The effect of Gd content ranging from 6.5 wt.%to 8.5 wt.%on microstructure evolution and dynamic mechanical behavior of Mg−xGd−3Y−0.5Zr alloys was investigated by optical microscopy,X-ray diffraction,scanning electron...The effect of Gd content ranging from 6.5 wt.%to 8.5 wt.%on microstructure evolution and dynamic mechanical behavior of Mg−xGd−3Y−0.5Zr alloys was investigated by optical microscopy,X-ray diffraction,scanning electron microscopy and split Hopkinson pressure bar.The microstructure of as-cast Mg−xGd−3Y−0.5Zr alloys indicates that the addition of Gd can promote grain refinement in the casting.Due to the rapid cooling rate during solidification,a large amount of non-equilibrium eutectic phase Mg_(24)(Gd,Y)_(5) appears at the grain boundary of as-cast Mg−xGd−3Y−0.5Zr alloys.After solution treatment at 520℃ for 6 h,the Mg_(24)(Gd,Y)_(5) phase dissolves into the matrix,and the rare earth hydrides(REH)phase appears.The stress−strain curves validate that the solution-treated Mg−xGd−3Y−0.5Zr alloys with optimal Gd contents maintain excellent dynamic properties at different strain rates.It was concluded that the variation of Gd content and the agglomeration of residual REH particles and dynamically precipitated fine particles are key factors affecting dynamic mechanical properties of Mg−xGd−3Y−0.5Zr alloys.展开更多
This work investigated the effects of different Y additions(0,1.5,3.0 and 4.5 wt.%)on the microstructural evolution and mechanical performance of cast Mg−3Nd−0.2Zn−0.5Zr alloy.The results show that as the Y content in...This work investigated the effects of different Y additions(0,1.5,3.0 and 4.5 wt.%)on the microstructural evolution and mechanical performance of cast Mg−3Nd−0.2Zn−0.5Zr alloy.The results show that as the Y content increases,the key secondary phases in as-cast alloys change from the Mg_(12)Nd type to the Mg_(24)Y_(5) type.Meanwhile,the number density of Zn−Zr particles in the grains of as-quenched alloys gradually decreases.HAADF-STEM observations of peak-aged samples reveal that element Y is greatly enriched in the globularβ¢precipitates,leading to a significantly increased volume fraction and promoted precipitation kinetics ofβ¢precipitates,resulting in enhanced strength of the alloy.Tensile tests reveal that,with the addition of 4.5 wt.%Y,the yield strength of the base alloy is substantially increased by 88 and 61 MPa after being aged at 200 and 225°C under peak-aged conditions,respectively.展开更多
In this work,a new(Y,Gd)H_(2) precipitate was identified and systematically investigated in the as-cast Mg-6Gd-3Y-0.5Zr alloy by XRD,SEM with EDS,TEM with EDS techniques and thermodynamics analysis.Results show that t...In this work,a new(Y,Gd)H_(2) precipitate was identified and systematically investigated in the as-cast Mg-6Gd-3Y-0.5Zr alloy by XRD,SEM with EDS,TEM with EDS techniques and thermodynamics analysis.Results show that the as-cast alloy contains α-Mg,Mg_(24)(Gd,Y)_(5),and(Y,Gd)H_(2) phase.The(Y,Gd)H_(2) phase usually forms near the eutectic phase Mg_(24)(Gd,Y)_(5) or in the α-Mg grains,displaying a rectangle-shape.The Mg_(24)(Gd,Y)_(5) and(Y,Gd)H_(2) phases crystalize in bcc and fcc structure,respectively,and the(Y,Gd)H_(2) phase has a semi-coherent relationship with α-Mg matrix.The thermodynamics calculation results reveal that the hydrogen dissolved in the melt leads to the formation of hydrides.It is also found that the(Y,Gd)H_(2) hydride can form directly from the liquid phase during solidification.Additionally,it can precipitate by the decomposition of Mg_(24)(Gd,Y)_(5) phase due to absorbing hydrogen from the remaining melt.展开更多
A precursor of BaCe0.5Zr0.4Y0. 1O3-α electrolytes was synthesized by the sol-gel method and sintered at temperature which were 150 - 250 ℃ lower than by solid state reaction. The AC impedance spectrums of electrolyt...A precursor of BaCe0.5Zr0.4Y0. 1O3-α electrolytes was synthesized by the sol-gel method and sintered at temperature which were 150 - 250 ℃ lower than by solid state reaction. The AC impedance spectrums of electrolytes were measured by AUTOLAB PGSTA30 electrochemical measuring device at different temperatures. The conductivities of the electrolytes are 1.62×10^-4 - 6.43×10^-3, 2.52×10^-5 - 3.73×10^-3S·cm^-1 in the temperature range of 350-800℃. The activity energies are 0.54 and 0.84 eV. At the same time BaCe0.9Y0.1O3-α was prepared by direct solid state reaction. The conductivity of BaCe0.9Y0.1O3-α is 1 × 10^-4- 4×10^-3 S·cm^-1 and the activation energy is 0.50 eV at the same condition. The results show that conduction of electrolyte prepared by sol-gel method is higher than the one by solid state reaction. As far as BaCe0.9Y0.1O3-α concerned, its conductivity of the Zr-substituted specimens is decreased.展开更多
The Zn,Cu,and Sc contents of 7xxx Al alloys were adjusted according to the chemical composition of a 7085 Al alloy,and the effects of Zn and Cu contents and Sc addition on the microstructures,hardness,and quench sensi...The Zn,Cu,and Sc contents of 7xxx Al alloys were adjusted according to the chemical composition of a 7085 Al alloy,and the effects of Zn and Cu contents and Sc addition on the microstructures,hardness,and quench sensitivity of the 7xxx Al alloys were studied.The alloys with high Zn content and Sc addition exhibited higher hardness than the 7085 alloy at the position 3 mm away from the quenching end.The density ofηand T phases increased with the increase in Zn and Cu contents,and the Sc addition led to the formation of the Y phase and moreηphases at the position 120 mm away from the quenching end.Compared with the 7085 alloy,the high Zn−high Cu and Sc-added alloys exhibited higher quench sensitivity,while the simultaneous increase in Zn content and decrease in Cu content could enhance the hardness and reduce the quench sensitivity of the 7085 alloy.展开更多
通过自制的"T"字形模具研究了不同配比的Zn对Mg-xZn-0.5Y-0.5Zr(x=1.5,2.5,3.5 and 4.5(%,质量分数))系合金热裂敏感性的影响。通过对"T"型试样热节处宏观热裂纹的观察以及石蜡渗透法测定的裂纹的体积来表征其热裂...通过自制的"T"字形模具研究了不同配比的Zn对Mg-xZn-0.5Y-0.5Zr(x=1.5,2.5,3.5 and 4.5(%,质量分数))系合金热裂敏感性的影响。通过对"T"型试样热节处宏观热裂纹的观察以及石蜡渗透法测定的裂纹的体积来表征其热裂倾向性大小。此外采用扫描电镜(SEM)进行合金的组织形貌微观分析和裂纹自由断口表面观察,并利用X射线衍射(XRD)及投射电镜(TEM)等实验手段对其进行物相分析,确定其低熔点相主要组成,进而研究对热裂缺陷的影响。整个熔炼浇注过程利用A/D数模转换器对凝固过程进行了温度-应力采集。结果表明,MgxZn-0.5Y-0.5Zr合金的主要相组成为α-Mg,W相(Mg3Zn3Y2)及I相(Mg3Zn6Y),随着Zn含量从1.5%增加到4.5%,低熔点析出相含量明显增多,提高了枝晶间残余液相的补缩能力,有效的防止了裂纹的萌生和扩展,当Zn含量较低时,液膜理论和凝固收缩补偿理论是诠释热裂纹萌生的主要理论基础。随着Zn含量的增加,残余液相的充分补偿,桥接理论是热裂形成的主要机理。此系合金热裂敏感性由大到小顺序为Mg-1.5Zn-0.5Y-0.5Zr,Mg-2.5Zn-0.5Y-0.5Zr,Mg-3.5Zn-0.5Y-0.5Zr,Mg-4.5Zn-0.5Y-0.5Zr。展开更多
This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5 Y（wt%） alloy, which was prepared by casting, and then homogenized and rolled...This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5 Y（wt%） alloy, which was prepared by casting, and then homogenized and rolled at 200℃. The rolling process was conducted with 10% reduction per pass and five different accumulated strains, varying from 10% to 70%. The results indicate that the as-cast and as-rolled Mg-8Li-3Al-2Zn-0.5Y alloys are composed of α-Mg, β-Li, AlLi and Al;Y phases. After rolling process,anisotropic microstructure was observed. a-Mg phase got elongated in both rolling direction and transverse direction with the addition of rolling strain. Consequently, the strength of the alloy in both directions was notably improved whereas the elongation declined, mainly caused by strain hardening and dispersion strengthening. The tensile properties of the as-rolled alloys in the RD, no matter the YS, UTS or the elongation, are higher than those of the TD due to their larger deformation strain and significant anisotropy in the hcp α-Mg phase. In addition, the fracture and strengthening mechanism of the tested alloys were also investigated systematically.展开更多
High-temperature compressive deformation behaviors of Mg–6Zn–1.5Y–0.5Ce–0.4Zr alloy were investigated at temperatures and strain rates ranging from 523 to 673 K and from 0.001 to 1 s~(-1),respectively.The studied ...High-temperature compressive deformation behaviors of Mg–6Zn–1.5Y–0.5Ce–0.4Zr alloy were investigated at temperatures and strain rates ranging from 523 to 673 K and from 0.001 to 1 s~(-1),respectively.The studied alloy was mainly composed ofα-Mg,Mg_(3)Zn_(6)Y(I phase),Mg–Zn–Ce and Mg_(3)Zn_(3)Y_(2)(W phase).The constitutive equation of Mg alloy was obtained,and the apparent activation energy(Q)was determined as 200.44 k J/mol,indicating that rare earth phase increases the difficulty of deformation.The work hardening involves three stages:(1)linear hardening stage;(2)strain hardening stage;and(3)softening and steady-state stage.During these three stages,the dislocation aggregation and tangling,dynamic recovery and recrystallization occur sequentially.To characterize the dynamic recrystallization(DRX)volume fraction,the DRX kinetics was investigated using the Avrami-type equation.The deformation mechanism of magnesium alloy under different Zener–Hollomon parameter(Z)value conditions was also studied.At high Z values and intermediate conditions,dislocations rapidly generate and pile up in the alloy.Recrystallization is hardly seen at this time.At low Z condition,the DRX occurs in the alloy.展开更多
基金supported by the National Natural Science Foundation of China (Nos.51575289,51705270)the Key Research and Development Project of Shandong Province,China (No.2019GHY112068)the Natural Science Foundation of Shandong Province,China (No.ZR2019PEE028)。
文摘The effect of Gd content ranging from 6.5 wt.%to 8.5 wt.%on microstructure evolution and dynamic mechanical behavior of Mg−xGd−3Y−0.5Zr alloys was investigated by optical microscopy,X-ray diffraction,scanning electron microscopy and split Hopkinson pressure bar.The microstructure of as-cast Mg−xGd−3Y−0.5Zr alloys indicates that the addition of Gd can promote grain refinement in the casting.Due to the rapid cooling rate during solidification,a large amount of non-equilibrium eutectic phase Mg_(24)(Gd,Y)_(5) appears at the grain boundary of as-cast Mg−xGd−3Y−0.5Zr alloys.After solution treatment at 520℃ for 6 h,the Mg_(24)(Gd,Y)_(5) phase dissolves into the matrix,and the rare earth hydrides(REH)phase appears.The stress−strain curves validate that the solution-treated Mg−xGd−3Y−0.5Zr alloys with optimal Gd contents maintain excellent dynamic properties at different strain rates.It was concluded that the variation of Gd content and the agglomeration of residual REH particles and dynamically precipitated fine particles are key factors affecting dynamic mechanical properties of Mg−xGd−3Y−0.5Zr alloys.
基金supported by the National Natural Science Foundation of China(Nos.U2037601,51775334 and 51821001)the National Key Research&Development Program of China(No.2016YFB0701205)+2 种基金the Joint Innovation Fund of CALT and College,China(No.CALT2020-TS07)the Open Fund of State Key Laboratory of Advanced Forming Technology and Equipment,China(No.SKL2020005)the Research Program of Joint Research Center of Advanced Spaceflight Technologies,China(No.USCAST2020-14).
文摘This work investigated the effects of different Y additions(0,1.5,3.0 and 4.5 wt.%)on the microstructural evolution and mechanical performance of cast Mg−3Nd−0.2Zn−0.5Zr alloy.The results show that as the Y content increases,the key secondary phases in as-cast alloys change from the Mg_(12)Nd type to the Mg_(24)Y_(5) type.Meanwhile,the number density of Zn−Zr particles in the grains of as-quenched alloys gradually decreases.HAADF-STEM observations of peak-aged samples reveal that element Y is greatly enriched in the globularβ¢precipitates,leading to a significantly increased volume fraction and promoted precipitation kinetics ofβ¢precipitates,resulting in enhanced strength of the alloy.Tensile tests reveal that,with the addition of 4.5 wt.%Y,the yield strength of the base alloy is substantially increased by 88 and 61 MPa after being aged at 200 and 225°C under peak-aged conditions,respectively.
基金financially supported by the Key Project of Equipment Pre-research Field Fund under Grant No.61409230407the National Natural Science Foundation of China(NSFC)under Grant No.51601054the Central Government Guides Local Science and Technology Development Fund Projects under Grant No.206Z1005G。
文摘In this work,a new(Y,Gd)H_(2) precipitate was identified and systematically investigated in the as-cast Mg-6Gd-3Y-0.5Zr alloy by XRD,SEM with EDS,TEM with EDS techniques and thermodynamics analysis.Results show that the as-cast alloy contains α-Mg,Mg_(24)(Gd,Y)_(5),and(Y,Gd)H_(2) phase.The(Y,Gd)H_(2) phase usually forms near the eutectic phase Mg_(24)(Gd,Y)_(5) or in the α-Mg grains,displaying a rectangle-shape.The Mg_(24)(Gd,Y)_(5) and(Y,Gd)H_(2) phases crystalize in bcc and fcc structure,respectively,and the(Y,Gd)H_(2) phase has a semi-coherent relationship with α-Mg matrix.The thermodynamics calculation results reveal that the hydrogen dissolved in the melt leads to the formation of hydrides.It is also found that the(Y,Gd)H_(2) hydride can form directly from the liquid phase during solidification.Additionally,it can precipitate by the decomposition of Mg_(24)(Gd,Y)_(5) phase due to absorbing hydrogen from the remaining melt.
文摘A precursor of BaCe0.5Zr0.4Y0. 1O3-α electrolytes was synthesized by the sol-gel method and sintered at temperature which were 150 - 250 ℃ lower than by solid state reaction. The AC impedance spectrums of electrolytes were measured by AUTOLAB PGSTA30 electrochemical measuring device at different temperatures. The conductivities of the electrolytes are 1.62×10^-4 - 6.43×10^-3, 2.52×10^-5 - 3.73×10^-3S·cm^-1 in the temperature range of 350-800℃. The activity energies are 0.54 and 0.84 eV. At the same time BaCe0.9Y0.1O3-α was prepared by direct solid state reaction. The conductivity of BaCe0.9Y0.1O3-α is 1 × 10^-4- 4×10^-3 S·cm^-1 and the activation energy is 0.50 eV at the same condition. The results show that conduction of electrolyte prepared by sol-gel method is higher than the one by solid state reaction. As far as BaCe0.9Y0.1O3-α concerned, its conductivity of the Zr-substituted specimens is decreased.
基金The authors are grateful for the financial supports from the Science and Technology Major Project of Guangxi,China(GKAA17202007).
文摘The Zn,Cu,and Sc contents of 7xxx Al alloys were adjusted according to the chemical composition of a 7085 Al alloy,and the effects of Zn and Cu contents and Sc addition on the microstructures,hardness,and quench sensitivity of the 7xxx Al alloys were studied.The alloys with high Zn content and Sc addition exhibited higher hardness than the 7085 alloy at the position 3 mm away from the quenching end.The density ofηand T phases increased with the increase in Zn and Cu contents,and the Sc addition led to the formation of the Y phase and moreηphases at the position 120 mm away from the quenching end.Compared with the 7085 alloy,the high Zn−high Cu and Sc-added alloys exhibited higher quench sensitivity,while the simultaneous increase in Zn content and decrease in Cu content could enhance the hardness and reduce the quench sensitivity of the 7085 alloy.
文摘通过自制的"T"字形模具研究了不同配比的Zn对Mg-xZn-0.5Y-0.5Zr(x=1.5,2.5,3.5 and 4.5(%,质量分数))系合金热裂敏感性的影响。通过对"T"型试样热节处宏观热裂纹的观察以及石蜡渗透法测定的裂纹的体积来表征其热裂倾向性大小。此外采用扫描电镜(SEM)进行合金的组织形貌微观分析和裂纹自由断口表面观察,并利用X射线衍射(XRD)及投射电镜(TEM)等实验手段对其进行物相分析,确定其低熔点相主要组成,进而研究对热裂缺陷的影响。整个熔炼浇注过程利用A/D数模转换器对凝固过程进行了温度-应力采集。结果表明,MgxZn-0.5Y-0.5Zr合金的主要相组成为α-Mg,W相(Mg3Zn3Y2)及I相(Mg3Zn6Y),随着Zn含量从1.5%增加到4.5%,低熔点析出相含量明显增多,提高了枝晶间残余液相的补缩能力,有效的防止了裂纹的萌生和扩展,当Zn含量较低时,液膜理论和凝固收缩补偿理论是诠释热裂纹萌生的主要理论基础。随着Zn含量的增加,残余液相的充分补偿,桥接理论是热裂形成的主要机理。此系合金热裂敏感性由大到小顺序为Mg-1.5Zn-0.5Y-0.5Zr,Mg-2.5Zn-0.5Y-0.5Zr,Mg-3.5Zn-0.5Y-0.5Zr,Mg-4.5Zn-0.5Y-0.5Zr。
基金supported by the National Key Research and Development Program of China(No.2016YFB0301004)the National Natural Science Foundation of China(No.51771115)+1 种基金the Science and Technology Innovation Project(No.009-031-001)Research Program of Joint Research Center of Advanced Spaceflight Technologies(Nos.USCAST2015-25 and USCAST2016-18)
文摘This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5 Y（wt%） alloy, which was prepared by casting, and then homogenized and rolled at 200℃. The rolling process was conducted with 10% reduction per pass and five different accumulated strains, varying from 10% to 70%. The results indicate that the as-cast and as-rolled Mg-8Li-3Al-2Zn-0.5Y alloys are composed of α-Mg, β-Li, AlLi and Al;Y phases. After rolling process,anisotropic microstructure was observed. a-Mg phase got elongated in both rolling direction and transverse direction with the addition of rolling strain. Consequently, the strength of the alloy in both directions was notably improved whereas the elongation declined, mainly caused by strain hardening and dispersion strengthening. The tensile properties of the as-rolled alloys in the RD, no matter the YS, UTS or the elongation, are higher than those of the TD due to their larger deformation strain and significant anisotropy in the hcp α-Mg phase. In addition, the fracture and strengthening mechanism of the tested alloys were also investigated systematically.
基金financially supported by the National Key R&D Program of China(2016YFB0301100)the Natural Science Foundation of Chongqing,China(cstc2019jcyj-msxmX0505)the support of the“111 Project”(B16007)by the Ministry of Education and Fundamental Research Fund of Central Universities in China(Grant No.2018CDJDCL0019)。
文摘High-temperature compressive deformation behaviors of Mg–6Zn–1.5Y–0.5Ce–0.4Zr alloy were investigated at temperatures and strain rates ranging from 523 to 673 K and from 0.001 to 1 s~(-1),respectively.The studied alloy was mainly composed ofα-Mg,Mg_(3)Zn_(6)Y(I phase),Mg–Zn–Ce and Mg_(3)Zn_(3)Y_(2)(W phase).The constitutive equation of Mg alloy was obtained,and the apparent activation energy(Q)was determined as 200.44 k J/mol,indicating that rare earth phase increases the difficulty of deformation.The work hardening involves three stages:(1)linear hardening stage;(2)strain hardening stage;and(3)softening and steady-state stage.During these three stages,the dislocation aggregation and tangling,dynamic recovery and recrystallization occur sequentially.To characterize the dynamic recrystallization(DRX)volume fraction,the DRX kinetics was investigated using the Avrami-type equation.The deformation mechanism of magnesium alloy under different Zener–Hollomon parameter(Z)value conditions was also studied.At high Z values and intermediate conditions,dislocations rapidly generate and pile up in the alloy.Recrystallization is hardly seen at this time.At low Z condition,the DRX occurs in the alloy.
