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....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.展开更多
Three high-nitrogen stainless steels with different N contents were successfully processed by equal-channel angular pressing for one pass, and their microstructures and mechanical properties were investigated. It was ...Three high-nitrogen stainless steels with different N contents were successfully processed by equal-channel angular pressing for one pass, and their microstructures and mechanical properties were investigated. It was found that the microstructure of the billet was heterogeneous across the billet thickness, resulting in the difference in the mechanical properties due to the different deformation conditions. A relatively low strength, high uniform elongation, and high work- hardening rate for the samples at the bottom of the billet was achieved in comparison with those processed at the top. Meanwhile, it was observed that the density of deformation twins increased with the content of N; accordingly, the strength and elongation of the alloys increase with the content of N, resulting in a good strength-ductility combination.展开更多
Equal-channel angular pressing （ECAP） process was applied to a 12 mm ×12 mm ×80 mm billet of pure copper （99.98 wt.%） at room temperature. The shear deformation characteristics, microstructure evolution,...Equal-channel angular pressing （ECAP） process was applied to a 12 mm ×12 mm ×80 mm billet of pure copper （99.98 wt.%） at room temperature. The shear deformation characteristics, microstructure evolution, and tensile properties were investigated. A combination of high strength （-420 MPa） and high elongation to failure （-25%） was achieved after eight ECAP passes at room temperature. The mixing of ultrafme grains （-0.2 μm） with nanocrystalline grains （-80 nm） resulted in high tensile strength and ductility.展开更多
In this work,a high-strength Mg-10Gd-2Y-1.5Zn-0.5Zr(wt%)alloy was prepared via eight passes of equal-channel angular pressing(ECAP).The microstructures and mechanical properties of as-cast and ECAP alloys were systema...In this work,a high-strength Mg-10Gd-2Y-1.5Zn-0.5Zr(wt%)alloy was prepared via eight passes of equal-channel angular pressing(ECAP).The microstructures and mechanical properties of as-cast and ECAP alloys were systematically investigated by X-ray diffraction(XRD),optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electronic universal testing machine.The obtained results indicate that the microstructure of as-cast alloy consists ofα-Mg dendrite,network Mg3(Gd,Y,Zn)phase and lamellar 14H long-period stacking ordered(LPSO)phase which is precipitated near the boundary of Mg3(Gd,Y,Zn)networks.After eight-pass ECAP,the network Mg3(Gd,Y,Zn)phase is deformed and broken.However,the refined Mg_3(Gd,Y,Zn)particles are not distributed uniformly in the matrix,but still aggregated at the interdendritic area.Moreover,the content of 14H lamellas increases obviously,and they become bent and kinked during severe deformation.DRX is activated in the region between Mg3(Gd,Y,Zn)particles and 14H clusters.Compression test at room temperature indicates that the ECAP alloy exhibits excellent mechanical property with compressive strength of 518 MPa and fracture strain of 21.6%.The comprehensive high strength and toughness could be ascribed to the refined Mg_3(Gd,Y,Zn)particles,DRX grains and kinked 14H LPSO phase.展开更多
As-extruded Mg-6Zn(wt.%)Alloy was subjected to severe plastic deformation(SPD)by the equal-channel angular pressing(ECAP)at 160 ℃.The results of tensile tests at room temperature showed that two passes ECAP resulted ...As-extruded Mg-6Zn(wt.%)Alloy was subjected to severe plastic deformation(SPD)by the equal-channel angular pressing(ECAP)at 160 ℃.The results of tensile tests at room temperature showed that two passes ECAP resulted in a remarkable improvement of strength,yield strength from 200 to 265 MPa and ultimate tensile strength from 260 to 340 MPa.However,with the deformation increasing,the samples processed by ECAP for four or six passes had insignificant difference than that processed by two-pass ECAP.Massive precipitates were observed in all the Mg-6Zn alloys specimens processed by ECAP.Transmission electron microscope and X-ray diffraction results indicated that ECAP treatment induced the precipitation of laves MgZn_(2) phase and transition Mg_(4)Zn_(7) phase.The spherical MgZn_(2) particles and irregular shape Mg_(4)Zn_(7) particles coexist in the microstructure of Mg-6Zn alloy after six pass ECAP.展开更多
Equal channel angular pressing （ECAP） processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment ...Equal channel angular pressing （ECAP） processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment was conducted at 300 ℃ in a die having an included angle of 90o between two channels by the BCZ route with the sheets rotated by 90°about the normal axis of plate plane. The tensile tests and conical cup tests were conducted at various temperatures from 20 to 250 ℃. The experimental results indicated that improving the working temperatures could lead to the soft in the material and the enhancement of ductility. Comparatively, the ECAPed AZ31 alloy sheets showed the lower yield strength and smaller conical cup value （CCV） than the unECAPed counterpart in the room temperature. The difference in yield strength between them became small in the elevated temperature, but the ECAPed samples still had the smaller CCV value, implying the improved formability. The texture of the AZ31 alloy sheets could be modified by ECAP and the decrease in the yield strength and more uniform deformation realized in the material, so the formability of AZ31 alloy sheets was improved.展开更多
The elliptical cross-section spiral equal-channel extrusion （ECSEE） process is simulated by using Deform-3D finite element software. The ratio m of major-axis to minor-axis length for ellipse-cross-section, the tors...The elliptical cross-section spiral equal-channel extrusion （ECSEE） process is simulated by using Deform-3D finite element software. The ratio m of major-axis to minor-axis length for ellipse-cross-section, the torsion angle u, the round-ellipse cross-section transitional channel L1, the elliptical rotation cross-section transitional channel L2 and the ellipse-round cross-section transitional channel L3 are destined for the extrusion process parameters. The average effective strain eave on cross-section of blank, the deformation uniformity coefficient a and the value of maximum damage dmax are chosen to be the optimize indexes, and the virtual orthogonal experiment of L16 （45） is designed. The correlation degree of the process factors affecting eave, a and dmax is analyzed by the numerical simulation results using the weights and grey association model. The process parameters are optimized by introducing the grey situation decision theory and the ECSEE optimal combination of process parameters is obtained： u of 120 , m of 1.55, L1 of 7 mm, L2 of 10 mm, and L3 of 10 mm. Simulation and experimental results show that the material can be refined with the optimized structural parameters of die. Therefore, the optimization results are satisfactory.展开更多
Equal-channel angular pressing （ECAP） is a prominent technique that imposes severe plastic deformation into materials to en- hance their mechanical properties. In this research, experimental and numerical approaches...Equal-channel angular pressing （ECAP） is a prominent technique that imposes severe plastic deformation into materials to en- hance their mechanical properties. In this research, experimental and numerical approaches were utilized to investigate the mechanical prop- erties, strain behavior, and damage prediction of ECAPed 7025 aluminum alloy in various conditions, such as die channel angle, outer comer angle, and friction coefficient. Experimental results indicate that, after the first pass, the yield strength, ultimate tensile strength, and hardness magnitude are improved by approximately 95%, 28%, and 48.5%, respectively, compared with the annealed state, mainly due to grain re- finement during the deformation. Finite element analysis shows that the influence of die channel angle is more important than that of outer comer angle or friction coefficient on both the strain behavior and the damage prediction. Also, surface cracks are the main cause of damage during the ECAP process for every die channel angle except for 90°; however, the cracks initiated from the neighborhood of the central re- gions are the possible cause of damage in the ECAPed sample with the die channel angle of 90°.展开更多
A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equalchannel angular pressing to obtain fine-grained micro structure. Stress corrosion cracking (SCC) behaviors of the fine...A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equalchannel angular pressing to obtain fine-grained micro structure. Stress corrosion cracking (SCC) behaviors of the fine-grained samples were studied by slow-strain-rate testing in air, distilled water and Hanks’solution at the strain rate of 1×10^(-6) s^(-1). All samples show a relatively low SCC sensitivity in distilled water but a great SCC tendency in Hanks’ solution. The microscopic observations of the fracture surfaces and the side surfaces reveal obvious active anodic dissolution and hydrogen embrittlement cracks, which indicate the higher SCC susceptibility in Hanks'solution. The fine-grained microstructure with more crystal defects promotes the passivation process of the oxide film and restrains the hydrogen induced cracking of the ME21 magnesium alloy, leading to the higher general corrosion resistance as well as SCC resistance.展开更多
An as-cast magnesium alloy with high Al content Mg15Al was subjected to equal-channel angular pressing （ECAP） through a die with an angle of φ= 90？ at 553 K following route Bc. It is found that the network β-Mg17...An as-cast magnesium alloy with high Al content Mg15Al was subjected to equal-channel angular pressing （ECAP） through a die with an angle of φ= 90？ at 553 K following route Bc. It is found that the network β-Mg17Al12 phases in the as-cast Mg15Al alloy are broken into small blocks and dispersed uniformly with increasing numbers of pressing passes. Moreover, many nano-sized Mg17Al12 particles precipitate in the ultra-fine α-Mg matrix. The grains are obviously refined. However, the grain structure is inhomogeneous in different areas of the alloy. The average size of the primary phase α-Mg is reduced to about 1 μm while grains of around 0.1-0.2 μm are obtained in some two-phase areas. With additional ECAP passes （up to 8）, coarsening of the grains occurs by dynamic recovery. Room temperature tensile tests show that the mechanical properties of Mg15Al alloys are markedly improved after 4 ECAP passes. The ultimate tensile strength and elongation to failure increase from 150 MPa to 269.3 MPa and from 0.05% to 7.4%, respectively. Compared with that after 4 passes, the elongation to failure of the alloy increases but the strength of the alloy slightly decreases after 8 ECAP passes. Fracture morphology of the ECAP-processed alloy exhibits dimple-like fracture characteristics while the as-cast alloy shows quasi-cleavage fractures.展开更多
Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route ...Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route B_(C)(i.e.,rotated 90° in the same sense between each pass).The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope(OM),X-ray diffraction(XRD),tensile test(at room temperature),and scanning electron microscope(SEM).The results show that the main strengthening phase of the alloy is MgZn_(2),whose content increases apparently after ECAP,the dislocation density increases by one order of magnitude,the hardness value of the 1 pass ECAPed sample increases by 53 %,the ultimate tensile strength(UTS)increases by 29 %,and the true strain increases by 15.4 %.But the further increase in the strength with the passes increasing would cost a slight drop in the true strain.The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.展开更多
In the present work, a CuCrZr alloy characterized by ultrafine grains and nanoscale particles was prepared by equalchannel angular pressing （ECAP） at 450℃. A desired combination of a tensile strength （580 MPa） an...In the present work, a CuCrZr alloy characterized by ultrafine grains and nanoscale particles was prepared by equalchannel angular pressing （ECAP） at 450℃. A desired combination of a tensile strength （580 MPa） and an electrical conductivity （81% International Annealed Copper Standard） is simultaneously obtained in the as-ECAP-processed CuCrZr alloy without additional aging treatment. The improved properties can be mainly attributed to the ultrafine grains and nanoscale precipitates. This processing may pave a way to develop the CuCrZr alloys having high strength and high electrical conductivity for engineering applications.展开更多
Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing（ECAP） have been examined after exposure to a low energy,high-flux deuterium（D） plasma at fluenc...Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing（ECAP） have been examined after exposure to a low energy,high-flux deuterium（D） plasma at fluences of 3×10^24 D/m^2 and 1×10^25 D/m^2 in a temperature range of 100 ℃-150 ℃.The methods used were scanning electron microscopy（SEM） and thermal desorption spectroscopy（TDS）.Sparse and small blisters（0.1 μm） were observed by SEM after D plasma irradiation on every irradiated surface;yet they did not exhibit significant structure or plasma fluence dependence.Larger blisters or protrusions appeared after subsequent TDS heating up to 1000 ℃.The TDS results showed a single D desorption peak at 220℃ for all samples and the D retention increased with increasing numbers of extrusion passes,i.e.,the decrease of grain sizes.The increased D retention in this low temperature range should be attributed to the faster diffusion of D along the larger volume fraction of grain boundaries introduced by ECAP.展开更多
Microstructural development of ultra low C, N, Fe-Cr alloy and pure copper processed by equal-channel angular pressing (ECAP) have been examined focusing on the initial stage of the formation of ultrafine grain struct...Microstructural development of ultra low C, N, Fe-Cr alloy and pure copper processed by equal-channel angular pressing (ECAP) have been examined focusing on the initial stage of the formation of ultrafine grain structure. Fe-Cr alloys were pressed at 423 K while pure copper at room temperature for 1 to 3 passes via the route Bc to compare at the equivalent homologous temperature. Microstructural evolutions were characterized by electron backscatter diffraction (EBSD) image and transmission electron microscopy (TEM). It was found that deformation structures were mostly deformation-induced subboundaries in both the materials after one pass, but the fraction of high-angle grain boundary became higher in the Fe-Cr alloys than in pure copper in subsequent passes by increasing misorientation of the boundaries. The more enhanced formation of high angle boundaries in Fe-Cr alloys was discussed in terms of the nature of crystal slip of FCC and BCC structures.展开更多
The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. ...The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. Such band structures diminish formability and become origin of the so-called ridging. A novel processing will be shown here, which involves strain-path change by introducing one-pass ECAP prior to cold-rolling, and facilitates recrystallisation. Indeed, the recrystallisation temperature was reduced by 100℃, compared with cold-rolling alone imposing an equivalent strain. Grain- scale microshear bands introduced during one-pass ECAP perturbed the banded structures in post-ECAP cold-rolling and enhanced the recrystallisation at the final annealing.展开更多
Semicontinuous equal-channel angular extrusion（ SC-ECAE） is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specime...Semicontinuous equal-channel angular extrusion（ SC-ECAE） is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specimens in the conventional ECAE,driving forces are applied to dies in SC-EACE. The deformation of interstitial-free（ IF） steel w as performed at room temperature,and individual specimens w ere repeatedly processed at various passes. An overall grain size of 0. 55 μm w as achieved after 10 passes. During SC-ECAE,the main textures of IF steel included { 111} ,{ 110} ,{ 112} ,{ 110} ,and { 110} At an early stage,increasing dislocations induce new textures and increase intensity. When the deformation continues,low-angle boundaries are formed betw een dislocation cell bands,w hich cause some dislocation cell bands to change their orientation,and therefore,the intensity of the textures begins to decrease. After more passes,the intensity of textures continues to decrease w ith high-angle boundaries,and the sub-grains in dislocation cell bands continuously increase. The present study reports the evolution of textures during deformation; these w ere examined and characterized using high-resolution electron backscattered diffraction（ EBSD） in a field emission scanning electron microscope. The mechanisms of texture evolution are discussed.展开更多
AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temper...AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP,in placing of {1 010},planes {1 011} and {1 012} become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane(0001).展开更多
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 AlCl3 and also by surfac...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 AlCl3 and also by surface analysis.Anodizing was conducted for 20 min at 200 and 400 A/m2 in a solution containing 1.53 mol/L H2SO4 and 0.018 5 mol/L Al2(SO4)3·16H2O at 20 ℃.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.展开更多
Equal-channel angular pressing(ECAP) is now recognized as an effective technique for fabricating ultrafine grained materials. The results show that prevalent macroscopic shear banding occurs in ECAP as long as the pre...Equal-channel angular pressing(ECAP) is now recognized as an effective technique for fabricating ultrafine grained materials. The results show that prevalent macroscopic shear banding occurs in ECAP as long as the pressing passes reach 2, and the severe macroscopic shear band extends from bottom to top surface and slants to the longitudinal axis of specimen at an angle of about 45°, develops at regular intervals, with a high shear strain accommodation of about 3.7 within the band. Different families of macroscopic shear bands may cut across each other, and over 60% of sample volume is occupied by macroscopic shear band when the ECAP reaches 4 passes.展开更多
基金Project(BK20131373)supported by the Natural Science Foundation of Jiangsu ProvinceChina
文摘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.
基金The National Natural Science Foundation of China(NSFC)under Grant Nos.5130117951331007+1 种基金31370976financially supported this work
文摘Three high-nitrogen stainless steels with different N contents were successfully processed by equal-channel angular pressing for one pass, and their microstructures and mechanical properties were investigated. It was found that the microstructure of the billet was heterogeneous across the billet thickness, resulting in the difference in the mechanical properties due to the different deformation conditions. A relatively low strength, high uniform elongation, and high work- hardening rate for the samples at the bottom of the billet was achieved in comparison with those processed at the top. Meanwhile, it was observed that the density of deformation twins increased with the content of N; accordingly, the strength and elongation of the alloys increase with the content of N, resulting in a good strength-ductility combination.
基金This work is financially supported by the Natural Science Foundation of Jiangsu Province, China (No. BK2001053), the International Cooperation Project Foundation of Jiangsu Province, China (No. BZ2006018), and the Science and Technol-ogy Project Foundation of Changzhou, China (No. CZ2006008).
文摘Equal-channel angular pressing （ECAP） process was applied to a 12 mm ×12 mm ×80 mm billet of pure copper （99.98 wt.%） at room temperature. The shear deformation characteristics, microstructure evolution, and tensile properties were investigated. A combination of high strength （-420 MPa） and high elongation to failure （-25%） was achieved after eight ECAP passes at room temperature. The mixing of ultrafme grains （-0.2 μm） with nanocrystalline grains （-80 nm） resulted in high tensile strength and ductility.
基金financially supported by the Natural Science Foundation of Jiangsu Province of China(No.BK20160869)the Nantong Science and Technology Project(No.GY12015009)the Fundamental Research Funds for the Central Universities(No.2015B01314)。
文摘In this work,a high-strength Mg-10Gd-2Y-1.5Zn-0.5Zr(wt%)alloy was prepared via eight passes of equal-channel angular pressing(ECAP).The microstructures and mechanical properties of as-cast and ECAP alloys were systematically investigated by X-ray diffraction(XRD),optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electronic universal testing machine.The obtained results indicate that the microstructure of as-cast alloy consists ofα-Mg dendrite,network Mg3(Gd,Y,Zn)phase and lamellar 14H long-period stacking ordered(LPSO)phase which is precipitated near the boundary of Mg3(Gd,Y,Zn)networks.After eight-pass ECAP,the network Mg3(Gd,Y,Zn)phase is deformed and broken.However,the refined Mg_3(Gd,Y,Zn)particles are not distributed uniformly in the matrix,but still aggregated at the interdendritic area.Moreover,the content of 14H lamellas increases obviously,and they become bent and kinked during severe deformation.DRX is activated in the region between Mg3(Gd,Y,Zn)particles and 14H clusters.Compression test at room temperature indicates that the ECAP alloy exhibits excellent mechanical property with compressive strength of 518 MPa and fracture strain of 21.6%.The comprehensive high strength and toughness could be ascribed to the refined Mg_3(Gd,Y,Zn)particles,DRX grains and kinked 14H LPSO phase.
基金support from The national natural science foundation of China(Grant No.51301151)Jiangsu province natural science foundation of China(Grant No.BK20130447).
文摘As-extruded Mg-6Zn(wt.%)Alloy was subjected to severe plastic deformation(SPD)by the equal-channel angular pressing(ECAP)at 160 ℃.The results of tensile tests at room temperature showed that two passes ECAP resulted in a remarkable improvement of strength,yield strength from 200 to 265 MPa and ultimate tensile strength from 260 to 340 MPa.However,with the deformation increasing,the samples processed by ECAP for four or six passes had insignificant difference than that processed by two-pass ECAP.Massive precipitates were observed in all the Mg-6Zn alloys specimens processed by ECAP.Transmission electron microscope and X-ray diffraction results indicated that ECAP treatment induced the precipitation of laves MgZn_(2) phase and transition Mg_(4)Zn_(7) phase.The spherical MgZn_(2) particles and irregular shape Mg_(4)Zn_(7) particles coexist in the microstructure of Mg-6Zn alloy after six pass ECAP.
文摘Equal channel angular pressing （ECAP） processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment was conducted at 300 ℃ in a die having an included angle of 90o between two channels by the BCZ route with the sheets rotated by 90°about the normal axis of plate plane. The tensile tests and conical cup tests were conducted at various temperatures from 20 to 250 ℃. The experimental results indicated that improving the working temperatures could lead to the soft in the material and the enhancement of ductility. Comparatively, the ECAPed AZ31 alloy sheets showed the lower yield strength and smaller conical cup value （CCV） than the unECAPed counterpart in the room temperature. The difference in yield strength between them became small in the elevated temperature, but the ECAPed samples still had the smaller CCV value, implying the improved formability. The texture of the AZ31 alloy sheets could be modified by ECAP and the decrease in the yield strength and more uniform deformation realized in the material, so the formability of AZ31 alloy sheets was improved.
基金co-supported by National Natural Science Foundation of China (No. 51275414)Aeronautical Science Foundation of China (No. 2011ZE53059)+1 种基金National Defense Basic Research Program (No. 51318040105)Graduate Starting Seed Fund of Northwestern Polytechnical University(No. Z2011006)
文摘The elliptical cross-section spiral equal-channel extrusion （ECSEE） process is simulated by using Deform-3D finite element software. The ratio m of major-axis to minor-axis length for ellipse-cross-section, the torsion angle u, the round-ellipse cross-section transitional channel L1, the elliptical rotation cross-section transitional channel L2 and the ellipse-round cross-section transitional channel L3 are destined for the extrusion process parameters. The average effective strain eave on cross-section of blank, the deformation uniformity coefficient a and the value of maximum damage dmax are chosen to be the optimize indexes, and the virtual orthogonal experiment of L16 （45） is designed. The correlation degree of the process factors affecting eave, a and dmax is analyzed by the numerical simulation results using the weights and grey association model. The process parameters are optimized by introducing the grey situation decision theory and the ECSEE optimal combination of process parameters is obtained： u of 120 , m of 1.55, L1 of 7 mm, L2 of 10 mm, and L3 of 10 mm. Simulation and experimental results show that the material can be refined with the optimized structural parameters of die. Therefore, the optimization results are satisfactory.
基金financially supported by the Scientific and Technological Research Council of Turkey(TüBITAK)under the 2216 Research Fellowship Program for Foreign Citizens
文摘Equal-channel angular pressing （ECAP） is a prominent technique that imposes severe plastic deformation into materials to en- hance their mechanical properties. In this research, experimental and numerical approaches were utilized to investigate the mechanical prop- erties, strain behavior, and damage prediction of ECAPed 7025 aluminum alloy in various conditions, such as die channel angle, outer comer angle, and friction coefficient. Experimental results indicate that, after the first pass, the yield strength, ultimate tensile strength, and hardness magnitude are improved by approximately 95%, 28%, and 48.5%, respectively, compared with the annealed state, mainly due to grain re- finement during the deformation. Finite element analysis shows that the influence of die channel angle is more important than that of outer comer angle or friction coefficient on both the strain behavior and the damage prediction. Also, surface cracks are the main cause of damage during the ECAP process for every die channel angle except for 90°; however, the cracks initiated from the neighborhood of the central re- gions are the possible cause of damage in the ECAPed sample with the die channel angle of 90°.
基金supported by the Key Research and Development Project of Jiangsu Province of China(BE2017148)the Fundamental Research Funds for the Central Universities(HHU2016B10314)Six Major Talent Peaks Project of Jiangsu Province of China(2014-XCL-023)
文摘A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equalchannel angular pressing to obtain fine-grained micro structure. Stress corrosion cracking (SCC) behaviors of the fine-grained samples were studied by slow-strain-rate testing in air, distilled water and Hanks’solution at the strain rate of 1×10^(-6) s^(-1). All samples show a relatively low SCC sensitivity in distilled water but a great SCC tendency in Hanks’ solution. The microscopic observations of the fracture surfaces and the side surfaces reveal obvious active anodic dissolution and hydrogen embrittlement cracks, which indicate the higher SCC susceptibility in Hanks'solution. The fine-grained microstructure with more crystal defects promotes the passivation process of the oxide film and restrains the hydrogen induced cracking of the ME21 magnesium alloy, leading to the higher general corrosion resistance as well as SCC resistance.
基金Funded by the Taiyuan Special Fund for Sci-Tech Star (No. 09121002)the Youth Science Foundation of Shanxi Province (No.2008021033)Shanxi Research Fund for Returned Scholars (No.2007-25)
文摘An as-cast magnesium alloy with high Al content Mg15Al was subjected to equal-channel angular pressing （ECAP） through a die with an angle of φ= 90？ at 553 K following route Bc. It is found that the network β-Mg17Al12 phases in the as-cast Mg15Al alloy are broken into small blocks and dispersed uniformly with increasing numbers of pressing passes. Moreover, many nano-sized Mg17Al12 particles precipitate in the ultra-fine α-Mg matrix. The grains are obviously refined. However, the grain structure is inhomogeneous in different areas of the alloy. The average size of the primary phase α-Mg is reduced to about 1 μm while grains of around 0.1-0.2 μm are obtained in some two-phase areas. With additional ECAP passes （up to 8）, coarsening of the grains occurs by dynamic recovery. Room temperature tensile tests show that the mechanical properties of Mg15Al alloys are markedly improved after 4 ECAP passes. The ultimate tensile strength and elongation to failure increase from 150 MPa to 269.3 MPa and from 0.05% to 7.4%, respectively. Compared with that after 4 passes, the elongation to failure of the alloy increases but the strength of the alloy slightly decreases after 8 ECAP passes. Fracture morphology of the ECAP-processed alloy exhibits dimple-like fracture characteristics while the as-cast alloy shows quasi-cleavage fractures.
基金financially supported by the National Natural Science Foundation of China (Nos.51175138, 50875072 and 51575153)the Program for New Century Excellent Talents in University (No.NCET-13-0765)。
文摘Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route B_(C)(i.e.,rotated 90° in the same sense between each pass).The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope(OM),X-ray diffraction(XRD),tensile test(at room temperature),and scanning electron microscope(SEM).The results show that the main strengthening phase of the alloy is MgZn_(2),whose content increases apparently after ECAP,the dislocation density increases by one order of magnitude,the hardness value of the 1 pass ECAPed sample increases by 53 %,the ultimate tensile strength(UTS)increases by 29 %,and the true strain increases by 15.4 %.But the further increase in the strength with the passes increasing would cost a slight drop in the true strain.The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.
基金supported by the National Natural Science Foundation of China(51671064)the Fundamental Research Funds for the Central UniversitiesKey Laboratory of Superlight Materials and Surface Technology(Harbin Engineering University),Ministry of Education
文摘In the present work, a CuCrZr alloy characterized by ultrafine grains and nanoscale particles was prepared by equalchannel angular pressing （ECAP） at 450℃. A desired combination of a tensile strength （580 MPa） and an electrical conductivity （81% International Annealed Copper Standard） is simultaneously obtained in the as-ECAP-processed CuCrZr alloy without additional aging treatment. The improved properties can be mainly attributed to the ultrafine grains and nanoscale precipitates. This processing may pave a way to develop the CuCrZr alloys having high strength and high electrical conductivity for engineering applications.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Nos.2013GB105001,2013GB105002,2015GB109001)National Natural Science Foundation of China(Nos.11305213,11405201)+1 种基金Technological Development Grant of Hefei Science Center of CAS(No.2014TDG-HSC003)China National Funds for Distinguished Young Scientists(No.51325103)
文摘Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing（ECAP） have been examined after exposure to a low energy,high-flux deuterium（D） plasma at fluences of 3×10^24 D/m^2 and 1×10^25 D/m^2 in a temperature range of 100 ℃-150 ℃.The methods used were scanning electron microscopy（SEM） and thermal desorption spectroscopy（TDS）.Sparse and small blisters（0.1 μm） were observed by SEM after D plasma irradiation on every irradiated surface;yet they did not exhibit significant structure or plasma fluence dependence.Larger blisters or protrusions appeared after subsequent TDS heating up to 1000 ℃.The TDS results showed a single D desorption peak at 220℃ for all samples and the D retention increased with increasing numbers of extrusion passes,i.e.,the decrease of grain sizes.The increased D retention in this low temperature range should be attributed to the faster diffusion of D along the larger volume fraction of grain boundaries introduced by ECAP.
文摘Microstructural development of ultra low C, N, Fe-Cr alloy and pure copper processed by equal-channel angular pressing (ECAP) have been examined focusing on the initial stage of the formation of ultrafine grain structure. Fe-Cr alloys were pressed at 423 K while pure copper at room temperature for 1 to 3 passes via the route Bc to compare at the equivalent homologous temperature. Microstructural evolutions were characterized by electron backscatter diffraction (EBSD) image and transmission electron microscopy (TEM). It was found that deformation structures were mostly deformation-induced subboundaries in both the materials after one pass, but the fraction of high-angle grain boundary became higher in the Fe-Cr alloys than in pure copper in subsequent passes by increasing misorientation of the boundaries. The more enhanced formation of high angle boundaries in Fe-Cr alloys was discussed in terms of the nature of crystal slip of FCC and BCC structures.
文摘The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. Such band structures diminish formability and become origin of the so-called ridging. A novel processing will be shown here, which involves strain-path change by introducing one-pass ECAP prior to cold-rolling, and facilitates recrystallisation. Indeed, the recrystallisation temperature was reduced by 100℃, compared with cold-rolling alone imposing an equivalent strain. Grain- scale microshear bands introduced during one-pass ECAP perturbed the banded structures in post-ECAP cold-rolling and enhanced the recrystallisation at the final annealing.
文摘Semicontinuous equal-channel angular extrusion（ SC-ECAE） is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specimens in the conventional ECAE,driving forces are applied to dies in SC-EACE. The deformation of interstitial-free（ IF） steel w as performed at room temperature,and individual specimens w ere repeatedly processed at various passes. An overall grain size of 0. 55 μm w as achieved after 10 passes. During SC-ECAE,the main textures of IF steel included { 111} ,{ 110} ,{ 112} ,{ 110} ,and { 110} At an early stage,increasing dislocations induce new textures and increase intensity. When the deformation continues,low-angle boundaries are formed betw een dislocation cell bands,w hich cause some dislocation cell bands to change their orientation,and therefore,the intensity of the textures begins to decrease. After more passes,the intensity of textures continues to decrease w ith high-angle boundaries,and the sub-grains in dislocation cell bands continuously increase. The present study reports the evolution of textures during deformation; these w ere examined and characterized using high-resolution electron backscattered diffraction（ EBSD） in a field emission scanning electron microscope. The mechanisms of texture evolution are discussed.
基金Project(08JK240) supported by the Special Program of Education Bureau of Shaanxi Province, ChinaProject(SLGQD0751) supported by the Scientific Research Startup Program for Introduced Talents of Shaanxi University of Technology, China
文摘AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP,in placing of {1 010},planes {1 011} and {1 012} become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane(0001).
文摘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 AlCl3 and also by surface analysis.Anodizing was conducted for 20 min at 200 and 400 A/m2 in a solution containing 1.53 mol/L H2SO4 and 0.018 5 mol/L Al2(SO4)3·16H2O at 20 ℃.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.
文摘Equal-channel angular pressing(ECAP) is now recognized as an effective technique for fabricating ultrafine grained materials. The results show that prevalent macroscopic shear banding occurs in ECAP as long as the pressing passes reach 2, and the severe macroscopic shear band extends from bottom to top surface and slants to the longitudinal axis of specimen at an angle of about 45°, develops at regular intervals, with a high shear strain accommodation of about 3.7 within the band. Different families of macroscopic shear bands may cut across each other, and over 60% of sample volume is occupied by macroscopic shear band when the ECAP reaches 4 passes.
