Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable st...Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results onfcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo- mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.展开更多
Ultrafine-grained(UFG)AA1060 sheets were fabricated via five-cycle accumulative roll bonding(ARB)and subsequent three-pass cold rolling(298 K),or cryorolling(83 K and 173 K).Microstructures of the aluminum samples wer...Ultrafine-grained(UFG)AA1060 sheets were fabricated via five-cycle accumulative roll bonding(ARB)and subsequent three-pass cold rolling(298 K),or cryorolling(83 K and 173 K).Microstructures of the aluminum samples were examined via transmission electron microscopy,and their mechanical properties were measured via tensile and microhardness testing.Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling,and the grain size became finer with reducing rolling temperature.The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm,respectively,via subsequent cold rolling or cryorolling(83 K).Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.展开更多
The fabrication of ultrafine-grained microstructures(grain size below 1μm)in titanium alloys is beneficial for improving their mechanical properties at room temperature and medium tempera-tures(400-550°C).Howeve...The fabrication of ultrafine-grained microstructures(grain size below 1μm)in titanium alloys is beneficial for improving their mechanical properties at room temperature and medium tempera-tures(400-550°C).However,a long-standing challenge involves the low-cost manufacturing of bulk ultrafine-grained titanium alloys.In this work,we developed a facile strategy through martensite de-composition at thermal-mechanical coupling conditions,to fabricate an equiaxed microstructure in a Ti6Al4Mo4Zr1W0.2Si model alloy with an averageαgrain size of 315±62 nm.The formation of the ultrafine-grained microstructure was because the lattice strain stored in the martensitic initial mi-crostructure enhanced the nucleation rate of dynamic recrystallization,meanwhile,the pinning role of martensite decomposition productsβand(Ti,Zr)_(5)Si_(3)phases suppressed grain coarsening at high tem-peratures.Compared to conventional(α+β)alloys,the tensile strength of this alloy improved by 20%-30%at both room temperature and 550°C,without decreasing its ductility.In situ SEM observations revealed that the ultrafine-grained microstructure would not only suppress dislocation motions but also contribute to the homogenous deformation in the matrix of the material,therefore,it resulted in higher mechanical performance.The research results may be of great significance to the development of next-generation aviation titanium alloys.展开更多
The influence of magnetic field(1 T)on dislocation morphology and precipitation behaviour of ultrafinegrained(UFG)Al 7075 alloy was investigated after ageing from 90 to 200℃ via wide angle X-ray scattering(WAXS),smal...The influence of magnetic field(1 T)on dislocation morphology and precipitation behaviour of ultrafinegrained(UFG)Al 7075 alloy was investigated after ageing from 90 to 200℃ via wide angle X-ray scattering(WAXS),small angle X-ray scattering(SAXS),and transmission electron microscopy(TEM).Experimental results reveal that the improved precipitation kinetics of alloys in the thickness plane(denoted as sample II)as compared to those in the rolling plane(denoted as sample I),which arises due to a higher dislocation density(morphology of dislocation cells)of the thickness plane than that of the rolling plane(morphology of dislocations and dislocation tangles).Specifically,because of different dislocation morphologies,the magnetic field positively and negatively affects the dislocation activity in samples I and II,leading to enhanced and suppressed precipitation behaviors,respectively.Interestingly,nucleation of theηphase is facilitated in the UFG alloy at the critical temperature(140℃)because it affords a faster rate of atom diffusion and a higher dislocation density as compared to those exhibited by its coarse-grained alloy.This systematic and comprehensive study provides new insights into dislocation morphology and precipitation behaviour of the UFG 7075 Al alloy,while enabling the optimization of precipitation kinetics.展开更多
Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However...Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However,the sintering concurrently becomes increasingly more difficult with increasing Re contents.Here we proposed that the sintering conundrum is caused by the lowered crystal symmetry and the wider dihedral angle distribution when body-center-cubic(BCC)W is alloyed with more hexagonal-close-packed(HCP)Re,which results in inefficient pore removal in the final stage sintering.We showed that the conundrum can be resolved by pressureless two-step sintering(TSS)which suppresses acceler-ating final-stage grain growth,and our proposal is supported by the data of the critical densityρc that is required to start the second step for successful TSS at different W-Re compositions.Dense ultrafine-grained W-Re alloys with∼300 nm average grain size and up to 25 wt%Re were successfully produced.Our work demonstrates the unique opportunities offered by two-step sintering to advance the scientific understanding and technological practices in powder metallurgy and related fields.展开更多
A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained a...A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP).Tension–compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests.The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior.The basal and prismaticslip are suppressed either for tension or compression,which is the easiest to activate.The tension twin system{1012}<1011> easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor,consequently resulting in a lower yield strength under compression than tension.ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement.The interaction among the dislocations,grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation,while the interaction between the dislocations and grain boundaries for tension deformation.Deformation twins lead to the higher work hardening under compression than tension.展开更多
Existence of tension–compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications.The present work is aimed at nullifying...Existence of tension–compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications.The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium–Silver–Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing.The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests.The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts.The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock–Mecking’s analysis.Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior.This was especially dominant with coarsening of grain size.Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations.The role of crystallographic texture for inducing the polarity to Tension–Compression yield asymmetry was corroborated.A critical grain size in Magnesium–Silver–Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.展开更多
C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated ...C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated with dislocation slip,twinning,and solute drag have not been reported yet.In this work,a C-N co-doped iHEA with nominal composition Fe_(48.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)N_(1.0)(at.%)was prepared,and the microstructures were tuned by cold-rolling and annealing treatments to improve mechanical properties.Upon cold-rolling with a strain of 1.74,the main microstructures in the iHEA are composed of nano-grains,nano-twins,HCP laminates,and high density of dislocations,leading to ultrahigh hardness of 466.7 HV and tensile strength of 1730 MPa at the expense of ductility(2.44%).Both the nanostructures and the high hardness of the iHEA can be maintained up to an annealing temperature of 600℃(462.5 HV).After annealing at 650℃ for 1 h,the UFG microstructures are obtained in the iHEA,containing re-crystallized grains with an average grain size of 0.91μm and nanoprecipitates with an average diameter of 90.8 nm.The combined strengthening and hardening effects of UFGs,nanoprecipitates,twinning,and solutes contribute to high strain hardening(n=0.81),gigapascal yield strength(984 MPa),and good duc-tility(20%).The C-N co-doping leads to a strong drag effect on dislocation slip,resulting in a nano-scale mean free path of dislocation slip λ(1.44 nm)and much small apparent activation volume V^(∗)(15.8 b^(3))of the UFG iHEA.展开更多
In this work,an ultrafine-grained high-Nb-TiAl alloy with a nominal composition of Ti-45Al-8Nb-0.2W-0.2B(at%)was prepared by cryomilling and subsequent spark plasma sintering(SPS)technique.The chemical composition,par...In this work,an ultrafine-grained high-Nb-TiAl alloy with a nominal composition of Ti-45Al-8Nb-0.2W-0.2B(at%)was prepared by cryomilling and subsequent spark plasma sintering(SPS)technique.The chemical composition,particle size,morphology and crystallite size of cryomilled powder were studied.It is found that cryomilling can effectively reduce the particle size and enhance grain refinement.The ingots sintered at 900 and 1000℃ show an equiaxed near-γmicrostructure with grain sizes<700 nm,while the sample sintered at 1100℃exhibits duplex microstructure.Especially,the one sintered at 1000℃ has excellent mechanical properties,whose compression yield strength,fracture strength,bending strength and plastic strain achieve 1310,2174,578 MPa and 16.8%,respectively.The reasons for the effect of cryomilling and the mechanical behavior of sintered ingots were discussed.It is suggested that cryomilling in combination with SPS is an effective way to synthesize high-NbTiAl alloy with ultrafine-grained structure.展开更多
Cold processing of magnesium （Mg） alloys is a challenge because Mg has a hexagonal close-packed （HCP） lattice with limited slip systems, which makes it difficult to plastically deform at low temperature. To addres...Cold processing of magnesium （Mg） alloys is a challenge because Mg has a hexagonal close-packed （HCP） lattice with limited slip systems, which makes it difficult to plastically deform at low temperature. To address this challenge, a combination of annealing of as-cast alloy and multi-axial forging was adopted ro obtain isotropic ultrafine-grained （UFG） structure in a lean Mg-2Zn-2Gd alloy with high strength （yield strength： ~227 MPa）-high ductility （% elongation： ～30%） combination. This combination of strength and ductility is excellent for the lean alloy, enabling an understanding of deformation processes in a formable high strength Mg-rare earth alloy. The nanoscale deformation behavior was studied via nanoindentation and electron microscopy, and the behavior was compared with its low strength （yield strength： ～46 MPa） - low ductility （% elongation： ～7%） coarse-grained （CG） counterpart. In the UFG alloy, extensive dislocation slip was an active deformation mechanism, while in the CG alloy, mechanical twinning occurred. The differences in the deformation mechanisms of UFG and CG alloys were reflected in the discrete burst in the load-displacement plots. The deformation of Mg-2Zn-2Gd alloys was significantly influenced by the grain structure, such that there was change in the deformation mechanism from dislocation slip （non-basal slip） to nanoscale twins in the CG structure. The high plasticity ofUFG Mg alloy involved high dislocation activity and change in activation volume.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 51501069, 51671093 and 51625402)Partial financial support came from the Science and Technology Development Program of Jilin Province (Nos. 20160519002JH and 20170520124JH)+1 种基金the Chang Bai Mountain Scholars Program (2013014)the talented youth lift project of Jilin province
文摘Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results onfcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo- mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.
基金financial supports from the National Key Research and Development Program of China (No. 2019YFB2006500)the National Natural Science Foundation of China (No. 51674303)+2 种基金the Huxiang High-level Talent Gathering Project of Hunan Province, China (No. 2018RS3015)the Innovation Driven Program of Central South University, China (No. 2019CX006)the Research Fund of the Key Laboratory of High Performance Complex Manufacturing at Central South University, China。
文摘Ultrafine-grained(UFG)AA1060 sheets were fabricated via five-cycle accumulative roll bonding(ARB)and subsequent three-pass cold rolling(298 K),or cryorolling(83 K and 173 K).Microstructures of the aluminum samples were examined via transmission electron microscopy,and their mechanical properties were measured via tensile and microhardness testing.Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling,and the grain size became finer with reducing rolling temperature.The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm,respectively,via subsequent cold rolling or cryorolling(83 K).Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.
基金supported by the Youth Innovation Promotion Association CAS(No.2020193)CAS Project for Young Scientists in Basic Research(No.YSBR-025)National Science and Technol-ogy Major Project(No.J2019-VI-0005-0119).
文摘The fabrication of ultrafine-grained microstructures(grain size below 1μm)in titanium alloys is beneficial for improving their mechanical properties at room temperature and medium tempera-tures(400-550°C).However,a long-standing challenge involves the low-cost manufacturing of bulk ultrafine-grained titanium alloys.In this work,we developed a facile strategy through martensite de-composition at thermal-mechanical coupling conditions,to fabricate an equiaxed microstructure in a Ti6Al4Mo4Zr1W0.2Si model alloy with an averageαgrain size of 315±62 nm.The formation of the ultrafine-grained microstructure was because the lattice strain stored in the martensitic initial mi-crostructure enhanced the nucleation rate of dynamic recrystallization,meanwhile,the pinning role of martensite decomposition productsβand(Ti,Zr)_(5)Si_(3)phases suppressed grain coarsening at high tem-peratures.Compared to conventional(α+β)alloys,the tensile strength of this alloy improved by 20%-30%at both room temperature and 550°C,without decreasing its ductility.In situ SEM observations revealed that the ultrafine-grained microstructure would not only suppress dislocation motions but also contribute to the homogenous deformation in the matrix of the material,therefore,it resulted in higher mechanical performance.The research results may be of great significance to the development of next-generation aviation titanium alloys.
基金financially supported by the National Key Research and Development Program of China(Nos.2017YFF0210002,2016YFF0203301,2016YFF0203305,2016YFC0801903)the National Natural Science Foundation of China(No.U1537212)。
文摘The influence of magnetic field(1 T)on dislocation morphology and precipitation behaviour of ultrafinegrained(UFG)Al 7075 alloy was investigated after ageing from 90 to 200℃ via wide angle X-ray scattering(WAXS),small angle X-ray scattering(SAXS),and transmission electron microscopy(TEM).Experimental results reveal that the improved precipitation kinetics of alloys in the thickness plane(denoted as sample II)as compared to those in the rolling plane(denoted as sample I),which arises due to a higher dislocation density(morphology of dislocation cells)of the thickness plane than that of the rolling plane(morphology of dislocations and dislocation tangles).Specifically,because of different dislocation morphologies,the magnetic field positively and negatively affects the dislocation activity in samples I and II,leading to enhanced and suppressed precipitation behaviors,respectively.Interestingly,nucleation of theηphase is facilitated in the UFG alloy at the critical temperature(140℃)because it affords a faster rate of atom diffusion and a higher dislocation density as compared to those exhibited by its coarse-grained alloy.This systematic and comprehensive study provides new insights into dislocation morphology and precipitation behaviour of the UFG 7075 Al alloy,while enabling the optimization of precipitation kinetics.
基金This work is financially supported by National Key R&D Pro-gram of China(no.2022YFB3700075)Natural Science Foundation of China(nos.52074032,51974029,52071013,52130407)+3 种基金Beijing Natural Science Foundation(no.2232084)Guangdong Basic and Applied Basic Research Foundation(no.2021B1515120033)Basic and Applied Basic Research Fund of Guangdong Province(no.BK20BE015)111 Project(no.B170003).
文摘Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However,the sintering concurrently becomes increasingly more difficult with increasing Re contents.Here we proposed that the sintering conundrum is caused by the lowered crystal symmetry and the wider dihedral angle distribution when body-center-cubic(BCC)W is alloyed with more hexagonal-close-packed(HCP)Re,which results in inefficient pore removal in the final stage sintering.We showed that the conundrum can be resolved by pressureless two-step sintering(TSS)which suppresses acceler-ating final-stage grain growth,and our proposal is supported by the data of the critical densityρc that is required to start the second step for successful TSS at different W-Re compositions.Dense ultrafine-grained W-Re alloys with∼300 nm average grain size and up to 25 wt%Re were successfully produced.Our work demonstrates the unique opportunities offered by two-step sintering to advance the scientific understanding and technological practices in powder metallurgy and related fields.
基金National Natural Science Foundation of China (No.51474170)Natural Science Foundation of Shaanxi Province (No.2023-JC-YB-312)Key Laboratory Project of Shaanxi Province Educational Committee (No.20JS075)。
文摘A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP).Tension–compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests.The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior.The basal and prismaticslip are suppressed either for tension or compression,which is the easiest to activate.The tension twin system{1012}<1011> easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor,consequently resulting in a lower yield strength under compression than tension.ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement.The interaction among the dislocations,grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation,while the interaction between the dislocations and grain boundaries for tension deformation.Deformation twins lead to the higher work hardening under compression than tension.
基金Department of Science and Technology,India[grant number of DST/TDT/AMT/2017/211(G)(MEE/18-19/412/DSTX/SUSH)for the financial supportFIST grant,Department of Science and Technology,India[grant number SR/FST/ET11-059/2012(G)]for funding electron microscope facility。
文摘Existence of tension–compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications.The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium–Silver–Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing.The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests.The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts.The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock–Mecking’s analysis.Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior.This was especially dominant with coarsening of grain size.Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations.The role of crystallographic texture for inducing the polarity to Tension–Compression yield asymmetry was corroborated.A critical grain size in Magnesium–Silver–Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.
文摘C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated with dislocation slip,twinning,and solute drag have not been reported yet.In this work,a C-N co-doped iHEA with nominal composition Fe_(48.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)N_(1.0)(at.%)was prepared,and the microstructures were tuned by cold-rolling and annealing treatments to improve mechanical properties.Upon cold-rolling with a strain of 1.74,the main microstructures in the iHEA are composed of nano-grains,nano-twins,HCP laminates,and high density of dislocations,leading to ultrahigh hardness of 466.7 HV and tensile strength of 1730 MPa at the expense of ductility(2.44%).Both the nanostructures and the high hardness of the iHEA can be maintained up to an annealing temperature of 600℃(462.5 HV).After annealing at 650℃ for 1 h,the UFG microstructures are obtained in the iHEA,containing re-crystallized grains with an average grain size of 0.91μm and nanoprecipitates with an average diameter of 90.8 nm.The combined strengthening and hardening effects of UFGs,nanoprecipitates,twinning,and solutes contribute to high strain hardening(n=0.81),gigapascal yield strength(984 MPa),and good duc-tility(20%).The C-N co-doping leads to a strong drag effect on dislocation slip,resulting in a nano-scale mean free path of dislocation slip λ(1.44 nm)and much small apparent activation volume V^(∗)(15.8 b^(3))of the UFG iHEA.
基金financially supported by the National Natural Science Foundation of China(No.11475118)。
文摘In this work,an ultrafine-grained high-Nb-TiAl alloy with a nominal composition of Ti-45Al-8Nb-0.2W-0.2B(at%)was prepared by cryomilling and subsequent spark plasma sintering(SPS)technique.The chemical composition,particle size,morphology and crystallite size of cryomilled powder were studied.It is found that cryomilling can effectively reduce the particle size and enhance grain refinement.The ingots sintered at 900 and 1000℃ show an equiaxed near-γmicrostructure with grain sizes<700 nm,while the sample sintered at 1100℃exhibits duplex microstructure.Especially,the one sintered at 1000℃ has excellent mechanical properties,whose compression yield strength,fracture strength,bending strength and plastic strain achieve 1310,2174,578 MPa and 16.8%,respectively.The reasons for the effect of cryomilling and the mechanical behavior of sintered ingots were discussed.It is suggested that cryomilling in combination with SPS is an effective way to synthesize high-NbTiAl alloy with ultrafine-grained structure.
文摘Cold processing of magnesium （Mg） alloys is a challenge because Mg has a hexagonal close-packed （HCP） lattice with limited slip systems, which makes it difficult to plastically deform at low temperature. To address this challenge, a combination of annealing of as-cast alloy and multi-axial forging was adopted ro obtain isotropic ultrafine-grained （UFG） structure in a lean Mg-2Zn-2Gd alloy with high strength （yield strength： ~227 MPa）-high ductility （% elongation： ～30%） combination. This combination of strength and ductility is excellent for the lean alloy, enabling an understanding of deformation processes in a formable high strength Mg-rare earth alloy. The nanoscale deformation behavior was studied via nanoindentation and electron microscopy, and the behavior was compared with its low strength （yield strength： ～46 MPa） - low ductility （% elongation： ～7%） coarse-grained （CG） counterpart. In the UFG alloy, extensive dislocation slip was an active deformation mechanism, while in the CG alloy, mechanical twinning occurred. The differences in the deformation mechanisms of UFG and CG alloys were reflected in the discrete burst in the load-displacement plots. The deformation of Mg-2Zn-2Gd alloys was significantly influenced by the grain structure, such that there was change in the deformation mechanism from dislocation slip （non-basal slip） to nanoscale twins in the CG structure. The high plasticity ofUFG Mg alloy involved high dislocation activity and change in activation volume.
