Number Of Equal Channel Angular Pressing Passes Research Articles

Enhancing grain refinement efficiency and fading resistance of Al–B master alloys processed by equal channel angular pressing

Abstract

Effect of equal channel angular pressing (ECAP) on hydrogen storage properties of commercial magnesium alloy AZ61

Cast commercial AZ61 magnesium alloys were processed through equal channel angular pressing (ECAP) and were comminuted into chips by filing with a rasp in order to measure their hydrogen storage properties. The effects of the number of ECAP passes and the processing route of ECAP on the hydrogen storage properties of AZ61 magnesium alloys were investigated. ECAP processing led to severe dynamic recrystallization and grain refinement of the AZ61 alloys. Of the analyzed samples, the AZ61 alloy processed via the Bc ECAP route with eight passes exhibited the smallest grain size, the fastest hydrogen absorption and desorption rates, and the highest gravimetric hydrogen storage capacity of 6.2 wt%.

Influence of ultrafine-grained structure produced by equal-channel angular pressing on the dynamic response of pure copper

Metallic materials with a nanocrystalline or ultrafine-grained (UFG) structure can exhibit increased strength, albeit with reduced ductility. The behaviour of such materials under high-speed and impact loads has been insufficiently explored. This work presents experimental results on the dynamic response of UFG pure copper (99.95%) processed by equal-channel angular pressing (ECAP) in comparison with its initial coarse-grained (CG) structure. The yield strength in the case of compression tests of cylindrical samples and the energy consumed for deformation and fracture in the case of a three-point bending of a beam with a V-notch are considered. The UFG copper has higher yield strength in compression tests, but its sensitivity to the loading rate is significantly less than that of the CG initial material and depends on the number of ECAP passes. The UFG material shows higher impact toughness KCV and energy consumption for the entire process of deformation and fracture under impact three-point bending.

Effect of pre-deformation cooling rate on the age-hardening response of ultrafine grained AA6063

In this article, effect of pre-deformation cooling rate after solution heat treatment on the evolution of microstructure and tensile properties of AA6063 aluminum alloy is investigated. For this purpose, samples of AA6063 are solution heat treated at 550°C for 6h. Followed by this treatment, some samples are furnace cooled (FC), some air cooled (AC) and the rest water quenched (WQ). After 2, 6 and 10 passes equal channel angular pressing (ECAP), significantly finer nanostructure was observed in the WQ samples. This was attributed to the effect of higher concentration of Mg in solid solution. In addition, the WQ samples showed higher initial tensile strength being attributed to the more enriched solid solution and more significant strengthening during severe plastic deformation which was attributed to higher dislocation density generated during deformation. In addition, it was found that the WQ samples in un-deformed and deformed conditions show a more significant response to aging in terms of strengthening. In fact, age hardening was observed for both AC and WQ samples in un-deformed condition and after 2 passes ECAP. Age hardening was as well observed in the WQ samples which were deformed for 6 and 10 passes. However, age softening was observed in the AC samples when the number of ECAP passes was increased to 6 and 10.

Characterization of precipitates in an Al-Zn-Mg alloy processed by ECAP and subsequent annealing

Experiments were conducted to examine the influence of equal-channel angular pressing (ECAP) and post-ECAP annealing on the microstructures of an Al-Zn-Mg alloy. The results show that precipitates, mainly of the η′, η (MgZn2), T (Al20Cu2Mn3) and E (Al18Mg3Cr2) phases, are fragmented to fine spherical precipitates during ECAP processing for 4 and 8 passes. After post-ECAP annealing at 393 and 473K for 20h, precipitates with larger sizes lie primarily along the grain boundaries and finer particles are evenly distributed within the grains. Increasing the numbers of ECAP passes from 4 to 8 leads to an increase in the volume fraction of the finer precipitates in the ECAP-processed and annealed alloy. After 4 passes and heat treatment at 473K, the precipitates are slightly larger compared with the alloy processed under identical conditions and annealed at 393K. Nevertheless, significant coarsening is evident after processing for 8 passes and increasing the annealing temperature from 393 to 473K. Different types of precipitates are effective in impeding grain growth during the post-ECAP annealing even at 473K for 20h. In addition, η precipitates form within the T and E phases after both ECAP and post-ECAP annealing.

Influence of Processing Parameters on Microstructural Evolution and Tensile Properties for 7075 Al Alloy Prepared by an ECAP-Based SIMA Process

A modified strain-induced melt activation (SIMA) process consisting of homogenization, equal-channel angular pressing (ECAP) and subsequent heating to the semisolid temperatures was introduced to prepare the 7075 aluminum alloy with superior thixotropic behaviors. The effects of both the homogenization and the number of ECAP passes, as well as the isothermal temperatures on the microstructural evolution, were investigated. The results indicate that ideal microstructure wherein fine and globular solid grains surrounded by uniform liquid films can be achieved through ECAP deformation–recrystallization mechanism. Increasing the number of ECAP passes accelerates the recrystallization of strained grains, thus reducing the average grain size and improving the grain sphericity. Moreover, higher holding temperatures and prolonged soaking time can improve the growth of the solid grains. Two main coarsening mechanisms, viz. coalescence and Ostwald ripening, contribute to the growth of the solid grains simultaneously and independently. The tensile strength of the 7075 alloys after four-pass ECAP-based SIMA and T6 heat treatment is relatively lower than the as-received billet, while the elongation of SIMA processed samples is much higher than that of as-received ones. Increasing the number of ECAP passes improves the tensile strength for alloys with and without T6 treatment due to the fine grain strengthening mechanism.

Microstructure and strengthening mechanisms in an Al-Mg-Si alloy processed by equal channel angular pressing (ECAP)

The microstructure, mechanical properties, and strengthening mechanisms of an Al-Mg-Si alloy (AA6060) subjected to severe plastic deformation using equal channel angular pressing (ECAP) were investigated. Samples were passed through a die with an inner angle of Φ = 90° and outer arc of curvature of ψ = 37° at room temperature up to 12 passes via route Bc. Electron backscatter diffraction (EBSD) was used to evaluate the microstructure and misorientation boundaries. The microstructure showed a large fraction of low-angle boundaries associated with subgrain formation in the first ECAP pass, while after eight and 12 passes, a heterogeneous ultrafine grain structure with an average grain size around 0.57 and 0.47 μm, respectively, was obtained. In order to characterize the mechanical properties, microhardness and tensile tests were carried out. Results of mechanical property tests show that microhardness, yield stress, and ultimate tensile strength increase as ECAP pass number increases up to a maximum value of 120 HV, 344 MPa, and 355 MPa, respectively, after five passes. The Hall–Petch effect, dislocation, solid solution, and precipitation strengthening were evaluated to determine the dependence of the yield stress on the ECAP pass number. The results show that the strength effect arises from the subgrain microstructure rather than from the high-angle grain boundaries developed.

Influence of Equal Channel Angular Pressing Passes on the Microstructures and Tensile Properties of Mg-8Sn-6Zn-2Al Alloy.

An I-phase containing Mg-8Sn-6Zn-2Al (wt %; TZA862) alloy was fabricated and subjected to different number of passes of equal channel angular pressing (ECAP) processing at 300 °C. The results showed that the alloys exhibited a bimodal microstructure, which consisted of fine dynamically recrystallized (DRX) grains and coarse non-DRX grains. When increasing the number of ECAP passes from 2 to 6, the fraction of DRX grains and the dispersed second phase particles subsequently increase. However, the fraction and particles then decrease once the number of ECAP passes increases to 8. After 6 ECAP passes, remarkable grain refinement was achieved and increasing the number of passes to 8 cannot further refine the microstructure. Furthermore, the alloys having undergone ECAP exhibited a strong ED-tilted texture, the intensity of which increased with an increase in the number of ECAP passes. The ultimate tensile strength (UTS; 338 MPa) and elongation (El.; 14.2%) of the alloy processed with 6 ECAP passes were considerably higher compared to those of the other materials that had undergone ECAP. These significant enhancements were attributed to extensive grain boundary strengthening, precipitation strengthening and a higher work-hardening capacity.

Wear Properties of ECAP-Processed AM80 Magnesium Alloy

AM80 magnesium alloy was subjected to equal-channel angular pressing (ECAP), and microstructural evolution was studied using scanning electron microscope (SEM). Grain size was found to decrease up to 3 µm after four passes. An increase in number of ECAP passes led to a corresponding increase in hardness of the processed samples. Unprocessed and ECAP-processed samples were subjected to wear test using pin-on-disk wear test machine to study the wear behavior. Effects of varying loads (30 and 40 N) with sliding distances (2500 and 5000 m) were studied. The results showed reduction in wear mass loss for the ECAP-processed samples in comparison with unprocessed condition. Coefficient of friction (COF) was studied for different loads, and improvement in COF values was observed for ECAP-processed samples compared to unprocessed condition. Worn surfaces were studied using SEM and energy-dispersive x-ray spectrometer, and they exhibited plastic deformation, delamination, plowing, wear debris and oxidation in the sliding direction. X-ray diffraction analysis was conducted on the worn surfaces to identify the phases. It revealed the presence of magnesium oxide and magnesium aluminum oxide which led to oxidation wear in the sliding direction. Wear mechanism was found to be abrasive and oxidation wear.

Microstructural Evolution and Strengthening of AM90 Magnesium Alloy Processed by ECAP

Equal-channel angular pressing (ECAP) was applied on AM90 magnesium alloy using processing route \(\hbox {B}_{\mathrm {C}}\) at \(275\,^\circ \)C up to four passes. Microstructural evolution and the corresponding modification in mechanical properties (strength, elongation and hardness) corresponding to the number of ECAP passes were evaluated using X-ray diffraction (XRD), electron backscatter diffraction, scanning electron microscopy, transmission electron microscopy, tensile test and microhardness test. Shear deformation was found to refine the microstructure by breaking it into smaller grains formed by dislocation reconstruction. Tensile strength and hardness were found to increase by \(\sim \)128 and 23%, respectively, for ECAP-processed 2-pass sample in comparison with that of the homogenized condition. After two passes, tensile strength and hardness started decreasing even though the grain size was still decreasing, which was found to be associated with texture modification during ECAP processing as observed by XRD analysis.

Equal Channel Angular Pressing (ECAP) of hollow profiles made of titanium

Cylindrical tubes made of commercially-pure titanium (CP-Ti) filled with various mandrels (metallic as well as non-metallic materials) were processed by Equal Channel Angular Pressing (ECAP). Different temperatures (500°C down to room temperature), routes (Bc, B120, C), tools and number of passes (1-6) were applied depending on the mandrel material. For reasons of comparison, solid bolts made of metallic mandrel materials were processed at the same ECAP conditions. The mechanical properties of as-received as well as ECAP tubes and core materials were characterised by hardness mappings (in order to reveal the homogeneity) and tensile tests. The results can be summarised as follows: i) It is feasible to process tubes by ECAP; ii) Using appropriate mandrels, tubes made of CP-Ti can be processed by ECAP at significantly lower temperatures, even at room temperature, as compared to solid bolts; iii) Mechanical properties of tubes and mandrel materials after ECAP are similar to or even better than those of their solid counterparts; iv) Tubes after ECAP at low temperatures show higher strength than what can be achieved in bulk material; v) Excellent homogeneity of microhardness is achieved at least when metallic mandrels and a sufficient number of ECAP passes are used.

Equal channel angular pressing of a TWIP steel: microstructure and mechanical response

A Fe–20.1Mn–1.23Si–1.72Al–0.5C TWIP steel with ultrafine grain structure was successfully processed through equal channel angular pressing (ECAP) at warm temperature up to four passes following the B C route. The microstructure evolution was characterized by electron backscattered diffraction to obtain the grain maps, which revealed an obvious reduction in grain size, as well as a decrease in the twin fraction, with increasing number of ECAP passes. The texture evolution during ECAP was analyzed by orientation distribution function. The results show that the annealed material presents brass (B) as dominant component. After ECAP, the one pass sample presents A 1* and A 2* as the strongest components, while the two passes and four passes samples change gradually toward $$ B/\bar{B} $$ components. TEM analysis shows that all samples present twins. The twin thickness is reduced with increasing the number of ECAP passes. Nano-twins, as a result of secondary twinning, are also observed in the one and two passes samples. In the four passes sample, the microstructure is extensively refined by the joint action of ultrafine subgrains, grains and twins. The mechanical behavior was studied by tensile samples, and it was found that the yield strength and the ultimate tensile strength are significantly enhanced at increasing number of ECAP passes. Although the ductility and strain hardening capability are reduced with ECAP process, the present TWIP steel shows significant uniform deformation periods with positive work hardening rates.

Deformation structures and strengthening mechanisms in an Al[sbnd]Mg[sbnd]Sc[sbnd]Zr alloy

The deformation structures, mechanical properties and strengthening mechanisms of an Al-5.4 Mg-0.4 Mn-0.2Sc-0.09Zr alloy subjected to equal-channel angular pressing (ECAP) for 12 passes at 573 K (300 °C) were studied. The yield stress (YS) increased gradually with increasing strain from 245 to 350 MPa, and the ultimate tensile strength (UTS) was nearly independent of the strain. An analysis of the strengthening mechanisms indicated that the increase in YS with the number of ECAP passes was attributable to increased contributions from dislocation and boundary strengthening. A “composite” Hall-Petch relationship, σ0.2=155+αMGbρ1/2+0.11×dGB−1/2, where dGB is the distance between boundaries with misorientations of >2°, ρ is the dislocation forest density, α is a constant, M is the Taylor factor, b is the Burger's vector, and G is the shear modulus, describes the effect of ECAP on the YS with a satisfactory accuracy. No change in the dispersion of the secondary phases during ECAP was observed; therefore, contributions from dispersion strengthening and solid solution strengthening to the overall YS were independent of the strain.

Formation and Corrosion Resistance of Micro-Arc Oxidation Coating on Equal-Channel Angular Pressed AZ91D Mg Alloy

A commercial AZ91D Mg alloy, after bulk grain refinement by various passes of equal-channel angular pressing (ECAP), was selected for micro-arc oxidation (MAO) in silicate electrolyte, corrosion testing in 3.5 wt % NaCl solution and morphology analyses. The results showed that a large number of ECAP passes resulted in the homogeneous ultrafine-grained (UFG) Mg substrate with broken second-phases. The high-energy defects in the ECAPed samples lowered the anodizing potential of the MAO process, but the partial discharge was severe for those samples below eight passes. Increasing the ECAP pass, the compactness and thickness of the MAO coating first decreased and then increased. Due to the compact coating and the existence of Mg2SiO4, the coated alloy with 16 ECAP passes has a lower corrosion rate and a larger Rt value. Besides the well-known strengthening-toughening effect, grain refinement via multi-pass ECAP can improve surface protection of the MAO coating on the UFG Mg alloy.

Combined effects of ECAP and subsequent heating parameters on semi-solid microstructure of 7075 aluminum alloy

The combined effects of equal channel angular pressing (ECAP) and subsequent heating to a semi-solid temperature on the microstructural characteristics of the 7075 aluminum alloy were investigated. The microstructure is influenced by several parameters including the number of ECAP passes, ECAP route, consequent heating temperature, and holding time. The effects of these parameters on the microstructural characteristics including grain size and shape factor of the 7075 aluminum alloy were studied using experimental tests and Taguchi method. The results indicate that five-pass ECAP in route BA and subsequent isothermal holding at 630 °C for 15 min are more appropriate for achieving a semi-solid microstructure. The processing route and holding time have the highest impact on the grain size while the number of ECAP passes and heating temperature have the least impact on the grain size. Meanwhile, the shape factor is significantly influenced by the processing route, holding time and heating temperature while it is less influenced by the number of ECAP passes.

Microstructure and grain refining performance of equal-channel angular-pressed Al–5%Ti–1%B master alloy on pure aluminum

Al–5%Ti–1%B master alloy was subjected to equal-channel angular pressing (ECAP) by route A at room temperature. The effect of the ECAP on the size and the distribution of Al3Ti and TiB2 particles, the fading resistance of the Al–5%Ti–1%B master alloy and the grain refining performance of pure Al ingots with the addition of the Al–5%Ti–1%B master alloy before and after ECAP have been investigated. The large platelet Al3Ti particles were fragmented into fine blocky Al3Ti particles from ~88 to ~25 μm after eight ECAP passes, and the TiB2 particles were well dispersed in the Al matrix. It has been revealed that grain refining efficiency was improved by adding the Al–5%Ti–1%B master alloy after ECAP to the Al melt. The mean grain size of α-Al was decreased from ~1220 to ~70 μm with increasing the number of ECAP passes. It has been proved that the grain size of α-Al could be well fitted by the length of Al3Ti particles and the growth restrict factor. Al–5%Ti–1%B master alloy after four ECAP passes appeared to have a better fading resistance due to fine blocky Al3Ti particles.

The influence of long-term annealing at room temperature on creep behaviour of ECAP-processed copper

Present work investigates the effect of long-term annealing at low homologous temperature (~0.22 Tm) on creep behaviour of pure copper (99.99%) processed by equal-channel angular pressing (ECAP). Coarse-grained pure copper was processed by 1 and 8 ECAP passes at room temperature. The ECAP-processed specimens were annealed at room temperature for 3 years. Microstructures of ECAP-processed specimens and their room temperature-annealed states were investigated by electron back scatter diffraction (EBSD) technique. Tensile tests were performed at room temperature under constant rate and at 373K in creep under constant load. It was found that long-term annealing at room temperature led to occurrence of large grains in microstructure which influenced the strength. The influence grew with number of ECAP passes.

Ambient-temperature nanoindentation creep in ultrafine-grained titanium processed by ECAP

Ultrafine-grained (UFG) Ti was prepared by equal channel angular pressing (ECAP) through 1 and 4 passes at room temperature. The ambient-temperature creep behavior and mechanism of UFG Ti were studied by nanoindentation creep tests at the loading strain rate of 0.005 and 0.1s−1. The effect of grain size on creep behavior and relevant creep parameters such as steady creep strain rate and creep stress exponent (n) was estimated for coarse-grained (CG) and UFG Ti. The results show that the creep resistance of UFG Ti is enhanced with respect to CG Ti. UFG Ti after 1 pass of ECAP exhibits the highest creep resistance. The creep resistance of UFG Ti decreases with increasing the number of ECAP passes. The creep stress exponents of UFG Ti are much higher than those of CG Ti while steady creep strain rates do not vary much with grain size. The creep stress exponents of CG and UFG Ti are dependent on the loading strain rate and increase with increasing the loading strain rate. The power-law creep with a stress exponent of 18.1–24.6 is consistent with dislocation process, especially for dislocation emission and annihilation at grain boundaries, which is a key mechanism in creep deformation of UFG Ti. Grain boundaries may play an important role in the creep behavior of UFG Ti.

Investigation of Microstructure and Mechanical Properties of ECAP-Processed AM Series Magnesium Alloy

Magnesium alloy Mg-Al-Mn (AM70) was processed by equal channel angular pressing (ECAP) at 275 °C for up to 4 passes in order to produce ultrafine-grained microstructure and improve its mechanical properties. ECAP-processed samples were characterized for microstructural analysis using optical microscopy, scanning electron microscopy, and transmission electron microscopy. Microstructural analysis showed that, with an increase in the number of ECAP passes, grains refined and grain size reduced from an average of 45 to 1 µm. Electron backscatter diffraction analysis showed the transition from low angle grain boundaries to high angle grain boundaries in ECAP 4 pass sample as compared to as-cast sample. The strength and hardness values an showed increasing trend for the initial 2 passes of ECAP processing and then started decreasing with further increase in the number of ECAP passes, even though the grain size continued to decrease in all the successive ECAP passes. However, the strength and hardness values still remained quite high when compared to the initial condition. This behavior was found to be correlated with texture modification in the material as a result of ECAP processing.

Simultaneous improvements of the strength and ductility of fine-grained AA6063 alloy with increasing number of ECAP passes

In this research, grain refinement through severe plastic deformation (SPD) in combination with a thermal treatment to create a fine initial grain structure with a high degree of supersaturation was taken as a viable approach to achieving simultaneous increases in the hardness, strength and ductility of the aluminum alloy AA6063 during further SPD. A recrystallized structure with grain sizes around 20µm was obtained after two passes of equal channel angular pressing (ECAP), followed by a thermal treatment at 500°C for 10s and water quenching. The alloy with the supersaturated α-Al matrix was subjected to further ECAP processing up to six passes to create a cellular structure on a nano scale. Hardness and tensile tests revealed the changes of hardness, strength and ductility along with increasing number of ECAP passes. It was found that after two ECAP passes, the ductility of the alloy decreased from the value after the prior two-pass ECAP and thermal treatment. However, by further ECAP processing up to six passes, the ductility increased along with the increases in hardness and strength. The remarkable improvement in ductility was attributed to a nanosized cellular structure with a large area of high-angle grain boundaries developed from the fine initial grain structure formed during the two-pass ECAP and thermal treatment applied earlier.