Accumulative roll-bonding （ARB） was applied to Mg-Al-Zn magnesium alloy sheets to prepare ultrafine-grain microstructure. Significant grain refinement is achieved after three cycles of ARB with average grain size of...Accumulative roll-bonding （ARB） was applied to Mg-Al-Zn magnesium alloy sheets to prepare ultrafine-grain microstructure. Significant grain refinement is achieved after three cycles of ARB with average grain size of about 1.3 μm. The microstructure is characterized by nearly uniform ultrafine equiaxed microstructure without twins. The evolution of the misorientation distribution during ARB was measured by EBSD. Grain refinement can be contributed to the grain subdivision induced by severe accumulated strain, the accumulated strain enhanced concurrent dynamic recovery and recrystallization as well as the complicated distribution of interface and shear strain during ARB.展开更多
Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angularextrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that withincreasing semi-solid isothermal treatment te...Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angularextrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that withincreasing semi-solid isothermal treatment temperature, the a phase solid grain size of processedMg-Al-Zn alloy by ECAE increases firstly due to coarsening of a phase solid grains, then decreasesdue to melting of a phase solid grains. With the increase of extrusion passes during ECAE, the aphase solid grain size in the following semi-solid isothermal treatment decreases. The a phase solidgrain size of processed Mg-Al-Zn alloy by ECAE under route B_C is the smallest, while the a phasesolid grain size of processed material by ECAE under route A is the largest. The primary mechanismof spheroid formation depends on the melting of recrystallizing boundaries and diffusion of soluteatoms in the semi-solid state.展开更多
A comparative study was carried out on the hot flow stress of AZ31,AZ61,and AZ91 magnesium alloys.Their hot working behaviors were studied through constitutive analysis based on a simple physically-based approach whic...A comparative study was carried out on the hot flow stress of AZ31,AZ61,and AZ91 magnesium alloys.Their hot working behaviors were studied through constitutive analysis based on a simple physically-based approach which accounts for the dependence of the Young's modulus and the self-diffusion coefficient of magnesium on temperature.Since the main difference between these alloys is the difference in their amount of aluminum,the differences in constitutive behavior were quantitatively characterized by relating the hot flow stress to amount of Al,which was not possible without the consideration of physically-based parameters.It was concluded that the used approach in the current work can be considered as a versatile tool in future hot working and alloy development studies.展开更多
Based on the Miedema model and Chou model, the activities of different solute components in Mg-Al-Zn, Mg-Ca-Zn and Mg-Al-Ca ternary systems were calculated. The results show that the variety of zinc content has little...Based on the Miedema model and Chou model, the activities of different solute components in Mg-Al-Zn, Mg-Ca-Zn and Mg-Al-Ca ternary systems were calculated. The results show that the variety of zinc content has little influence on the activity of Al or Ca, and the interaction of Zn and Al or Ca can be neglected when the mass fraction of Zn is lower than 2% in the AZ91 alloy containing calcium (noted as Mg-Al-Zn-Ca system). Therefore, the possible intermetallic compounds in the Mg-Al-Zn-Ca system can be predicted by directly calculating the Gibbs free energies of the reactions in Mg-Al-Ca system. The calculated Gibbs free energies in the Mg-Al-Ca system indicate that Al2Ca phase can take priority of depositing, which agrees with the experimental results in references. The consistency of calculation and experiment proves that the intermetallic compounds in the Mg-Al-Zn-Ca system can be predicted by the Miedema model and Chou model.展开更多
The effects of extrusion temperature on the microstructure and tensile properties of extruded AZ61 and AZ91 alloys are investigated by subjecting them to hot extrusion at 300 and 400℃.Although the average grain size ...The effects of extrusion temperature on the microstructure and tensile properties of extruded AZ61 and AZ91 alloys are investigated by subjecting them to hot extrusion at 300 and 400℃.Although the average grain size of the extruded AZ61 alloy slightly increases from 9.5 to 12.6μm with increasing extrusion temperature,its resultant microstructural variation is insignificant.In contrast,the average grain size of the extruded AZ91 alloy significantly increases from 5.7 to 22.5μm with increasing extrusion temperature,and the type of Mg17Al12 precipitates formed in it changes from fine dynamic precipitates with a spherical shape to coarse static precipitates with a lamellar structure.As the extrusion temperature increases,the tensile yield strength of the extruded AZ61 alloy increases from 183 to 197 MPa while that of the extruded AZ91 alloy decreases from 232 to 224 MPa.The tensile elongations of the extruded AZ61 and AZ91 alloys decrease with increasing extrusion temperature,but the degree of decrease is significant in the latter alloy.These different extrusion temperature dependences of the tensile properties of the extruded AZ61 and AZ91 alloys are discussed in terms of their microstructural characteristics,strengthening mechanisms,and crack initiation sites.展开更多
The effects of yttrium(Y)and yttrium+calcium(Y+Ca)additions on the electrochemical properties and discharge performance of the as-extruded Mg−8Al−0.5Zn−0.2Mn(AZ80)anodes for Mg−air batteries were investigated.The resu...The effects of yttrium(Y)and yttrium+calcium(Y+Ca)additions on the electrochemical properties and discharge performance of the as-extruded Mg−8Al−0.5Zn−0.2Mn(AZ80)anodes for Mg−air batteries were investigated.The results show that the addition of 0.2 wt.%Y increased the corrosion resistance and discharge activity of AZ80 anode.This was attributed to the fine and sphericalβ-Mg_17)Al_(12) phases dispersing evenly in AZ80+0.2Y alloy,which suppressed the localized corrosion and severe“chunk effect”,and facilitated the rapid activation ofα-Mg.Combinative addition of 0.2 wt.%Y and 0.15 wt.%Ca generated grain refinement and a reduction of theβ-Mg_17)Al_(12) phase,resulting in a further enhancement in discharge voltage.However,the incorporation of Ca in Mg_17)Al_(12) and Al_(2)Y compounds compromised the corrosion resistance and anodic efficiency of AZ80+0.2Y+0.15Ca anode.Consequently,AZ80+0.2Y anode exhibited excellent overall discharge performance,with the peak discharge capacity and anodic efficiency of 1525 mA·h·g^(−1) and 67%at 80 mA/cm^(2),13%and 14%higher than those of AZ80 anode,respectively.展开更多
Al,Ca,and Zn are representative commercial alloying elements for Mg alloys.To investigate the effects of these elements on the deformation and recrystallization behaviors of Mg alloys,we develop interatomic potentials...Al,Ca,and Zn are representative commercial alloying elements for Mg alloys.To investigate the effects of these elements on the deformation and recrystallization behaviors of Mg alloys,we develop interatomic potentials for the Al-Ca,Al-Zn,Mg-Al-Ca and Mg-Al-Zn systems based on the second nearest-neighbor modified embedded-atom method formalism.The developed potentials describe structural,elastic,and thermodynamic properties of compounds and solutions of associated alloy systems in reasonable agreement with experimental data and higher-level calculations.The applicability of these potentials to the present investigation is confirmed by calculating the generalized stacking fault energy for various slip systems and the segregation energy on twin boundaries of the Mg-Al-Ca and Mg-Al-Zn alloys,accompanied with the thermal expansion coefficient and crystal structure maintenance of stable compounds in those alloys.展开更多
This study investigates the effects of extrusion temperature on the dynamic recrystallization(DRX)behavior of a Mg-3Al-1Zn-0.3Mn(AZ31,wt%)alloy during hot extrusion and on the microstructural characteristics and mecha...This study investigates the effects of extrusion temperature on the dynamic recrystallization(DRX)behavior of a Mg-3Al-1Zn-0.3Mn(AZ31,wt%)alloy during hot extrusion and on the microstructural characteristics and mechanical properties of materials extruded at 350 and 450℃.An increase in the extrusion temperature causes a decrease in the amount of strain energy accumulated in the material during extrusion,because of promoted activation of pyramidal<c+a>slip and dynamic recovery.This reduced strain energy weakens the DRX behavior during extrusion,which eventually results in a decrease in the area fraction of recrystallized grains of the extruded material.The material extruded at 450℃has coarser grains and a stronger basal fiber texture than that extruded at 350℃.As the extrusion temperature increases from 350 to 450℃,the tensile yield strength(TYS)of the extruded material increases from 191.8 to 201.5 MPa,whereas its compressive yield strength(CYS)decreases from 122.5 to 111.0 MPa;consequently,its tension-compression yield stress ratio(CYS/TYS)decreases from 0.64 to 0.55.The increase in the TYS is attributed mainly to the stronger texture hardening and strain hardening effects of the extruded material,and the decrease in the CYS is attributed to the reduced twinning stress resulting from grain coarsening and texture intensification.The microstructural and textural evolutions of the materials during extrusion and the deformation and hardening mechanisms of the extruded materials are discussed in detail.展开更多
In recent years,wire-arc directed energy deposition(wa DED),which is also commonly known as wire-arc additive manufacturing(WAAM),has emerged as a promising new fabrication technique for magnesium alloys.The major rea...In recent years,wire-arc directed energy deposition(wa DED),which is also commonly known as wire-arc additive manufacturing(WAAM),has emerged as a promising new fabrication technique for magnesium alloys.The major reason for this is the possibility of producing parts with a complex geometry as well as a fine-grained microstructure.While the process has been shown to be applicable for Mg-Al-Zn alloys,there is still a lack of knowledge in terms of the influence of the WAAM process on the age-hardening response.Consequently,this study deals with the aging response of a WAAM AZ91 alloy.In order to fully understand the mechanisms during aging,first,the as-built condition was analyzed by means of high-energy X-ray diffraction(HEXRD)and scanning electron microscopy.These investigations revealed a finegrained,equiaxed microstructure with adjacent areas of alternating Al content.Subsequently,the difference between single-and double-step aging as well as conventional and direct aging was studied on the as-built WAAM AZ91 alloy for the first time.The aging response during the various heat treatments was monitored via in situ HEXRD experiments.Corroborating electron microscopy and hardness studies were conducted.The results showed that the application of a double-step aging heat treatment at 325℃with pre-aging at 250℃slightly improves the mechanical properties when compared to the single-step heat treatment at 325℃.However,the hardness decreases considerably after the pre-aging step.Thus,aging at lower temperatures is preferable within the investigated temperature range of 250-325℃.Moreover,no significant difference between the conventionally aged and directly aged samples was found.Lastly,the specimens showed enhanced precipitation kinetics during aging as compared to cast samples.This could be attributed to a higher amount of nucleation sites and the particular temperature profile of the solution heat treatment.展开更多
The effects of sulfate ion concentration,temperature and medium pH on the corrosion of Mg–Al–Zn–Mn alloy in 30%aqueous ethylene glycol solution have been investigated by electrochemical techniques such as potentiod...The effects of sulfate ion concentration,temperature and medium pH on the corrosion of Mg–Al–Zn–Mn alloy in 30%aqueous ethylene glycol solution have been investigated by electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy methods.Surface morphology of the alloy was examined before and after immersing in the corrosive media by scanning electron microscopy(SEM)and energy dispersion X-ray(EDX)analysis.Activation energy,enthalpy of activation and entropy of activation were calculated from Arrhenius equation and transition state theory equation.The obtained results indicate that,the rate of corrosion increases with the increase in sulfate ion concentration and temperature of the medium and decreases with the increase in the pH of the medium.展开更多
Shock responses of Mg-Al-Zn alloy are investigated by the molecular dynamics(MD)method.The wave propagation,plastic deformation behavior and failure mechanism along the[0001]and[1010]orientations are analyzed.For both...Shock responses of Mg-Al-Zn alloy are investigated by the molecular dynamics(MD)method.The wave propagation,plastic deformation behavior and failure mechanism along the[0001]and[1010]orientations are analyzed.For both orientations,simulation results show that the shock wave has an obvious double-wave structure(plastic-elastic)under a piston velocity of 1200 m/s.A higher Hugoniot elastic limit(HEL)is observed for[0001]-oriented shock.When the shock pressure is along the[1010]direction,the distance between plastic and elastic waves is closer,and higher dislocation density and more twins are observed.Moreover,the spall strength for[1010]-oriented shock is predicted to be higher.In addition,the wave interactions,HEL and spall strength predicted for Mg-Al-Zn alloy are compared with the experimental results and MD simulation results of Mg single crystal in the literature.It is concluded that the shock performance of Mg-Al-Zn is better than that of Mg single crystal.展开更多
In the present investigation a wrought magnesium alloy AZ31 was successfully processed by the accumulative roll-bonding （ARB） at gradient temperature up to six cycles with the lowest temperature of 250 °C. This...In the present investigation a wrought magnesium alloy AZ31 was successfully processed by the accumulative roll-bonding （ARB） at gradient temperature up to six cycles with the lowest temperature of 250 °C. This is performed through different thermomechanical processing routes （different ARB cycles at different temperatures of 350-200 °C）. The microstructures and mechanical properties were investigated. The results indicate that significant grain refinement is observed after the first two cycles at the highest ARB temperature as a result of dynamic recrystallization, which is necessary for the subsequently ARB cycles at relatively lower temperature with the aim to restrict grain growth. No significant finer grain size was observed through the fifth and sixth cycles while the microstructure homogeneity is further improved. The grain structure can be effectively refined at lower ARB processing temperature and higher cycles. The resulting material exhibited high strength and relatively high ductility at ambient temperature when ARB deformed above 250 °C. The mechanical properties of the ARB deformed materials are strongly dependent on several main factors： the amount and the homogeneity of strain achieved, grain size and microstructure homogeneity, textures developed during ARB and interface bonding quality.展开更多
AZ31 alloy sheet fabricated by rolling was processed by friction stir processing(FSP) with different passes. The effect of FSP on the microstructure and damping capacity of AZ31 alloy sheet was discussed. The fine and...AZ31 alloy sheet fabricated by rolling was processed by friction stir processing(FSP) with different passes. The effect of FSP on the microstructure and damping capacity of AZ31 alloy sheet was discussed. The fine and equiaxed grains were obtained in the stirred zone(SZ) for FSPed samples from 1 pass to 3 passes with the average grain size of 10.6, 10.4 and 13.6 μm, respectively. The damping peak P_1 was presented on the curves of temperature-dependent damping capacity for FSPed samples. The damping peak P_2 was restrained after FSP and the damping peak P_1 was a relaxation process. The FSPed samples(2-pass FSP and 3-pass FSP) obtained high damping capacity. The best damping valuesQ_0^(-1)(ε=10_(-4)) and damping values Q_H^(-1)(ε=10^(-3)) of the sample subjected to 3-pass FSP(0.0131 and 0.0496) increased by 33.7% and 157.0%, respectively.展开更多
Developing low-cost rolled Mg alloys with both high strength and ductility is desirable,while the improved strength is generally accompanied with decreased ductility.Here,by using rotated hard-plate rolling(RHPR)with ...Developing low-cost rolled Mg alloys with both high strength and ductility is desirable,while the improved strength is generally accompanied with decreased ductility.Here,by using rotated hard-plate rolling(RHPR)with a total thickness reduction of~85%,we obtained a Mg-8Al-0.5Zn-0.8Ce(wt.%,AZ80-0.8Ce)alloy with a high strength-ductility synergy,i.e.,the yield strength(YS),ultimate tensile strength(UTS)and elongation-to-failure(EF)are~308 MPa,~360 MPa and~13.8%,respectively.It reveals that the high YS is mainly originated from grain boundary strengthening(~212 MPa),followed by dislocation strengthening(~43 MPa)and precipitation hardening(~25 MPa).It is found that a relatively homogeneous fine grain structure containing a large fraction(~62%)of low angle boundaries(LABs)is achieved in the RHPRed alloy,which is benefit for the high tensile EF value.It demonstrates that LABs have important contributions to strengthening and homogenizing tensile deformation process,leading to the simultaneous high strength and high EF.Our work provides a new insight for fabrication of low-cost high performance Mg alloys with an excellent strength-ductility synergy.展开更多
Semisolid stir welding of AZ91 was investigated with focus on the joining temperature and rotational speed. An Mg-25%Zn interlayer was located between two AZ91 pieces and the system was heated up to the semisolid stat...Semisolid stir welding of AZ91 was investigated with focus on the joining temperature and rotational speed. An Mg-25%Zn interlayer was located between two AZ91 pieces and the system was heated up to the semisolid state of base metal and interlayer. The weld seam was stirred using a drill-tip at different joining temperatures and rotational speeds. Optical and scanning electron microscopes were employedto study microstructure, cavity formation, and segregation. Hardness profile and shear punch test werealso employed to rank the welds based on their quality and homogeneity. Results showed that the lowest cavity content （2.1%） withthemaximum ultimate shear strength （about 188 MPa） was obtained in weld with the joining temperatureof530℃ and the rotational speedof1600 r/min. Low quality welds and a reduction of ultimate shear strength were observed at very high orlow rotational speeds and joining temperatures. The process, in conclusion, produced close mechanical properties to those of thebase metal and homogenous quality throughout the joint, when the intermediate temperature and rotational speeds were employed.展开更多
基金Project (50801027) supported by the National Natural Science Foundation of ChinaProject(2007001) supported by the Public Foundation of Guangdong Key Laboratory for Advanced Metallic Materials Processing,South China University of Technology,China
文摘Accumulative roll-bonding （ARB） was applied to Mg-Al-Zn magnesium alloy sheets to prepare ultrafine-grain microstructure. Significant grain refinement is achieved after three cycles of ARB with average grain size of about 1.3 μm. The microstructure is characterized by nearly uniform ultrafine equiaxed microstructure without twins. The evolution of the misorientation distribution during ARB was measured by EBSD. Grain refinement can be contributed to the grain subdivision induced by severe accumulated strain, the accumulated strain enhanced concurrent dynamic recovery and recrystallization as well as the complicated distribution of interface and shear strain during ARB.
基金Projects(50475029,50605015) supported by the National Natural Science Foundation of China
文摘Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angularextrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that withincreasing semi-solid isothermal treatment temperature, the a phase solid grain size of processedMg-Al-Zn alloy by ECAE increases firstly due to coarsening of a phase solid grains, then decreasesdue to melting of a phase solid grains. With the increase of extrusion passes during ECAE, the aphase solid grain size in the following semi-solid isothermal treatment decreases. The a phase solidgrain size of processed Mg-Al-Zn alloy by ECAE under route B_C is the smallest, while the a phasesolid grain size of processed material by ECAE under route A is the largest. The primary mechanismof spheroid formation depends on the melting of recrystallizing boundaries and diffusion of soluteatoms in the semi-solid state.
文摘A comparative study was carried out on the hot flow stress of AZ31,AZ61,and AZ91 magnesium alloys.Their hot working behaviors were studied through constitutive analysis based on a simple physically-based approach which accounts for the dependence of the Young's modulus and the self-diffusion coefficient of magnesium on temperature.Since the main difference between these alloys is the difference in their amount of aluminum,the differences in constitutive behavior were quantitatively characterized by relating the hot flow stress to amount of Al,which was not possible without the consideration of physically-based parameters.It was concluded that the used approach in the current work can be considered as a versatile tool in future hot working and alloy development studies.
文摘Based on the Miedema model and Chou model, the activities of different solute components in Mg-Al-Zn, Mg-Ca-Zn and Mg-Al-Ca ternary systems were calculated. The results show that the variety of zinc content has little influence on the activity of Al or Ca, and the interaction of Zn and Al or Ca can be neglected when the mass fraction of Zn is lower than 2% in the AZ91 alloy containing calcium (noted as Mg-Al-Zn-Ca system). Therefore, the possible intermetallic compounds in the Mg-Al-Zn-Ca system can be predicted by directly calculating the Gibbs free energies of the reactions in Mg-Al-Ca system. The calculated Gibbs free energies in the Mg-Al-Ca system indicate that Al2Ca phase can take priority of depositing, which agrees with the experimental results in references. The consistency of calculation and experiment proves that the intermetallic compounds in the Mg-Al-Zn-Ca system can be predicted by the Miedema model and Chou model.
基金This research was supported by the National Research Foundation of Korea(NRF)grant(No.2019R1A2C1085272)funded by the Ministry of Science,ICT,and Future Planning(MSIP,South Korea).
文摘The effects of extrusion temperature on the microstructure and tensile properties of extruded AZ61 and AZ91 alloys are investigated by subjecting them to hot extrusion at 300 and 400℃.Although the average grain size of the extruded AZ61 alloy slightly increases from 9.5 to 12.6μm with increasing extrusion temperature,its resultant microstructural variation is insignificant.In contrast,the average grain size of the extruded AZ91 alloy significantly increases from 5.7 to 22.5μm with increasing extrusion temperature,and the type of Mg17Al12 precipitates formed in it changes from fine dynamic precipitates with a spherical shape to coarse static precipitates with a lamellar structure.As the extrusion temperature increases,the tensile yield strength of the extruded AZ61 alloy increases from 183 to 197 MPa while that of the extruded AZ91 alloy decreases from 232 to 224 MPa.The tensile elongations of the extruded AZ61 and AZ91 alloys decrease with increasing extrusion temperature,but the degree of decrease is significant in the latter alloy.These different extrusion temperature dependences of the tensile properties of the extruded AZ61 and AZ91 alloys are discussed in terms of their microstructural characteristics,strengthening mechanisms,and crack initiation sites.
基金financial supports from the Key Development Project of Sichuan Province,China (No.2017GZ0399)the National Natural Science Foundation of China (No.52061040)the Open Projects of the Key Laboratory of Advanced Technologies of Materials,Ministry of Education,Southwest Jiaotong University,China (No.KLATM202003)。
文摘The effects of yttrium(Y)and yttrium+calcium(Y+Ca)additions on the electrochemical properties and discharge performance of the as-extruded Mg−8Al−0.5Zn−0.2Mn(AZ80)anodes for Mg−air batteries were investigated.The results show that the addition of 0.2 wt.%Y increased the corrosion resistance and discharge activity of AZ80 anode.This was attributed to the fine and sphericalβ-Mg_17)Al_(12) phases dispersing evenly in AZ80+0.2Y alloy,which suppressed the localized corrosion and severe“chunk effect”,and facilitated the rapid activation ofα-Mg.Combinative addition of 0.2 wt.%Y and 0.15 wt.%Ca generated grain refinement and a reduction of theβ-Mg_17)Al_(12) phase,resulting in a further enhancement in discharge voltage.However,the incorporation of Ca in Mg_17)Al_(12) and Al_(2)Y compounds compromised the corrosion resistance and anodic efficiency of AZ80+0.2Y+0.15Ca anode.Consequently,AZ80+0.2Y anode exhibited excellent overall discharge performance,with the peak discharge capacity and anodic efficiency of 1525 mA·h·g^(−1) and 67%at 80 mA/cm^(2),13%and 14%higher than those of AZ80 anode,respectively.
文摘Al,Ca,and Zn are representative commercial alloying elements for Mg alloys.To investigate the effects of these elements on the deformation and recrystallization behaviors of Mg alloys,we develop interatomic potentials for the Al-Ca,Al-Zn,Mg-Al-Ca and Mg-Al-Zn systems based on the second nearest-neighbor modified embedded-atom method formalism.The developed potentials describe structural,elastic,and thermodynamic properties of compounds and solutions of associated alloy systems in reasonable agreement with experimental data and higher-level calculations.The applicability of these potentials to the present investigation is confirmed by calculating the generalized stacking fault energy for various slip systems and the segregation energy on twin boundaries of the Mg-Al-Ca and Mg-Al-Zn alloys,accompanied with the thermal expansion coefficient and crystal structure maintenance of stable compounds in those alloys.
基金supported by the National Research Foundation of Korea(NRF)grant(No.2019R1A2C1085272)funded by the Ministry of Science,ICT and Future Planning(MSIP,South Korea).
文摘This study investigates the effects of extrusion temperature on the dynamic recrystallization(DRX)behavior of a Mg-3Al-1Zn-0.3Mn(AZ31,wt%)alloy during hot extrusion and on the microstructural characteristics and mechanical properties of materials extruded at 350 and 450℃.An increase in the extrusion temperature causes a decrease in the amount of strain energy accumulated in the material during extrusion,because of promoted activation of pyramidal<c+a>slip and dynamic recovery.This reduced strain energy weakens the DRX behavior during extrusion,which eventually results in a decrease in the area fraction of recrystallized grains of the extruded material.The material extruded at 450℃has coarser grains and a stronger basal fiber texture than that extruded at 350℃.As the extrusion temperature increases from 350 to 450℃,the tensile yield strength(TYS)of the extruded material increases from 191.8 to 201.5 MPa,whereas its compressive yield strength(CYS)decreases from 122.5 to 111.0 MPa;consequently,its tension-compression yield stress ratio(CYS/TYS)decreases from 0.64 to 0.55.The increase in the TYS is attributed mainly to the stronger texture hardening and strain hardening effects of the extruded material,and the decrease in the CYS is attributed to the reduced twinning stress resulting from grain coarsening and texture intensification.The microstructural and textural evolutions of the materials during extrusion and the deformation and hardening mechanisms of the extruded materials are discussed in detail.
基金supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020the financial support of the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(Grant No.771146 TOUGHIT)funded within the AIT’s strategic research portfolio 2022 and by the European Commission within the framework INTERREG V-A Austria–Czech Republic in the project“ReMaP“(Interreg project no.ATCZ229)。
文摘In recent years,wire-arc directed energy deposition(wa DED),which is also commonly known as wire-arc additive manufacturing(WAAM),has emerged as a promising new fabrication technique for magnesium alloys.The major reason for this is the possibility of producing parts with a complex geometry as well as a fine-grained microstructure.While the process has been shown to be applicable for Mg-Al-Zn alloys,there is still a lack of knowledge in terms of the influence of the WAAM process on the age-hardening response.Consequently,this study deals with the aging response of a WAAM AZ91 alloy.In order to fully understand the mechanisms during aging,first,the as-built condition was analyzed by means of high-energy X-ray diffraction(HEXRD)and scanning electron microscopy.These investigations revealed a finegrained,equiaxed microstructure with adjacent areas of alternating Al content.Subsequently,the difference between single-and double-step aging as well as conventional and direct aging was studied on the as-built WAAM AZ91 alloy for the first time.The aging response during the various heat treatments was monitored via in situ HEXRD experiments.Corroborating electron microscopy and hardness studies were conducted.The results showed that the application of a double-step aging heat treatment at 325℃with pre-aging at 250℃slightly improves the mechanical properties when compared to the single-step heat treatment at 325℃.However,the hardness decreases considerably after the pre-aging step.Thus,aging at lower temperatures is preferable within the investigated temperature range of 250-325℃.Moreover,no significant difference between the conventionally aged and directly aged samples was found.Lastly,the specimens showed enhanced precipitation kinetics during aging as compared to cast samples.This could be attributed to a higher amount of nucleation sites and the particular temperature profile of the solution heat treatment.
文摘The effects of sulfate ion concentration,temperature and medium pH on the corrosion of Mg–Al–Zn–Mn alloy in 30%aqueous ethylene glycol solution have been investigated by electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy methods.Surface morphology of the alloy was examined before and after immersing in the corrosive media by scanning electron microscopy(SEM)and energy dispersion X-ray(EDX)analysis.Activation energy,enthalpy of activation and entropy of activation were calculated from Arrhenius equation and transition state theory equation.The obtained results indicate that,the rate of corrosion increases with the increase in sulfate ion concentration and temperature of the medium and decreases with the increase in the pH of the medium.
基金This research are funded by the National Natural Science Foundation of China(11402183,51604206 and 51974217)the Fundamental Research Funds for the Central Universities of China(WUT:2017IA002)National Defense Science and technology foundation strengthening program.
文摘Shock responses of Mg-Al-Zn alloy are investigated by the molecular dynamics(MD)method.The wave propagation,plastic deformation behavior and failure mechanism along the[0001]and[1010]orientations are analyzed.For both orientations,simulation results show that the shock wave has an obvious double-wave structure(plastic-elastic)under a piston velocity of 1200 m/s.A higher Hugoniot elastic limit(HEL)is observed for[0001]-oriented shock.When the shock pressure is along the[1010]direction,the distance between plastic and elastic waves is closer,and higher dislocation density and more twins are observed.Moreover,the spall strength for[1010]-oriented shock is predicted to be higher.In addition,the wave interactions,HEL and spall strength predicted for Mg-Al-Zn alloy are compared with the experimental results and MD simulation results of Mg single crystal in the literature.It is concluded that the shock performance of Mg-Al-Zn is better than that of Mg single crystal.
基金supported by the National Natural Science Foundation of China(No.50801027)Public Foundation of Guangdong Key Laboratory for Advanced Metallic Materials Processing, South China University of Technology, China(No.2007001)
文摘In the present investigation a wrought magnesium alloy AZ31 was successfully processed by the accumulative roll-bonding （ARB） at gradient temperature up to six cycles with the lowest temperature of 250 °C. This is performed through different thermomechanical processing routes （different ARB cycles at different temperatures of 350-200 °C）. The microstructures and mechanical properties were investigated. The results indicate that significant grain refinement is observed after the first two cycles at the highest ARB temperature as a result of dynamic recrystallization, which is necessary for the subsequently ARB cycles at relatively lower temperature with the aim to restrict grain growth. No significant finer grain size was observed through the fifth and sixth cycles while the microstructure homogeneity is further improved. The grain structure can be effectively refined at lower ARB processing temperature and higher cycles. The resulting material exhibited high strength and relatively high ductility at ambient temperature when ARB deformed above 250 °C. The mechanical properties of the ARB deformed materials are strongly dependent on several main factors： the amount and the homogeneity of strain achieved, grain size and microstructure homogeneity, textures developed during ARB and interface bonding quality.
基金Project(51301077)supported by the National Natural Science Foundation,ChinaProject(BK20130470)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject supported by Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘AZ31 alloy sheet fabricated by rolling was processed by friction stir processing(FSP) with different passes. The effect of FSP on the microstructure and damping capacity of AZ31 alloy sheet was discussed. The fine and equiaxed grains were obtained in the stirred zone(SZ) for FSPed samples from 1 pass to 3 passes with the average grain size of 10.6, 10.4 and 13.6 μm, respectively. The damping peak P_1 was presented on the curves of temperature-dependent damping capacity for FSPed samples. The damping peak P_2 was restrained after FSP and the damping peak P_1 was a relaxation process. The FSPed samples(2-pass FSP and 3-pass FSP) obtained high damping capacity. The best damping valuesQ_0^(-1)(ε=10_(-4)) and damping values Q_H^(-1)(ε=10^(-3)) of the sample subjected to 3-pass FSP(0.0131 and 0.0496) increased by 33.7% and 157.0%, respectively.
基金primarily supported by The Natural Science Foundation of China under Grant Nos.51922048,51871108 and 52001133the Fundamental Research Funds for the Central Universities,JLU,Program for JLU Science and Technology Innovative Research Team(JLUSTIRT,2017TD-09)The Science and Technology Development Program of Jilin Province(Nos.20200201193JC and 20210201115GX)。
文摘Developing low-cost rolled Mg alloys with both high strength and ductility is desirable,while the improved strength is generally accompanied with decreased ductility.Here,by using rotated hard-plate rolling(RHPR)with a total thickness reduction of~85%,we obtained a Mg-8Al-0.5Zn-0.8Ce(wt.%,AZ80-0.8Ce)alloy with a high strength-ductility synergy,i.e.,the yield strength(YS),ultimate tensile strength(UTS)and elongation-to-failure(EF)are~308 MPa,~360 MPa and~13.8%,respectively.It reveals that the high YS is mainly originated from grain boundary strengthening(~212 MPa),followed by dislocation strengthening(~43 MPa)and precipitation hardening(~25 MPa).It is found that a relatively homogeneous fine grain structure containing a large fraction(~62%)of low angle boundaries(LABs)is achieved in the RHPRed alloy,which is benefit for the high tensile EF value.It demonstrates that LABs have important contributions to strengthening and homogenizing tensile deformation process,leading to the simultaneous high strength and high EF.Our work provides a new insight for fabrication of low-cost high performance Mg alloys with an excellent strength-ductility synergy.
基金Innovatum (Trollhattan, Sweden) for the financial supporting the researcher in this paper
文摘Semisolid stir welding of AZ91 was investigated with focus on the joining temperature and rotational speed. An Mg-25%Zn interlayer was located between two AZ91 pieces and the system was heated up to the semisolid state of base metal and interlayer. The weld seam was stirred using a drill-tip at different joining temperatures and rotational speeds. Optical and scanning electron microscopes were employedto study microstructure, cavity formation, and segregation. Hardness profile and shear punch test werealso employed to rank the welds based on their quality and homogeneity. Results showed that the lowest cavity content （2.1%） withthemaximum ultimate shear strength （about 188 MPa） was obtained in weld with the joining temperatureof530℃ and the rotational speedof1600 r/min. Low quality welds and a reduction of ultimate shear strength were observed at very high orlow rotational speeds and joining temperatures. The process, in conclusion, produced close mechanical properties to those of thebase metal and homogenous quality throughout the joint, when the intermediate temperature and rotational speeds were employed.
