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journal of Materials Science & Technology 2020年第6期41卷 127-138页

作者： Y.X.Lai W.Fan M.j.Yin C.L.Wu j.h.chen Center for high-Resolution Electron Microscopy College of Materials Science&EngineeringHunan UniversityChangsha 410082China Electron Microscopy Center Shenzhen UniversityShenzhen 518060China

In the slightly deformed Al-Mg-Si alloys,dislocation-induced precipitates are frequently observed,and they usually line up,forming sophisticated precipitation *** atomic-resolution electron microscopy in association with hardness measurements,we systematically investigated these precipitates in relation to the age-hardening responses of the *** study reveals that the majority of dislocation-induced complex precipitates are actually short-range ordered while long-range disordered polycrystalline precipitates and multiphase composite precipitates,including polycrystalline U2 precipitates,B’/U2,B’-2/U2,B’/B’-2/U2 and’/U2 composite *** is suggested that the formation of these complex precipitates is mainly owing to a high nucleation rate and rapid growth of different precipitate phases parallel to the associated dislocation *** dislocation-induced precipitates consume more Mg than Si from the matrix and have a high formation kinetics,they will have different impacts on the matrix precipitation in different types of Al-Mg-Si *** results further demonstrate that for the"normally-β"-hardened"alloy,their formation leads to a coarser precipitate microstructure in the matrix,whereas for the"normally-β’-hardened"alloy,their formation reverses the precipitation pathway in the matrix,resulting in a reduced age-hardening potential of the former alloy and an improved age-hardening potential of the latter alloy.

关键词： Al-Mg-Si alloys Precipitation Dislocation Age-hardening Electron microscopy

Atomic-scale roles of Zn element in age-hardened AlMgSiZn alloys

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journal of Materials Science & Technology 2021年第11期70卷 105-112页

作者： N.N.jiao Y.X.Lai S.L.chen P.Gao j.h.chen Center for high-Resolution Electron Microscopy College of Materials Science&EngineeringHunan UniversityChangsha410082China Electron Microscopy Laboratory and International Center for Quantum Materials School of PhysicsPeking UniversityBeijing100871China

Adding alloying elements to improve the performances or the manufacturing processes of Al-Mg-Si alloys has long been a serious issue in developing advanced automotive aluminum *** Zn element,among those promising ones,has demonstrated positive alloying effects on Al-Mg-Si ***,the atomic-scale roles of Zn in an age-hardened Al-Mg-Si-Zn alloy have not been adequately *** atomic-resolution electron microscopy,here we report the precise locations of Zn elements in all hardening precipitates involved and their alloying mechanism at the atomic scale when alloying the *** results show that Zn atoms enter all the major hardening phases to occupy specific featured atomic sites of the original elements,*** Si1 and Mg2 sites in theβ’-2 phase,and modify their crystal structures,interfacial structures and morphologies in characteristic *** is revealed that for theβ’-phase,Zn atoms occupy unique atomic sites,whereas for other phases,they demonstrate similar behaviors as other additive alloying elements such as Ag and Cu do.

关键词： Al-Mg-Si alloy Zn addition Precipitate Electron microscopy

Anisotropic Inter-granular Corrosion Behaviors and Microstructures of AlMgSiCu Alloy Sheets Made by Thermal–Mechanical Treatments

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Acta Metallurgica Sinica(English Letters) 2022年第2期35卷 275-284页

作者： L.M.Liu Y.X.Lai C.L.Wu Z.Zhang j.h.chen Center for high-Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China

This study investigates the microstructure and local corrosion behavior of an Al-Mg-Si-Cu alloy,which has been subjected to cold-rolling with different deformation strain ratios(DSRs)and followed by artificial *** corrosion tests show that peak-aged samples with a small DSR(5-10%)are sensitive to inter-granular corrosion(IGC)along both the normal and rolling *** the DSR increases to medium strength(20-40%),IGC sensitivity decreases along both directions and corrosion propagates *** the DSR is 60-80%,IGC sensitivity along the normal direction continues to decrease,but increases along the rolling direction,indicating pronounced corrosion *** characterization reveals the decreased IGC sensitivity is mainly attributed to a reduction in element segregation at high-angle grain boundaries and the kinked and discontinuous grain boundary corrosion *** increased IGC sensitivity along the rolling direction could be related to the significantly flattened grains.

关键词： Al alloys Local corrosion Anisotropy Transmission electron microscopy(TEM) Electron backscattering diffraction(EBSD)

Empirical model for estimating vertical concentration profiles of re-suspended, sediment-associated contaminants

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Acta Mechanica Sinica 2017年第5期33卷 846-854页

作者： h.W.Zhu P.D.cheng W.Li j.h.chen Y.Pang D.Z.Wang Shanghai Investigation Design & Research Institute Co. Ltd Institute of Environmental Science and Engineering Hohai University Key Laboratory for Mechanics in Fluid Solid Coupling System Institute of Mechanics Chinese Academy of Science Shanghai Institute of Applied Mathematics and Mechanics Shanghai University

Vertical distribution processes of sediment contaminants in water were studied by flume experiments. Experimental results show that settling velocity of sediment particles and turbulence characteristics are the major hydrodynamic factors impacting distribution of pollutants, especially near the bottom where particle diameter is similar in size to vortex structure. Sediment distribution was uniform along the distance, while contaminant distribution slightly lagged behind the sediment. The smaller the initial sediment concentration was, the more time it took to achieve a uniform concentration distribution for suspended sediment. A contaminants transportation equation was established depending on mass conservation equations. Two mathematical estimation models of pollutant distribution in the overlying water considering adsorption and desorption were devised based on vertical distribution of suspended sediment: equilibrium partition model and dynamic micro-diffusion model. The ratio of time scale between the sediment movement and sorption can be used as the index of the models. When this ratio was large, the equilibrium assumption was reasonable, but when it was small, it might require dynamic micro-diffusion model.

关键词： Sediment resuspension Pollutants Concentration distribution Desorption Partition coefficient

Nano-phase transformation of composite precipitates in multicomponent Al-Mg-Si(-Sc)alloys

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journal of Materials Science & Technology 2022年第15期110卷 216-226页

作者： S.B.Wang C.F.Pan B.Wei X.Zheng Y.X.Lai j.h.chen Key Laboratory of LCR Materials and Devices of Yunnan Province National Center for International Research on Photoelectric and Energy MaterialsSchool of Materials and EnergyYunnan UniversityKunming 650091China Collaborative Innovation Center of Renewable Energy Materials and Department of Physics Guangxi UniversityNanning 530004China Center for high-Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China

Sc-addition can significantly enhance the performance of the micro-alloyed Al-Mg-Si-Sc ***,the mechanisms by which the Sc element modifies the microstructure of the alloys are still unknown in many ***,using atomic-scale transmission electron microscopy and atomic-resolution spectroscopy,we have revealed the microstructural differences between two age-hardened Al-0.5Mg-0.4Si(wt.%)alloys with and without *** first significant effect of Sc-addition on the precipitation microstructure of the Al-Mg-Si-Sc alloy is that Sc-atoms may distribute at theβ"-precipitate/Al-matrix interface and therefore accelerate aging kinetics at the initial stage of *** second significant effect of Sc-addition is that in the transition from theβ"-hardened peak-age stage to theβ′-hardened late stage,Sc-atoms can greatly improve the stability of transitionalβ"/B'/β′composite precipitates by entering the B'-substructures and/or locating at the precipitate/Al *** such Sc-atoms effectively suppressβ"toβ'transformation and cross-sectional coarsening of bothβ"and composite precipitates,leading to much finer precipitate needles with smaller diameter but much larger length,as compared with those precipitate needles formed in the alloy without ***,the alloy with Sc-addition exhibits a much better thermal stability than that without Sc.

关键词： Al alloy Strengthening mechanism Phase transition Transmission electron microscopy

Electron tomography for sintered ceramic materials by a neural network algebraic reconstruction technique

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journal of Materials Science & Technology 2022年第5期100卷 75-81页

作者： R.h.Shen Y.T.he W.Q.Ming Y.Zhang X.D.Xu j.h.chen Centre for high Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China

The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and *** artifacts produced in tomographic reconstruction of bulk materials can be very severe,particularly for sintered bulk ceramic materials in which there are often nano-pores or pore-like microstructure ***,we report a neural network algebraic reconstruction algorithm with no prior knowledge to perform electron tomography for a sintered SiC material with nano carbon *** results show that the proposed algorithm has a great suppressive effect on the missing wedge artifacts and a high tolerance for *** information in the missing wedge can be partly recovered by this ***,both the shape of the bulk SiC specimen and its irregular inner pore-like features are correctly retrieved in the obtained 3D *** study shows the effectiveness of the neural network algorithm for improving the reconstruction accuracy of electron tomography,in order to reveal sophisticated 3D microstructures generally existing in sintered ceramic materials.

关键词： Neural network Missing wedge Electron tomography Sintered ceramics

A hidden precipitation scenario of theθ’-phase in Al-Cu alloys

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journal of Materials Science & Technology 2021年第16期75卷 126-138页

作者： L.Zhou C.L.Wu P.Xie F.j.Niu W.Q.Ming K.Du j.h.chen center for high-resolution electron microscopy college of materials science and engineeringhunan universitychangshahunan410082china shenyang national laboratory for materials science institute of metal researchchinese academy of sciences.shenyan7.110016china

Al-Cu binary alloys are important and interesting industry *** to date,the formation mechanisms of the key strengthening precipitates,namedθ’-phase,in the alloys are still ***,we report that for non-deformed bulk Al-Cu alloys theθ’-phase actually has its own direct precursors that can form only at elevated aging temperature(>ca.200℃).These high-temperature precursors have the same plate-like morphology as theθ’-phase precipitates but rather different *** imaging reveals that they have a tetragonal structure with a=0.405 nm and c=1.213 nm,and an average composition of Al_(5-x)Cu_(1+x)(0≤xherent with the *** precursor phase may initiate with a composition of Al5 Cu and evolve locally towards Al_(4)Cu_(2)in composition,eventually leading to a consequent structural transformation into theθ’-phase(Al4 Cu2=Al2 Cu).There are evidences that because of their genetic links in structure,such a high-temperature precursor may transform to theθ’-phase without having to change their morphology and interface *** study reveals a well-defined and previously hidden precipitation scenario for theθ’-phase to form in Al-Cu alloys at an elevated aging temperature.

关键词： AlCu alloy Age-hardening Precipitation Electron microscopy

TEMPERATURE DEPENDENCE OF VISCOSITY OF Al-Si ALLOY MELTS

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Acta Metallurgica Sinica(English Letters) 2005年第2期18卷 159-163页

作者： h.R.Geng R.Wang Z.X.Yang j.h.chen C.j.Sun Y.Wang SchoolofMaterialsScienceandEngineering JinanUniversityJinan250022China SchoolofMaterialsScienceandEngineering ShandongUniversityJinan250061China

The relationship between the viscosity and temperature of Al-Si alloy melts was investigated. The viscosity of three different types of Al-Si alloy melts was measured. It was showed that the relationship between the viscosity and temperature of hypoeutectic Al-5%Si and eutectic Al- 12.5%Si alloy melts is approximately exponential except for some special zones, but that of the hypereutectic melt is different. The paper discussed the correlation of the viscosity and atomic density, which is thought that the viscosity corresponds to the atomic density to some extent.

关键词： Al-Si alloy melt viscosity liquid metal atomic density

The hardening precipitates in high strength aluminum alloys studied by atomic-resolution electron microscopy

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The hardening precipitates in high strength aluminum alloys ...

Unveiling anneal hardening in dilute Al-doped Al_(x)CoCrFeMnNi(x = 0,0.1) high-entropy alloys

第二届海峡两岸功能材料科技与产业峰会（2015）

作者： j.h.chen Center for high-Resolution Electron Microscopy College of Materials Science and EngineeringHunan University

Developments of high-strength aluminum alloys have always faced a difficult problem:owing to their small size,the early-stage strengthening precipitates are difficult to characterize in terms of composition,structure and *** we employ atomic-resolution transmission electron microscopy(TEM)imaging and first-principles energy calculations to address these *** years,we have investigated tens of

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journal of Materials Science & Technology 2021年第32期91卷 270-277页

作者： Q.cheng X.D.Xu P.Xie L.L.han j.Y.he X.Q.Li j.Zhang Z.T.Li Y.P.Li B.Liu T.G.Nieh M.W.chen j.h.chen Centre for high Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China Applied Materials Physics Department of Materials Science and EngineeringKTH-Royal Institute of TechnologyStockholm SE10044Sweden Department of Materials Science and Engineering University of TennesseeKnoxvilleTN37996United States Department of Materials Science and Engineering Johns Hopkins UniversityBaltimoreMD 21214USA

Anneal hardening has been one of the approaches to improve mechanical properties of solid solution alloys with the face-centered cubic(FCC) structure,whereby a considerable strengthening can be attained by annealing of cold-worked alloys below the recrystallization temperature(T_(rx)).Microscopically,this hardening effect has been ascribed to several mechanisms,*** segregation to defects(dislocation and stacking fault) and short-range chemical ordering,***,none of these mechanisms can well explain the anneal hardening recently observed in phase-pure and coarse-grained FCC-structured high-entropy alloys(hEAs).here we report the observations,using high-resolution electron channeling contrast imaging and transmission electron microscopy,of profuse and stable dislocation substructures in a cold-rolled CoCrFeMnNi hEA subject to an annealing below T_(rx).The dislocation substructures are observed to be thermally stable up to T_(rx),which could arise from the chemical complexity of the high-entropy system where certain elemental diffusion retardation *** microstructure feature is markedly different from that of conventional dilute solid solution alloys,in which dislocation substructures gradually vanish by recovery during annealing,leading to a strength ***,dilute addition of 2 at.% Al leads to a reduction in both microhardness and yield strength of the cold-rolled and subsequently annealed(≤500℃) *** Al induced softening effect,could be associated with the anisotropic formation of dislocation substructure,resulting from enhanced dislocation planar slip due to glide plane softening *** findings suggest that the strength of hEAs can be tailored through the anneal hardening effect from dislocation substructure strengthening.

关键词： Annealing hardening Dislocation substructure strengthening high-entropy alloy Solid solution structure