Equal Channel Angular Pressing Procedure Research Articles

Improved corrosion resistance and mechanical properties of severely deformed ZM31 alloy

The hexagonal close-packed (HCP) crystal structure of Mg alloys lead to poor formability as well as other undesirable mechanical behaviors in an otherwise highly sought-after alloy for commercial use. This study investigates the evolution of microstructure, texture, corrosion and mechanical behaviors in Mg–Zn–Mn (ZM31) alloy after processing using Equal Channel Angular Pressing (ECAP). Dynamic recrystallization was evident in the ECAP-processed samples, correlated with a substantial fiber structure, and resulted in the attainment of notable grain refinement and high lattice strain. Average grain sizes of 2.2 and 2 μm were achieved via 2 and 4-Pass Bc processing, respectively. This significant refinement yielded lower corrosion rates through enhancement of the thickness, coherency, and stability of formed protective oxide layers. The corrosion rate in the NaCl medium was substantially enhanced by 99.5% after four passes via route Bc. The recrystallized fine structure was found to have contributed to yield strength, ultimate strength, and microhardness improvements. Deformation enhanced yield and ultimate strengths by 132% and 64%, respectively. The distinctive grain refinement mechanism exhibited through the current ECAP procedure has potential to pave the way for novel and impactful utilizations of ZM31 in industries that demand exceptional mechanical and corrosion performance.

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.

Temperature Effect on Twin Initiation during Equal-Channel Angular Pressing and Mechanical Properties of Twinning-Induced Plasticity Steel

To examine the effect of temperature on twinning initiation and strain accumulation, a twinning-induced plasticity (TWIP) steel with chemical composition of Fe-25Mn-1.66Si-1.23Al was successfully prepared and subjected to severe plastic deformation (SPD) with equal-channel angular pressing (ECAP) at room temperature and warm temperature (300 °C), respectively. The microstructure was analyzed using different techniques, while its mechanical properties were measured by performing micro-tensile tests before and after the ECAP procedure. With such analyzed microstructure after ECAP procedure, the grains of the investigated TWIP steel are found to be elongated and the grain size decreases sharply especially at room temperature, compared to that before the ECAP procedure. The transmission electronic microscope (TEM) micrographs confirmed the existence of twins in all ECAP extruded conditions; however, at room temperature and after multiple passes of ECAP process at a higher temperature, it is easier to initiate secondary twins with a complex morphology. One pass of ECAP at room temperature can cause a strain effect of two passes at 300 °C. Strain hardening behavior was analyzed through ln(dσ/de) − lnσ plot; the results show that the annealing samples present a relatively high strain hardening capability while the strain hardening capability of ECAP-ed samples reduces gradually with the amount of total strain applied by the ECAP.

Microstructural control and mechanical properties of a high Li-containing Al-Mg-Li alloy

AlLi alloys, as promising ultra-light airframe structural materials, have attracted extensive attention with respect to improving their mechanical properties. However, due to the detrimental effect of Li, the strength and ductility of Al-Mg-Li alloys have been found to be relatively low. In this work, high strength and simultaneously improved ductility were achieved in an Al-Mg-Li alloy with a high Li content by accurately controlling the microstructure through equal channel angular pressing (ECAP) and post-heat treatment. During the ECAP procedure, ultrafine grains with precipitating S1 phases were obtained in the alloy. Then, relatively coarse S1 phases due to the high Li content were effectively refined, large amounts of fine metastable δ’ phase particles uniformly precipitated without precipitate-free zones (PFZs), and ultrafine grains remained during subsequent heat treatment, thus achieving a combination of high strength (>450 MPa) and good ductility (>13.5%). The heat treatment including short-term solution and ageing after severe plastic deformation (SPD) was verified to be applicable to other AlLi alloys to adjust the ultrafine microstructure and achieve an optimal combination of strength and ductility, which can increase the applications of AlLi alloys for lightweight key components in the aerospace field

Impact of Equal Channel Angular Pressing (ECAP) on the machinability of an aluminium alloy (EN AW-6082)

The scope of this paper was to examine the effects of the ECAP procedure on the machinability of aluminium (EN AW-6082) based on turning tests. The behaviour of the ECAP material was investigated and compared to the as-received (AR) material. Since limited information on the machinability of ECAP materials is available, it was necessary to conduct an evaluation on basis of the untreated material. For this purpose, a defined range of cutting parameters, which were raised based on recommendations of the tool manufacturer were used for the first experiments. In order to analyse the effects of ECAP on the machinability the following comparative criteria were pulled up: the quality of the machined surfaces, appearing forces and chips produced.

Mechanical properties and structure of AZ61 magnesium alloy processed by equal channel angular pressing

An equal channel angular pressing (ECAP) procedure has been developed to produce a fine-grained AZ61 magnesium alloy. The results show that the microstructure can be effectively refined with increasing equivalent strain during ECAP. For increasing ECAP process efficiency was conventional tool as a helix in the horizontal part of channel built. This fine-grained alloy has an excellent strength accompanied by reasonable good tensile ductility. The success of the development of this ECAP procedure can offer a good opportunity for the development of magnesium alloys with good mechanical properties.

Improving corrosion resistance of Al‐11mass%Si alloy through a large number of ECAP passes

AbstractUltrafine‐grained (UFG) Al‐11mass%Si alloy, processed by multi‐pass equal‐channel angular pressing (ECAP) at 573 K, was investigated on corrosion behavior in 0.6 M NaCl solution. Potentiodynamic polarization tests and scanning electron microscopy observation showed that a large number of ECAP passes resulted in lower corrosion current density, more positive corrosion potential, and rather smooth corroded surface with shallow corrosion pits. The uniform distribution of fine secondary‐phase particles on UFG Al matrix weakened the susceptibility to pitting corrosion while inhibited general microgalvanic reactions. The present results indicate that grain refinement of aluminum matrix to the UFG state and uniform redistribution of broken particles (including eutectic silicon and secondary phases), via severe plastic deformation at elevated temperature undergoing dynamic recrystallization, can significantly improve the corrosion resistance of Al alloys, besides the known exceptional mechanical advantages. The simple and effective ECAP procedure makes UFG Al alloys more attractive for high strength structural application in corrosive environment.

Some factors affecting the creep behaviour of metallic materials processed by equal-channel angular pressing

Abstract Very few reports describing the creep behaviour of materials processed by equal-channel angular pressing (ECAP) have shown that there are both similarities and differences between the creep behaviour of coarse-grained metals and alloys and their ultrafine-grained counterparts. This paper examines these differences and evaluates some factors affecting the creep behaviour of pure aluminium, pure copper, and the binary Al-0.2 wt.% Sc alloy processed by ECAP. It was found that the creep behaviour of pressed material depends strongly on the number of ECAP passes and successive passes result in a gradual decrease in the creep resistance which may be attributed to microstructural changes, homogenization of the microstructure and the microtexture, nanoporosity induced by the ECAP procedure and thermal instability of the pressed material during creep exposure.

Effect of temperature on texture formation of 6061 aluminum sheet in equal-channel angular pressing

A novel equal-channel angular pressing (ECAP) procedure was conducted on 6061 aluminum sheet at temperature up to 513 K to investigate temperature effect on microstructure and texture formation. The deformed microstructures were examined by transmission electron microscopy and the macrotexture evolution was investigated by orientation distribution functions (ODFs). The results shown that when ECAP at temperature below 433 K the microstructures exhibit high dislocation density within subgrains with thick and waved non-equilibrium boundaries, and the textures are characterized by the formation of Rotated cube component or a pair of textures components near Rotated cube component, such as {0 3 1}〈5 1 3〉 and {0 1 3}〈5 1 3〉or {0 4 1}〈6 1 4〉 and {0 1 4}〈6 4 1〉. Whereas under certain procedure condition, i.e. at 513 K, the ECAP procedure is capable of producing microstructure with low density dislocations subgrains separated by regular boundaries, and a preferable 〈1 1 1〉//ND texture fiber is formed with the R-value as higher as 1.5. The texture results show that the ECAP procedure could be expected to be a potential application to enhance the formability of aluminum sheet.

Effect of texture evolution on tensile properties of Al–Ni eutectic alloy fabricated by equal channel angular pressing

The present study investigated in detail the effect of texture evolution on the mechanical properties of an Al–5·7 wt-%Ni eutectic alloy, which was subjected to severe plastic deformation by the equal channel angular pressing (ECAP) technique. The ECAP procedure was carried out using two strain introduction methods, route BC and route A, at a temperature of 298 K and a pressing rate of 0·33 mm s−1. The as pressed microstructures were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results indicated that the Al–Ni eutectic alloy specimens after ECAP processing by route BC and route A methods had very different microstructures, which strongly affected the tensile properties of the specimens. It was demonstrated that after ECAP processing by route BC, fine Al3Ni particles of ∼300 nm were homogeneously dispersed in the aluminium matrix, and the specimens showed no clear anisotropy in tensile properties. After ECAP processing by route A, however, eutectic textures containing α-Al and Al3Ni fibrous dispersoids had a highly anisotropic distribution and were demonstrated to have significantly anisotropic tensile properties. Based on the experimental results, the fracture mechanism during tensile testing of the Al–Ni eutectic alloy using different strain induction methods is discussed.

Severe plastic deformation as a processing tool for developing superplastic metals

Processing through the imposition of severe plastic deformation (SPD) provides an opportunity to achieve significant grain refinement in metallic alloys. Typically, the materials processed in this way have grain sizes in the submicrometer or the nanometer range. This paper describes the application of SPD processing through the procedure of Equal-Channel Angular Pressing (ECAP) in which a metal is pressed through a die constrained within a channel that is bent through an abrupt angle generally equal to, or very close to, 90°. Provided these ultrafine grain sizes are reasonably stable at high temperatures, these materials are capable of exhibiting very significant superplastic ductilities when pulled in tension at elevated temperatures. Typical examples of this superplastic behavior are presented for several aluminum-based alloys and for a magnesium alloy.

Mechanical properties of a two-phase alloy Mg–8%Li–1%Al processed by equal channel angular pressing

The microstructural evolution and room temperature tensile properties of Mg–8%Li–1%Al alloy processed by equal channel angular pressing (ECAP) at 403 K were investigated. It was found that the strength could be improved pass by pass. The elongation-to-failure decreased dramatically after the first ECAP pass, but could be improved pass by pass during the subsequent ECAP procedure. The microstructure analysis gave the explanations for these phenomena.

Réalisation de superplasticité à grande vitesse dans des alliages Al_Mg_Sc_Zr par utilisation de l'extrusion dans des canaux déviés

Abstract The processing of metallic alloys through the procedure of equal-channel angular pressing (ECAP) provides an opportunity for achieving superplastic ductilities at very high strain rates. This paper reports experimental data from an investigation of a series of AlMgScZr alloys processed by ECAP. The results show the occurrence of high tensile ductilities at testing strain rates above 10 −2 s −1 .

Low-temperature superplasticity in a Cu–Zn–Sn alloy processed by severe plastic deformation

A copper alloy containing ∼38% Zn and ∼3% Sn was subjected to severe plastic deformation at a temperature of 400°C using the procedure of equal-channel angular pressing (ECAP). The microstructures produced by ECAP were relatively heterogeneous with areas of both recrystallized and unrecrystallized grains. Within the recrystallized areas, the average grain size was ∼1.5 μm. Tensile testing after ECAP revealed the occurrence of superplasticity with elongations up to ∼900%. Superplastic ductilities were recorded at temperatures as low as 300°C corresponding to an homologous temperature of ∼0.51T m, where T m is the absolute melting temperature of the alloy. These results demonstrate the potential for achieving low temperature superplasticity in this alloy through ECAP. As in conventional superplastic Cu-based alloys, specimens failed because of the development of internal cavities.

Developing Ultrafine Grain Sizes Using Severe Plastic Deformation

Severe plastic deformation may be used as a processing tool to achieve a refinement in grain size in metallic alloys to the submicrometer or nanometer range. This paper describes recent developments using the procedure of equal-channel angular pressing (ECAP) in which samples are pressed through a die containing a channel bent into an L-shaped configuration. The shearing associated with passage through the die introduces bands of subgrains which evolve, with additional pressings, into arrays of grains separated by boundaries having high angles of misorientation. The process of ECAP is a useful tool for both increasing the strength and toughness of an alloy at ambient temperatures and achieving a potential for superplastic forming of the alloy at rapid strain rates at elevated temperatures.

Improving the mechanical properties of magnesium and a magnesium alloy through severe plastic deformation

Pure Mg and Mg alloys generally exhibit only limited ductilities at ambient temperatures. Experiments were conducted to evaluate the potential for improving the mechanical properties of pure Mg and an Mg–0.9% Al alloy at room temperature by subjecting these materials to severe plastic deformation through the procedure of equal-channel angular pressing (ECAP). It is shown that ECAP may be applied successfully to these materials at elevated temperatures and this leads to grain refinement due to the occurrence of recrystallization during the pressing process and to significant improvements in the strength and ductility of these materials. Since these improvements are apparent after only a single pass through the ECAP die, it is concluded that the introduction of ECAP provides a simple and effective procedure for improving the ambient temperature mechanical properties of materials, such as hcp metals, where the measured ductilities are generally limited.