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Journal of Magnesium and Alloys 2022年第4期10卷 979-992页

作者： Isaac Dinaharan Shuai Zhang gaoqiang chen Qingyu Shi IDM-Joint Lab Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China The State Key Laboratory of Tribology Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China

Poor ductility is the primary concern of magnesium matrix composites(MMCs)inflicted by non-deformable ceramic particle reinforcements.Metal particles which melt at elevated temperature can be used as reinforcement to improve the deformation characteristics.Ti-6Al-4V particles reinforced AZ31 MMCs were produced through friction stir processing(FSP)which was carried out in a traditional vertical milling machine.The microstructural features as well as the response to external tensile load were explored.A homogenous distribution of Ti-6Al-4V was achieved at every part of the stir zone.There was no chemical decomposition of Ti-6Al-4V.Further,Ti-6Al-4V did not react with Al and Zn present in AZ31 alloy to form new compounds.A continuous strong interface was obtained around Ti-6Al-4V particle with the matrix.Ti-6Al-4V particles underwent breakage during processing due to severe plastic strain.There was a remarkable refinement of grains in the composite caused by dynamic recrystallization in addition to the pinning of smaller size broken particles.Dense dislocations were observed in the matrix because of plastic deformation and the associated strain misfit.Ti-6Al-4V particles improved the tensile behavior and assisted to obtain appreciable deformation before fracture.Brittle mode of failure was avoided.

关键词： Magnesium matrix composite Friction stir processing Ti-6Al-4V Microstructure Tensile strength

Simultaneous enhancement of mechanical properties and corrosion resistance of as-cast Mg-5Zn via microstructural modification by friction stir processing

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镁合金学报(英文) 2023年第6期11卷 1931-1943页

作者： Fei Long gaoqiang chen Mengran Zhou Qingyu Shi Qu Liu State Key Laboratory of Tribology Tsinghua UniversityBejjing 100084China Department of Mechanical Engineering Tsinghua UniversityBejjing 100084China

Magnesium alloys are ideal lightweight materials;however,their applications are extremely limited due to their low strength,poor ductility,and weak corrosion resistance.In the present study,a friction stir processing(FSP)treatment was employed to optimize the mechanical properties and corrosion resistance of an as-cast Mg-5Zn alloy.The average grain size of the Mg-5Zn alloy was refined from 133.8μm to1.3μm as a result of FSP.Along different directions,FSP exhibited the enhancement effects on different mechanical properties.Furthermore,according to the potentiodynamic polarization results,the corrosion current density at the free-corrosion potential of the FSPed sample,was 4.1×10^(-6)A/cm^(2)in 3.5 wt.%Na Cl aqueous solution,which was significantly lower than that of the as-cast sample.Electrochemical impedance spectroscopy revealed that the polarization impedance,Rp,of the FSPed sample was 1534Ω/cm^(2)in 3.5 wt.%NaCl aqueous solution,which was 71.4%greater than that of the as-cast sample.The corrosion morphology of the FSPed sample in 3.5 wt.%NaCl aqueous solution exhibited largely uniform corrosion,rather than severe localized corrosion characteristics,which further reduced the corrosion depth on the basis of reducing the corrosion current density.The results presented herein indicate that FSP is a viable technique for simultaneously improving the mechanical properties and corrosion resistance of the as-cast Mg-5Zn alloy.

关键词： Friction stir processing Magnesium alloy Corrosionmode Texture softening Anisotropy in mechanical properties

Improved distortion prediction in additive manufacturing using an experimental-based stress relaxation model

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Journal of Materials Science & Technology 2020年第24期59卷 83-91页

作者： Ruishan Xie Qingyu Shi gaoqiang chen State Key Laboratory of Tribology Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China Key Laboratory for Advanced Material Processing Technology Ministry of EducationBeijing 100084China

In additive manufacturing(AM),numerous thermal cycles make stress relaxation a significant factor in affecting the material mechanical response.However,the traditional material constitutive model cannot describe repeated annealing behavior.Here,we propose an improved constitutive model based on a serial of stress relaxation experiments,which can descript the temperature and time-dependent stress relaxation behavior during AM.By using the proposed relaxation model,the prediction accuracy is significantly improved due to the recovery of inelastic strain during multilayer deposition.The results are validated by both in-situ and final distortion measurements.The influence mechanism of the relaxation behavior on material mechanical response is explained by the three-bar model in thermo-elastic-plastic theory.The relaxation behavior during the whole AM process is clarified.The stress behavior is found to have a limited effect when merely depositing several layers;nevertheless,it becomes a prominent impact when depositing multiple layers.The proposed model can enhance modeling accuracy both in AM and in multilayer welding.

关键词： Additive manufacturing Welding Thermo-mechanical modeling Distortion prediction Stress relaxation

Thermo-mechanical Analysis of Friction Stir Welding:A Review on Recent Advances

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Acta Metallurgica Sinica(English Letters) 2020年第1期33卷 3-12页

作者： gaoqiang chen Shuai Zhang Yucan Zhu chengle Yang Qingyu Shi State Key Laboratory of Tribology Department of Mechanical EngineeringTsinghua University1 Tsinghua Yuan ParkBeijing 10084China

In recent studies,critical research interest exists in the thermo-mechanical analysis of the friction stir welding(FSW)process by numerical simulation.In this review,the thermo-mechanical analysis for FSW is overviewed regarding the computational approaches,the heat generation,the temperature,and the material fl ow behavior.Current concerns,challenges,and opportunities in current studies are discussed considering the application of the thermo-mechanical analysis.Generally,larger computational scale and better computational effi ciency are required to allow better spatial resolution in future analysis.The concepts and approaches demonstrated in the thermo-mechanical analysis for FSW open up quantitative prospects for the design of the FSW process.

关键词： Friction stir welding Temperature Heat generation Material flow Microstructure Defect

Computational fluid dynamics simulation of friction stir welding:A comparative study on different frictional boundary conditions

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Journal of Materials Science & Technology 2018年第1期34卷 128-134页

作者： gaoqiang chen Qingxian Ma Shuai Zhang Jianjun Wu Gong Zhang Qingyu Shi Department of Mechanical Engineering Tsinghua University State Key Laboratory of Tribology Tsinghua University

Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.

关键词： Friction stir welding Numerical simulation Frictional boundary condition Heat transfer Material deformation

搅拌摩擦加工调控Mg-5Zn-0.6Zr合金耐蚀性的研究

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材料导报 2024年第10期38卷 151-156页

作者：龙飞刘瞿朱艺星周梦然陈高强史清宇清华大学机械工程系清洁高效透平动力装备全国重点实验室北京100084 先进成形制造教育部重点实验室北京100084

作为一种储量足、比强度和比模量高的轻质结构材料和功能材料,镁的应用前景十分广阔,然而镁的耐蚀性不佳严重限制了其应用范围,较大尺寸的沉淀相导致的电偶腐蚀是镁合金耐蚀性不佳的重要原因。本工作选取铸态Mg-5Zn-0.6Zr合金作为研究对... 详细信息

作为一种储量足、比强度和比模量高的轻质结构材料和功能材料,镁的应用前景十分广阔,然而镁的耐蚀性不佳严重限制了其应用范围,较大尺寸的沉淀相导致的电偶腐蚀是镁合金耐蚀性不佳的重要原因。本工作选取铸态Mg-5Zn-0.6Zr合金作为研究对象,对该合金进行了搅拌摩擦加工处理,并对搅拌摩擦加工前后合金的组织结构和电化学性能进行了检测分析。结果表明,搅拌摩擦加工处理后的Mg-5Zn-0.6Zr合金形成了较强的(0001)基面织构,且大部分区域位错密度较低,晶粒尺寸从66.4μm细化到1.6μm,沉淀相发生了一定程度的破碎和弥散分布,在3.5%(下文如无特别说明,均指质量分数)NaCl水溶液中开路电位下的腐蚀电流密度由38.3μA/cm^(2)降至17.0μA/cm^(2),极化电阻由48.98Ω·cm^(2)提升至197.02Ω·cm^(2)。研究表明,搅拌摩擦加工可以有效提高镁合金的耐蚀性。

关键词：搅拌摩擦加工镁合金耐蚀性动态再结晶

A novel aluminum-carbon nanotubes nanocomposite with doubled strength and preserved electrical conductivity

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Nano Research 2021年第8期14卷 2776-2782页

作者： Shuai Zhang gaoqiang chen Timing Qu Jinquan Wei Yufan Yan Qu Liu Mengran Zhou Gong Zhang Zhaoxia Zhou Huan Gao Dawei Yao Yuanwang Zhang Qingyu Shi Hua Zhang State Key Laboratory of Tribology Key Laboratory for Advanced Materials Processing Technology Ministry of Education of ChinaDepartment of Mechanical Engineering Tsinghua UniversityBeijing 100084China Key Lab for Advanced Materials Processing Technology of Education Ministry School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Loughborough materials characterization center Department of materialsLoughborough UniversityLoughboroughLEU 3TUUK State Key Laboratory of Special Cable Technology Shanghai Electric Cable Research Institute Co.Ltd.Shanghai 200093China School of Mechanical Engineering Beijing Institute of Petrochemical Technology Beijing 102617China

Enhancing the mechanical strength of highly conductive pure metals usually causes significant reduction in their electrical conductivity.For example,introducing phase/matrix interfaces or more grain boundaries,are common and effective methods to strengthen metals.But it simultaneously increases the electron scattering at the interface,thus reducing the electrical conductivity.In this study,we demonstrate that pure aluminum(Al)/carbon nanotubes(CNTs)nanocomposites prepared by friction stir processing have successfully broken through these limitations.The yield strength and tensile strength of Al/CNTs nanocomposites have improved by 104.7%and 51.8%compared to pure Al,while the electrical conductivity remained comparable to that of pure Al.To explore the potential mechanisms,the interface between CNTs and Al was examined and characterized by transmission electron microscopy(TEM)and Raman spectroscopy.Little interfacial reaction compounds were present and no visible physical gaps were observed at CNTs and Al interfaces.We defined it as a clean and tightly bonded interface.Although the quantity of phase interface has increased,the electrical conductivity of the nanocomposite remains approximately unchanged.We attribute the preserved electrical conductivity to the clean and tightly bonded CNTs/Al interface in the nanocomposite.

关键词： carbon nanotubes/aluminum nanocomposites mechanical properties electrical conductivity friction stir processing interface

Effect of annealing on the electrical performance of N-polarity GaN Schottky barrier diodes

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Journal of Semiconductors 2024年第4期45卷 48-55页

作者： Nuo Xu gaoqiang Deng Haotian Ma Shixu Yang Yunfei Niu Jiaqi Yu Yusen Wang Jingkai Zhao Yuantao Zhang State Key Laboratory of Integrated Optoelectronics College of Electronic Science and EngineeringJilin UniversityChangchun 130012China

A nitrogen-polarity(N-polarity)GaN-based high electron mobility transistor(HEMT)shows great potential for high-fre-quency solid-state power amplifier applications because its two-dimensional electron gas(2DEG)density and mobility are mini-mally affected by device scaling.However,the Schottky barrier height(SBH)of N-polarity GaN is low.This leads to a large gate leakage in N-polarity GaN-based HEMTs.In this work,we investigate the effect of annealing on the electrical characteristics of N-polarity GaN-based Schottky barrier diodes(SBDs)with Ni/Au electrodes.Our results show that the annealing time and tem-perature have a large influence on the electrical properties of N-polarity GaN SBDs.Compared to the N-polarity SBD without annealing,the SBH and rectification ratio at±5 V of the SBD are increased from 0.51 eV and 30 to 0.77 eV and 7700,respec-tively,and the ideal factor of the SBD is decreased from 1.66 to 1.54 after an optimized annealing process.Our analysis results suggest that the improvement of the electrical properties of SBDs after annealing is mainly due to the reduction of the inter-face state density between Schottky contact metals and N-polarity GaN and the increase of barrier height for the electron emis-sion from the trap state at low reverse bias.

关键词： nitrogen polarity GaN Schottky barrier diodes annealing interface state

搅拌摩擦加工Mg-Zn合金空蚀—腐蚀交互作用研究

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稀有金属材料与工程 2023年第2期52卷 692-698页

作者：李阳刘瞿龙飞廉影陈高强清华大学机械工程系北京100084 河北工程大学机械与装备工程学院河北邯郸056038

采用搅拌摩擦加工(FSP)技术对铸态Mg-Zn合金进行表面处理,以提高其耐空蚀—腐蚀性能。使用SEM、EDS、XRD、显微硬度计观察和测定表面改性层的显微组织、元素分布、相组成和显微硬度,使用超声振动空蚀设备和电化学工作站研究其耐空蚀—... 详细信息

采用搅拌摩擦加工(FSP)技术对铸态Mg-Zn合金进行表面处理,以提高其耐空蚀—腐蚀性能。使用SEM、EDS、XRD、显微硬度计观察和测定表面改性层的显微组织、元素分布、相组成和显微硬度,使用超声振动空蚀设备和电化学工作站研究其耐空蚀—腐蚀性能。结果表明:FSP技术能够细化和均匀铸态组织,消除成分偏析,提高材料表面硬度。FSP合金在人工海水中更易形成腐蚀产物膜,其保护性能更优,是FSP样品耐腐蚀性能提升的主要原因。铸态样品经FSP改性后硬度依然较低,故蒸馏水条件下的耐空蚀性能未获提升,但改性后合金良好的耐腐蚀性能提升了其在人工海水条件下的耐空蚀性能。

关键词：搅拌摩擦加工铸态Mg-Zn合金耐空蚀-腐蚀性能

Artificial-neural-network-based storage method for three-dimensional temperature field data during friction stir welding

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China Welding 2022年第3期31卷 1-7页

作者：韩策张乾史清宇唐天祥刘新张弓陈高强 Department of Mechanical Engineering Tsinghua UniversityBeijing 100084China Informatization and Industrialization Integration Research Institute China Academy of Information and Communications TechnologyBeijing 100191China

In this paper,a new storage method for the three-dimensional temperature field data based on artificial neural network(ANN)was proposed.A multilayer perceptron that takes the coordinate(x,y,z)as inputs and temperature T as output,is used to fit the three-dimension-al welding temperature field.Effect of number of ANN layers and number of neurons on the fitting errors is investigated.It is found that the errors decrease with the number of hidden layers and neural numbers per layers generally.When the number of hidden layers increases from 1 to 6,the maximum temperature error decreases from 74.74℃to less than 2℃.The three-dimensional temperature field data is obtained by finite element simulation,and the experimental verification is completed by comparing the simulation peak temperatures with the measured results.As an example,an ANN with 4 hidden layers and 12 neurons in each layer were applied to test the performance of the proposed method in storage of the three-dimensional temperature field data during friction stir welding.It is found that the average error between the temperature data stored in ANN and the original simulation data that stored point-by-point is 0.517℃,and the error on the maximum temper-ature is 0.193℃,while the occupied disk space is only 0.27%of that is required in the conventional point-by-point storage.

关键词： friction stir welding temperature field artificial neural network numerical simulation