Effect Of Equal Channel Angular Pressing Research Articles

Stress Corrosion Cracking Behavior of Fine-Grained AZ61 Magnesium Alloys Processed by Equal-Channel Angular Pressing

The effect of equal-channel angular pressing (ECAP) on stress corrosion cracking (SCC) behavior of a cast AZ61 Mg alloy was investigated in distilled water (DW) using the slow strain rate tensile test (SSRT) at a strain rate of 1 × 10−6 s−1. The fine-grained alloy after ECAP showed a greater SCC susceptibility but a higher ultimate tensile strength, compared with the as-cast counterpart. The results were attributed to refined grains, high-density dislocations and increased proportion of high-angle grain boundaries induced by severe plastic deformation, as well as isolated fine β-phase particles transiting from net-like β-phase.

A Study on the Synergistic Effect of ECAP and Aging Treatment on the Mechanical Properties of AA6082

In this study, the synergistic effect of equal-channel angular pressing (ECAP) and aging temperature-time on the mechanical properties of AA6082 has been investigated. The treatments include post-ECAP artificial aging and dynamic aging which was achieved by ECAP processing at 140 °C to 1 pass. It was observed that both routes were effective in enhancing the strength of the alloy. The Vickers microhardness measurements were recorded at three different aging temperatures with varying time intervals. The hardness values of the ECAP-processed alloy to 1 and 2 passes, followed by artificial peak aging was found to be 112.3 and 130 Hv, respectively. Compared to the yield strength of solution-treated alloy, the synergistic effect of ECAP processing to 1 pass and 2 passes followed by artificial aging has resulted in an increase in the yield strength of the alloy by 140 and 183%, respectively. The dynamic aging resulted in an overall increase in the yield strength of the alloy by 177%. The correlation from the modified Johnson-Cook model was close to the observed experimental responses.

Effect of equal-channel angular pressing and aging on corrosion behavior of ZK60 Mg alloy

Commercial ZK60 Mg alloy was processed by multi-pass equal-channel angular pressing (ECAP) and subsequent aging to investigate the effect of grain refinement and second-phase redistribution on its corrosion behavior. Electrochemical tests show that the fine-grained samples after more ECAP passes have higher corrosion current densities (Jcorr) in the polarization curves, lower charge-transfer resistance (Rt) values in the EIS plots. The severe plastic deformation decreases the alloy corrosion resistance besides the well-known strengthening and toughening. Scanning Kelvin probe (SKP) measurement shows that the anodic and cathode sites are homogeneously distributed on the surface of the fine-grained alloy, which inhibits localized corrosion. The SKP potential, having linear relationship with the corrosion potential (φcorr), decreases with increasing the ECAP pass. Furthermore, the post-ECAP aging can slightly improve the corrosion resistance of the fine-grained ZK60 Mg alloy and enhance the comprehensive performances, due to the stress relief and uniform distribution of second-phase particles.

Effect of equal-channel angular pressing and aging on the microstructure and mechanical properties of an Al-Cu-Mg-Si alloy

The effect of intermediate equal-channel angular pressing (ECAP) and final aging at 170°C on the mechanical properties and microstructure of aluminum alloy belonging to Al-Cu-Mg-Si system stress with a Cu/Mg ratio (AA2014) is considered. After quenching and aging (treatment T6), the yield stress (σ0.2) and ultimate tensile strength (σu) are ∼415 and ∼450 MPa, respectively; the elongation to fracture (δ) is 4.2%. The precipitation strengthening is reached due to the precipitation of θ″-, θ′-, β″-, and Q′/C-phase particles. After intermediate ECAP and subsequent aging for 0.5 h, σ0.2 and σu increase to 470 and 535 MPa, respectively; δ increases to ∼9.5%. The plastic deformation leads to the formation of a microstructure that consists of deformation bands characterized by a high density of dislocations. During aging for 0.5 h, the partial decomposition of supersaturated solid solution and formation of segregations within grains and at dislocations and precipitation of the Guinier-Preston zones and β″ phase also occur; all of this ensure the maximum increase in the strength of the AA2014 alloy. As the aging time increases to 8 h, the slight decrease in both σ0.2 and σu to 465 and 515 MPa and δ to ∼6% takes place. It has been shown that the intermediate ECAP does not affect the sequence of the precipitation of main strengthening θ″ and θ′ phases during aging. However, in this case, the volume fraction of strengthening particles decreases significantly and their dispersivity increases.

Effects of equal-channel angular pressing and accumulative roll-bonding on hydrogen storage properties of a commercial ZK60 magnesium alloy

The hydrogen storage properties of a commercial ZK60 magnesium alloy were investigated after processing by equal-channel angular pressing (ECAP) and accumulative roll-bonding (ARB). Samples were prepared by 6 passes of ECAP and subsequently rolled 25 times. Microstructural characterization was performed using scanning and transmission electron microscopy. The kinetics of hydrogen absorption and desorption were measured in a Sievert-type apparatus. Processing only by ECAP resulted in a very low hydrogen storage capacity of 0.5 wt. %. Additional processing by ARB refined the microstructure and improved the hydrogen absorption. Despite this improvement, the hydrogen capacity was limited to less than 4 wt. %. This limitation was overcome by crushing the materials into small thin plates. The crushed sample from the ECAP material absorbed 4.77 wt. % of hydrogen in 24 h while the capacity of the sample processed by ECAP and ARB was 6.4 wt. %. The results are discussed in terms of morphology and microstructure of the samples.

Refinement of tungsten microstructure upon severe plastic deformation

The effect of equal-channel angular pressing and high-pressure torsion on the formation of an ultrafine-grained structure in commercially pure tungsten has been studied. The structure was tested by the methods of transmission and scanning electron microscopy using electron backscatter diffraction analysis. The material microhardness depending on the stored deformation has been evaluated. In the samples subjected to severe plastic deformation, the quantitative structure characteristics (the average size of grains/subgrains and misorientation-angle distribution) have been determined.

Structure and annealing behavior of an Al-Mg-TM alloy processed by equal channel angular pressing

Effects of equal-channel angular pressing (ECAP) at 325°C to a strain, e~10 and post-ECAP annealing for 1 hr in the temperature range of 350-520 ^oC on structure of the cast and homogenized Al-Mg-Sc-Zr alloy 01570C were analyzed. It is found that annealing of ECAP processed material containing near homogeneous ultrafine-grained (UFG) structure with ~1 µm grain size led to normal grain growth, accompanied by coarsening of Al3(Sc,Zr) dispersoids. As compared to the cast alloy, the coarsening of dispersoids in the deformed alloy started at lower temperature and occurred more intensely, and resulted in more rapid loss of their coherency with surrounding matrix.

CREEP DAMAGE OF Al AND Al-Sc ALLOY PROCESSED BY ECAP

Experiments were conducted to determine an effect of equal-channel angular pressing (ECAP) on the creep damage and the microstructure of pure aluminium and an Al-Sc alloy. The coarse-grained materials in their as-received states were subjected to ECAP at room temperature using a die, which had a 90° angle between the channels. Creep tests in tension were performed on the as-pressed samples at 473 K under an applied stress range between 10 to 50 MPa. For comparison purposes, some creep tests were performed also on both investigated materials in their as-received states. Following ECAP and creep testing samples were prepared for examination by scanning electron microscopy equipped with an electron back scattering diffraction unit. The observation of the free surfaces of the ECAP samples after creep exposure showed the occurrence of mesoscopic shear bands exceeding considerably an average grain size. The formation of these bands could be influenced by inhomogeneity of microstructure created during ECAP. It was observed the cavities and microcracks nucleate and propagate along the mesoscopic shear bands. Their growth and coalescence lead to ductile fracture mode with dimples on the creep fracture surface. The evolution of creep damage and fracture of ultrafine-grained specimens could be influenced by synergetic effects of grain boundary sliding, formation of shear bands which were oriented along the direction of the last ECAP pass and cavitation.

Effect of Equal-Channel Angular Pressing on Pitting Corrosion of Pure Aluminum

The effect of equal-channel angular pressing (ECAP) on the pitting corrosion of pure Al was investigated using electrochemical techniques in solutions containing 0.1 m mol·dm−3of Na2SO4and 8.46 mol·dm−3of NaCl (300 ppm Cl−) and followed by surface analysis. The potential for pitting corrosion of pure Al was clearly shifted in the noble direction by the ECAP process indicating that this process improves resistance to pitting corrosion. The time dependence of corrosion potential and the anodic potential at 1 A·m−2revealed that the rate of formation of Al oxide films increased due to a decrease in the grain size of the Al after ECAP. Since there exists a negligible amount of impurity precipitates in pure Al, the improvement in pitting corrosion resistance of pure Al by ECAP appears to be attributable to an increase in the rate of formation of Al oxide films.

Quantitative Characterization of Microstructure in Copper Processed by Equal-Channel Angular Pressing

Experiments were conducted on extremely coarse-grained pure copper to evaluate the effect of equal-channel angular pressing (ECAP) on microstructure evolution in the as-pressed state and after creep exposure using various stereological methods. The microstructure formed by severe plastic deformation is an unusual structure which can be hardly characterized only by the mean grain size especially after low number of ECAP passes. The purpose of this paper is a detailed examination of (sub)boundaries and grain boundaries in the microstructures of the pressed material. The inhomogeneity of deformed microstructures is also evaluated. The detailed description of ECAP microstructures should contribute to the better understanding of mechanical properties of the pressed materials.

Effect of equal-channel angular pressing and annealing conditions on the texture, microstructure, and deformability of an MA2-1 alloy

Equal-channel angular pressing (ECAP) of am MA2-1 alloy according to routes A and Bc is used to study the possibility of increasing the low-temperature deformability of the alloy due to grain refinement and a change in its texture. To separate the grain refinement effect from the effect of texture on the deformability of the alloy, samples after ECAP are subjected to recrystallization annealing that provides grain growth to the grain size characteristic of the initial state (IS) of the alloy. Upon ECAP, the average grain size is found to decrease to 2–2.4 μm and the initial sharp axial texture changes substantially (it decomposes into several scattered orientations). The type of orientations and the degree of their scattering depend on the type of ECAP routes. The detected change in the texture is accompanied by an increase in the deformability parameters (normal plastic anisotropy coefficient R, strain-hardening exponent n, relative uniform elongation δu) determined upon tensile tests at 20°C for the states of the alloy formed in the IS-4A-4Bc and IS-4Ao-4BcO sequences. The experimental values of R agree with the values calculated in terms of the Taylor model of plastic deformation in the Bishop-Hill approximation using quantitative texture data in the form of orientation distribution function coefficients with allowance for the activation of prismatic slip, especially for ECAP routes 4Bc and 4BcO. When the simulation results, the Hall-Petch relation, and the generalized Schmid factors are taken into account, a correlation is detected between the deformability parameter, the Hall-Petch coefficient, and the ratio of the critical shear stresses on prismatic and basal planes.

Effect of equal-channel angular pressing routes on high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy

The effect of equal-channel angular pressing (ECAP) route on the high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy was investigated. The 8-pass ECAPed specimens deformed via three different routes consisted of ultra-fine grains 0.5 μm in size, and contained a considerable amount of second-phase particles, which were fragmented and distributed in the matrix. In the torsion tests, the maximum shear stress significantly increased with increasing number of ECAP passes, while the maximum shear stress and fracture shear strain were lowest in the specimen deformed via route A among the three 8-pass ECAPed specimens. Observation of the deformed area beneath the fractured surface revealed the adiabatic shear bands of 100 μm in width in the specimen deformed via route A, which minimized the maximum shear stress and fracture shear strain, whereas they were hardly formed in the specimens deformed via route B or C. The formation of adiabatic shear bands was explained in terms of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.

Effect of Equal Channel Angular Pressing on the Pitting Corrosion Resistance on the Aluminum Alloys with/without Anodization

The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of Al (AA1100) and Al-Mg (AA5052) alloy with anodization and without was investigated by means of polarization curves in solutions containing 300 ppm or 0.6 mol/L of Cl- and by surface analysis. In Al and Al-Mg alloy without anodization, the potentials for pitting corrosion were evidently shifted to the noble direction by ECAP process, indicating that this process improves resistance to pitting corrosion. SEM observation revealed that the pitting corrosion occurred near the impurity precipitates and the size of impurity precipitated decreased with ECAP process. The time-dependence of corrosion potential and the polarization resistance determined by AC impedance technique suggested that the formation rate of Al oxide films was increased with ECAP process. The improvement in pitting corrosion resistance of Al and Al-Mg by ECAP seems to be attributable to the decrease in the size of impurity precipitates and the increase in the formation rate of Al oxide films. On the other hand, the time required for initiating pitting corrosion of anodised Al was longer with ECAP than without, indicating improvement in the pitting corrosion resistance by application of ECAP. However, the pitting corrosion of anodized Al-Mg alloy occurred earlier with ECAP than without, showing that the corrosion resistance was worse with ECAP than without. In anodized Al-Mg alloy, cracks occurred in the anodic oxide films during initial corrosion and the cracks were larger with ECAP than without. It is assumed that the pitting corrosion was promoted by the cracks due to the higher internal stress resulting from ECAP.

Ａｌ‐Ｃｕ合金の耐孔食性に及ぼす強歪み加工ＥＣＡＰ処理の影響

Effects of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of Al-Cu (AA2024) alloy with and without anodization were investigated using surface analysis and polarization curves in solutions containing 300 ppm or 0.6 mol·dm−3 of Cl−. The pitting corrosion potential and corrosion rate of Al-Cu alloy revealed no effect of ECAP on the pitting corrosion resistance of Al-Cu. The Al-Cu alloy contained such precipitates as Al2Cu, Al2CuMn and Al-Cu-Si-Fe-Mn intermetallic compounds, around which pitting corrosion occurred. Actually, ECAP pulverized these precipitates to decrease their size, but it had no effect on the pitting corrosion resistance of Al-Cu alloy because pitting corrosion occurred even around small precipitates of Al2Cu. In contrast, the time to initiate pitting corrosion of Al-Cu alloy while maintaining a constant potential of 1.2 V was longer with ECAP than without, indicating that ECAP improved the pitting corrosion resistance. Although the precipitates of Al2Cu and Al2CuMn disappeared because of oxidation during anodization, Al-Cu-Si-Fe-Mn intermetallic compounds were present and formed defects in anodic oxide films. Pitting corrosion of the anodized Al-Cu alloy occurred around the Al-Cu-Si-Fe-Mn precipitates. The improved pitting corrosion resistance of anodized Al-Cu alloy by ECAP appears to be attributable to the decreased size of the precipitates that initiate pitting corrosion.

Effect of equal-channel angular pressing on pitting corrosion resistance of anodized aluminum-copper alloy

The effect of equal-channel angular pressing(ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L AlCl 3 and also by surface analysis. Anodizing was conducted for 20 min at 200 and 400 A/m 2 in a solution containing 1.53 mol/L H 2SO 4 and 0.018 5 mol/L Al 2(SO 4) 3·16H 2O at 20 °C. Anodized Al-Cu alloy was immediately dipped in boiling water for 20 min to seal the micro pores present in anodic oxide films. The time required before initiating pitting corrosion of anodized Al-Cu alloy is longer with ECAP than without, indicating that ECAP process improves the pitting corrosion resistance of anodized Al-Cu alloy. Second phase precipitates such as Si, Al-Cu-Mg and Al-Cu-Si-Fe-Mn intermetallic compounds are present in Al-Cu alloy and the size of these precipitates is greatly decreased by application of ECAP. Al-Cu-Mg intermetallic compounds are dissolved during anodization, whereas the precipitates composed of Si and Al-Cu-Si-Fe-Mn remain in anodic oxide films due to their more noble corrosion potential than Al. FE-SEM and EPMA observation reveal that the pitting corrosion of anodized Al-Cu alloy occurs preferentially around Al-Cu-Si-Fe-Mn intermetallic compounds, since the anodic oxide films are absent at the boundary between the normal oxide films and these impurity precipitates. The improvement of pitting corrosion resistance of anodized Al-Cu alloy processed by ECAP appears to be attributed to a decrease in the size of precipitates, which act as origins of pitting corrosion.

Microstructural Evolution and Creep of an Al-0.2wt.%Sc Alloy after Equal-Channel Angular Pressing

Experiments were conducted on an Al-0.2wt.%Sc alloy to evaluate the effect of equalchannel angular pressing (ECAP) on its creep behaviour. ECAP was conducted at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The subsequent extrusion passes were performed by route BC up to 8 ECAP passes. Creep tests in tension were performed on the as-pressed samples at 473 K under an applied stress range between 10 to 50 MPa. For comparison purposes, some creep tests were performed also on the unpressed alloy. Following ECAP and creep testing, samples were prepared for examination by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with an electron back scattering diffraction (EBSD) unit. The observation of the surface of the ECAPed samples after creep exposure showed the occurrence of mesoscopic shear bands. The EBSD data reveal that these bands are separated by high angle grain boundaries. The creep resistance of an alloy is a little decreased after one ECAP pass. However, successive ECAP pressing lead to a noticeable decrease of the creep properties. Thus, the Al-0.2wt.%Sc alloy processed by 8 ECAP passes exhibited faster creep rate by about two and/or three orders of magnitude than the unpressed alloy when creep testing at 473 K and at the same applied stress. The detrimental effect of ECAP on the creep resistance is probably a consequence of a synergetic effect of mesoscopic sliding of groups of grains along shear bands, more intensive grain boundary sliding and creep cavitation in creep of the ultrafine-grained material.

Pitting Corrosion Resistance of Anodized Aluminum-Copper Alloy Processed by Severe Plastic Deformation

The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of anodized Al and Al-Mg alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L of AlCl 3 and by surface analysis. The time required for initiating pitting corrosion of anodized Al was longer with ECAP than without, indicating improvement in the pitting corrosion resistance by application of ECAP. However, in anodized Al-Mg alloy, the pitting corrosion occurred earlier with ECAP than without, showing that the corrosion resistance was worse with ECAP than without. SEM and EPMA observation revealed that pitting corrosion of anodized Al occurred around the impurity precipitates and that the size of the impurity precipitates decreased as a result of the ECAP. The improvement in pitting corrosion resistance of anodized Al by ECAP appears to be attributable to a decrease in the size of impurity precipitates. On the other hand, in anodized Al-Mg alloy, cracks occurred in the anodic oxide films during initial corrosion and the cracks were larger with ECAP than without. It is assumed that the pitting corrosion was promoted by the cracks due to the higher internal stress resulting from ECAP.

強ひずみ加工を施した Al-Cu 合金の陽極酸化膜の耐孔食性

The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L of AlCl3 and also by surface analysis. The time required before initiating pitting corrosion of anodized Al-Cu alloy was longer with ECAP than without, indicating improvement in the pitting corrosion resistance by application of ECAP. Second phase precipitates were present in Al-Cu alloy matrix and the size of these precipitates was greatly decreased by application of ECAP. The precipitates composed of Si and Al-Cu-Si-Fe-Mn were not oxidized during anodization, and the anodic oxide film were absent at the boundary between the normal oxide films and these impurity precipitates. The pitting corrosion of anodized Al-Cu alloy occurred preferentially around these precipitates, the improvement of pitting corrosion resistance of anodized Al-Cu alloy by ECAP appears to be attributable to a decrease in the size of precipitates, which act as origins of pitting corrosion.

On the effect of equal-channel angular pressing on creep of tempered martensite ferritic steels

The effect of long-term aging and equal-channel angular pressing (ECAP) on creep of the tempered martensite ferritic steel P91 at 650 °C and 120 MPa was studied. We compare the creep behaviour of a material which was subjected to a standard heat treatment (austenitizing and air cooling followed by tempering and air cooling) to the creep properties of an overaged (standard heat treatment followed by 1 week overaging at 700 °C) and an overaged and severely plastically deformed (ECAP, one 90° pass at 250 °C) material. During overaging, carbides coarsen and as a consequence, the creep-rate of the overaged material is higher than that of the material after a standard heat treatment. Severe plastic deformation of the overaged material results in an increase of room-temperature hardness. But as a striking new result, the creep-rate of this material increases after ECAP. This result is discussed on the basis of a scenario where a high density of mobile dislocations results in higher creep rates.

Effect of Equal-Channel Angular Pressing (ECAP) on Creep in Aluminium Alloys

This paper examines the effect of equal-channel angular pressing (ECAP) on creep behaviour of pure aluminium, binary Al-0.2wt.%Sc alloy and ternary Al-3wt.%Mg-0.2wt.%Sc alloy. The ECAP was conducted at room temperature with a die that had a 90° angle between the channels and 8 repetitive ECAP passes followed route BC. Constant stress compression creep tests were performed at 473 K and stresses ranging between 16 to 80 MPa on ECAP materials and, for comparison purposes, on the initial coarse-grained materials. The results showed that the creep resistance of the ECAP processed Al-Sc and Al-Mg-Sc alloys was markedly deteriorated with respect to unpressed coarse-grained materials.