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| 1 | Enhanced Mechanical Properties of Friction Stir Welded 5083Al-H19 Joints with Additional Water Cooling显示文摘3-mm-thick 5083Al-H19 rolled plates were friction stir welded(FSW) at tool rotation rates of 800 and200 rpm with and without additional water cooling. With decreasing the rotation rate and applying water cooling, softening in the FSW joint was significantly reduced. At a low rotation rate of 200 rpm with additional water cooling, almost no obvious softening was observed in the FSW joint, and therefore a FSW5083Al-H19 joint with nearly equal strength to the base material(BM) was obtained. Furthermore, the grains in the nugget zone were considerably refined with reducing the heat input and ultrafine equiaxed grains of about 800 nm were obtained in the lowest heat input condition. This work provides an effective method to achieve high property FSW joints of precipitate-hardened and work-hardened Al alloys. | B.B.Wang F.F.Chen F.Liu W.G.Wang P.Xue Z.Y.Ma | 2017 | Journal of Materials Science & Technology2017，33，9： | 16 |
| 2 | Achieving ultra-high strength friction stir welded joints of high nitrogen stainless steel by forced water cooling显示文摘The microstructure and properties of water-cooled and air-cooled friction stir welded(FSW) ultra-high strength high nitrogen stainless steel joints were comparatively studied. With additional rapid cooling by flowing water, the peak temperature and duration at elevated temperature during FSW were significantly reduced. Compared to those in the air-cooled joint, nugget zone with finer grains(900 nm) and heat affected zone with higher dislocation density were successfully obtained in the water-cooled joint,leading to significantly improved mechanical properties. The wear of the welding tool was significantly reduced with water cooling, resulting in better corrosion resistance during the immersion corrosion test. | H.Zhang D.Wang P.Xue L.H.Wu D.R.N B.L.Xiao Z.Y.Ma | 2018 | Journal of Materials Science & Technology2018，34，11： | 5 |
| 3 | Achieving a strong polypropylene/aluminum alloy friction spot joint via a surface laser processing pretreatment显示文摘Strong metal/non-polar plastic dissimilar joints are highly demanded for the lightweight design in many fields,which,however,are rather challenging to achieve directly via welding.In this study,we designed a laser processing pretreatment on the Al alloy to create a deep porous Al surface structure,which was successfully joined to the polypropylene(PP) via friction spot welding.A maximum joint strength of29 MPa was achieved,the same as that of the base PP(i.e.the joint efficiency reached 100%),much larger than ever reported.The joining mechanism of the Al alloy and the PP was mainly attributed to the large mechanical interlocking effect between the laser processed Al porous structure and the re-solidified PP and the formation of chemical bond at the interface.The deep porous Al surface structure modified by laser processing largely changed the Al-PP reaction feature.The evidence of the C-O-Al chemical bond was first time found at the non-polar plastic/Al joint interface,which was the reaction result between the oxide on the Al alloy surface and thermal oxidization products of the PP during welding.This study provides a new way for enhancing metal-plastic joints via surface laser treatment techniques. | S.C.Han L.H.Wu C.Y.Jiang N.Li C.L.Jia P.Xue H.Zhang H.B.Zhao D.R.Ni B.L.Xiao Z.Y.Ma | 2020 | Journal of Materials Science & Technology2020，47，15： | 4 |
| 4 | Evolution mechanisms of microstructure and mechanical properties in a friction stir welded ultrahigh-strength quenching and partitioning steel显示文摘Ultrahigh-strength quenching and partitioning(Q&P) steels have attracted strong interests in the auto manufactory,while the comprehensive understanding in the microstructure and mechanical behavior of their welded joints is highly needed to enrich their applications.In the present work,it is designed to make an insight into these imperative conundrums.Equal strength Q&P 1180 steel joints to parent metal were successfully fabricated via friction stir welding(FSW) technique under different parameters. Apparent hardening and softening were observed in stir zone(SZ) and heat-affected zone(HAZ) respectively,whose microstructures strongly depended on the peak temperature and cooling rate during welding.The formation of fresh martensite was the main mechanism for the SZ hardening,while the decomposition of metastable phases played key roles in the microhardness drop of the HAZ.A heat source zone-isothermal phase transition layer model was proposed to clarify the impregnability of the joint strength under parameter variation.The dual-phase structure,nano-carbide particles,tempered initial martensite,and ultrafine-grained ferrite synergistically improved the strain hardening ability of the HAZ,which eventually resulted in the equal strength FSW joints. | Z.W.Wang J.F.Zhang G.M.Xie L.H.Wu H.Zhang P.Xue D.R.Ni B.L.Xiao Z.Y.Ma | 2022 | Journal of Materials Science & Technology2022，，7： | 3 |
| 5 | Fabrication of large-bulk ultrafine grained 6061 aluminum alloy by rolling and low-heat-input friction stir welding显示文摘In this study, the ultrafine grained(UFG) 6061 Al alloys fabricated by cold rolling were friction stir welded(FSW) with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input parameters of 400 rpm rotation rate in water(400-Water) could effectively inhibit the coarsening of recrystallized grains, reduce the precipitation rate, and retain more dislocations of the UFG 6061 Al parent metal. 400-Water joint showed high lowest-hardness value, narrow low-hardness zone, and high tensile strength, attributing to the effect of dislocation, grain boundary, solid-solution, and precipitation hardening. This work provides an effective strategy to fabricate large-sized bulk UFG Al alloy by cold rolling with large deformation and low-heat-input FSW. | C.Y.Liu B.Qu P.Xue Z.Y.Ma K.Luo M.Z.Ma R.P.Liu | 2018 | Journal of Materials Science & Technology2018，34，1： | 3 |
| 6 | Ventilation of air-conditioned residential buildings: A case study in Hong Kong显示文摘More and more studies reported that there were insufficient ventilation and excessive CO_2 concentration in air-conditioned residential buildings, but few solutions were provided. This study investigates the overnight evolution of CO_2 concentration in air-conditioned residential buildings and then focuses mainly on the evaluation of three ventilation strategies, including overnight natural ventilation, short-term mechanical ventilation and short-term natural ventilation. On-site measurements were conducted in a typical residential bedroom in Hong Kong in September. The indoor and outdoor CO_2 concentration, air temperature and relative humidity as well as the outdoor wind speed during the measurements were analysed. Ventilation rates were calculated based on the time series of CO_2 concentration. This study confirms that additional ventilation is usually needed in air-conditioned residential buildings. Overnight natural ventilation with even a small opening is associated with excessive energy consumption and deteriorated indoor thermal environment. Short-term natural ventilation strategies are inefficient and uncontrollable. Compared to the best short-term natural ventilation strategy, a reasonably designed short-term mechanical ventilation strategy requires only a 41% of ventilation period to complete one full replacement of indoor air and to reach a lower indoor CO_2 concentration. Nighttime case studies and a theoretical analysis suggest that a few several-minute mechanical ventilation periods could potentially maintain an acceptable indoor air quality for a normal sleeping period of 8 h. | Z.T.Ai C.M.Mak D.J.Cui P.Xue 侯恩哲 | 2016 | 建筑节能2016，44，9： | 2 |
| 7 | Effect of post weld artificial aging and water cooling on microstructure and mechanical properties of friction stir welded 2198-T8 Al-Li joints显示文摘Friction stir welding(FSW)under both air cooling and water cooling conditions with welding parameters of 800-1200 rpm rotation rates and 50-200 mm/min welding speeds was carried out on 2198-T8 Al-Li alloys,and post weld artificial aging was performed on the air cooled joints.No welding defects other than lazy S were observed in the nugget zone(NZ)for all joints.Under air cooling condition,the lowest hardness zone(LHZ)occurred in the heat affected zone(HAZ).FSW resulted in gradual dissolution of original T_(1),θ′andδ′/β′from the base material(BM)to the thermo-mechanically affected zone(TMAZ),and complete dissolution of all precipitates in the NZ withδ′/β′and Guinier-Preston zones precipitating during cooling.The air cooled joints exhibited no noticeable changes in intrinsic tensile strength with a joint strength reaching 81.3%of the BM,but varied elongation with welding parameters,which was closely related to failure in the NZ and fracture along lazy S.Post weld artificial aging led to the largest hardness recovery in the TMAZ but smaller hardness recovery in the initial LHZ and the NZ.Different aging kinetics across the joint was determined by volume fraction of both original precipitate dissolu-tion during welding and coarse particles formed during aging,and by dislocation density inherited from welding.Post weld artificial aging greatly enhanced the joint strength with the ultimate tensile strength reaching 87.3%of the BM.As compared to air cooling condition,water cooling hardly affected the NZ hardness and did not improve the joint strength,and the reason was discussed in light of precipitates,hardness changes and fracture behavior. | Y.Tao Z.Zhang P.Xue D.R.Ni B.L.Xiao Z.Y.Ma | 2022 | Journal of Materials Science & Technology2022，，28： | 2 |
| 8 | Effect of heat-input on pitting corrosion behavior of friction stir welded high nitrogen stainless steel显示文摘In this study, different welding param eters were selected to investigate the effects of heat-in put on the microstructure and corrosion resistance of the friction stir welded high nitrogen stainless steel joints. The results show ed that, the welding speed had major influence on the duration at elevated tem perature rather than the peak tem perature. The hardness distribution and tensile properties of the nugget zones (NZs) for various joints were very similar while the pitting corrosion behavior of various NZs showed major differences. Large heat-input resulted in the ferrite bands being the pitting location, while tool wear bands were sensitive to pitting corrosion in the low heat-input joints. Cr diffusion and tool wear were the main reasons for pitting. The mechanisms of pitting corrosion in the NZs were analyzed in detail. | H.Zhang P.Xue D.Wang L.H.Wu D.R.Ni B.L.Xiao Z.Y.Ma | 2019 | Journal of Materials Science & Technology2019，35，7： | 2 |
| 9 | Microstructural refinement mechanism and its effect on toughness in the nugget zone of high-strength pipeline steel by friction stir welding显示文摘High-strength pipeline steel was subjected to friction stir welding(FSW)at rotation rates of 400-700 rpm,and the grain refinement mechanism of the nugget zone(NZ)was determined.The thermomechanical process during FSW in the NZ was simulated by multi-pass thermal compression,thereby achieving the austenitic non-recrystallization temperature(T_(nr)).The austenitic non-recrystallization in the NZ at the lowest rotation rate of 400 rpm caused a significant grain refinement.Furthermore,the reduced rotation rate also resulted in the formation of a high ratio of island-like martensite-austenite(M-A)constituent.The toughness of the NZs was enhanced as the rotation rate decreased,which is attributed to the fine effective grains and homogeneously distributed fine M-A constituents dramatically inhibiting crack initiation and propagation. | R.H.Duan G.M.Xie P.Xue Z.Y.Ma Z.A.Luo C.Wang R.D.K.Misra | 2021 | Journal of Materials Science & Technology2021，，34： | 1 |
| 10 | 查看详情显示文摘 | P.Xue X.D.Song X.R.Cao | | 0，，： | 1 |
| 11 | Static spheroidization and its effect on superplasticity of fine lamellae in nugget of a friction stir welded Ti-6Al-4V joint显示文摘The spheroidization of the lamellar structure can greatly contribute to the superplasticity of the nugget zone(NZ)of Ti alloy welds,which is the key to achieve the integral superplastic forming of welds for the fabrication of large-scale complex components.However,the spheroidization process is complex and costly since it cannot be obtained generally,unless the lamellae suffers from a large deformation.In this study,the static spheroidization was achieved for the fine lamellae structure in the nugget of a friction stir welded(FSW)Ti-6Al-4V joint,particularly by the annealing without any deformation.The specialα/βinterface obeying a Burgers orientation relationship(BOR)after FSW was first time directly observed,whose effect on the spheroidization was discussed.A new static spheroidization mechanism with the gradual coalescence of the adjacent lamellae was discovered,which we named as“termination coalescence”.There was a slower coarsening rate in the lamellar structure than in the classical equiaxed one,due to the BOR in the lamellae,although both of them exhibited a volume diffusion character during annealing.Consequently,the similar superplasticity can be achieved for the base material and NZ after annealing.This study can provide a new way to the spheroidization and a theoretical basis for the integral superplastic forming of welds during production. | C.L.Jia L.H.Wu P.Xue H.Zhang D.R.Ni B.L.Xiao Z.Y.Ma | 2022 | Journal of Materials Science & Technology2022，，24： | 0 |
| 12 | Effect of static annealing on superplastic behavior of a friction stir welded Ti-6Al-4V alloy joint and microstructural evolution during deformation显示文摘Structural integration is one of the most critical developing directions in the modern aerospace field,in which large-scale complex components of Ti alloys are proposed to be fabricated via the method of welding + superplastic forming.However,the undesired strain localization appeared during superplastic deformation of the entire joint has largely hindered the development of this method.In our study,a combination process of friction stir welding(FSW) + static annealing+ superplastic deformation was first time proposed to eliminate severe local deformation.To achieve this result,a fully fine lamellar structure was obtained in the nugget zone(NZ) via FSW,which was totally different from the mill-annealed structure in the base material(BM).After annealing at 900℃ for 180 min,the BM and NZ then exhibited the similar elongation of> 500% and similar flow stress at 900 ℃,3 × 10^(-3)s^(-1),which was the precondition for achieving uniform superplastic deformation in the entire joint.Moreover,the different microstructures in the BM and NZ tended to become the similar equiaxed structure after deformation,which was the result of different microstructural evolution mechanisms in the NZ and BM.For the NZ,there was a static and dynamic spheroidization of the fully lamellar structure during the process,which could largely reduce the flow softening of the fully lamellar structure.For the BM,a new view of 'Langdon-CRSS theory'(CRSS,critical resolved shear stress) was proposed to describe the fragmentation of the coarse equiaxed structure,which established the relationship between grain boundary sliding and intragranular deformation during deformation. | C.L.Jia L.H.Wu P.Xue D.R.Ni B.L.Xiao Z.Y.Ma | 2022 | Journal of Materials Science & Technology2022，，35： | 0 |
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