Stacking faults(SFs)and the interaction between solute atoms and SFs in a Mg–Bi alloy are investigated using aberration-corrected scanning transmission electron microscopy.It is found that abundant I_(1)SFs are gener...Stacking faults(SFs)and the interaction between solute atoms and SFs in a Mg–Bi alloy are investigated using aberration-corrected scanning transmission electron microscopy.It is found that abundant I_(1)SFs are generated after cold rolling and are mainly distributed inside{1012}twins.After aging treatment,the formation of single-layer and three-layer Bi atom segregation in the vicinity of I_(1)fault are clearly observed.Bi segregation also occurs at the 1/6<2203>bounding Frank partial dislocation cores.The segregation behaviors in I_(1)fault and Frank dislocations are discussed and rationalized using first-principles calculations.展开更多
Magnesium alloys have received considerable research interest due to their lightweight,high specific strength and excellent castability.However,their plastic deformation is more complicated compared to cubic materials...Magnesium alloys have received considerable research interest due to their lightweight,high specific strength and excellent castability.However,their plastic deformation is more complicated compared to cubic materials,primarily because their low-symmetry hexagonal closepacked(hcp) crystal structure.Deformation twinning is a crucial plastic deformation mechanism in magnesium,and twins can affect the evolution of microstructure by interacting with other lattice defects,thereby affecting the mechanical properties.This paper provides a review of the interactions between deformation twins and lattice defects,such as solute atoms,dislocations and twins,in magnesium and its alloys.This review starts with interactions between twin boundaries and substitutional solutes like yttrium,zinc,silver,as well as interstitial solutes like hydrogen and oxygen.This is followed by twin-dislocation interactions,which mainly involve those between {10■2} tension or {10■1} compression twins and , or type dislocations.The following section examines twin-twin interactions,which occur either among the six variants of the same {10■2} or {10■1} twin,or between different types of twins.The resulting structures,including twin-twin junctions or boundaries,tension-tension double twin,and compression-tension double twin,are discussed in detail.Lastly,this review highlights the remaining research issues concerning the interactions between twins and lattice defects in magnesium,and provides suggestions for future work in this area.展开更多
This paper presents a re-evaluation of the room temperature mechanical properties and high temperature creep resistance of magnesium die-casting alloy AE44(Mg-4Al-4RE)in light of the influence of minor Mn addition.It ...This paper presents a re-evaluation of the room temperature mechanical properties and high temperature creep resistance of magnesium die-casting alloy AE44(Mg-4Al-4RE)in light of the influence of minor Mn addition.It is shown that the Mn-containing AE44 exhibits distinct age hardening response upon direct ageing(T5)due to the precipitation of nanoscale Al-Mn particles,as reported previously in a similar alloy.The T5 ageing leads to a significant improvement in strength with similar ductility.Consequently,the T5-aged AE44 has a remarkably better strength-ductility combination than most Mg die-casting alloys and even the Al die-casting alloy A380.Minor Mn addition is also shown to be critical for the creep resistance of AE44 whereas the influence of the RE constituent is not as significant as previously thought,which reaffirms that precipitation hardening of theα-Mg matrix is more important than grain boundary reinforcement by intermetallic phases for the creep resistance of die-cast Mg alloys.The findings in this work could provide new application perspectives for AE44,particularly in the automotive industry.展开更多
Selection of appropriate thermomechanical processing parameters is crucial for control of the crystallographic texture and grain size distribution in wrought magnesium alloys, which in turn dictate their mechanical pr...Selection of appropriate thermomechanical processing parameters is crucial for control of the crystallographic texture and grain size distribution in wrought magnesium alloys, which in turn dictate their mechanical properties. In this work, the recrystallization behavior of binary Mg-Zn alloys are examined after warm rolling as a function of alloy content and heat treatment temperature. The Avrami exponent increased with increasing heat treatment temperature up to the Mg Zn solvus, while the strength of the recrystallization texture decreased.Neither the Avrami exponent nor the qualitative trends in texture evolution were sensitive to the Zn alloying content in the examined range.EBSD and transmission electron microscopy observations revealed that the changes in texture and recrystallization kinetics could be attributed to differences in the nucleation behavior of basal and off-basal orientations.展开更多
The major interface betweenβ-Mg_(3)Sn precipitate plate and theα-Mg matrix in a Mg-9.8wt.%alloy has been investigated using aberrationcorrected scanning transmission electron microscopy and first-principles calculat...The major interface betweenβ-Mg_(3)Sn precipitate plate and theα-Mg matrix in a Mg-9.8wt.%alloy has been investigated using aberrationcorrected scanning transmission electron microscopy and first-principles calculations.It is found that Sn atoms orderly distribute in the single layer of theα-Mg matrix immediately adjacent to the broad surface ofβat the early stage of ageing.These Sn atoms substitute Mg atoms located at the centers of equilateral triangles constituted by three Mg columns in the outmost layer ofβ.First-principles calculations suggest that the ordered Sn distribution is energetically favored and it not only decreases the interfacial energy of theβ-matrix interface but also hinders the occurrence of 1/3<01■0>αshear that thickens theβplate.展开更多
Precipitation-hardenable commercial Mg alloy QE22(Mg-2.5Ag-2.ONd-0.7Zr,wt.%)has excellent mechan-ical properties,but precipitates in this alloy have not been well understood.In this work,precipitate phasesγ",γ,...Precipitation-hardenable commercial Mg alloy QE22(Mg-2.5Ag-2.ONd-0.7Zr,wt.%)has excellent mechan-ical properties,but precipitates in this alloy have not been well understood.In this work,precipitate phasesγ",γ,andδformed during the isothermal ageing process at 150,200,250,and 300℃have been characterized using atomic-resolution high-angle annular dark-field scanning transmission electron mi-croscopy and atomic-scale energy-dispersive X-ray spectroscopy.The morphology,crystal structure,and orientation relationship of these precipitate phases have been determined.Domain boundaries usually exist in a singleγparticle,which can be characterized by a separation vector of[1(1)01]_(α).Theδphase forms in situ from its precursorγphase,consequently leading to the formation of three different variants within a single 8 particle.The nucleation of theδphase is strongly related to the domain boundaries of the y phase.The formation of theγphase may be promoted by its precursorγ"phase.The similarities in atomic structures of theγ",γ,andδphases are described and discussed,indicating that transfor-mations between these precipitate phases can be accomplished through the diffusion of added alloying elements.展开更多
Interactions of solute atoms in biodegradable zinc alloys and their effect on alloy mechanical properties have been less investigated.In this work,the interactions between the common solutes(Li,Mg,Mn,Cu,and Ag)used in...Interactions of solute atoms in biodegradable zinc alloys and their effect on alloy mechanical properties have been less investigated.In this work,the interactions between the common solutes(Li,Mg,Mn,Cu,and Ag)used in the biodegradable Zn alloys,including a solute-solute pair with the same element or with two different elements,are investigated based on first-principles calculations.It is found that the energetically favorable configuration is the third nearest-neighboring for most solute-solute pairs in the bulk lattice because of the relatively strong electronic interaction between solute and Zn atoms or the relatively small local elastic deformation associated with the configuration.Considering that interfacial cleavage is a key fracture mode of zinc,the segregation ability of these solutes and their effect on the{1012}twin boundary cohesion are also examined.The result shows that Li tends to fully occupy its preferred site in the twin boundary,while Mg,Mn,Cu,or Ag has a concentration limitation in the twin boundary.The twin boundary cohesion can be significantly enhanced by the segregation of Mn,followed by Cu and Ag,because of the contribution of their d states close to the Fermi level.Furthermore,the co-segregation ability of two solute atoms in the twin boundary increases with increasing the binding tendency of these two solute atoms in the boundary.Mn and Li or Mg show a relatively strong co-segregation ability in the twin boundary.Adding Mn to Zn-Li or Zn-Mg alloys can significantly enhance the resistance to fracture of twin boundaries.展开更多
Stress corrosion cracking(SCC)may lead to brittle,unexpected failure of medical devices.However,available researches are limited to Mg-based biodegradable metals(BM)and pure Zn.The stress corrosion behaviors of newly-...Stress corrosion cracking(SCC)may lead to brittle,unexpected failure of medical devices.However,available researches are limited to Mg-based biodegradable metals(BM)and pure Zn.The stress corrosion behaviors of newly-developed Zn alloys remain unclear.In the present work,we conducted slow strain rate testing(SSRT)and constant-load immersion test on a promising Zn-0.8 wt%Li alloy in order to investigate its SCC susceptibility and examine its feasibility as BM with pure Zn as control group.We observed that Zn-0.8 wt%Li alloy exhibited low SCC susceptibility.This was attributed to variations in microstructure and deformation mechanism after alloying with Li.In addition,both pure Zn and Zn-0.8 wt%Li alloy did not fracture over a period of 28 days during constant-load immersion test.The magnitude of applied stress was close to physiological condition and thus,we proved the feasibility of both materials as BM.展开更多
Mg-9Al-6Sn-3Zn （wt%） alloy was extruded and heat treated in T5 and T6 conditions, and its mechanical properties and microstructures were investigated. The extruded product can be slightly strengthened by the T5 trea...Mg-9Al-6Sn-3Zn （wt%） alloy was extruded and heat treated in T5 and T6 conditions, and its mechanical properties and microstructures were investigated. The extruded product can be slightly strengthened by the T5 treatment as a result of sparse and heterogeneous precipitation. Significant increase in strength is achieved by the T6 treatment, and this is mostly attributed to the formation of lamellar discontinuous Mg17Al12 precipitates. The segregation of Al and Zn at grain boundaries is responsible for the discontinuous Mg17Al12 nucleation. The T6-treated alloy exhibits a tensile yield strength of 341 MPa and an ultimate tensile strength of 409 MPa, together with an elongation to fracture of 4%.展开更多
Magnesium alloys, while boasting light weight, suffer from a major drawback in their relatively low strength. Identifying the microstructural features that are most effective in strengthening is therefore a pressing c...Magnesium alloys, while boasting light weight, suffer from a major drawback in their relatively low strength. Identifying the microstructural features that are most effective in strengthening is therefore a pressing challenge. Deformation twinning often mediates plastic yielding in magnesium alloys. Unfortunately, due to the complexity involved in the twinning mechanism and twin-precipitate interactions, the optimal precipitate morphology that can best impede twinning has yet to be singled out. Based on the understanding of twinning mechanism in magnesium alloys, here we propose that the lamellar precipitates or the network of plate-shaped precipitates are most effective in suppressing deformation twinning. This has been verified through quantitative in situ tests inside a transmission electron microscope on a series of magnesium alloys containing precipitates with different morphology. The insight gained is expected to have general implications for strengthening strategies and alloy design. 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.展开更多
Aberration-corrected scanning transmission electron microscopy has been used to study a novel metastable phase,designated asβ’’phase,induced to form by electron beam irradiation in a Mg-9.8 wt.%Sn alloy.This phase ...Aberration-corrected scanning transmission electron microscopy has been used to study a novel metastable phase,designated asβ’’phase,induced to form by electron beam irradiation in a Mg-9.8 wt.%Sn alloy.This phase is spherical in three dimensions,having a D019 structure with the lattice parameters of a=0.642 nm,c=0.521 nm and space group of P63/mmc.Its chemical formula is Mg_(3)Sn,like theβ’metastable precipitate phase.The orientation relationship between theβ’’phase and theα-Mg matrix is such that■_(β)’’//■_(α)and(0001)_(β)’’//(0001)_(α).Its formation involves solely the ordering of Sn atoms in the solid solution magnesium matrix.First-principles calculations indicate that the formation of theβ’’phase is energetically favored.展开更多
Successive gliding of twinning disconnections(TDs)creates three-dimensional twins in parent crystal and accommodates shear deformation.It is generally recognized that TD is subject to the same Peierls stress as it gli...Successive gliding of twinning disconnections(TDs)creates three-dimensional twins in parent crystal and accommodates shear deformation.It is generally recognized that TD is subject to the same Peierls stress as it glides forward or backward because of its dislocation character and the twofold rotation symmetry of the twin plane.Based on atomistic simulations,we demonstrate that the glide of TDs may be subject to a symmetric or asymmetric resistance corresponding to step character,symmetric resistance for A/A type steps but asymmetric resistance for A/B type steps,where A and B represent crystallographic planes in twin and matrix.Furthermore,we experimentally demonstrate that the asymmetric resistance results in asymmetric propagation and growth of twins in Mg alloys.展开更多
基金support by the National Natural Science Foundation of China(52071033)Open Foundation of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body(32115016).
文摘Stacking faults(SFs)and the interaction between solute atoms and SFs in a Mg–Bi alloy are investigated using aberration-corrected scanning transmission electron microscopy.It is found that abundant I_(1)SFs are generated after cold rolling and are mainly distributed inside{1012}twins.After aging treatment,the formation of single-layer and three-layer Bi atom segregation in the vicinity of I_(1)fault are clearly observed.Bi segregation also occurs at the 1/6<2203>bounding Frank partial dislocation cores.The segregation behaviors in I_(1)fault and Frank dislocations are discussed and rationalized using first-principles calculations.
基金support from the Australian Research Council (DP200102985 and DP180100048)supported by computational resources provided by the Australian Government through National Computational Infrastructure (Raijin) and Pawsey supercomputing centre (Magnus) under the National Computational Merit Allocation Scheme (NCMAS)。
文摘Magnesium alloys have received considerable research interest due to their lightweight,high specific strength and excellent castability.However,their plastic deformation is more complicated compared to cubic materials,primarily because their low-symmetry hexagonal closepacked(hcp) crystal structure.Deformation twinning is a crucial plastic deformation mechanism in magnesium,and twins can affect the evolution of microstructure by interacting with other lattice defects,thereby affecting the mechanical properties.This paper provides a review of the interactions between deformation twins and lattice defects,such as solute atoms,dislocations and twins,in magnesium and its alloys.This review starts with interactions between twin boundaries and substitutional solutes like yttrium,zinc,silver,as well as interstitial solutes like hydrogen and oxygen.This is followed by twin-dislocation interactions,which mainly involve those between {10■2} tension or {10■1} compression twins and , or type dislocations.The following section examines twin-twin interactions,which occur either among the six variants of the same {10■2} or {10■1} twin,or between different types of twins.The resulting structures,including twin-twin junctions or boundaries,tension-tension double twin,and compression-tension double twin,are discussed in detail.Lastly,this review highlights the remaining research issues concerning the interactions between twins and lattice defects in magnesium,and provides suggestions for future work in this area.
基金supported by Australian Research Council(LP160100690)Magontec Ltd.Monash Centre for Electron Microscopy(MCEM)。
文摘This paper presents a re-evaluation of the room temperature mechanical properties and high temperature creep resistance of magnesium die-casting alloy AE44(Mg-4Al-4RE)in light of the influence of minor Mn addition.It is shown that the Mn-containing AE44 exhibits distinct age hardening response upon direct ageing(T5)due to the precipitation of nanoscale Al-Mn particles,as reported previously in a similar alloy.The T5 ageing leads to a significant improvement in strength with similar ductility.Consequently,the T5-aged AE44 has a remarkably better strength-ductility combination than most Mg die-casting alloys and even the Al die-casting alloy A380.Minor Mn addition is also shown to be critical for the creep resistance of AE44 whereas the influence of the RE constituent is not as significant as previously thought,which reaffirms that precipitation hardening of theα-Mg matrix is more important than grain boundary reinforcement by intermetallic phases for the creep resistance of die-cast Mg alloys.The findings in this work could provide new application perspectives for AE44,particularly in the automotive industry.
基金the University of California Santa Barbara for the support of a Regents’ Special Fellowshipthe support of Office of Naval Research Grant number N00014-17-1-2810+3 种基金supported by the MRSEC Program of the NSF under Award No. DMR 1121053a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org)partially supported by the IMI Program of the National Science Foundation under Award No. DMR 08-43934the support of the Australian Research Council。
文摘Selection of appropriate thermomechanical processing parameters is crucial for control of the crystallographic texture and grain size distribution in wrought magnesium alloys, which in turn dictate their mechanical properties. In this work, the recrystallization behavior of binary Mg-Zn alloys are examined after warm rolling as a function of alloy content and heat treatment temperature. The Avrami exponent increased with increasing heat treatment temperature up to the Mg Zn solvus, while the strength of the recrystallization texture decreased.Neither the Avrami exponent nor the qualitative trends in texture evolution were sensitive to the Zn alloying content in the examined range.EBSD and transmission electron microscopy observations revealed that the changes in texture and recrystallization kinetics could be attributed to differences in the nucleation behavior of basal and off-basal orientations.
基金financially National Natural Science Foundation of China(52101167 and 52071033)Natural Science Foundation Project of CQ(cstc2020jcyjmsxm X0832)+3 种基金the Fundamental Research Funds for the Central Universities(2020CDJ-LHZZ-085)State Key Laboratory of Powder Metallurgy,Central South University,Changsha,Chinasupported in part by the High Performance Computing center of the Central South UniversityJFN acknowledges the support from the Australian Research Council and computational resources provided by the Australian Government through Pawsey under the National Computational Merit Allocation Scheme and the use of the National Computational Infrastructure。
文摘The major interface betweenβ-Mg_(3)Sn precipitate plate and theα-Mg matrix in a Mg-9.8wt.%alloy has been investigated using aberrationcorrected scanning transmission electron microscopy and first-principles calculations.It is found that Sn atoms orderly distribute in the single layer of theα-Mg matrix immediately adjacent to the broad surface ofβat the early stage of ageing.These Sn atoms substitute Mg atoms located at the centers of equilateral triangles constituted by three Mg columns in the outmost layer ofβ.First-principles calculations suggest that the ordered Sn distribution is energetically favored and it not only decreases the interfacial energy of theβ-matrix interface but also hinders the occurrence of 1/3<01■0>αshear that thickens theβplate.
基金HWC acknowledges the support from the National Key Research and Development Program of China(No.2021YFB03702101)National Natural Science Foundation of China(Nos.52071033,52101150)+3 种基金Sichuan Science and Technology Program(No.2022YFG0287)Fundamental Research Funds for the Central Universities(No.2682021CX114)Project on Function Development of Large-scale Instruments of Chongqing University(No.gnkf2022017)JFN acknowledges the financial support from the Australian Research Council.
文摘Precipitation-hardenable commercial Mg alloy QE22(Mg-2.5Ag-2.ONd-0.7Zr,wt.%)has excellent mechan-ical properties,but precipitates in this alloy have not been well understood.In this work,precipitate phasesγ",γ,andδformed during the isothermal ageing process at 150,200,250,and 300℃have been characterized using atomic-resolution high-angle annular dark-field scanning transmission electron mi-croscopy and atomic-scale energy-dispersive X-ray spectroscopy.The morphology,crystal structure,and orientation relationship of these precipitate phases have been determined.Domain boundaries usually exist in a singleγparticle,which can be characterized by a separation vector of[1(1)01]_(α).Theδphase forms in situ from its precursorγphase,consequently leading to the formation of three different variants within a single 8 particle.The nucleation of theδphase is strongly related to the domain boundaries of the y phase.The formation of theγphase may be promoted by its precursorγ"phase.The similarities in atomic structures of theγ",γ,andδphases are described and discussed,indicating that transfor-mations between these precipitate phases can be accomplished through the diffusion of added alloying elements.
基金The authors acknowledge the financial support from the Australian Research Council(No.DP190102373)This work was supported by computational resources provided by the Australian Gov-ernment through National Computational Infrastructure(Raijin)and Pawsey supercomputing centre(Magnus)under the National Computational Merit Allocation Scheme(NCMAS).
文摘Interactions of solute atoms in biodegradable zinc alloys and their effect on alloy mechanical properties have been less investigated.In this work,the interactions between the common solutes(Li,Mg,Mn,Cu,and Ag)used in the biodegradable Zn alloys,including a solute-solute pair with the same element or with two different elements,are investigated based on first-principles calculations.It is found that the energetically favorable configuration is the third nearest-neighboring for most solute-solute pairs in the bulk lattice because of the relatively strong electronic interaction between solute and Zn atoms or the relatively small local elastic deformation associated with the configuration.Considering that interfacial cleavage is a key fracture mode of zinc,the segregation ability of these solutes and their effect on the{1012}twin boundary cohesion are also examined.The result shows that Li tends to fully occupy its preferred site in the twin boundary,while Mg,Mn,Cu,or Ag has a concentration limitation in the twin boundary.The twin boundary cohesion can be significantly enhanced by the segregation of Mn,followed by Cu and Ag,because of the contribution of their d states close to the Fermi level.Furthermore,the co-segregation ability of two solute atoms in the twin boundary increases with increasing the binding tendency of these two solute atoms in the boundary.Mn and Li or Mg show a relatively strong co-segregation ability in the twin boundary.Adding Mn to Zn-Li or Zn-Mg alloys can significantly enhance the resistance to fracture of twin boundaries.
基金supported by National Natural Science Foundation of China(Grant No.51931001).
文摘Stress corrosion cracking(SCC)may lead to brittle,unexpected failure of medical devices.However,available researches are limited to Mg-based biodegradable metals(BM)and pure Zn.The stress corrosion behaviors of newly-developed Zn alloys remain unclear.In the present work,we conducted slow strain rate testing(SSRT)and constant-load immersion test on a promising Zn-0.8 wt%Li alloy in order to investigate its SCC susceptibility and examine its feasibility as BM with pure Zn as control group.We observed that Zn-0.8 wt%Li alloy exhibited low SCC susceptibility.This was attributed to variations in microstructure and deformation mechanism after alloying with Li.In addition,both pure Zn and Zn-0.8 wt%Li alloy did not fracture over a period of 28 days during constant-load immersion test.The magnitude of applied stress was close to physiological condition and thus,we proved the feasibility of both materials as BM.
文摘Mg-9Al-6Sn-3Zn （wt%） alloy was extruded and heat treated in T5 and T6 conditions, and its mechanical properties and microstructures were investigated. The extruded product can be slightly strengthened by the T5 treatment as a result of sparse and heterogeneous precipitation. Significant increase in strength is achieved by the T6 treatment, and this is mostly attributed to the formation of lamellar discontinuous Mg17Al12 precipitates. The segregation of Al and Zn at grain boundaries is responsible for the discontinuous Mg17Al12 nucleation. The T6-treated alloy exhibits a tensile yield strength of 341 MPa and an ultimate tensile strength of 409 MPa, together with an elongation to fracture of 4%.
基金supports by the National Key Research and Development Program of China (Nos. 2017YFB0702001)National Natural Science Foundation of China (Nos. 51601141, 51231005 and 51621063)+1 种基金the Science and Technology Department of Shaanxi Province (Nos. 2016KTZDGY04-03 and 2016KTZDGY-04-04)support from the China Postdoctoral Science Foundation (2016M600788)
文摘Magnesium alloys, while boasting light weight, suffer from a major drawback in their relatively low strength. Identifying the microstructural features that are most effective in strengthening is therefore a pressing challenge. Deformation twinning often mediates plastic yielding in magnesium alloys. Unfortunately, due to the complexity involved in the twinning mechanism and twin-precipitate interactions, the optimal precipitate morphology that can best impede twinning has yet to be singled out. Based on the understanding of twinning mechanism in magnesium alloys, here we propose that the lamellar precipitates or the network of plate-shaped precipitates are most effective in suppressing deformation twinning. This has been verified through quantitative in situ tests inside a transmission electron microscope on a series of magnesium alloys containing precipitates with different morphology. The insight gained is expected to have general implications for strengthening strategies and alloy design. 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.
基金financially supported by National Natural Science Foundation of China(51771036 and 51421001)。
文摘Aberration-corrected scanning transmission electron microscopy has been used to study a novel metastable phase,designated asβ’’phase,induced to form by electron beam irradiation in a Mg-9.8 wt.%Sn alloy.This phase is spherical in three dimensions,having a D019 structure with the lattice parameters of a=0.642 nm,c=0.521 nm and space group of P63/mmc.Its chemical formula is Mg_(3)Sn,like theβ’metastable precipitate phase.The orientation relationship between theβ’’phase and theα-Mg matrix is such that■_(β)’’//■_(α)and(0001)_(β)’’//(0001)_(α).Its formation involves solely the ordering of Sn atoms in the solid solution magnesium matrix.First-principles calculations indicate that the formation of theβ’’phase is energetically favored.
文摘Successive gliding of twinning disconnections(TDs)creates three-dimensional twins in parent crystal and accommodates shear deformation.It is generally recognized that TD is subject to the same Peierls stress as it glides forward or backward because of its dislocation character and the twofold rotation symmetry of the twin plane.Based on atomistic simulations,we demonstrate that the glide of TDs may be subject to a symmetric or asymmetric resistance corresponding to step character,symmetric resistance for A/A type steps but asymmetric resistance for A/B type steps,where A and B represent crystallographic planes in twin and matrix.Furthermore,we experimentally demonstrate that the asymmetric resistance results in asymmetric propagation and growth of twins in Mg alloys.
