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Modeling of friction stir welding process for tools design

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Frontiers of Materials Science 2011年第2期5卷 236-245页

作者： san-bao lin Yan-Hua ZHAO Zi-Qiu HE lin WU State Key Lab of Advanced Welding Production Technology Harbin Institute of Technology Harbin 150001 China

A three-dimensional friction stir welding （FSW） process model has been developed based on fluid mechanics. The material transport in the welding process has been regarded as a laminar, viscous, and non-Newtonian liquid that flows past a rotating pin. A criterion to divide the weld zone has been given on the basis of cooperation of velocity field and viscosity field. That is, the η0-easy-flow zone that existed near the tool pin corresponded to the weld nugget zone; the area between the η0-easy-flow zone and η1-viscosity band is corresponded to the thermal-mechanical affected zone （TMAZ）. The model gives some useful information to improve the understanding of material flow in FSW through the simulation result of velocity distribution. In order to appraise the friction stir pin design, three kinds of pin geometry, one is column pin, the second is taper pin, and the last one is screw threaded taper pin, were used in the model. The pin geometry seriously affected the simulation result of velocity distribution in the η0-easy-flow zone. The velocity distribution in the η0-easy-flow zone can be considered as the criterion of optimizing friction stir tool design. This study will benefit to direct the friction stir tool design.

关键词： friction stir welding (FSM) 2014Al alloy, model, flow, fdction stir pin

Effect of Ultrasonic Impact on the Microstructure of Welded Joint of 2195 Al–Li Alloy

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Acta Metallurgica Sinica(English Letters) 2016年第4期29卷 367-372页

作者： Qi-Hao Chen san-bao lin Chun-Li Yang Cheng-Lei Fan State Key Laboratory of Advanced Welding and Joining Harbin Institute of Technology

It is known that an ultrasonic impact during tungsten inert gas welding can refine the grains and improve the mechanical properties of the welded joints of aluminum alloys. However, the influence mechanism of the ultrasonic impact on the microstructures is still unclear. In this research, the effects of the mechanical and ultrasonic impact on the microstructures of the welded joint of 2195 Al-Li alloy are analyzed. It is found that the mechanical impact could not refine the grains, but the ultrasonic impact could refine the grains. The grains become smaller in the weld center with an increase in the ultrasonic amplitude. Possible mechanisms for the grain refinement are discussed. The results show that the small temperature gradient promotes formation of the equiaxed grain and the cavitation promotes heterogeneous nucleation.

关键词： Ultrasound TIG welding Microstructure Al-Li alloy

Long-term Evolution of Solar Activity and Prediction of the Following Solar Cycles

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Research in Astronomy and Astrophysics 2024年第3期24卷 194-204页

作者： Pei-Xin Luo bao-lin Tan National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China

Solar activities have a great impact on modern high-tech systems,such as human aerospace activities,satellite communication and navigation,deep space exploration,and related scientific ***,studying the long-term evolution trend of solar activity and accurately predicting the future solar cycles are highly *** on the wavelet transform and empirical function fitting of the longest recorded data of the annual average relative sunspot number(ASN)series of 323 yr to date,this work decisively verifies the existence of the solar century cycles and confirms that its length is about 104.0 yr,and the magnitude has a slightly increasing trend on the timescale of several hundred *** on this long-term evolutionary trend,we predict solar cycles 25 and26 by using phase similar prediction *** for solar cycle 25,its maximum ASN will be about146.7±33.40,obviously stronger than solar cycle *** peak year will occur approximately in 2024,and the period will be about 11±1 *** for solar cycle 26,it will start around 2030,and reach its maximum between2035 and 2036,with maximum ASN of about 133.0±3.200,and period of about 10 yr.

关键词： Sun activity-Sun evolution-(Sun) sunspots-methods data analysis

Effect of Ultrasound on Heterogeneous Nucleation in TIG Welding of Al–Li Alloy

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Acta Metallurgica Sinica(English Letters) 2016年第12期29卷 1081-1088页

作者： Qi-Hao Chen san-bao lin Chun-Li Yang Cheng-Lei Fan Hong-Liang Ge State Key Laboratory of Advanced Welding and Joining Harbin Institute of Technology

The effect of ultrasound on heterogeneous nucleation in a tungsten inert gas （TIG） weld pool of 2195 Al-Li alloy has been investigated by a series of experiments. An ultrasonic vibration was imposed on the surface of base material before turning off the welding arc during the TIG welding implemented at a fixed point. The results suggest that ultrasound could promote heterogeneous nucleation in the TIG weld pool of 2195 Al-Li alloy. The grain around the fusion zone is changed from a column grain to an equiaxed grain after applying the ultrasonic treatment. To study the influencing mechanism of ultrasound on heterogeneous nucleation, further investigations were implemented where the welding arc was turned off after turning off the ultrasonic power. The results show that the equiaxed grain around the fusion zone disappeared gradually with an increase in heat input after turning off the ultrasonic power. It suggests that ultrasound could promote the heterogeneous nucleation particle to nucleate in advance before turning off the welding arc and the crystal nucleus could again be melted with an increase in heat input after turning off the ultrasonic power. Moreover, the effects of the welding current and ultrasonic amplitude on heterogeneous nucleation in the weld pool of 2195 Al-Li alloy were also investigated. Possible influencing mechanism of the welding current and ultrasonic amplitude on heterogeneous nucleation was discussed.

关键词： Ultrasound TIG welding Grain Al-Li alloy

Microstructure and Corrosion Behavior of Friction Stir Welded Al Alloy Coated by In Situ Shot-Peening-Assisted Cold Spray

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Acta Metallurgica Sinica(English Letters) 2020年第1期33卷 172-182页

作者： Hua Zhang Chang-Yu Zhao Qi-Long Guo Rui-Sheng Yang Li-Yuan Liu san-bao lin School of Mechanical Engineering Beijing Institute of Petrochemical TechnologyBeijing 102617China Beijing Institute of Astronautical Systems and Engineering Beijing 100076China State Key Laboratory of Advanced Welding and Joining Harbin Institute of TechnologyHarbin 150001China

To improve the corrosion resistance of friction stir welded(FSW)joints,in situ shot-peening-assisted cold spray coating was applied to the surface of FSW *** microstructure and corrosion behavior of the coatings were *** results showed that a dense coating was obtained by cold spraying ***,the use of in situ shot-peeningassisted technology significantly reduced the porosity of the coating,which has a positive impact on the microstructure and the mechanical *** corrosion tests showed that the coating aff ected positively on the corrosion *** the coated surface,the craters caused by shot-peening particles were corroded in the form of exfoliation corrosion,while the exposed particles were corroded in the form of intercrystalline *** work provides a new approach to the corrosion protection of FSW joints.

关键词： Aluminum alloy coating Cold spray Friction stir welding In situ shot-peening Intergranular corrosion

An isolated symmetrical 2T2R cell enabling high precision and high density for RRAM-based in-memory computing

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Science China(Information Sciences) 2024年第5期67卷 287-294页

作者： Yaotian linG Zongwei WANG Yuhang YANG lin bao Shengyu bao Qishen WANG Yimao CAI Ru HUANG School of Integrated Circuits Beijing Advanced Innovation Center for Integrated Circuits Peking University State Key Laboratory of Information Photonics and Optical Communications Beijing University of Posts and Telecommunications

In-memory computing(IMC), leveraging emerging memories, holds significant promise in overcoming memory limitations and improving energy efficiency. However, the prevailing IMC array structure based on serially connected transistors and memory cells(1T1R/2T2R), along with the signed weight mapping scheme, can lead to asymmetrical weight sensing issues(AWS) due to electrical asymmetry within the1T1R/2T2R structure, particularly in highly scaled cells where the transistor's resistance becomes significant. In this paper, we propose and fabricate an electrically symmetric memory cell based on a physically isolated 2T2R structure for IMC. This design aims to enhance the precision and density of RRAM-based IMC arrays. The 2T2R cells are manufactured using the back-end-of-line(BEOL) process of a commercial40 nm technology platform. The feasibility of this design is verified through measured and simulated results,showcasing its capability to address the issue of AWS. Compared to conventional 2T2R cells, this design achieves a considerably smaller transistor footprint without compromising accuracy, while also improving integration density by 42.2%. These innovative memory cell advancements have the potential to further advance high-energy-efficient IMC technology.

关键词： RRAM 2T2R multi-level storage weight asymmetry in-memory computing

Effect of Mo and cold forging deformation on strength and ductility of cobalt-based alloy L605

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Journal of Iron and Steel Research(International) 2024年第7期31卷 1811-1823页

作者： Zhong-lin Wang Zhi-hua Gong Quan Li Han-sheng bao School of Materials and Metallurgy Inner Mongolia University of Science and TechnologyBaotou 014017Inner MongoliaChina Institute of Special Steels Central Iron and Steel Research Institute Co.Ltd.Beijing 100081China

Mo element was added to cobalt-based alloy L605,and cold forging deformation was *** effects of the addition and cold forging deformation on the microstructure and mechanical properties of the alloy were studied by thermodynamic calculation,electron backscatter diffraction,transmission electron microscopy,and X-ray *** stacking fault energy(SFE)of the alloy decreased after the addition,and the formation of stacking faults and intersections were promoted to improve the strength and *** tensile strength of the alloy with Mo increased from 1190 to 1702 MPa after 24%cold deformation,producing significant work *** strengthening mechanism is strain-induced martensitic transformation(SIMT)and deformation *** alloy,combined with Mo and after 24%deformation,had both high strength and ductility in comparison with the original cobalt-based alloy *** is attributed to the lower SFE which caused the increase in stacking fault *** the tensile process,theε-hcp phase was easily generated at the stacking fault to reduce the stress concentration and increase the *** SIMT by adjusting the density of stacking faults can improve the mechanical properties of cobalt-based ***ε-hcp phase,the interaction between deformation twins and dislocations,and the interaction between e-hcp phases during cold forging deformation caused local stress concentration,lowering ductility and toughness.

关键词： Cobalt-based alloy-Stacking fault energy Strain-induced martensitic transformation Deformation twin Cold forging deformation

Gas metal arc welding of high nitrogen stainless steel with AreN_(2)-O_(2)ternary shielding gas

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Defence Technology（防务技术） 2021年第3期17卷 923-931页

作者： Zeng Liu Cheng-lei Fan Zhu Ming Chao Chen Ang Liu Chun-li Yang san-bao lin Lang-ping Wang State Key Laboratory of Advanced Welding and Joining Harbin Institute of TechnologyHarbin150001China Inner Mongolia Metal Material Research Institute BaotouChina

High nitrogen stainless steel with nitrogen content of 0.75%was welded by gas metal arc welding with Ar-N_(2)-O_(2)ternary shielding *** effect of the ternary shielding gas on the retention and improvement of nitrogen content in the weld was *** test was conducted first to compare the ability of O_(2)and CO_(2)in prompting nitrogen *** nitrogen content of the surfacing metal with O_(2)is slightly higher than CO_(2).And then AreN_(2)-O_(2)shielding gas was applied to weld high nitrogen stainless *** using N_(2)-containing shielding gas,the nitrogen content of the weld was improved by 0.1 wt%.As N_(2)continued to increase,the increment of nitrogen content was not obvious,but the ferrite decreased from the top to the *** the proportion of N_(2)reached 20%,a full austenitic weld was obtained and the tensile strength was improved by 8.7%.Combined with the results of surfacing test and welding test,it is concluded that the main effect of N_(2)is to inhibit the escape of nitrogen and suppress the nitrogen diffusion from bottom to the top in the molten pool.

关键词： High nitrogen stainless steel AreN2-O2 shielding gas Action mechanism

Mechanism and control of nonuniform phase transformation of microalloyed dual-phase steel during cooling process after hot rolling

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Journal of Iron and Steel Research(International) 2024年第2期31卷 428-441页

作者： Wen-quan Sun Sheng-yi Yong Tie-heng Yuan Chao Liu san-bao Zhou Rui-chun Guo Meng-xia Tang National Engineering Research Center for Advanced Rolling and Intelligent Manufacturing University of Science and Technology BeijingBeijing100083China Strip Production Plant Xichang Steel and Vanadium Corporation of Pangang GroupXichang615000SichuanChina

After cooling in the hot rolling process,the metallographic structure of microalloyed dual-phase steel is nonuniform along the rolling direction,while the thickness fluctuation of microalloyed dual-phase steel with a nonuniform metallographic structure will occur during cold *** mechanism of nonuniform phase transformation of microalloyed dual-phase steels was studied during the cooling process after hot rolling,and the nonuniform phase transformation of microalloyed dual-phase steel was regulated during the cooling process after hot rolling through process ***,the empirical equation of phase transformation temperature was measured by a dilatometer considering thermal ***,the phase field and temperature field of laminar cooling process were calculated to provide initial boundary conditions for the finite element *** that,the coupling finite element model of the temperature phase transformation of the strip steel in coiling transportation process was *** simulation results show that the different thermal contact conditions of the microalloyed dual-phase steel during coil transportation lead to uneven cooling of the coil,which leads to nonuniform transformation of the coil along the rolling *** addition,by prolonging the time interval from coiling to unloading,the phenomenon of nonuniform phase transformation of microalloyed dual-phase steel can be effectively *** simulation results are applied to industrial *** application results show that prolonging the time interval from coiling to unloading can effectively improve the nonuniform phase transformation of microalloyed dual-phase steel in the cooling process after hot rolling.

关键词： Microalloyed dual-phase steel Thickness fluctuation Cooling Heat conduction Nonuniform phase transition Finite element method