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mICROSTRUCTURES AND PROPERTIES OF RECIPROCATINGLY EXTRUDED mg-6.4zn-1.1Y ALLOYS

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Acta metallurgica Sinica(English Letters) 2008年第1期21卷 37-42页

作者： z.m. zhang C.J. Xu X.F. Guo School of materials Science ＆ Engineering Xi＇an University of Technology Xi＇an 710048 China

An icosahedral mg3 Yzn6 quasicrystalline phase can be produced in mg-zn- Y system alloys when a proper amount of zn and Y is contained, and it is feasible to prepare the quasicrystal phase-reinforced low-density magnesium alloy. In this article, phase constituents and the effect of reciprocating extrusion on microstructures and properties of the as-cast mg-6.4zn-1.1 Y alloy are analyzed. The microstructure of the as-cast mg-6.4zn-1.1 Y alloy consists of the α-mg solid solution, icosahedral mg3Yzn6 quasicrystal, and mg3 Y2zn3 and mgzn2 compounds. After the alloy was reciprocatingly extruded for four passes, grains were refined, mg3 Y2 zn3 and mgzn2 phases dissolved into the matrix, whereas, mg3 Yzn6 precipitated and distributed uniformly. The alloy possesses the best performance at this state; the tensile strength, yield strength, and elongation are 323.4 mPa, 258.2 mPa, and 19.7%, respectively. In comparison with that of the as-cast alloy, the tensile strength, yield strength, and elongation of the reciprocatingly extruded alloy increase by 258.3%, 397.5%, and 18 times, respectively. It is concluded that reciprocating extrusion can substantially improve the properties of the as-cast mg-6.4zn-1.1 Y alloy, particularly for elongation. The high performance of the mg-6.4zn-1.1 Y alloy after reciprocating extrusion can be attributed to dispersion strengthening and grain-refined microstructures.

关键词： Reciprocating extrusion mg-zn- Y alloy Icosahedral quasicrystal

RECIPROCATING EXTRUSION OF IN SITU mg_2Si REINFORCED mg-Al BASED COmPOSITE

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Acta metallurgica Sinica(English Letters) 2008年第3期21卷 169-177页

作者： z.m. zhang C.J. Xu X.F. Guo S.z. Jia School of materials Science ＆ Engineering Xi＇an University of Technology Xi＇an 710048 China

m92Si reinforced mg-Al based composite with high amount o/silicon was prepared by permanent mould casting, and then extruded by reciprocating extrusion （RE） after the composite was processed by homogenization heat treatment. The effect of RE processing on the morphology and size of m92Si and the mechanical properties of the com- posite were investigated, to develop new ways to refine the m928i phase and improve its shape. The result showed that RE was very useful in refining the m92Si phase. The more the RE processing passes, the better the refining effect would be. moreover, the uniform distribution of m928i phases would be more in the composite. After the composite was processed by RE for 12 passes, most m92Si phases were equiaxed, with granular diameter below 20 μm, and distributed uniformly in the matrix of the composite. The mechanical properties of the composite could be increased prominently by RE processing, and were much higher than that in the as-cast state. As the temperature rises, the tensile strength is reduced. For the composite RE processed for 12 passes, the tensile strength, yield strength, and elongation are 325.9 mPa, 211.4 mPa, and 3.3% at room temperature, whereas, 288.2 mPa, ,207.7 mPa, and 7.8%, respectively, at 150℃. In comparison with the properties at room temperature, the tensile strength and yield strength are high and only decrease by 11.6% and 1.8% at 150℃. The m928i reinforced mg-Al based composite possesses good heat resistance at 150℃. The excellent resistance to effect of heat is attributed to the high melting tempera- ture and good thermal stability of fine mg2Si phases, which are distributed uniformly in the composite, and effectively hinder the grain boundary gliding and dislocation movement.

关键词： Reciprocating extrusion magnesium alloy In situ composite Elevated temperature property

EFFECT OF ANNEALING ON DAmPING CAPACITIES OF AS-CAST zA27 ALLOY

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Acta metallurgica Sinica(English Letters) 2006年第5期19卷 379-384页

作者： z.m. zhang J. C. Wang H.z. Liu X.F. Guo School of materials Science ＆ Engineering Xi＇an University of TechnologyXi＇an 710048 China State Key Laboratory of Solidification Processing Northwestern PolytechnicalUniversity Xi＇an 710072 China

zA27 alloy was prepared by casting with permanent mold and then annealed at 250℃ for 1-4h. The damping capaciG of the alloy was measured using a testing apparatus based on the cantilever beam technique. It was found that the as-cast zA27 alloy possesses high damping capacity with the value of 1.3 × 10^4 at 320Hz. After annealed at 250℃ for lh, the damping capacity decreases to 1.1 × 10^-3 and then remains constant even when the annealing time is increased to 4h. The microstructure of the as-cast zA27 alloy consists of large dendrites of Al-rich PrimaG （x-phases, eutectoid （α ＋ η） and nonequilibrium eutectic phases （α ＋ η ＋ ε）. After annealing at 250℃ for lh, the e phase disappears due to dissolution into the matrix, and the spacing between the flakes of eutectoid increases. The further increase in the annealing time has little effect on the spacing. The damping mechanism of the alloy was discussed considering the thermoelastic damping and defect damping. The value of thermoelastic damping accounts only for 7%-8% in the overall damping in cantilever beam damping measurements and the damping capacity of the zA27 alloy came mainly from defect damping.

关键词： damping capacity zA27 alloy annealing

DAmPING BEHAVIOR OF ULTRAFINE-GRAINED PURE ALUmINUm L2 AND THE DAmPING mECHANISm

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Acta metallurgica Sinica(English Letters) 2006年第3期19卷 223-227页

作者： z.m. zhang C.J. Xu J.C. Wang H.z. Liu School of materials Science ＆ Engineering Xi＇an University of Technology Xi＇an 710048 Ghina State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 Ghina

Ultrafine-grained pure aluminum L2 with a mean grain size of 1.01μm was produced by equal channel angular pressing （ECAP） and annealing at 150℃ for 2h. Damping behavior of the alloy was measured using a dynamic mechanical thermal analyzer. The alloy had an excellent damping capacity Q^-1 with the ambient value being 9.8×10^-3 at 1.0Hz when the strain amplitude was 2.0×10^-5. The damping behavior of the alloy showed a non-linear damping variation tendency, that is, with an increase in temperature and a decrease of frequency, the damping capacity of the alloy increased. The damping capacity increased with the strain amplitude when the strain amplitude was less than 4.6×10^-5. When the strain amplitude was higher than 4.6×10^-5, the damping capacity became a constant and independent of strain amplitude. The high damping capacity was attributed to dislocation unpinning and a drag of dislocation on pinning points.

关键词： ECAP ultrafine grain damping capacity aluminum alloy

mICROSTRUCTURE OF BINARY mg-Al EUTECTIC ALLOY WIRES PRODUCED BY THE OHNO CONTINUOUS CASTING PROCESS

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Acta metallurgica Sinica(English Letters) 2008年第4期21卷 275-281页

作者： z.m. zhang T. Lü C.J. Xu X.F. Guo School of materials Science ＆ Engineering Xi＇an University of Technology Xi＇an 710048 China

Directionally solidified binary mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting （OCC） process and the microstructure was examined. It was found that the wires possess obvious unidirectional growth characteristic along its axial direction. The microstructure consists of parallel columnar grains that resulted from the competitive growth of equiaxed grains solidified on the head of dummy bar. Each columnar grain comprises regular eutectic a-mg and β-mg17 Al12 phases, which grew along the axial direction of the wires. The morphology of the eutectic is mainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the ＂bridging effect＂ caused by incidental elements in the alloy.

关键词： mg-Al alloy Eutectic structure Directional solidification OCC process

mONTE CARLO SImULATION STUDY OF SURFACE ELECTRONIC EXCITATION OF NOBLE mETALS

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Acta metallurgica Sinica(English Letters) 2002年第2期15卷 191-197页

作者： H.m. Li, z.J. Ding, Q.R. Pu and z.m. zhang Structural Research Laboratory and Department of Astronomy and Applied Physics, University of Science and Technology of China, Hefei 230026, China Dept. of Astron. and Appl. Phys. Univ. of Sci. and Technol. of China Hefei 230026 China

In this work we present a numerical simulation of REELS-spectrum for noblemetals, Au and Ag. The calculation is based on an electron-surface inelastic scattering modelpreviously developed. The differential inelastic cross section is obtained from an inhomogeneouselectron self-energy in the surface region, which provides full information of the dependency of thetotal and differential cross section on the kinetic energy, the distance from the surface and themoving direction of electrons, accommodating the formulation to the practical situation in surfaceelectron spectroscopes. A novel monte Carlo simulation code of electron interaction with a surfaceincorporating the local scattering mean free path has been developed. The comparison of thesimulated REELS-spectra with the experimental measurements shows a remarkable agreement on thespectrum shape, which then confirms that the present model for electron-surface inelastic scatteringis quite reasonable. The simulation has further shown the component to surface excitation due tothe individual scattering processes along trajectory part, i.e., the loss in vacuum beforereflection, the loss in vacuum after reflection and loss in metal events.

关键词： monte Carlo surface plasmon REELS Ag Au

Effects of multiple shapes for steady flow with transformer oil+Fe_(3)O_(4)+TiO_(2) between two stretchable rotating disks

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Applied mathematics and mechanics(English Edition) 2024年第2期45卷 373-388页

作者： m.RAHmAN m.TURKYILmAzOGLU z.m.SHTAQ Department of mathematics Mirpur University of Science and TechnologyMirpur 10250Pakistan Department of mathematics Hacettepe UniversityBeytepeAnkara 06532Turkiye

In this study,we examine the effects of various shapes of nanoparticles in a steady flow of hybrid nanofluids between two stretchable rotating *** steady flow of hybrid nanofluids with transformer oil as the base fluid and Fe_(3)O_(4)+TiO_(2)as the hybrid nanofluid is *** shapes of Fe_(3)O_(4)+TiO_(2)hybrid nanofluids,including sphere,brick,blade,cylinder,and platelet,are *** shape exists in the same volume of a *** leading equations(partial differential equations(PDEs))are transformed to the nonlinear ordinary differential equations(ODEs)with the help of similarity *** system of equations takes the form of ODEs depending on the boundary conditions,whose solutions are computed numerically by the bvp4c mATLAB *** outputs are compared with the previous findings,and an intriguing pattern is discovered,such that the tangential velocity is increased for the rotation parameter,while it is decreased by the stretching values because of the lower *** the reaction rate parameter,the concentration boundary layer becomes shorter,and the activation energy component increases the rate at which mass transfers come to the higher disk but have the opposite effect on the bottom *** ranges of various parameters taken into account are Pr=6.2,Re=2,m=1.0,φ_(1)=φ_(2)=0.03,K=0.5,S=-0.1,Br=0.3,Sc=2.0,α_(1)=0.2,γ=0.1,E_(n)=2.0,and q=1.0,and the rotation factor K is within the range of 0 to 1.

关键词： transformer oil Brinkman number skin friction coefficient double rotating disk Nusselt number Sherwood number

Precipitation of multi-type nano-quasicrystals in a mg-zn-Y alloy

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Journal of magnesium and Alloys 2024年第3期12卷 997-1008页

作者： W.z.Wang X.z.zhou L.F.zhang H.Q.Ye z.Q.Yang Shenyang National Laboratory for materials Science Institute of Metal ResearchChinese Academy of ScienceShenyang 110016China Ji Hua Laboratory Foshan 528251China Foshan University Foshan 528231China

mg-6zn-1Y(at.%)ribbons with strengthening precipitates of multi-type nanoquasicrystals were prepared by melt-spinning followed by aging *** evolution of the rapidly solidified ribbons during isothermal aging was comprehensively studied using various electron microscopy *** new kinds of decagonal quasicrystals were formed in aged ribbons,in addition to precipitation of nanometer icosahedral ***-resolution observations reveal that both decagonal quasicrystals can be modeled by quasiperiodic tiling with decagonal clusters of 2.5 nm in diameter,but overlap of neighboring clusters in both decagonal quasicrystals is different from the Gummelt model observed in other quasicrystals.A shell composed of complex Laves mg-zn domains was formed surrounding each decagonal quasicrystal precipitate upon prolonged *** addition,all kinds of nanoprecipitates exhibit excellent structure and size stability at 573 *** findings may have implications for not only fundamental studies about quasicrystals,but also microstructural manipulation of high-performance mg alloys.

关键词： Quasicrystal mg alloys Rapid solidification Scanning-transmission electron microscopy.

Rational design of AgGaS/znS/znS quantum dots with a near-unity photoluminescence quantum yield via double shelling scheme

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Journal of materials Science & Technology 2024年第2期169卷 235-242页

作者： H.X.Lu H.Liu z.z.Fu Y.Y.Chen H.Q.Dai z.Hu W.L.zhang R.Q.Guo Institute for Electric Light Sources School of Information Science and TechnologyFudan UniversityShanghai 200433China Institute of Future Lighting Academy for Engineering and TechnologyFudan UniversityShanghai 200433China Yiwu Research Institute of Fudan University YiwuZhejiang 322000China zhongshan-Fudan Joint Innovation Center Zhongshan 528437China

In this study,a two-step method was used to synthesize highly luminescent AgGaS/znS/znS quantum dots(QDs).In the first step,an inner znS shell was formed via a one-pot method,which resulted in a smaller lattice mismatch between the AgGaS core and the outer znS shell,thereby facilitating the formation of a thick outer *** the two-step shelling process,the synthesized AgGaS/znS/znS QDs showed an excellent photoluminescence quantum yield(PLQY)of 96.4%with a peak wavelength of 508 nm,repre-senting the highest PLQY reported thus far for AgGaS ***,the effect of halogen ions in zn precursors on the shelling process was *** was proposed that the capacity of halogen ions to coordinate with the QDs influenced the balance between zn cation diffusion and znS shelling ***,the znS shelling reaction was dominant when znCl_(2)was employed,while zn cation diffusion was the dominant process under the I^(−)-rich *** work provides insights into the interfacial restructuring during the znS shelling and offers a clear map for the tailored synthesis of core/shell QDs.

关键词： AgGaS Quantum dots Photoluminescence Core/shell Alloyed core/shell interface