics of ductile failure. It has been shown that I-ECAP is an effective method for improving strength characteristics of CP-Ti.

Finite element analysis of die angle at constant offset length in two-turn ECAP

Severe plastic deformation (SPD) is the process used to produce smaller grain in the range of 1-pm. These materials have been classified as equiaxed ultrafine grain (UFG) metals. These metals are characterised by high defect density and improved mechanical properties which make them suitable for advanced structural applications. From all available SPD techniques, two turn incremental equal channel angular pressing (ECAP), S-shape channel discussed in this paper to double the effective strain in single press. Analysis of ECAP technique by changing die geometry and process parameter helps to produce defect free UFG metals. ECAP channel continuously pressed a very long billet in which repetitions accumulate large plastic strain. Two turn ECAP is useful to increase the productivity. However, any changes in channel angle, corner angle as well as offset length are cause for variation in mechanical properties of metals. In order to check the die suitability of two-turn ECAP with variation of die angle a finite element analysis (FEA) simulation is carried out and the suitable tool geometry with process kinematics are established. ECAP channels at two different channel angles are used to study the flow behaviour of metal through 15mm offset length. The mode of material flow is the same as in the well-established classical L-shape ECAP process following route C pass, while continuous character and improved productivity suggest that new S-shape ECAP process might be suitable for grain refinement of metals as well as minimization of deformation load on an industrial scale.

Development of Nano-Structured Metals Processed by Severe Plastic Deformation

Severe Plastic Deformation is the most promising technique which can produce Bulk Nano-Structured Materials (BNMs). Among various SPD techniques Accumulative Roll Bonding (ARB) and Equal Channel Angular Pressing (ECAP) have a broad significance due to its unusual mechanical performance. In this paper, the principle and merits of ARB and ECAP technique are pointed out, and also a model based on simulation is established for investigating SPD developments. Pure Copper after sixteen numbers of ARB cycles discloses greater strength by more rises in ductility as compared to that of coarse-grained metals. Similarly in pure Titanium after five numbers of ARB cycles incredibly substantial increase in strength together with an only small decrease of ductility has obtained. The result shows that it is achievable to get high strength, except only with significantly reduced ductility.Additionally, a simulated model, founded on lattice defect kinetics has established. This model holds true parameters like dislocation density, vacancy concentration, grains size, etc., found appropriate for the grain refinement throughout and after the SPD process of simulation. It presents quantitatively consistent outcome for the hardening performance and micro-structural development in pre and post SPD deformation. The new results of SPD-processed nano-structured materials are elucidated, particularly considering viable uses. The advantages of nano-structured metals and alloys mostly for aerospace engineering, automotive engineering, electronic industry and for biocompatible are pointed out such as improved hydrogen storage kinetics (Mg-alloys) for fuel cell technology, superior magnets, Ti, Mg-alloys for prostheses, implants, and stents, etc.

In vitro and in vivo studies of biodegradable fine grained AZ31 magnesium alloy produced by equal channel angular pressing

The objective of the present work is to investigate the role of different grain sizes produced by equal channel angular pressing (ECAP) on the degradation behavior of magnesium alloy using in vitro and in vivo studies. Commercially available AZ31 magnesium alloy was selected and processed by ECAP at 300°C for up to four passes using route Bc. Grain refinement from a starting size of 46μm to a grain size distribution of 1–5μm was successfully achieved after the 4th pass. Wettability of ECAPed samples assessed by contact angle measurements was found to increase due to the fine grain structure. In vitro degradation and bioactivity of the samples studied by immersing in super saturated simulated body fluid (SBF 5×) showed rapid mineralization within 24h due to the increased wettability in fine grained AZ31 Mg alloy. Corrosion behavior of the samples assessed by weight loss and electrochemical tests conducted in SBF 5× clearly showed the prominent role of enhanced mineral deposition on ECAPed AZ31 Mg in controlling the abnormal degradation. Cytotoxicity studies by MTT colorimetric assay showed that all the samples are viable. Additionally, cell adhesion was excellent for ECAPed samples particularly for the 3rd and 4th pass samples. In vivo experiments conducted using New Zealand White rabbits clearly showed lower degradation rate for ECAPed sample compared with annealed AZ31 Mg alloy and all the samples showed biocompatibility and no health abnormalities were noticed in the animals after 60days of in vivo studies. These results suggest that the grain size plays an important role in degradation management of magnesium alloys and ECAP technique can be adopted to achieve fine grain structures for developing degradable magnesium alloys for biomedical applications.

Design of the Main Working Tools for Non-Ferrous Alloys Processing Using Multi-Pass ECAP Technique

Equal-Channel Angular Pressing (ECAP) is a very interesting method for modifying microstructure in producing ultra-fine grained materials (UFG) and nanomaterials (NM). In the ECAP processing a sample is pressed through a die in which two channels of equal cross-section intersect at an angle of ϕ and an additional angle of ψ define the arc of curvature at the outer point of intersection of the two channels. ECAP is unique because significant cold work can be accomplished without reduction in the cross sectional area of the deformed workpiece. The key feature of ECAP processing is almost as a general rule the die design and manufacture as there is limited knowledge about ECAP and especially about ECAP die design, present paper offering an optimum solution to this problem, applied to multi-pass ECAP processing of an aluminum alloy. In this study a number of three ECAP dies with vertical configuration were considered, thereby combining the ease of execution with a relatively high maneuverability and posing minimum difficulties when extracting samples from the output channel. An optimum solution is also given by the present paper for designing and manufacturing the punches used for pressing the aluminum alloy through the three ECAP dies, minimizing this way the force required for plastic deformation and the power consumption and improving the ECAP process efficiency and stability.

English

Wide use of titanium (Ti) materials in medicine gives impetus to a search for development new techniques with elevated properties such as strength, corrosion resistance and Young's modulus close to that of bone tissue. This article presents most recent state of the art on the use of equal channel angular pressing (ECAP) technique in evolving mechanical characteristics of the ultrafine-grained bio-grade Ti materials. Over past few decades, research activities in this area have grown enormously and have produced interesting results, including achieving combination of conflicting properties that are desirable for biomedical applications by severe plastic deformation (SPD) processing. A review of the most recent work in this area is systematically presented. The challenges in processing ultrafinegrained Ti materials are identified and discussed. An overview of the biomedical Ti alloys processed with ECAP technique is given in this review, along with a summary of their effect on the important mechanical properties that can be achieved by SPD processing. The paper also offers insights in the mechanisms underlying SPD.

Optimized Design of an ECAP Die Using the Finite Element Method for Obtaining Nanostructured Materials

An alloy type A16060 was exposed to severe plastic deformation to study its reaction using the finite element method (FEM). To perform this, six different configurations were used in the design of the die’s channel for ECAP (equal channel angular pressing) to obtain nanostructure materials and to optimize the process. Thanks to simulation performed with FEM, it is possible to study the homogeneity in the deformation due to the variation of conditions affecting directly the material being processed using the ECAP technique, such as the friction coefficient, extrusion speed, and mainly the die’s channel geometry being utilized in the ECAP process. Due to the tensile strain area being located mainly in the upper part of the deformed test cylinder (plastic deformation area) which increases the fracture and cracking tendency preventing the processing through ECAP the die being utilized was modified to eliminate the tensile strain area favoring the appearance of compressive stress which reduces the cracking tendency and the fracture of the sample being processed. The FEM analysis demonstrated that the strain state changed significantly from tension to compression when the modified die was used, facilitating the processing of the piece by ECAP.

Homogenization of AlSi7MgCu0.5 Alloy as-Cast Structure by ECAP Processing

The homogenization of AlSi7MgCu0.5 alloy as-cast structure by using an equal channel angular pressing (ECAP) was investigated. The heat treatment of as-cast alloy applied before ECAP processing was required to increase alloy plasticity. Therefore, the samples of analyzed alloy were solution annealed at temperature of 550 °C for 4 hours and subsequently water quenched. Quenched samples were artificially aged at temperature of 300 °C for 5 hours to obtain an over-aged alloy state. The solution annealing of as-cast alloy state caused a partial spheroidization and coarsening of eutectic Si-particles. During artificial aging of analyzed alloy, the incoherent particles precipitated uniformly from α-solid solution. The ECAP technique at room temperature homogenized its heterogeneous dendritic microstructure and formed the ultra-fine grains of solid solution. A redistribution and fragmentation of the eutectic Si-particles and precipitated particles was occurred.