An extruded Mg-4Zn-0.2Mn-0.2Ca alloy was developed as potential biodegradable bone-plate due to its excellent biocompatibility.Long term in vitro immersion in Hank’s solution and bending test were used to evaluate th...An extruded Mg-4Zn-0.2Mn-0.2Ca alloy was developed as potential biodegradable bone-plate due to its excellent biocompatibility.Long term in vitro immersion in Hank’s solution and bending test were used to evaluate the degradability and the mechanical integrity of the alloy.The results revealed that the degradation rate of the bone-plate increased in the first 7 days and then decreased with the prolonged immersion time before it finally reached a steady stage(about 0.84 mm/a)after immersion for 90 days.The bending strength after immersion for 60 days was 67.6 MPa,indicating that the bone-plate could support certain mechanical load after long term degradation.The formation of corrosion pits after degradation stemmed from the separation of the continuously distributed second phases from Mg matrix under the action of micro-galvanic couples.As a result,the mechanical performance of Mg-4Zn-0.2Mn-0.2Ca alloy was aggravated owing to the corrosion holes on its surface.展开更多
The hot deformation behaviors of as-solution Mg?xZn?yEr alloys (x/y=6, x=3.0, 4.5 and 6.0; y=0.50, 0.75 and 1.00) wereinvestigated on Gleeble?1500 thermal simulator in a temperature range of 200?450 °C at a strai...The hot deformation behaviors of as-solution Mg?xZn?yEr alloys (x/y=6, x=3.0, 4.5 and 6.0; y=0.50, 0.75 and 1.00) wereinvestigated on Gleeble?1500 thermal simulator in a temperature range of 200?450 °C at a strain rate of 0.001?1 s?1. The truestress?strain curves showed the dynamic competition between the working hardening and working softening mainly due to thedynamic recrystallization (DRX) occurring during hot compression. The constitutive equations were constructed which couldaccurately predict the peak stress of the alloys. The addition of Zn and/or Er resulted in higher deformation activation energy forMg?3Zn?0.5Er (alloy A). The processing maps were constructed as function of the temperature and the strain rate, providing theoptimum hot working conditions (i.e., at strain of 0.3, Mg?3Zn?0.5Er (alloy A): 380?430 ?C, <0.1 s?1; Mg?4.5Zn?0.75Er (alloy B):380?450 ?C, 0.01?0.1 s?1; Mg?6Zn?1Er (alloy C): 390?440 ?C, 0.01?0.1 s?1). The as-solution treated Mg?4.5Zn?0.75Er (alloy B)demonstrated more optimum hot working window comparing with Mg?3Zn?0.5Er (alloy A) and Mg?6Zn?1Er (alloy C).展开更多
The microstructure evolution and strengthening mechanisms of Mg-10Gd-1Er-1Zn-0.6Zr(wt.%) alloy were focused in the view of the size parameters and volume fraction(fp) of dual phases(long period stacking ordered(LPSO) ...The microstructure evolution and strengthening mechanisms of Mg-10Gd-1Er-1Zn-0.6Zr(wt.%) alloy were focused in the view of the size parameters and volume fraction(fp) of dual phases(long period stacking ordered(LPSO) structures and β’ precipitates).Results show that two types of LPSO phases with different morphologies formed,and the morphology and size of both LPSO phases varied with the solution conditions.However,the volume fraction decreased monotonously with increasing solution temperature,which in turn raised the volume fraction of β’ phase during aging.The alloy exhibited an ultimate tensile strength of 352 MPa,a yield strength of 271 MPa,and an elongation of 3.5% after solution treatment at 500℃ for 12 h and aging at 200℃ for 114 h.In contrast to the LPSO phase,the β’ phase seems to play a more important role in enhancing the yield strength,and consequently,a decreased fLPSO/fβ’,ratio results in an increased yield strength.展开更多
The effects of kinds of secondary phases on texture and mechanical properties of Mg-Zn-Er alloys were investigated. The results suggest that the I-phase has a great effect on modification of the texture via the discon...The effects of kinds of secondary phases on texture and mechanical properties of Mg-Zn-Er alloys were investigated. The results suggest that the I-phase has a great effect on modification of the texture via the discontinuous dynamic recrystallization mechanism（DDRX）, which tends to form well-developed equiaxed recrystallized grains. Meanwhile, the W-phase plays an important role in refining the grain size via continuous dynamic recrystallization（CDRX）, companied with a higher maximum texture intensity. Thus, the Mg-6Zn-1 Er alloy containing I-phase shows a performance of higher elongation of 20.4%. The Mg-2Zn-2Er alloy including W-phase displays a better tensile strength, and the yield strength（YS） is about 247 MPa.展开更多
The microstructure and texture evolutions in Mg-Zn-Er alloy during hot compression were investigated by using opticalmicroscope （OM）, field emission scanning electron microscope （EBSD） and transmission electron mi...The microstructure and texture evolutions in Mg-Zn-Er alloy during hot compression were investigated by using opticalmicroscope （OM）, field emission scanning electron microscope （EBSD） and transmission electron microscope （TEM）. The resultsindicate that the temperature plays an important role in dynamic recrystallization （DRX） mechanism. The twin dynamicrecrystallization （TDRX） is induced at a strain of 0.6 because of the activation of non-basal slip （a＋c ） dislocations at 200 ℃.Meanwhile, the continuous DRX （CDRX） occurs at 350℃, which is identified by the typical necklace-like structure around theresidual initial grains. The DRX contributes to the modification of texture significantly. The tension twins are responsible for theweak texture at 200 ℃. Meanwhile, the decrease in the basal texture is ascribed to the DRX sites which transfer from twinboundaries to initial grain boundaries as the temperature is increased from 200 to 350 ℃.展开更多
The corrosion behaviors and mechanism of the as-rolled Mg-x Zn-0.5Er(x=0.5, 2.0, 3.0 and 4.0, in wt.%)alloys were investigated. The potential difference between the second phase and matrix was determined by the type a...The corrosion behaviors and mechanism of the as-rolled Mg-x Zn-0.5Er(x=0.5, 2.0, 3.0 and 4.0, in wt.%)alloys were investigated. The potential difference between the second phase and matrix was determined by the type and size of the second phases. The dominated nano-scale W-phase on matrix in the Mg-0.5Zn-0.5Er alloy induced a sharp local pitting corrosion. However, as the volume fraction of the coarse W-phase or I-phase increased, the corrosion reaction was inclined to happen around the coarse W-phase or I-phase preferentially, leading to an obvious uniform corrosion and great acceleration of corrosion rate. The long-term immersion(14 d) results indicated that the corrosion resistance decreasing sequence was Mg-0.5Zn-0.5Er > Mg-2.0Zn-0.5Er > Mg-3.0Zn-0.5Er > Mg-4.0Zn-0.5Er.展开更多
The Mg–12Gd–1Er–1Zn–0.9 Zr(wt%)alloy with ultra-high strength and ductility was developed via hot extrusion combined with pre-deformation and two-stage aging treatment.The age-hardening behavior and microstructure...The Mg–12Gd–1Er–1Zn–0.9 Zr(wt%)alloy with ultra-high strength and ductility was developed via hot extrusion combined with pre-deformation and two-stage aging treatment.The age-hardening behavior and microstructure evolution were investigated.Pre-deformation introduced a large number of dislocations,resulting in strain hardening and higher precipitation strengthening in the subsequent two-stage aging.As a result,the alloy showed a superior strength–ductility balance with a yield strength of 506 MPa,an ultimate tensile strength of 549 MPa and an elongation of 8.2%at room temperature.The finer and denserβ’precipitates significantly enhanced the strength,and the bimodal structure,smallβ-Mg5RE phase as well as denseγ’precipitates ensured the good ductility of the alloy.It is suggested that the combination of pre-deformation and two-stage aging treatment is an eff ective method to further improve the mechanical properties of wrought Mg alloys.展开更多
The magnesium alloy has a unique advantage in 3C fields due to its high specific strength and excellent electromagnetic shielding characteristic.However,it is difficult to deform homogeneously because of hexagonal clo...The magnesium alloy has a unique advantage in 3C fields due to its high specific strength and excellent electromagnetic shielding characteristic.However,it is difficult to deform homogeneously because of hexagonal close-packed structure.In the present work,the microstructure,mechanical properties and stretch formability of magnesium alloy sheets with different alloying elements were investigated.It was indicated that a trace addition of Zn or/and Er made a key role in modifying texture,activating shear bands formation and precipitating nanoscale second phases,respectively,which resulted in an obvious improvement in both stretch formability and mechanical properties.The results suggested that the Mg-0.5 Zn-0.5 Er alloy sheet exhibited higher tensile strength along the rolling direction,i.e.,yield strength of 180 MPa and ultimate tensile strength of 201 MPa,accompanying with superior Erichsen value of 7.0 mm at room temperature.The good performances of the sheet were ascribed to weakening basal texture intensity,formation of shear bands and precipitation of nanoscale W-phase(Mg_(3)Zn_(3)Er_(2)).展开更多
The particles of Mg-Zn-Gd icosahedral quasicrystal master alloy were added into the AZ31 alloy by the repeated plastic working(RPW)process in order to improve the mechanical properties of the AZ31 alloy at room temper...The particles of Mg-Zn-Gd icosahedral quasicrystal master alloy were added into the AZ31 alloy by the repeated plastic working(RPW)process in order to improve the mechanical properties of the AZ31 alloy at room temperature.The microstructure and tensile properties of composites were investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and tensile testing machine at room temperature.The results suggest that the RPW process can effectively refine the matrix and make the I-phase particles distribute uniformly.The ultimate tensile strength and the yield strength of the composites reach their maximum values of 362.3 and 330.5 MPa,respectively,when the amount of I-phase particles added is10 %.Meanwhile,the elongation of the composites decreases sharply.展开更多
The present study aims to improve electrochemical properties of the La-Mg-Ni-based hydrogen storage alloys through partial substitution for La by mischmetal（MM）.The La_（0.8-x）MM_xMg_（0.2）Ni_（3.1）Co_（0.3）Al_...The present study aims to improve electrochemical properties of the La-Mg-Ni-based hydrogen storage alloys through partial substitution for La by mischmetal（MM）.The La_（0.8-x）MM_xMg_（0.2）Ni_（3.1）Co_（0.3）Al_（0.1）（x=0,0.1,0.2,0.3）alloys were prepared by inductive melting,and their phase structures and electrochemical properties were studied by X-ray diffraction（XRD）,scanning electron microscope（SEM）,energy-dispersive X-ray spectrometry（EDX）and electrochemical tests.Results show that the alloys mainly consist of La_2Ni_7-type phase,La_5Ni_（19）-type phase,LaNi_5-type phase and LaNi_3-type phase.The addition of MM does not change the phase compositions,while it leads to more uniform phase distribution and obviously promotes the formation of La_2Ni_7-type phase which possesses favorable electrochemical properties.Electrochemical studies indicate that the substitution for La by MM could effectively improve the high rate dischargeability（HRD）of the alloy electrode,and the optimal value of HRD_（1500）（HRD at 1500 mA·g^（-1））increases from 40.63%（x=0）to 60.55%（x=0.3）.Although the activation properties of the alloy electrodes keep almost unchanged,both the maximum discharge capacity（C_（max））and the cycling stability are significantly improved by MM addition.展开更多
The effects of homogenization and isothermal aging treatment on the mechanical properties of Mg-12Gd- 2Er-1Zn-0.6Zr （wt%） alloy were investigated. The precipitated long-period stacking order （LPSO） structure and t...The effects of homogenization and isothermal aging treatment on the mechanical properties of Mg-12Gd- 2Er-1Zn-0.6Zr （wt%） alloy were investigated. The precipitated long-period stacking order （LPSO） structure and the aging precipitation sequence of the conditioned alloys were observed and analyzed, respectively. The results indicate that the 14H-LPSO structure occurs after the homogenization treatment and the 131 phase forms after the isothermal aging process. These two independent processes could be controlled by the precipitation temperature range. The significant increase in the elongation of the as-cast alloy after homogenization treatment is attributed to the disappearance of the coarse primary Mgs（Gd, Er, Zn） phase and the presence of the 14H-LPSO structure. The precipitation sequence of the investigated alloy is α-Mg（SSS）/β″（D019）/β′（cbco）/β. Furthermore, the yield tensile strength （YTS） and ultimate tensile strength （UTS） values of the isothermal aging alloy have a great improvement, which could be attributed to the high density of the precipitated β′ phase.展开更多
The microstructures of as-cast and as-solution Mg–12Gd–2Er–1Zn–0.6Zr alloys were investigated by optical microscopy（OM）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, highresoluti...The microstructures of as-cast and as-solution Mg–12Gd–2Er–1Zn–0.6Zr alloys were investigated by optical microscopy（OM）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, highresolution transmission electron microscopy（HRTEM）X-ray diffraction（XRD） and selected-area electron diffraction（SAED） in the present investigation. The results show that the primary eutectic phase Mg5（Gd, Er, Zn） and some flocculent features are found in the as-cast alloy; the SAED pattern indicates that these flocculent features are the dense areas of stacking faults. The 14H-LPSO structure precipitates in the temperature range of 673–793 K, and the volume fraction of 14H-LPSO structure increases with the extension of heating time; however, there is no precipitation of 14H-LPSO structure when the temperature reaches up to 803 K. In addition, the Mg5（Gd, Er, Zn） phase dissolves gradually along with the precipitation of 14H-LPSO structure.展开更多
The effects of heat treatment on microstructures and hardening response of Mg-6Zn4）.5Er4）.5Ca （wt%） alloy were investigated by optical microscope （OM）, scanning elec- tron microscope （SEM）, and transmission el...The effects of heat treatment on microstructures and hardening response of Mg-6Zn4）.5Er4）.5Ca （wt%） alloy were investigated by optical microscope （OM）, scanning elec- tron microscope （SEM）, and transmission electron microscope （TEM） in this paper. The results show that the Mg（Zn4）.5Er- 0.5Ca alloy contains Mg3Zn6Erx quasicrystalline phase （I- phase） and Ca2Mg6Zn3 phase under as-cast condition. Most of the Ca2Mg6Zn3 phases and I-phases dissolve into matrix during heat treatment at 475 ℃ for 5 h. After the as-solution alloy was aged at 175 ℃ for 36 h, a large amount of MgZn2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which in- creases about 40 % compared with that of as-cast alloy.展开更多
基金Projects(2016YFB0301001,2016YFB0301101)supported by the National Key Research and Development Program of ChinaProject(51801004)supported by the National Natural Science Foundation of China+1 种基金Project(KM201710005005)supported by Beijing Municipal Education Commission,ChinaProjects(2172013,2192006)supported by Beijing Natural Science Foundation,China
文摘An extruded Mg-4Zn-0.2Mn-0.2Ca alloy was developed as potential biodegradable bone-plate due to its excellent biocompatibility.Long term in vitro immersion in Hank’s solution and bending test were used to evaluate the degradability and the mechanical integrity of the alloy.The results revealed that the degradation rate of the bone-plate increased in the first 7 days and then decreased with the prolonged immersion time before it finally reached a steady stage(about 0.84 mm/a)after immersion for 90 days.The bending strength after immersion for 60 days was 67.6 MPa,indicating that the bone-plate could support certain mechanical load after long term degradation.The formation of corrosion pits after degradation stemmed from the separation of the continuously distributed second phases from Mg matrix under the action of micro-galvanic couples.As a result,the mechanical performance of Mg-4Zn-0.2Mn-0.2Ca alloy was aggravated owing to the corrosion holes on its surface.
基金Project(2142005)supported by Beijing Natural Science Foundation,ChinaProject(51401005)supported by the National Natural Science Foundation of China+2 种基金Project(KM201410005014)supported by the Beijing Municipal Commission of Education,ChinaProject(2015-RX-L11)supported by the Ri Xin Talents Plan of Beijing University of Technology,ChinaProject(009000514316007)supported by the Advanced Medical Instruments of Beijing University of Technology,China
文摘The hot deformation behaviors of as-solution Mg?xZn?yEr alloys (x/y=6, x=3.0, 4.5 and 6.0; y=0.50, 0.75 and 1.00) wereinvestigated on Gleeble?1500 thermal simulator in a temperature range of 200?450 °C at a strain rate of 0.001?1 s?1. The truestress?strain curves showed the dynamic competition between the working hardening and working softening mainly due to thedynamic recrystallization (DRX) occurring during hot compression. The constitutive equations were constructed which couldaccurately predict the peak stress of the alloys. The addition of Zn and/or Er resulted in higher deformation activation energy forMg?3Zn?0.5Er (alloy A). The processing maps were constructed as function of the temperature and the strain rate, providing theoptimum hot working conditions (i.e., at strain of 0.3, Mg?3Zn?0.5Er (alloy A): 380?430 ?C, <0.1 s?1; Mg?4.5Zn?0.75Er (alloy B):380?450 ?C, 0.01?0.1 s?1; Mg?6Zn?1Er (alloy C): 390?440 ?C, 0.01?0.1 s?1). The as-solution treated Mg?4.5Zn?0.75Er (alloy B)demonstrated more optimum hot working window comparing with Mg?3Zn?0.5Er (alloy A) and Mg?6Zn?1Er (alloy C).
基金Project(2016YFB0301101)supported by the National Key Research and Development Program of ChinaProject(Z161100002116033)supported by Beijing Municipal Science and Technology Commission,China+1 种基金Project(KZ201810005005)supported by Key Science and Technology Program of Beijing Municipal Commission of Education,ChinaProject(2172013)supported by Beijing Natural Science Foundation,China
文摘The microstructure evolution and strengthening mechanisms of Mg-10Gd-1Er-1Zn-0.6Zr(wt.%) alloy were focused in the view of the size parameters and volume fraction(fp) of dual phases(long period stacking ordered(LPSO) structures and β’ precipitates).Results show that two types of LPSO phases with different morphologies formed,and the morphology and size of both LPSO phases varied with the solution conditions.However,the volume fraction decreased monotonously with increasing solution temperature,which in turn raised the volume fraction of β’ phase during aging.The alloy exhibited an ultimate tensile strength of 352 MPa,a yield strength of 271 MPa,and an elongation of 3.5% after solution treatment at 500℃ for 12 h and aging at 200℃ for 114 h.In contrast to the LPSO phase,the β’ phase seems to play a more important role in enhancing the yield strength,and consequently,a decreased fLPSO/fβ’,ratio results in an increased yield strength.
基金Project(51401005)supported by the National Natural Science Foundation of ChinaProjects(2172013,2164055)supported by Beijing Natural Science Foundation,China+1 种基金Project(2016YFB0301101-1)supported by the National Key Research and Development Program,ChinaProject(2015-RX-L11)supported by Ti Xin Talents Plan of Beijing University of Technology,China
文摘The effects of kinds of secondary phases on texture and mechanical properties of Mg-Zn-Er alloys were investigated. The results suggest that the I-phase has a great effect on modification of the texture via the discontinuous dynamic recrystallization mechanism（DDRX）, which tends to form well-developed equiaxed recrystallized grains. Meanwhile, the W-phase plays an important role in refining the grain size via continuous dynamic recrystallization（CDRX）, companied with a higher maximum texture intensity. Thus, the Mg-6Zn-1 Er alloy containing I-phase shows a performance of higher elongation of 20.4%. The Mg-2Zn-2Er alloy including W-phase displays a better tensile strength, and the yield strength（YS） is about 247 MPa.
基金Project(2172013)supported by the Natural Science Foundation of Beijing,ChinaProject(2016YFB0301101)supported by the National Key Research and Development Program,ChinaProject(KZ201810005005)supported by Key Science and Technology Program of Beijing Municipal Commission of Education,China
文摘The microstructure and texture evolutions in Mg-Zn-Er alloy during hot compression were investigated by using opticalmicroscope （OM）, field emission scanning electron microscope （EBSD） and transmission electron microscope （TEM）. The resultsindicate that the temperature plays an important role in dynamic recrystallization （DRX） mechanism. The twin dynamicrecrystallization （TDRX） is induced at a strain of 0.6 because of the activation of non-basal slip （a＋c ） dislocations at 200 ℃.Meanwhile, the continuous DRX （CDRX） occurs at 350℃, which is identified by the typical necklace-like structure around theresidual initial grains. The DRX contributes to the modification of texture significantly. The tension twins are responsible for theweak texture at 200 ℃. Meanwhile, the decrease in the basal texture is ascribed to the DRX sites which transfer from twinboundaries to initial grain boundaries as the temperature is increased from 200 to 350 ℃.
基金the financial supports from Beijing Natural Science Foundation, China (2172013)the National Key Research and Development Program, China (2016YFB0301101)。
文摘The corrosion behaviors and mechanism of the as-rolled Mg-x Zn-0.5Er(x=0.5, 2.0, 3.0 and 4.0, in wt.%)alloys were investigated. The potential difference between the second phase and matrix was determined by the type and size of the second phases. The dominated nano-scale W-phase on matrix in the Mg-0.5Zn-0.5Er alloy induced a sharp local pitting corrosion. However, as the volume fraction of the coarse W-phase or I-phase increased, the corrosion reaction was inclined to happen around the coarse W-phase or I-phase preferentially, leading to an obvious uniform corrosion and great acceleration of corrosion rate. The long-term immersion(14 d) results indicated that the corrosion resistance decreasing sequence was Mg-0.5Zn-0.5Er > Mg-2.0Zn-0.5Er > Mg-3.0Zn-0.5Er > Mg-4.0Zn-0.5Er.
基金supported by the National Key Research and Development Program of China(Nos.2016YFB0301101 and 2016YFB0301000)the Key Science and Technology Program of Beijing Municipal Commission of Education(No.KZ201810005005)+1 种基金the National Natural Science Fund of China(No.51801004)the Beijing Natural Science Foundation(No.2192006)。
文摘The Mg–12Gd–1Er–1Zn–0.9 Zr(wt%)alloy with ultra-high strength and ductility was developed via hot extrusion combined with pre-deformation and two-stage aging treatment.The age-hardening behavior and microstructure evolution were investigated.Pre-deformation introduced a large number of dislocations,resulting in strain hardening and higher precipitation strengthening in the subsequent two-stage aging.As a result,the alloy showed a superior strength–ductility balance with a yield strength of 506 MPa,an ultimate tensile strength of 549 MPa and an elongation of 8.2%at room temperature.The finer and denserβ’precipitates significantly enhanced the strength,and the bimodal structure,smallβ-Mg5RE phase as well as denseγ’precipitates ensured the good ductility of the alloy.It is suggested that the combination of pre-deformation and two-stage aging treatment is an eff ective method to further improve the mechanical properties of wrought Mg alloys.
基金financially supported by Beijing Natural Science Foundation(No.2172013)the National Key Research and Development Program(No.2016YFB0301101)+1 种基金Beijing Municipal Commission of Education Key Science,Technology Projects(No.KZ201810005005)the National Natural Science Foundation of China(No.51801048)。
文摘The magnesium alloy has a unique advantage in 3C fields due to its high specific strength and excellent electromagnetic shielding characteristic.However,it is difficult to deform homogeneously because of hexagonal close-packed structure.In the present work,the microstructure,mechanical properties and stretch formability of magnesium alloy sheets with different alloying elements were investigated.It was indicated that a trace addition of Zn or/and Er made a key role in modifying texture,activating shear bands formation and precipitating nanoscale second phases,respectively,which resulted in an obvious improvement in both stretch formability and mechanical properties.The results suggested that the Mg-0.5 Zn-0.5 Er alloy sheet exhibited higher tensile strength along the rolling direction,i.e.,yield strength of 180 MPa and ultimate tensile strength of 201 MPa,accompanying with superior Erichsen value of 7.0 mm at room temperature.The good performances of the sheet were ascribed to weakening basal texture intensity,formation of shear bands and precipitation of nanoscale W-phase(Mg_(3)Zn_(3)Er_(2)).
基金financially supported by Beijing Municipal Science and Technology Commission(No.Z131100003213019)National Natural Science Foundation of China(Nos.51101002 and 51301006)Beijing Municipal Commission of Education(Nos.KM201310005001 and KM201110005001)
文摘The particles of Mg-Zn-Gd icosahedral quasicrystal master alloy were added into the AZ31 alloy by the repeated plastic working(RPW)process in order to improve the mechanical properties of the AZ31 alloy at room temperature.The microstructure and tensile properties of composites were investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and tensile testing machine at room temperature.The results suggest that the RPW process can effectively refine the matrix and make the I-phase particles distribute uniformly.The ultimate tensile strength and the yield strength of the composites reach their maximum values of 362.3 and 330.5 MPa,respectively,when the amount of I-phase particles added is10 %.Meanwhile,the elongation of the composites decreases sharply.
基金financially supported by State Key Laboratory of Advanced Metals and Materials(No.2011-ZD06)Beijing Municipal Science and Technology Commission(No.Z131100003213019)+1 种基金the RiXin Talents Plan of Beijing University of Technology(2014-RX-L07)Beijing Natural Science Foundation(No.2144043)
文摘The present study aims to improve electrochemical properties of the La-Mg-Ni-based hydrogen storage alloys through partial substitution for La by mischmetal（MM）.The La_（0.8-x）MM_xMg_（0.2）Ni_（3.1）Co_（0.3）Al_（0.1）（x=0,0.1,0.2,0.3）alloys were prepared by inductive melting,and their phase structures and electrochemical properties were studied by X-ray diffraction（XRD）,scanning electron microscope（SEM）,energy-dispersive X-ray spectrometry（EDX）and electrochemical tests.Results show that the alloys mainly consist of La_2Ni_7-type phase,La_5Ni_（19）-type phase,LaNi_5-type phase and LaNi_3-type phase.The addition of MM does not change the phase compositions,while it leads to more uniform phase distribution and obviously promotes the formation of La_2Ni_7-type phase which possesses favorable electrochemical properties.Electrochemical studies indicate that the substitution for La by MM could effectively improve the high rate dischargeability（HRD）of the alloy electrode,and the optimal value of HRD_（1500）（HRD at 1500 mA·g^（-1））increases from 40.63%（x=0）to 60.55%（x=0.3）.Although the activation properties of the alloy electrodes keep almost unchanged,both the maximum discharge capacity（C_（max））and the cycling stability are significantly improved by MM addition.
基金financially supported by Beijing Natural Science Foundation(No.2142005)the National Natural Science Foundation of China(No.51401005)the Ri Xin Talents Plan of Beijing University of Technology(Nos.2014-RX-L07 and2015-RX-L11)
文摘The effects of homogenization and isothermal aging treatment on the mechanical properties of Mg-12Gd- 2Er-1Zn-0.6Zr （wt%） alloy were investigated. The precipitated long-period stacking order （LPSO） structure and the aging precipitation sequence of the conditioned alloys were observed and analyzed, respectively. The results indicate that the 14H-LPSO structure occurs after the homogenization treatment and the 131 phase forms after the isothermal aging process. These two independent processes could be controlled by the precipitation temperature range. The significant increase in the elongation of the as-cast alloy after homogenization treatment is attributed to the disappearance of the coarse primary Mgs（Gd, Er, Zn） phase and the presence of the 14H-LPSO structure. The precipitation sequence of the investigated alloy is α-Mg（SSS）/β″（D019）/β′（cbco）/β. Furthermore, the yield tensile strength （YTS） and ultimate tensile strength （UTS） values of the isothermal aging alloy have a great improvement, which could be attributed to the high density of the precipitated β′ phase.
基金financially supported by the Projects of Beijing Municipal Science and Technology Commission (No. Z131100003213019)the Projects of Beijing Municipal Commission of Education (Nos. KM201110005001 and KM201310005001)Beijing Natural Science Foundation (No. 2144043)
文摘The microstructures of as-cast and as-solution Mg–12Gd–2Er–1Zn–0.6Zr alloys were investigated by optical microscopy（OM）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, highresolution transmission electron microscopy（HRTEM）X-ray diffraction（XRD） and selected-area electron diffraction（SAED） in the present investigation. The results show that the primary eutectic phase Mg5（Gd, Er, Zn） and some flocculent features are found in the as-cast alloy; the SAED pattern indicates that these flocculent features are the dense areas of stacking faults. The 14H-LPSO structure precipitates in the temperature range of 673–793 K, and the volume fraction of 14H-LPSO structure increases with the extension of heating time; however, there is no precipitation of 14H-LPSO structure when the temperature reaches up to 803 K. In addition, the Mg5（Gd, Er, Zn） phase dissolves gradually along with the precipitation of 14H-LPSO structure.
基金financial supported by the National Natural Science Foundation of China(No.51301006)the Projects of Beijing Municipal Science and Technology Commission(No.Z131100003213019)+1 种基金the Projects of Beijing Municipal Commission of Education(Nos.KM201310005001 and KM201410005014)Beijing Natural Science Foundation(No.2142005)
文摘The effects of heat treatment on microstructures and hardening response of Mg-6Zn4）.5Er4）.5Ca （wt%） alloy were investigated by optical microscope （OM）, scanning elec- tron microscope （SEM）, and transmission electron microscope （TEM） in this paper. The results show that the Mg（Zn4）.5Er- 0.5Ca alloy contains Mg3Zn6Erx quasicrystalline phase （I- phase） and Ca2Mg6Zn3 phase under as-cast condition. Most of the Ca2Mg6Zn3 phases and I-phases dissolve into matrix during heat treatment at 475 ℃ for 5 h. After the as-solution alloy was aged at 175 ℃ for 36 h, a large amount of MgZn2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which in- creases about 40 % compared with that of as-cast alloy.
