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4 pages, 142 KiB

Open AccessEditorial

Ultrafine-Grained Metals

by Heinz Werner Höppel

Metals 2015, 5(4), 2393-2396; https://doi.org/10.3390/met5042393 - 16 Dec 2015

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Abstract

Ultrafine-grained (UFG) metallic materials are at the cutting edge of modern materials science as they exhibit outstanding properties which make them very interesting for prospective structural or functional engineering applications. [...] Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

Research

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17 pages, 730 KiB

Open AccessArticle

Enhanced Mechanical Properties and Electrical Conductivity in Ultrafine-Grained Al 6101 Alloy Processed via ECAP-Conform

by Maxim Murashkin, Andrey Medvedev, Vil Kazykhanov, Alexander Krokhin, Georgy Raab, Nariman Enikeev and Ruslan Z. Valiev

Metals 2015, 5(4), 2148-2164; https://doi.org/10.3390/met5042148 - 20 Nov 2015

Cited by 67 | Viewed by 8875

Abstract

This paper studies the effect of equal channel angular pressing-Conform (ECAP-C) and further artificial aging (AA) on microstructure, mechanical, and electrical properties of Al 6101 alloy. As is shown, ECAP-C at 130 °C with six cycles resulted in the formation of an ultrafine-grained [...] Read more.

This paper studies the effect of equal channel angular pressing-Conform (ECAP-C) and further artificial aging (AA) on microstructure, mechanical, and electrical properties of Al 6101 alloy. As is shown, ECAP-C at 130 °C with six cycles resulted in the formation of an ultrafine-grained (UFG) structure with a grain size of 400–600 nm containing nanoscale spherical metastable β′ and stable β second-phase precipitates. As a result, processed wire rods demonstrated the ultimate tensile strength (UTS) of 308 MPa and electrical conductivity of 53.1% IACS. Electrical conductivity can be increased without any notable degradation in mechanical strength of the UFG alloy by further AA at 170 °C and considerably enhanced by additional decomposition of solid solution accompanied by the formation of rod-shaped metastable β′ precipitates mainly in the ultrafine grain interior and by the decrease of the alloying element content in the Al matrix. It is demonstrated that ECAP-C can be used to process Al-Mg-Si wire rods with the specified UFG microstructure. The mechanical strength and electrical conductivity in this case are shown to be much higher than those in the industrial semi-finished products made of similar material processed by the conventional T6 or T81 treatment. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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13 pages, 1674 KiB

Open AccessArticle

High Temperature Flow Response Modeling of Ultra-Fine Grained Titanium

by Seyed Vahid Sajadifar and Guney Guven Yapici

Metals 2015, 5(3), 1315-1327; https://doi.org/10.3390/met5031315 - 22 Jul 2015

Cited by 18 | Viewed by 5390

Abstract

This work presents the mechanical behavior modeling of commercial purity titanium subjected to severe plastic deformation (SPD) during post-SPD compression, at temperatures of 600-900 °C and at strain rates of 0.001-0.1 s−1. The flow response of the ultra-fine grained microstructure is modeled using [...] Read more.

This work presents the mechanical behavior modeling of commercial purity titanium subjected to severe plastic deformation (SPD) during post-SPD compression, at temperatures of 600-900 °C and at strain rates of 0.001-0.1 s−1. The flow response of the ultra-fine grained microstructure is modeled using the modified Johnson-Cook model as a predictive tool, aiding high temperature forming applications. It was seen that the model was satisfactory at all deformation conditions except for the deformation temperature of 600 °C. In order to improve the predictive capability, the model was extended with a corrective term for predictions at temperatures below 700 °C. The accuracy of the model was displayed with reasonable agreement, resulting in error levels of less than 5% at all deformation temperatures. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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10 pages, 741 KiB

Open AccessCommunication

Mechanical Behavior of Ultrafine Gradient Grain Structures Produced via Ambient and Cryogenic Surface Mechanical Attrition Treatment in Iron

by Heather A. Murdoch, Kristopher A. Darling, Anthony J. Roberts and Laszlo Kecskes

Metals 2015, 5(2), 976-985; https://doi.org/10.3390/met5020976 - 3 Jun 2015

Cited by 16 | Viewed by 6274

Abstract

Ambient and cryogenic surface mechanical attrition treatments (SMAT) are applied to bcc iron plate. Both processes result in significant surface grain refinement down to the ultrafine-grained regime; the cryogenic treatment results in a 45% greater grain size reduction. However, the refined region is [...] Read more.

Ambient and cryogenic surface mechanical attrition treatments (SMAT) are applied to bcc iron plate. Both processes result in significant surface grain refinement down to the ultrafine-grained regime; the cryogenic treatment results in a 45% greater grain size reduction. However, the refined region is shallower in the cryogenic SMAT process. The tensile ductility of the grain size gradient remains low (<10%), in line with the expected behavior of the refined surface grains. Good tensile ductility in a grain size gradient requires the continuation of the gradient into an undeformed region. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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19 pages, 1761 KiB

Open AccessArticle

Fatigue Behavior of Ultrafine-Grained Medium Carbon Steel with Different Carbide Morphologies Processed by High Pressure Torsion

by Christoph Ruffing, Aaron Kobler, Eglantine Courtois-Manara, Robby Prang, Christian Kübel, Yulia Ivanisenko and Eberhard Kerscher

Metals 2015, 5(2), 891-909; https://doi.org/10.3390/met5020891 - 29 May 2015

Cited by 13 | Viewed by 7829

Abstract

The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect [...] Read more.

The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT) treatment of SAE 1045 steels. The two initial carbide morphologies are spheroidized as well as tempered states. The HPT processing increased the hardness of the spheroidized and tempered states from 169 HV and 388 HV to a maximum of 511 HV and 758 HV, respectively. The endurance limit increased linearly with hardness up to about 500 HV independent of the carbide morphology. The fracture surfaces revealed mostly flat fatigue fracture surfaces with crack initiation at the surface or, more often, at non-metallic inclusions. Morphology and crack initiation mechanisms were changed by the severe plastic deformation. The residual fracture surface of specimens with spheroidal initial microstructures showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with a tempered initial microstructure showed rather brittle and rough residual fracture surfaces after HPT. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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12 pages, 1202 KiB

Open AccessArticle

Influence of Particulate Reinforcement and Equal-Channel Angular Pressing on Fatigue Crack Growth of an Aluminum Alloy

by Lisa Köhler, Kristin Hockauf and Thomas Lampke

Metals 2015, 5(2), 790-801; https://doi.org/10.3390/met5020790 - 18 May 2015

Cited by 6 | Viewed by 6030

Abstract

The fatigue crack growth behavior of unreinforced and particulate reinforced Al 2017 alloy, manufactured by powder metallurgy and additional equal-channel angular pressing (ECAP), is investigated. The reinforcement was done with 5 vol % Al₂O₃ particles with a size fraction of [...] Read more.

The fatigue crack growth behavior of unreinforced and particulate reinforced Al 2017 alloy, manufactured by powder metallurgy and additional equal-channel angular pressing (ECAP), is investigated. The reinforcement was done with 5 vol % Al₂O₃ particles with a size fraction of 0.2–2 µm. Our study presents the characterization of these materials by electron microscopy, tensile testing, and fatigue crack growth measurements. Whereas particulate reinforcement leads to a drastic decrease of the grain size, the influence of ECAP processing on the grain size is minor. Both reinforced conditions, with and without additional ECAP processing, exhibit reduced fatigue crack growth thresholds as compared to the matrix material. These results can be ascribed to the well-known effect of the grain size on the crack growth, since crack deflection and closure are directly affected. Despite their small grain size, the thresholds of both reinforced conditions depend strongly on the load ratio: tests at high load ratios reduce the fatigue threshold significantly. It is suggested that the strength of the particle-matrix-interface becomes the critical factor here and that the particle fracture at the interfaces dominates the failure behavior. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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13 pages, 1401 KiB

Open AccessArticle

Manufacturing Ultrafine-Grained Ti-6Al-4V Bulk Rod Using Multi-Pass Caliber-Rolling

by Taekyung Lee, Donald S. Shih, Yongmoon Lee and Chong Soo Lee

Metals 2015, 5(2), 777-789; https://doi.org/10.3390/met5020777 - 15 May 2015

Cited by 26 | Viewed by 8073

Abstract

Ultrafine-grained (UFG) Ti-6Al-4V alloy has attracted attention from the various industries due to its good mechanical properties. Although severe plastic deformation (SPD) processes can produce such a material, its dimension is generally limited to laboratory scale. The present work utilized the multi-pass caliber-rolling [...] Read more.

Ultrafine-grained (UFG) Ti-6Al-4V alloy has attracted attention from the various industries due to its good mechanical properties. Although severe plastic deformation (SPD) processes can produce such a material, its dimension is generally limited to laboratory scale. The present work utilized the multi-pass caliber-rolling process to fabricate Ti-6Al-4V bulk rod with the equiaxed UFG microstructure. The manufactured alloy mainly consisted of alpha phase and showed the fiber texture with the basal planes parallel to the rolling direction. This rod was large enough to be used in the industry and exhibited comparable tensile properties at room temperature in comparison to SPD-processed Ti-6Al-4V alloys. The material also showed good formability at elevated temperature due to the occurrence of superplasticity. Internal-variable analysis was carried out to measure the contribution of deformation mechanisms at elevated temperatures in the manufactured alloy. This revealed the increasing contribution of phase/grain-boundary sliding at 1073 K, which explained the observed superplasticity. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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14 pages, 994 KiB

Open AccessArticle

Ultrafine-Grained Precipitation Hardened Copper Alloys by Swaging or Accumulative Roll Bonding

by Igor Altenberger, Hans-Achim Kuhn, Mozhgan Gholami, Mansour Mhaede and Lothar Wagner

Metals 2015, 5(2), 763-776; https://doi.org/10.3390/met5020763 - 13 May 2015

Cited by 27 | Viewed by 9357

Abstract

There is an increasing demand in the industry for conductive high strength copper alloys. Traditionally, alloy systems capable of precipitation hardening have been the first choice for electromechanical connector materials. Recently, ultrafine-grained materials have gained enormous attention in the materials science community as [...] Read more.

There is an increasing demand in the industry for conductive high strength copper alloys. Traditionally, alloy systems capable of precipitation hardening have been the first choice for electromechanical connector materials. Recently, ultrafine-grained materials have gained enormous attention in the materials science community as well as in first industrial applications (see, for instance, proceedings of NANO SPD conferences). In this study the potential of precipitation hardened ultra-fine grained copper alloys is outlined and discussed. For this purpose, swaging or accumulative roll-bonding is applied to typical precipitation hardened high-strength copper alloys such as Corson alloys. A detailed description of the microstructure is given by means of EBSD, Electron Channeling Imaging (ECCI) methods and consequences for mechanical properties (tensile strength as well as fatigue) and electrical conductivity are discussed. Finally the role of precipitates for thermal stability is investigated and promising concepts (e.g. tailoring of stacking fault energy for grain size reduction) and alloy systems for the future are proposed and discussed. The relation between electrical conductivity and strength is reported. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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13 pages, 2056 KiB

Open AccessArticle

Ultrafine-Grained Austenitic Stainless Steels X4CrNi18-12 and X8CrMnNi19-6-3 Produced by Accumulative Roll Bonding

by Mathis Ruppert, Lisa Patricia Freund, Thomas Wenzl, Heinz Werner Höppel and Mathias Göken

Metals 2015, 5(2), 730-742; https://doi.org/10.3390/met5020730 - 7 May 2015

Cited by 7 | Viewed by 7050

Abstract

Austenitic stainless steels X4CrNi18-12 and X8CrMnNi19-6-3 were processed by accumulative roll bonding (ARB). Both materials show an extremely high yield strength of 1.25 GPa accompanied by a satisfactory elongation to failure of up to 14% and a positive strain rate sensitivity after two [...] Read more.

Austenitic stainless steels X4CrNi18-12 and X8CrMnNi19-6-3 were processed by accumulative roll bonding (ARB). Both materials show an extremely high yield strength of 1.25 GPa accompanied by a satisfactory elongation to failure of up to 14% and a positive strain rate sensitivity after two ARB cycles. The strain-hardening rate of the austenitic steels reveals a stabilization of the stress-strain behavior during tensile testing. Especially for X8CrMnNi19-6-3, which has an elevated manganese content of 6.7 wt.%, necking is prevented up to comparatively high plastic strains. Microstructural investigations showed that the microstructure is separated into ultrafine-grained channel like areas and relatively larger grains where pronounced nano-twinning and martensite formation is observed. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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10 pages, 6190 KiB

Open AccessArticle

Production of Bulk Metallic Glasses by Severe Plastic Deformation

by Lisa Krämer, Karoline S. Kormout, Daria Setman, Yannick Champion and Reinhard Pippan

Metals 2015, 5(2), 720-729; https://doi.org/10.3390/met5020720 - 30 Apr 2015

Cited by 21 | Viewed by 7220

Abstract

The aim of this study was to show the possibility to produce bulk metallic glass with severe plastic deformation. High pressure torsion was used to consolidate Zr-based metallic glass powder and deform it further to weld the powder particles together. The produced samples [...] Read more.

The aim of this study was to show the possibility to produce bulk metallic glass with severe plastic deformation. High pressure torsion was used to consolidate Zr-based metallic glass powder and deform it further to weld the powder particles together. The produced samples were investigated with Scanning electron microscope (SEM), Transmission electron microscope (TEM), Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) to check if the specimens are fully dense and have an amorphous structure. The results show that the specimens remain amorphous during high pressure torsion and the density depends on the applied strain. Additional Vickers hardness measurements enable a comparison with literature and show for Zr-based metallic glass powder typical values (approximately 500 HV). Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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13 pages, 1901 KiB

Open AccessArticle

Development of Nanocrystalline 304L Stainless Steel by Large Strain Cold Working

by Marina Odnobokova, Andrey Belyakov and Rustam Kaibyshev

Metals 2015, 5(2), 656-668; https://doi.org/10.3390/met5020656 - 22 Apr 2015

Cited by 71 | Viewed by 9038

Abstract

The microstructural changes leading to nanocrystalline structure development and the respective tensile properties were studied in a 304L stainless steel subjected to large strain cold rolling at ambient temperature. The cold rolling was accompanied by the development of deformation twinning and martensitic transformation. [...] Read more.

The microstructural changes leading to nanocrystalline structure development and the respective tensile properties were studied in a 304L stainless steel subjected to large strain cold rolling at ambient temperature. The cold rolling was accompanied by the development of deformation twinning and martensitic transformation. The latter readily occurred at deformation microshear bands, leading the martensite fraction to approach 0.75 at a total strain of 3. The deformation twinning followed by microshear banding and martensitic transformation promoted the development of nanocrystalline structure consisting of a uniform mixture of austenite and martensite grains with their transverse sizes of 120–150 nm. The developed nanocrystallites were characterized by high dislocation density in their interiors of about 3 × 10¹⁵ m⁻² and 2 × 10¹⁵ m⁻² in austenite and martensite, respectively. The development of nanocrystalline structures with high internal stresses led to significant strengthening. The yield strength increased from 220 MPa in the original hot forged state to 1600 MPa after cold rolling to a strain of 3. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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13 pages, 905 KiB

Open AccessArticle

Fatigue Behavior of an Ultrafine-Grained Al-Mg-Si Alloy Processed by High-Pressure Torsion

by Maxim Murashkin, Ilchat Sabirov, Dmitriy Prosvirnin, Ilya Ovid'ko, Vladimir Terentiev, Ruslan Valiev and Sergey Dobatkin

Metals 2015, 5(2), 578-590; https://doi.org/10.3390/met5020578 - 10 Apr 2015

Cited by 32 | Viewed by 7553

Abstract

The paper presents the evaluation of the mechanical and fatigue properties of an ultrafine-grained (UFG) Al 6061 alloy processed by high-pressure torsion (HPT) at room temperature (RT). A comparison is made between the UFG state and the coarse-grained (CG) one subjected to the [...] Read more.

The paper presents the evaluation of the mechanical and fatigue properties of an ultrafine-grained (UFG) Al 6061 alloy processed by high-pressure torsion (HPT) at room temperature (RT). A comparison is made between the UFG state and the coarse-grained (CG) one subjected to the conventional aging treatment Т6. It is shown that HPT processing leads to the formation of the UFG microstructure with an average grain size of 170 nm. It is found that yield strength (σ_0.2), ultimate tensile strength (σ_UTS) and the endurance limit (σ_f) in the UFG Al 6061 alloy are higher by a factor of 2.2, 1.8 and 2.0 compared to the CG counterpart subjected to the conventional aging treatment Т6. Fatigue fracture surfaces are analyzed, and the fatigue behavior of the material in the high cycle and low cycle regimes is discussed. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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13 pages, 939 KiB

Open AccessArticle

Experimental Investigation of the Equal Channel Forward Extrusion Process

by Mahmoud Ebrahimi, Faramarz Djavanroodi, Sobhan Alah Nazari Tiji, Hamed Gholipour and Ceren Gode

Metals 2015, 5(1), 471-483; https://doi.org/10.3390/met5010471 - 16 Mar 2015

Cited by 28 | Viewed by 8212

Abstract

Among all recognized severe plastic deformation techniques, a new method, called the equal channel forward extrusion process, has been experimentally studied. It has been shown that this method has similar characteristics to other severe plastic deformation methods, and the potential of this new [...] Read more.

Among all recognized severe plastic deformation techniques, a new method, called the equal channel forward extrusion process, has been experimentally studied. It has been shown that this method has similar characteristics to other severe plastic deformation methods, and the potential of this new method was examined on the mechanical properties of commercial pure aluminum. The results indicate that approximate 121%, 56%, and 84% enhancements, at the yield strength, ultimate tensile strength, and Vickers micro-hardness measurement are, respectively, achieved after the fourth pass, in comparison with the annealed condition. The results of drop weight impact test showed that the increment of 26% at the impact force, and also decreases of 32%, 15%, and 4% at the deflection, impulse, and absorbed energy, are respectively attained for the fourth pass when compared to the annealed condition. Furthermore, the electron backscatter diffraction examination revealed that the average grain size of the final pass is about 480 nm. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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10 pages, 1168 KiB

Open AccessArticle

Nanocrystalline Ti Produced by Cryomilling and Consolidation by Severe Plastic Deformation

by Irina Semenova, Ilana Timokhina, Rinat Islamgaliev, Enrique Lavernia and Ruslan Valiev

Metals 2015, 5(1), 206-215; https://doi.org/10.3390/met5010206 - 5 Feb 2015

Cited by 8 | Viewed by 6386

Abstract

We report on a study of the nanocrystalline structure in Ti, which was produced by cryogenic milling followed by subsequent consolidation via severe plastic deformation using high pressure torsion. The mechanisms that are believed to be responsible for the formation of grains smaller [...] Read more.

We report on a study of the nanocrystalline structure in Ti, which was produced by cryogenic milling followed by subsequent consolidation via severe plastic deformation using high pressure torsion. The mechanisms that are believed to be responsible for the formation of grains smaller than 40 nm are discussed and the influence of structural characteristics, such as nanometric grains and oxide nanoparticles, on Ti hardening is established. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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20 pages, 2151 KiB

Open AccessArticle

Effect of Strain Localization on Pitting Corrosion of an AlMgSi0.5 Alloy

by Daniela Nickel, Dagmar Dietrich, Thomas Mehner, Philipp Frint, Dagobert Spieler and Thomas Lampke

Metals 2015, 5(1), 172-191; https://doi.org/10.3390/met5010172 - 3 Feb 2015

Cited by 28 | Viewed by 9126

Abstract

The corrosion susceptibility of an age-hardened aluminum alloy in different processing conditions, especially after a single pass of equal-channel angular pressing (ECAP), is examined. The main question addressed is how corrosive attack is changed by strain localization. For that purpose, an AlMgSi0.5 alloy [...] Read more.

The corrosion susceptibility of an age-hardened aluminum alloy in different processing conditions, especially after a single pass of equal-channel angular pressing (ECAP), is examined. The main question addressed is how corrosive attack is changed by strain localization. For that purpose, an AlMgSi0.5 alloy with a strain localized microstructure containing alternating shear bands was subjected to potentiodynamic polarization on a macro-scale and micro-scale using the micro-capillary technique. Pitting potentials and the corrosion appearance (pit depth, corroded area fractions and volumes) are discussed with respect to microstructural evolution due to casting, extrusion and ECAP. Size, shape and orientation of grains, constituent particle fragmentation, cell size and microstrain were analyzed. Stable pitting of shear bands results in less positive potentials compared to adjacent microstructure. More pits emerge in the shear bands, but the pit depth is reduced significantly. This is attributed to higher microstrains influencing the stability of the passivation layer and the reduced size of grains and constituent particles. The size of the crystallographic pits is associated with the deformation-induced cell size of the aluminum alloy. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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11 pages, 1227 KiB

Open AccessArticle

Grain Refinement and High-Performance of Equal-Channel Angular Pressed Cu-Mg Alloy for Electrical Contact Wire

by Aibin Ma, Chengcheng Zhu, Jianqing Chen, Jinghua Jiang, Dan Song, Shizhan Ni and Qing He

Metals 2014, 4(4), 586-596; https://doi.org/10.3390/met4040586 - 9 Dec 2014

Cited by 23 | Viewed by 7504

Abstract

Multi-pass equal-channel angular pressing (EACP) was applied to produce ultrafine-grained (UFG) Cu-0.2wt%Mg alloy contact wire with high mechanical/electric performance, aim to overcome the catenary barrier of high-speed trains by maximizing the tension and improving the power delivery. Microstructure evolution and overall properties of [...] Read more.

Multi-pass equal-channel angular pressing (EACP) was applied to produce ultrafine-grained (UFG) Cu-0.2wt%Mg alloy contact wire with high mechanical/electric performance, aim to overcome the catenary barrier of high-speed trains by maximizing the tension and improving the power delivery. Microstructure evolution and overall properties of the Cu-Mg alloy after different severe-plastic-deformation (SPD) routes were investigated by microscopic observation, tensile and electric tests. The results show that the Cu-Mg alloy after multi-pass ECAP at 473 K obtains ultrafine grains, higher strength and desired conductivity. More passes of ECAP leads to finer grains and higher strength, but increasing ECAP temperature significantly lower the strength increment of the UFG alloy. Grain refinement via continuous SPD processing can endow the Cu-Mg alloy superior strength and good conductivity characteristics, which are advantageous to high-speed electrification railway systems. Full article

(This article belongs to the Special Issue Ultrafine-grained Metals)

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