Route Bc Research Articles

Microstructure and properties of Cu–Mg-Ca alloy processed by equal channel angular pressing

A Cu-0.41Mg-0.06Ca (wt.%) alloy was designed and prepared by melting and casting in air atmosphere, followed by equal channel angular pressing (ECAP) process up to 12 passes via Bc route at room temperature. The microstructure and properties of the alloy were investigated by means of hardness test, tensile test, electrical conductivity measurement and electron microscopes observation. After 12 ECAP passes, the initial coarse grains were refined significantly and the average grain sizes decreased to 0.57 μm. The coarse Cu5Ca phase was also fragmented and had the sizes of about 1–3 μm. The Cu-Mg-Ca alloy after 12 ECAP passes showed excellent comprehensive properties, with a yield strength of 619 MPa, an electrical conductivity of 67.86 %IACS and a total elongation of 10.4%. Compared with the Cu-Mg alloy under the same condition, the yield strength of the designed alloy after 12 ECAP passes was improved by 30 MPa and the electrical conductivity increased by 0.63 %IACS accompanied by almost same total elongation. The good comprehensive properties were attributed to the ECAP process and the addition of Ca. The ECAP process provided much high yield strength increments which accounted for more than 80% of the yield strengths after 12 ECAP passes. In addition, the addition of Ca in the Cu-Mg alloy promoted the grain refinement, improved the work hardening ratio, and increased the electrical conductivity.

Microhardness evolution of pure titanium deformed by equal channel angular extrusion

Microhardness homogeneity was assessed on commercial pure titanium processed by equal channel angular extrusion (ECAE). The operation was performed with die channel angle of 90° and processing temperature of 450 °C by route BC up to six passes. The Vickers microhardness measurements were investigated on both cross-sectional and longitudinal planes of the annealed, one-, two-, four-, and six-pass ECAEed titanium. It was found that the application of the process and the addition of pass numbers lead to the improvement of hardness magnitude. It was shown that there are some areas of microhardness heterogeneity in surrounding and bottom regions of the one-pass and two-pass specimens at the cross-sectional plane which is slightly disappeared by adding the pass numbers. Furthermore, there is a suitable amount of hardness homogeneity in the longitudinal plane, irrespective of the specimen condition. It can be concluded that a desirable homogeneity of hardness can be attained after imposing six passes of ECAE process on both cross-sectional and longitudinal planes of titanium.

Erosion Corrosion Behavior of Nanostructure Commercial Pure Titanium in Simulated Body Fluid

To date, ECAP technique have been successfully employed to produce Ultra-fine/Nanostructure grain materials, but some materials such as hexagonal closed-packed (HCP) alloys are difficult to process by ECAP at room temperature. In this work, Transmission Electron Microscopy (TEM), Vickers hardness test and Torsion test were employed to confirm the attainment of ultrafine/nanostructured grain (UFG/NSG) commercial pure titanium (CP-Ti) Titanium fabricated by ECAP as a sever plastic deformation process. The samples were pressed by ECAP (route BC) up to four passes at elevated temperature (400° C). Finally, the Erosion-Corrosion (E-C) behavior of ultrafine/nanostructured grain (UFG/NSG) Titanium in a simulated body fluid were investigated through weight loss measurement.

Microstructure, Mechanical Properties and Strengthening Mechanism Analysis in an AlMg5 Aluminium Alloy Processed by ECAP and Subsequent Ageing

A coarse-grained microstructure of solution treated AlMg5 aluminium alloy was prepared by equal channel angular pressing through route BC. Microstructure evolution of the alloy was analysed by using an optical microscope, X-ray diffraction, and EBSD (electron backscatter diffraction). The results reported that grains were refined due to the interactions of shear bands with low-to-moderate grain boundaries, and this structure was transformed into a bimodal after ageing at 180 °C for 4 h. Moreover, the results of the tensile testing showed that the yield strength was increased from 110 to 326 MPa, and the corresponding tensile strength increased from 269 to 395 MPa, maintaining an appropriate elongation of ~18%. After ageing at 180 °C elongation increased to 23% and the sample still kept high yield strength of 255 MPa, which may be associated with the mutual influence of the dislocation density decrease and recrystallization processes.

Nanostructured Cobalt Obtained by Combining Bottom-Up and Top-Down Approach

Nanostructured metallic materials can be obtained by two major processing strategies: a bottom-up approach that starts with powdered metals to be mechanically and chemically compacted via different compaction methodologies, and a top-down approach that starts with bulk conventional metallic materials that are induced to a sometimes-extraordinary grain size reduction via different severe plastic deformation (SPD) methods. In the present study, a dual strategy was followed to obtain a sound and stable nanostructured commercially pure cobalt. Powdered cobalt of 2 μm was compacted by ball-milling (BM) followed by spark-plasma sintering (SPS) to obtain a bulk metallic material whose relative mass density reached a value of 95.8%. This process constituted a bottom-up strategy to obtain ultrafine submicrometer-grained bulk cobalt, and a top-down strategy of subjecting the BM + SPS submicrometer-grained cobalt to a specific SPD technique, namely equal-channel angular pressing (ECAP). The latter was carried out in one to four passes following so-called route BC, reaching 98.4% density and a nanometric-grained microstructure. The material was microstructurally and mechanically characterized by TEM (transmission electron microscope) and nanoindentation. The obtained results are a representative solid example for obtaining nanostructured metallic materials using both grain-refining strategies, bottom-up and top-down.

Influence of dynamic recrystallization and shear banding on the localized corrosion of severely deformed Al–Mg–Si alloy

The low intergranular corrosion resistance of extruded aluminum alloys is a limiting criteria for several applications. In this work, we investigated the effects of shear deformation, dynamic recrystallization and peak aging on the corrosion susceptibility of an AA6061 alloy up to seven ECAP passes following route Bc. We assessed intergranular corrosion susceptibility using the standard ISO test 11846 (Method B). Our results show that dynamic recrystallization improves the localized corrosion resistance of severely deformed AA6061 by reducing the fraction of shear bands in the material. We found a clear difference in surface reactivity between the recrystallized grains inside and outside the shear bands, suggesting that in this material grain-stored energy influences corrosion more than grain boundary precipitation. In parallel, we characterized the degradation of conventionally extruded AA6061-T6. The results reveal that shear deformation is a promising process for extruded aluminum alloys with improved strength and intergranular corrosion resistance.

Microstructure and texture development during solid consolidation recycling of Ti-6Al-4V

Ti-6Al-4V machining chips were recycled using equal channel angular pressing (ECAP). The microstructural and texture evolution of the recycled Ti-6Al-4V have been investigated using scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy. For samples consolidated at 500 °C with a back-pressure of 100 MPa, the as-pressed density reached up to 99.9% after 8 passes. Pronounced grain refinement was also observed with increasing number of passes. The morphology of the grains has been changed from elongated and coarse to equiaxed and ultrafine as the number of passes increases. Strong textures were also introduced during multiple passes via Bc route. Texture has been developed with basal planes parallel to the inclination direction which is at 21° of the extrusion direction. After 4 and 8 passes, basal planes were rotated towards the transverse direction. No oxide can be detected at the chip-chip boundaries when the Ti-Al-4 V machining chips was consolidated at 500 °C. When the sample was processed at 550 °C, significant grain growth and clear oxide layers at the chip-chip interface were observed. In addition, the c-axis were rotated towards the longitudinal direction due to the non-basal slip activity. TEM observation revealed the <a→+c→> dislocations presence in the 550 °C ECAP-processed sample.

Analysis of the micro and substructural evolution during severe plastic deformation of ARMCO iron and consequences in mechanical properties

ARMCO iron processed by ECAP up to a maximum equivalent strain of sixteen ECAP passes following route Bc was investigated by Electron Back Scattering Diffraction (EBSD), Transmission Electron Microscopy (TEM), TEM-EBSD and X-ray Diffraction Line Profile Analysis (XRDLPA). Different values of grain size were obtained with each technique. The lower values were obtained by XRDLPA whereas, the higher values were achieved by TEM-EBSD. Dislocation densities were also calculated by different techniques obtaining values of statistically stored and geometrically necessary dislocations as a function of the deformation. All differences in values allowed a better understanding of the nature of microstructures of the materials processed by severe plastic deformation (SPD). Mechanical properties showed a considerable increment in the material strength due to the progressive reduction of the grain size because of the Continuous Dynamic Recrystallization (CDRX) mechanism and the increment in the dislocation density.

Influence of the initial state on the microstructure and mechanical properties of AX41 alloy processed by ECAP

This study investigates the influence of the initial state of the commercial AX41 magnesium alloy on the microstructure evolution and mechanical properties after equal-channel angular pressing. Two initial conditions, an as-cast one with a grain size of 200 μm and a random crystallographic texture, and an extruded one having a grain size of 10 μm and a strong fibre texture, are compared. ECAP processing was performed at the temperature of 220 °C up to 8 passes via route BC. A much smaller grain size was obtained in the ECAP-processed as-cast material compared to the extruded one. This difference was attributed to the different evolution of the dislocation density and its fractions in different slip systems. Consequently, different refinement mechanisms were dominant in the later stage of ECAP processing. It was shown that ECAP processing leads to the formation of similar crystallographic textures for both initial states, having dominant basal texture component. The mechanical properties investigation showed improvement in the microhardness, tensile strength and elongation in both ECAP-processed samples.

Effect of the equal channel angular pressing route on the microstructural and mechanical behavior of Al-5086 alloy

The present paper analyzes the effect of the equal channel angular pressing (ECAP) routes A and Bc on the recrystallization conditions and mechanical properties of Al-5086 alloy. The specimens were processed up to 10 passes at 150 °C in a die with 120° inner angle. The recrystallized grains developed after the tenth pass in the route A. By increasing the number of passes the grains became finer and after the tenth pass, the average grain size became finer than 2 µm. The tensile and hardness tests results showed that in all passes, the route Bc had a stronger effect on the simultaneous improvement of strength and ductility. The fracture surfaces analyses showed that the local ductile behavior improves as increasing the number of passes. The textures analyses showed that the dominant component was altered from (111) to (200) and (220) plane by increasing the number of passes through both routes. Also, the dislocation density increased by increasing the number of passes.

Precipitate evolution during severe plastic deformation of cast Al-Zn-Mg alloys and their thermal stability

In the current investigation, an effort was made to understand the precipitate evolution process during equal channel angular pressing (ECAP) of an alloy composed of only aluminium, zinc and magnesium. For this purpose, three different compositions of cast Al-Zn-Mg alloys were selected and ECAP processed in route BC upto four passes. Microstructural observations indicated that, ECAP processing leads to refined structure possessing high density dislocations and large amount of grains with high angle grain boundaries. The precipitate volume in the alloys increased with increase in the zinc quantity in the alloy. Microstructural characterization through transmission electron microscope (TEM) and differential scanning calorimeter (DSC) revealed that, processing by ECAP results in structure having stable η phase precipitates without the presence of GP zones and intermediate η′ phase precipitates. Thereby demonstrates that, ECAP process accelerates the precipitation kinetics and also shifts the morphology of the precipitates. Higher mechanical properties were noticed in the alloy containing large quantity of MgZn2 precipitates.

Microstructure and Mechanical Properties of Cast Al-5Zn-2Mg Alloy Subjected to Equal-Channel Angular Pressing

In the present work, cast Al-5Zn-2Mg alloy was processed through equal-channel angular pressing (ECAP) in route BC up to four number of passes. Microstructure and mechanical properties were investigated on processed and unprocessed materials. In cast condition, the material was composed of dendritic structure. After homogenization treatment, large-sized grains were observed. After ECAP processing, significant grain refinement was observed. After ECAP processing, high-density dislocations and high degree of misorientation between the grains were observed. In cast material, rod-shaped precipitates were observed, while, after ECAP processing, spherical-shaped precipitates were observed. ECAP processing leads to a noticeable improvement in the mechanical properties of the material. After four passes, 122% improvement in the microhardness and 135% improvement in the ultimate tensile strength of the material were observed. After three passes, a slight decrease in the mechanical properties was observed. This is attributed to the dissolution of the metastable η′ phase, annihilation of dislocations, dynamic recrystallization and texturing during ECAP processing. Brittle fracture mode was observed in tensile testing cast and homogenized samples. After ECAP processing, fracture mode was changed into shear fracture mode.

The Strength and Fracture Mechanism of Unalloyed Medium-Carbon Steel with Ultrafine-Grained Structure under Single Loads

This work is devoted to the study of the tensile strength, static crack resistance (К1С), and impact toughness of unalloyed medium-carbon (0.45% C) steel with ultrafine-grained (UFG) structure obtained by equal-channel angular pressing (ECAP) in comparison with coarse-grained (CG) steel after quenching and high tempering. The ECAP was carried out in the following regime: austenitization for 1 hour at 800°C + quenching in water + medium tempering (350°C) + ECAP at 350°C (Bc route, n = 6, φ = 120°). Our work shows that the K1С of steel in the UFG state is 53 MPa m1/2 and, in the CG state, 69 MPa m1/2. The static failure of steel samples in the CG- and UFG states occurred under conditions of planar deformation. The relation between the depth of the plastic zone below the surface of the fractures in the region of crack propagation and the static crack resistance of steel in the CG- and UFG states is described by the equations hy = 1/12π(K1C/σ0.2)2 and hy = 1/8π(K1C/σ0.2)2. After ECAP, a narrowing of the ductile–brittle transition interval of steel and its shift towards low temperatures by 70–80°C can be observed. Moreover, the temperature dependence of the size of the shear lips at the surface of the fractures correlates with the temperature dependence of the impact toughness of the steel. The dominant fracture mechanism of CG steel in the lower and middle regions of the ductile–brittle transition is a cleavage, and that of UFG steels, a quasi-cleavage. In the upper region of the ductile–brittle transition, the steel under study fractures with the formation of a pit microrelief.

Study of the Microstructure, Tensile Properties and Hardness of AZ61 Magnesium Alloy Subjected to Severe Plastic Deformation

Hot extruded (EX) AZ61 magnesium alloy was processed by the twist channel angular pressing (TCAP) method, which combines equal channel angular pressing (ECAP) and twist extrusion (TE) processes and significantly improves the efficiency of the grain refinement process. Both the initial hot extruded AZ61 alloy and the alloy after completion of TCAP processing were examined by using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) and their corresponding micro-tensile testing (M-TT) and hardness testing at room temperature. The results showed that the microstructure of hot extruded alloy was refined well by TCAP due to dynamic recrystallization (DRX) caused by TCAP. The tensile properties, investigated by micro-tensile testing (M-TT), of the AZ61 alloy were significantly improved due to refined microstructure. The highest tensile properties including YS of 240.8 MPa, UTS of 343.6 MPa and elongation of 21.4% of the fine-grained alloy with average grain size below 1.5 µm was obtained after the third TCAP pass at 200 °C using the processing route Bc.

Secondary phase precipitation and thermally stable microstructure refinement induced by ECAP on Mg-Y-Nd (WN43) alloy

Magnesium alloy Mg-4Y-3Nd (WN43) was subjected to ECAP at T∼300 °C up to 8 passes, using route BC. The initial as-extruded material with average grain size of ∼10 μm, was effectively refined down to sub-micrometer scale, reaching a grain size of ∼380 nm, after 8 passes. At the same time, secondary phase particle precipitation of β′-Mg12Nd2Y, and β-Mg14Nd2Y was induced. At 8 passes, fragmentation and coarsening of these phases occurred. Both grain refinement and β′/β precipitation strengthened the alloy. The strengthening was detected by nanoindentation hardness and accounted of up to 30% increment at 8 ECAP pass, compared to the initial extruded condition.

Microstructure and strengthening model of Al-3%Mg alloy in a heat treated state subjected to ECAP process

Purpose: The aim of this paper is to investigate the microstructure evolution of a heat treated Al-3%Mg aluminium alloy subjected to the ECAP (equal channel angular pressing process). Design/methodology/approach: Commercial Al-3%Mg alloy subjected to the solution treatment followed by an artificial aging was subjected to the 6 ECAP passes using a processing route Bc. Then the microstructure investigations using a light microscopy, scanning electron microscopy and transmission electron microscopy were carried out. Additionally the XRD technique was used to calculate lattice micro strain and dislocation density. Findings: The experimental results showed that the obtained microstructure is refined by mutual interactions of shear and microshear bands. The TEM investigation revealed typical for deformed aluminium alloys structure constituents such as dislocation-free grains, nonequilibrium grain boundaries, dislocation cell and (sub)grain structures. Research limitations/implications: The presented investigation results were carried out on samples, not on final products. Practical implications: Current research is moving towards to develop high strength material having a ultra-fine grained microstructure and increased mechanical strength. Originality/value: The paper focuses on the microstructure characterization of ECAP processed Al-3%Mg aluminium alloy. The relationship between the obtained microstructure and its contribution to the Yield strength is investigated.

Influence of Grain Refinement via ECAP to the Corrosion Behaviour of SAC 305 Solder

Equal Channel Angular Pressing or ECAP has been generating interest due to the ability to form bulk ultra-fine grains (UFG) or nanostructured materials. This formation of ultra-fine grains leads to a favorable combination of strength and ductility. Solder materials, which function as the mechanical bridge joining chip to substrate, or package to mother board, could very well benefit from this combination. High strength would offer better joint, and enhanced ductility would enable solder to have better fracture toughness and drop-impact resistance as solder joint regularly being subjected to vibration and impact. This paper reports about corrosion behaviour of ECAPed SAC 305 alloy formed via route Bc up to four passes. The focus is on the effect of grain refinement on corrosion behaviour of bulk solder in 3.5 wt.% NaCl solution. The resulting microstructure was observed by Scanning Electron Microscope (SEM). The grains formed after different passes of ECAP were observed, along with the distribution of intermetallic compound or IMC within the bulk solder. Finer grains were formed with increasing number of ECAP passes leading to reduction of corrosion rate and increased strength of SAC305. The high fraction of grain boundaries in the microstructure with increased of ECAP passes reduced the corrosion rates by accelerating the passivation process.

Exploration of equal channel angular pressing routes for efficiently achieving ultrafine microstructure in magnesium

This research explored the equal channel angular pressing (ECAP) routes for efficient microstructure refinement of pure magnesium. The samples were processed for a series of numbers of ECAP passes through three different routes (i.e. A, Bc, and C routes). The utilized ECAP mold had a large channel angle of 142° and the processing temperature was 200 °C. The microstructure and texture of the processed samples were characterized using optical microscope and x-ray diffraction technique. The results show that tension twinning deformation mechanism during an ECAP pass led to the formation of profuse twins in magnesium and the twinning/detwinning dominated microstructure refinement mechanisms. After 8 ECAP passes, both Bc and C routes reduced the length and width of twins to ~ 13 µm and ~ 3 µm respectively. Bc and C routes can refine the microstructure of magnesium more efficiently than A route. Among the three studied routes, Bc route achieved the most homogeneous microstructure with uniformly distributed twins, while both A and C routes resulted in heterogeneous microstructure.

Three-dimensional microstructural analysis of fragmentation behavior of platelet Al3Ti particles in Al-Al3Ti composite deformed by equal-channel angular pressing

The fragmentation of platelet Al3Ti particles in an Al-Al3Ti composite by equal-channel angular pressing (ECAP) is investigated using three-dimensional (3D) microstructural evaluation and crystallography. The Al-Al3Ti composite comprises coarse platelet Al3Ti particles in an α-Al matrix. The ECAP of this composite is performed for up to 4 passes under processing routes A, Bc, and C. Route Bc produces the smallest Al3Ti particle fragments in comparison with the fragments produced under routes A and C. This is because that route Bc produces the largest number of shearing directions and shearing planes. Platelet Al3Ti particle fragments in the specimen deformed by ECAP under route A are homogeneously distributed along the deformation axis. In contrast, in the specimens deformed by four ECAP passes under routes Bc and C, the Al3Ti particle fragments are gathered into several groups. The fragment groups have a length similar to the initial length of the platelet Al3Ti particles. These spatial distributions of particle fragments can be explained by material flow of α-Al matrix during ECAP. Moreover, from 3D microstructural evaluation and crystallographic analysis of the Al3Ti particle fragments, it is found that the Al3Ti particles are preferentially fragmented on the twin boundary plane of {112}Al3Ti. Therefore, it is concluded that fragmentation of a platelet Al3Ti particle by ECAP occurs along the twin boundary plane after twin deformation.

Superplasticity of Friction-Stir Welds of Zr-Modified 5083 Aluminum Alloy with Ultrafine-Grained Structure

The commercial Zr-modified 5083 aluminum alloy was homogenized to precipitate nanoscale Al6Mn particles and then undergone to equal-channel angular pressing (ECAP) at 300 °C to a true strain of ~12 via BC route. The obtained ultrafine-grained material was subjected to friction-stir welding (FSW). The welding variables were selected to provide reasonable homogeneous microstructure distribution across the weld zone and thus to ensure a highly uniform elongation during subsequent superplastic tests of the joints. Superplastic behavior of the obtained welds is discussed.