Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing addit...Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.展开更多
Optimizing pyrolysis processes is critical for improving the efficiency of pyrolysis furnaces.This study presents a strategy to enhance heat transfer through agitation,employing Fluent for detailed numerical simulatio...Optimizing pyrolysis processes is critical for improving the efficiency of pyrolysis furnaces.This study presents a strategy to enhance heat transfer through agitation,employing Fluent for detailed numerical simulation of the thermal behavior.The simulation results show strong agreement with experimental measurements of localized fluid temperature rise.Forced convection induced by impeller rotation significantly improves heat transfer between the fluid and the furnace walls,effectively reducing thermal stratification.At an impeller speed of 240 RPM,the axial temperature difference decreases from 200 K to 50 K compared with stationary conditions,while the average heat transfer coefficient increases by approximately 50%throughout the heating process.The swirl flow generated by impeller motion disrupts the thermal boundary layer,achieving a more uniform temperature distribution and faster thermal response.展开更多
This work examines the microstructure and corrosion properties of fine-grained Al 7075 across different regions under varying cooling conditions during friction stir welding.The findings demonstrate that forced coolin...This work examines the microstructure and corrosion properties of fine-grained Al 7075 across different regions under varying cooling conditions during friction stir welding.The findings demonstrate that forced cooling significantly improves the corrosion resistance of the welded joints.Specifically,the corrosion resistance was the highest in the stir zone,followed by the thermo-mechanical affected zone,and then the heat affected zone.Forced cooling mitigates grain growth by controlling the welding thermal effects,thereby increasing the proportion ofΣ3 grain boundaries.The modification of these microstructural characteristics promotes the formation of a dense oxide layer,thereby enhancing the corrosion resistance.Furthermore,forced cooling mitigates the precipitation and coarsening of the anodic phase in the stir zone,which in turn reduces the susceptibility of the joint to pitting corrosion.Additionally,the lower recrystallization texture content in the joint,resulting from forced cooling,contributes to a reduction in the number of corrosion-active sites,thereby further improving the corrosion performance of the welded joint.展开更多
High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as not...High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as notable solid-state welding and processing techniques,have been proved effectiveness in enhancing microstructures and mechanical properties of HEAs.This review article summarizes the current status of FSW/P of HEAs.The welding materials and conditions used for FSW/P in HEAs are reviewed and discussed.The effects of FSW/P on the evolutions of grain structure,texture,dislocation,and secondary phase for different HEAs are highlighted.Furthermore,the influences of FSW/P on the mechanical properties of various HEAs are analyzed.Finally,potential applications,challenges,and future directions of FSW/P in HEAs are forecasted.Overall,FSW/P enable to refine grains of HEAs through dynamic recrystallization and to activate diverse deformation mechanisms of HEAs through tailoring phase structures,thereby significantly improving the strength,hardness,and ductility of both single-and dual-phase HEAs.Future progress in this field will rely on comprehensive optimization of processing parameters and alloy composition,integration of multi-scale modeling with advanced characterization for in-depth exploration of microstructural mechanisms,systematic evaluation of functional properties,and effective bridging of the gap between laboratory research and industrial application.The review aims to provide an overview of recent advancements in the FSW/P of HEAs and encourage further research in this area.展开更多
The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural ...The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.展开更多
The differences between shouldered and shoulderless tools in the micro-friction stir welding of 0.8 mm thin plates were evaluated.Employing a suite of advanced characterization methods,including white light interferom...The differences between shouldered and shoulderless tools in the micro-friction stir welding of 0.8 mm thin plates were evaluated.Employing a suite of advanced characterization methods,including white light interferometry,electron backscatter diffraction(EBSD),and scanning electron microscopy,the formation of weld surface,joint microstructure distribution,and fracture characteristics were studied.The enhancement mechanism of mechanical properties was explained through the Hall-Petch relationship and Taylor's hardening law.Results indicate that the main reason for the increased yield strength observed in shoulderless tool joints is the combined mechanism of dislocation strengthening and fine-grain strengthening.Specifically,the utilization of shouldered tools results in a smooth weld surface,with an average grain size of 11.24μm and a high-angle grain boundary content of 16.80%in the nugget zone.The primary texture components are the{011}<100>Goss and{112}<111>copper textures,yielding a maximum texture strength of 3.70.Simultaneously,the fracture dimples exhibit a reduction in size and an increase in depth.Whereas the welds produced with shoulderless tools display slight burrs on the surface.The experimental results demonstrate that the average grain size in the nugget zone of these joints is significantly reduced to 0.59μm,while the high-angle grain boundary content reaches 34.34%.This process is accompanied by the formation of{111}<110>Shear textures and{001}<110>rotated cubic textures as the main components,resulting in a significant increase in maximum texture strength to 6.65.展开更多
An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-...An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-LEMS were investigated by establishing a three-dimensional numerical simulation model and a pilot continuous casting simulation experiment and compared with the conventional rotary electromagnetic stirring(REMS).The results show that a longitudinally symmetric linear magnetic field is formed in the liquid core of the bloom by applying CV-LEMS,which induces a strong longitudinal circulation flow both on the inner arc side and the outer arc side in the liquid core of the bloom.The height of the melt longitudinal effective mixing range under CV-LEMS reaches 0.9 m,which is greater than that of the REMS and makes up for the deficiency of REMS sensitivity to the position of the final solidification zone.CV-LEMS strongly promotes the mixing of upper melt with high temperature and the lower part melt with low temperature in the liquid core,improves the uniformity of melt temperature distribution and significantly increases the melt temperature near the solidification front,and the width of the liquid core increases by 4.2 mm at maximum.This shows that the appliction of CV-LEMS is more helpful to strengthen the feeding effect of the upper melt to the solidification shrinkage of the lower melt than the conventional REMS and inhibits the formation of porosity,shrinkage cavity and crack defects in the center of the bloom.展开更多
Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with ...Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with the decrease in welding heat input,the weld surface is smoother.The Ti/Al joint interface is flat without obvious Ti and Al mixed structure,and the hook structure is not formed under optimal parameters.Due to the enhanced breaking effect of the stirring head,the hook structural defects and intermetallic compounds are more likely to form at the Ti/Al interface at high rotational speed of 1000 r/min,thereby deteriorating the mechanical properties of joints.Decreasing the heat input is beneficial to hardness enhancement of the aluminum alloy in the weld nugget zone.Under the optimal parameters of rotation speed of 800 r/min and welding speed of 120 mm/min,the maximum tensile shear strength of joint is 289 N/mm.展开更多
The composite structures/components made by friction stir lap welding(FSLW)of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles.To further impr...The composite structures/components made by friction stir lap welding(FSLW)of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles.To further improve the joint quality,the ultrasonic vibration(UV)is exerted in FSLW,and the UV enhanced FSLW(UVeFSLW)was developed for making Mg-to-Al dissimilar joints.The numerical analysis and experimental investigation were combined to study the process mechanism in Mg/Al UVeFSLW.An equation related to the temperature and strain rate was derived to calculate the grain size at different locations of the weld nugget zone,and the effect of grain size distribution on the threshold thermal stress was included,so that the prediction accuracy of flow stress was further improved.With such modified constitutive equation,the numerical simulation was conducted to compare the heat generation,temperature profiles and material flow behaviors in Mg/Al UVeFSLW/FSLW processes.It was found that the exerted UV decreased the temperature at two checking points on the tool/workpiece interface from 707/671 K in FSLW to 689/660 K in UVeFSLW,which suppressed the IMCs thickness at Mg-Al interface from 1.7μm in FSLW to 1.1μm in UVeFSLW.The exerted UV increased the horizontal materials flow ability,and decreased the upward flow ability,which resulted in the increase of effective sheet thickness/effective lap width from 2.01/3.70 mm in FSLW to 2.04/4.84 mm in UVeFSLW.Therefore,the ultrasonic vibration improved the tensile shear strength of Mg-to-Al lap joints by 18%.展开更多
Friction stir welding(FSW)is a relatively new welding technique that has significant advantages compared to the fusion welding techniques in joining non weld able alloys by fusion,such as aluminum alloys.Three FSW sea...Friction stir welding(FSW)is a relatively new welding technique that has significant advantages compared to the fusion welding techniques in joining non weld able alloys by fusion,such as aluminum alloys.Three FSW seams of AA6061-T6 plates were made us-ing different FSW parameters.The structure of the FSW seams was investigated using X-ray diffraction(XRD),scanning electron mi-croscope(SEM)and non destructive testing(NDT)techniques and their hardness was also measured.The dominated phase in the AA6061-T6 alloy and the FSW seams was theα-Al.The FSW seam had lower content of the secondary phases than the AA6061-T6 al-loy.The hardness of the FSW seams was decreased by about 30%compared to the AA6061-T6 alloy.The temperature distributions in the weld seams were also studied experimentally and numerically modeled and the results were in a good agreement.展开更多
Welding high-entropy alloy(HEA)to Mg alloy has gained increasing attention for multi-metal structure design,while intrinsic sluggish diffusion kinetics of HEA confines diffusion-controlled interfacial reactions and mak...Welding high-entropy alloy(HEA)to Mg alloy has gained increasing attention for multi-metal structure design,while intrinsic sluggish diffusion kinetics of HEA confines diffusion-controlled interfacial reactions and makes it challenging to establish robust metallurgical bonding.This study investigated welding of FeCoCrNiMn HEA to commercial AZ31 as a model combination to pioneer thisfield.Interfacial phase separation phenomenon was observed,with the diffusion accelerated by in-situ engineering a submicron-scale thick(∼400–500 nm)HEA nearby the interface into nanocrystalline-structure during friction stir welding.Abundant grain boundaries generated in this nanocrystalline-interlayer serve as diffusion short-circuits and energetically preferred nucleation-sites,which promoted Al in AZ31 to diffuse into HEA and triggered quick separation into body-centered cubic AlNi-type and tetragonal FeCr-type intermetallics.HEA and AZ31 were thus metallurgically bonded by these interfacial intermetallics.The joint shows exceptional strength in tensile lap-shear testing with fracture largely occurred within AZ31 rather than right along interface as commonly reported previously for dissimilar joints.展开更多
The effects of tungsten inert gas arc-assisted friction stir welding(TIG-FSW)on the microstructure,tensile properties and corrosion resistance of AA6016 and AA2519 alloys lap joints were investigated by means of optic...The effects of tungsten inert gas arc-assisted friction stir welding(TIG-FSW)on the microstructure,tensile properties and corrosion resistance of AA6016 and AA2519 alloys lap joints were investigated by means of optical microscope,scanning electron microscope,tensile test at room temperature,corrosion immersion tests and electrochemical measurements.The results show that the introduction of TIG arc during FSW process results in a more uniform microstructure of the joint with no tunnel hole defects.Furthermore,it enhances tensile strength and elongation of the joint with increased rates of 11.5%and 50.0%,respectively;meanwhile,the corrosion current density and largest corrosion depth are decreased with reduction rates of 78.2%and 45.7%,respectively.TIG-FSW can promote flow,contact and diffusion of materials,thus improving microstructure of the joint.Additionally,it reduces the size and number of secondary phase particles.Consequently,these factors contribute to the higher tensile properties and corrosion resistance of the joints.展开更多
Interlayer friction stir processing(FSP)has been proved to be an efective method of enhancing the mechanical properties of wire arc-directed energy deposited(WA-DED)samples.However,the original deposition structure wa...Interlayer friction stir processing(FSP)has been proved to be an efective method of enhancing the mechanical properties of wire arc-directed energy deposited(WA-DED)samples.However,the original deposition structure was still retained in the FSP-WA-DED component besides the processed zone(PZ),thus forming a composite structure.Considering the material utilization and practical service process of the deposited component,more attention should be paid on this special composite structure,but the relevant investigation has not been carried out.In this study,an Al–Mg–Sc alloy was prepared by WA-DED with interlayer FSP treatment,and the composite structure was frstly investigated.Almost all of the pores were eliminated under the pressure efect from the tool shoulder.The grains were further refned with an average size of about 1.2μm in the PZ.Though no severe plastic deformation was involved in the retained WA-DED deposition zone,comparable tensile properties with the PZ sample were obtained in the composite structure.Low ultimate tensile strength(UTS)of 289 MPa and elongation of 3.2%were achieved in the WA-DED sample.After interlayer FSP treatment,the UTS and elongation of the PZ samples were signifcantly increased to 443 MPa and 16.3%,while those in the composite structure remained at relatively high levels of 410 MPa and 13.5%,respectively.Meanwhile,a high fatigue strength of 180 and 130 MPa was obtained in the PZ and composite structure samples,which was clearly higher than that of the WA-DED sample(100 MPa).It is concluded that the defects in traditional WA-DED process can be eliminated in the composite structure after interlayer FSP treatment,resulting in enhanced tensile and fatigue properties,which provides an efective method of improving the mechanical properties of the WA-DED sample.展开更多
Thickness of the intermetallic compounds(IMC)layer at the interface has a significant effect on the mechanical properties of Mg/Al dissimilar joints.However,the thickness of IMC layer can be only obtained by metallurg...Thickness of the intermetallic compounds(IMC)layer at the interface has a significant effect on the mechanical properties of Mg/Al dissimilar joints.However,the thickness of IMC layer can be only obtained by metallurgical microscopy,which is destructive and has to break down the weld.Therefore,it is crucial to find a reliable approach that can non-destructively predict the thickness of IMC layer in practical application.In the current study,Mg alloy and Al alloy were friction stir butt welded(FSW)under different tool rotation speeds(TRS)to obtain different thicknesses of IMC layers.As the TRS increased from 400 rpm to 1000 rpm,thickness of the IMC layer increased from 0.4μm to 1.3μm,the peak welding temperatures increased from 259℃to 402℃,and the Z-axis downforces decreased from10.5 kN to 3.2 k N during welding process.Higher TRS would generally induce higher welding heat input,which promotes the growth of the IMC layer and the softening of base materials.The IMC layer formed through solid-state diffusion and transformation instead of eutectic reaction according to the welding temperature history and interfacial microstructure,and its evolution process was clearly observed by plan view.In order to incorporate the effect of dramatic change of welding temperature which is the characteristic feature of FSW,Psd Voigt function was used to fit the welding temperature histories.A new prediction formula was then established to predict thicknesses of IMC layers with considering sharp welding temperature change.Predicted thicknesses gave good agreement with measured thicknesses obtained experimentally under different welding parameters,which confirmed the accuracy and reliability of the new prediction formula.Based on this prediction formula,the time period of temperature higher than 200℃during welding was found critical for the thickening of interfacial IMC layers.展开更多
Ti-10V-2Fe-3Al alloy with fine-grainedβphases was fabricated by friction stir processing with opti-mized processing parameters.The superplastic behavior of the specimens was investigated by tensile deformation at dif...Ti-10V-2Fe-3Al alloy with fine-grainedβphases was fabricated by friction stir processing with opti-mized processing parameters.The superplastic behavior of the specimens was investigated by tensile deformation at different strain rates and temperatures,and an optimal superplastic elongation of 634%was achieved at 700℃ and 3×10^(-4)/s.An annealing treatment at 650℃ for 60 min showed a mi-crostructure withαprecipitates distributed in theβmatrix in the friction stir specimen.Such pre-heat treatment improves the superplasticity of the specimen,achieving an elongation of up to 807%at 750℃ and 3×10^(-4)/s.The influences of tensile temperatures and strain rates on the microstructural evolution,such as grain size variation,grain morphology,and phase transformations,were discussed.The super-plastic deformation behavior of fine-grained Ti-10V-2Fe-3Al alloy is controlled by grain boundary sliding and accompanied by dynamic phase transformation and recrystallization.展开更多
The difference in the microstructure,texture in the stir zone(SZ)of the AZ31(Mg-3 Al-1 Zn,wt.%)alloy after friction stir welding(FSW)and subsequent annealing at 400℃for 1 h was characterized by scanning electron micr...The difference in the microstructure,texture in the stir zone(SZ)of the AZ31(Mg-3 Al-1 Zn,wt.%)alloy after friction stir welding(FSW)and subsequent annealing at 400℃for 1 h was characterized by scanning electron microscopy(SEM)with electron backscatter diffraction(EBSD)measurements at the surface and core regions.The findings indicate that FSW produced grain refinement where the mean grain size decreases from 19μm(base metal)to 5.1 and 3.5μm at the surface and core regions,respectively.The c-axis of the grains at the surface region was aligned with the normal direction(<0001>//ND)due to the additional strain of the tool shoulder.In contrast,the core region shows a typical shear texture,where the c-axis tends to be oriented parallel to the welding direction(<0001>//WD).The Vickers microhardness mapping across the SZ revealed that the core region was soften than the surface region due to the dynamic recrystallization and texture weakening.The microstructure of the SZ remains principally deformed after annealing treatment except for the development of massive Mg_(17)Al_(12)precipitates and the abnormal grain growth of a few grains with<11-20>//WD orientation at the upper side of the surface region.The c-axis of the grains at the surface region was tilted about 10°toward WD,while an inclined<0001>//WD orientation about 30°from WD was developed at the core region.Consequently,the distribution of microhardness values across the SZ was more heterogeneous than the FSW sample.The results were discussed in the light of grain boundary misorientation,dislocation density and the pinning effect of Mg_(17)Al_(12)precipitates.Additionally,Schmid factor analysis was used to examine the activation of the basal slip mode to characterize the associated mechanical response.展开更多
For a long time,the conventional superplastic forming temperature for Ti alloys is generally too high(~900-920℃),which leads to too long production cycles,heavy surface oxidation,and property reduction.In this study,...For a long time,the conventional superplastic forming temperature for Ti alloys is generally too high(~900-920℃),which leads to too long production cycles,heavy surface oxidation,and property reduction.In this study,an ultrafine bimodal microstructure,consisting of ultrafine equiaxed microstructure(0.66μm)and 43.3%lamellar microstructure,was achieved in the Ti-6Al-4V alloy by friction stir processing(FSP).The low-temperature superplastic behavior and deformation mechanism of the FSP Ti-6Al-4V alloy were investigated at temperatures of 550-675℃and strain rates ranging from 1×10^(−4)to 3×10^(−3)s^(−1).The FSP alloy exhibited superplastic elongations of>200%at the temperature range from 550 to 650℃,and an optimal superplastic elongation of 611%was achieved at 625℃and 1×10^(−4)s^(−1).This is the first time to report the low-temperature superplasticity of the bimodal microstructure in Ti alloys.Grain boundary sliding was identified as the dominant deformation mechanism,which was effectively accommodated by the comprehensive effect of dislocation-inducedβphase precipitation and dynamic spheroidization of the lamellar structure.This study provides a novel insight into the low-temperature superplastic deformation behavior of the bimodal microstructure.展开更多
In this study,friction stir processing(FSP)was employed to modify the as-cast Mg-14Gd-0.6Ce-0.5Zr alloy,and the effects of texture evolution and distribution of second phases on mechanical properties were systematical...In this study,friction stir processing(FSP)was employed to modify the as-cast Mg-14Gd-0.6Ce-0.5Zr alloy,and the effects of texture evolution and distribution of second phases on mechanical properties were systematically investigated.The results show that friction stir processing effectively refined the coarse Mg_(5)Gd phases into nanoscale second phases uniformly distributed along grain boundaries.The synergistic effect of texture weakening and second phases refinement significantly enhanced the tensile strength and elongation of the FSP-1000-120 alloy to 302.1 MPa and 18.3%,respectively,representing increases of 20.8%and 281.3%compared to the as-cast alloy.The as-cast alloy has a lower corrosion rate in the initial stage due to fewer micro-galvanic corrosion sites.However,the uniform distribution of the second phase in the FSP-treated(FSPed)alloy contributes to the formation of a more complete and dense corrosion product film.After 120 h of immersion,the as-cast alloy forms deep pits due to the continuous dissolution at the second phase-matrix interface,with the average corrosion rate increasing from 0.31 to 0.47 mL/cm^(2)/h.The long-term corrosion rates of FSP-1000-60,FSP-1000-120,and FSP-1200-120 samples are stable at 0.36,0.43,and 0.50 mL/cm^(2)/h,respectively.Research reveals that FSP regulates texture and second phase distribution to achieve synergistic strengthening of alloy strength plasticity,and the homogenization of second phase distribution is a key factor in improving the long-term corrosion resistance of alloys.展开更多
Fractal theory provides a new strategy for equipment design.In this work,we propose a novel H-like fractal(HLF)impeller to improve the uniformity of the distribution of hydrodynamics in stirred tanks.The impellers are...Fractal theory provides a new strategy for equipment design.In this work,we propose a novel H-like fractal(HLF)impeller to improve the uniformity of the distribution of hydrodynamics in stirred tanks.The impellers are constructed by replacing two vertical blades or four legs with two or four H-like subblades by fractal iterations,respectively.Flow characteristics including velocity and turbulent kinetic energy(TKE)distributions,vortices,power number,are predicted by large eddy simulation.Compared with Rushton turbine(RT)impeller when H/T=1(or dual RTs when H/T=1.5,triple RTs when H/T=2),the HLF impeller can produce a flow field with more uniform distributions of larger velocities and TKE level.The impeller with more fractal iteration times can further improve the distribution uniformity of hydrodynamics in the case of high H/T.Power analysis shows that this is mainly due to the improved energy utilization efficiency by the fractal structure design.展开更多
基金National Key Research and Development Program of China(2022YFB4600902)Shandong Provincial Science Foundation for Outstanding Young Scholars(ZR2024YQ020)。
文摘Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.
基金supported by the National Natural Science Foundation of China(Grant No.52166004)the Yunnan Fundamental Research Projects(Grant No.202501AS070131).
文摘Optimizing pyrolysis processes is critical for improving the efficiency of pyrolysis furnaces.This study presents a strategy to enhance heat transfer through agitation,employing Fluent for detailed numerical simulation of the thermal behavior.The simulation results show strong agreement with experimental measurements of localized fluid temperature rise.Forced convection induced by impeller rotation significantly improves heat transfer between the fluid and the furnace walls,effectively reducing thermal stratification.At an impeller speed of 240 RPM,the axial temperature difference decreases from 200 K to 50 K compared with stationary conditions,while the average heat transfer coefficient increases by approximately 50%throughout the heating process.The swirl flow generated by impeller motion disrupts the thermal boundary layer,achieving a more uniform temperature distribution and faster thermal response.
基金Project(ASM-20240)supported by the Key Laboratory of Advanced Structural Materials(Changchun University of Technology),Ministry of Education,ChinaProject(2022TD-30)supported by the Scientific and Technological Innovation Team Project of Shaanxi Innovation Capability Support Plan,China。
文摘This work examines the microstructure and corrosion properties of fine-grained Al 7075 across different regions under varying cooling conditions during friction stir welding.The findings demonstrate that forced cooling significantly improves the corrosion resistance of the welded joints.Specifically,the corrosion resistance was the highest in the stir zone,followed by the thermo-mechanical affected zone,and then the heat affected zone.Forced cooling mitigates grain growth by controlling the welding thermal effects,thereby increasing the proportion ofΣ3 grain boundaries.The modification of these microstructural characteristics promotes the formation of a dense oxide layer,thereby enhancing the corrosion resistance.Furthermore,forced cooling mitigates the precipitation and coarsening of the anodic phase in the stir zone,which in turn reduces the susceptibility of the joint to pitting corrosion.Additionally,the lower recrystallization texture content in the joint,resulting from forced cooling,contributes to a reduction in the number of corrosion-active sites,thereby further improving the corrosion performance of the welded joint.
基金supported by National Natural Science Foundation of China(Grant No.52171032)Hebei Natural Science Foundation(Grant No.E2023501002)Fundamental Research Funds for the Central Universities(Grant No.2024GFYD003)。
文摘High entropy alloys(HEAs)have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields.Friction stir welding and processing(FSW/P),as notable solid-state welding and processing techniques,have been proved effectiveness in enhancing microstructures and mechanical properties of HEAs.This review article summarizes the current status of FSW/P of HEAs.The welding materials and conditions used for FSW/P in HEAs are reviewed and discussed.The effects of FSW/P on the evolutions of grain structure,texture,dislocation,and secondary phase for different HEAs are highlighted.Furthermore,the influences of FSW/P on the mechanical properties of various HEAs are analyzed.Finally,potential applications,challenges,and future directions of FSW/P in HEAs are forecasted.Overall,FSW/P enable to refine grains of HEAs through dynamic recrystallization and to activate diverse deformation mechanisms of HEAs through tailoring phase structures,thereby significantly improving the strength,hardness,and ductility of both single-and dual-phase HEAs.Future progress in this field will rely on comprehensive optimization of processing parameters and alloy composition,integration of multi-scale modeling with advanced characterization for in-depth exploration of microstructural mechanisms,systematic evaluation of functional properties,and effective bridging of the gap between laboratory research and industrial application.The review aims to provide an overview of recent advancements in the FSW/P of HEAs and encourage further research in this area.
基金supported by the National Natural Science Foundation of China (Nos. 52075449, 51975480)。
文摘The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.
基金National Nature Science Foundation of China(52261013)。
文摘The differences between shouldered and shoulderless tools in the micro-friction stir welding of 0.8 mm thin plates were evaluated.Employing a suite of advanced characterization methods,including white light interferometry,electron backscatter diffraction(EBSD),and scanning electron microscopy,the formation of weld surface,joint microstructure distribution,and fracture characteristics were studied.The enhancement mechanism of mechanical properties was explained through the Hall-Petch relationship and Taylor's hardening law.Results indicate that the main reason for the increased yield strength observed in shoulderless tool joints is the combined mechanism of dislocation strengthening and fine-grain strengthening.Specifically,the utilization of shouldered tools results in a smooth weld surface,with an average grain size of 11.24μm and a high-angle grain boundary content of 16.80%in the nugget zone.The primary texture components are the{011}<100>Goss and{112}<111>copper textures,yielding a maximum texture strength of 3.70.Simultaneously,the fracture dimples exhibit a reduction in size and an increase in depth.Whereas the welds produced with shoulderless tools display slight burrs on the surface.The experimental results demonstrate that the average grain size in the nugget zone of these joints is significantly reduced to 0.59μm,while the high-angle grain boundary content reaches 34.34%.This process is accompanied by the formation of{111}<110>Shear textures and{001}<110>rotated cubic textures as the main components,resulting in a significant increase in maximum texture strength to 6.65.
基金the National Natural Science Foundation of China(Grant No.U1760206 and Grant No.51574083)the 111 Project(2.0)of China(No.BP0719037)for the financial support。
文摘An opposite combined vertical linear electromagnetic stirring(CV-LEMS)was proposed,which is applied in the final solidification zone of bloom continuous casting.The melt flow,heat transfer,and solidification under CV-LEMS were investigated by establishing a three-dimensional numerical simulation model and a pilot continuous casting simulation experiment and compared with the conventional rotary electromagnetic stirring(REMS).The results show that a longitudinally symmetric linear magnetic field is formed in the liquid core of the bloom by applying CV-LEMS,which induces a strong longitudinal circulation flow both on the inner arc side and the outer arc side in the liquid core of the bloom.The height of the melt longitudinal effective mixing range under CV-LEMS reaches 0.9 m,which is greater than that of the REMS and makes up for the deficiency of REMS sensitivity to the position of the final solidification zone.CV-LEMS strongly promotes the mixing of upper melt with high temperature and the lower part melt with low temperature in the liquid core,improves the uniformity of melt temperature distribution and significantly increases the melt temperature near the solidification front,and the width of the liquid core increases by 4.2 mm at maximum.This shows that the appliction of CV-LEMS is more helpful to strengthen the feeding effect of the upper melt to the solidification shrinkage of the lower melt than the conventional REMS and inhibits the formation of porosity,shrinkage cavity and crack defects in the center of the bloom.
基金National Natural Science Foundation of China(52275349)Key Research and Development Program of Shandong Province(2021ZLGX01)。
文摘Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with the decrease in welding heat input,the weld surface is smoother.The Ti/Al joint interface is flat without obvious Ti and Al mixed structure,and the hook structure is not formed under optimal parameters.Due to the enhanced breaking effect of the stirring head,the hook structural defects and intermetallic compounds are more likely to form at the Ti/Al interface at high rotational speed of 1000 r/min,thereby deteriorating the mechanical properties of joints.Decreasing the heat input is beneficial to hardness enhancement of the aluminum alloy in the weld nugget zone.Under the optimal parameters of rotation speed of 800 r/min and welding speed of 120 mm/min,the maximum tensile shear strength of joint is 289 N/mm.
基金supported by the National Natural Science Foundation of China(Grant No.52035005)the Key R&D Program of Shandong Province in China(Grant No.2021ZLGX01).
文摘The composite structures/components made by friction stir lap welding(FSLW)of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles.To further improve the joint quality,the ultrasonic vibration(UV)is exerted in FSLW,and the UV enhanced FSLW(UVeFSLW)was developed for making Mg-to-Al dissimilar joints.The numerical analysis and experimental investigation were combined to study the process mechanism in Mg/Al UVeFSLW.An equation related to the temperature and strain rate was derived to calculate the grain size at different locations of the weld nugget zone,and the effect of grain size distribution on the threshold thermal stress was included,so that the prediction accuracy of flow stress was further improved.With such modified constitutive equation,the numerical simulation was conducted to compare the heat generation,temperature profiles and material flow behaviors in Mg/Al UVeFSLW/FSLW processes.It was found that the exerted UV decreased the temperature at two checking points on the tool/workpiece interface from 707/671 K in FSLW to 689/660 K in UVeFSLW,which suppressed the IMCs thickness at Mg-Al interface from 1.7μm in FSLW to 1.1μm in UVeFSLW.The exerted UV increased the horizontal materials flow ability,and decreased the upward flow ability,which resulted in the increase of effective sheet thickness/effective lap width from 2.01/3.70 mm in FSLW to 2.04/4.84 mm in UVeFSLW.Therefore,the ultrasonic vibration improved the tensile shear strength of Mg-to-Al lap joints by 18%.
文摘Friction stir welding(FSW)is a relatively new welding technique that has significant advantages compared to the fusion welding techniques in joining non weld able alloys by fusion,such as aluminum alloys.Three FSW seams of AA6061-T6 plates were made us-ing different FSW parameters.The structure of the FSW seams was investigated using X-ray diffraction(XRD),scanning electron mi-croscope(SEM)and non destructive testing(NDT)techniques and their hardness was also measured.The dominated phase in the AA6061-T6 alloy and the FSW seams was theα-Al.The FSW seam had lower content of the secondary phases than the AA6061-T6 al-loy.The hardness of the FSW seams was decreased by about 30%compared to the AA6061-T6 alloy.The temperature distributions in the weld seams were also studied experimentally and numerically modeled and the results were in a good agreement.
基金supported by the National Natural Science Foundation of China[Grant numbers:52475385,52305392]the China Postdoctoral Science Foundation(Grant No.2022M722048).
文摘Welding high-entropy alloy(HEA)to Mg alloy has gained increasing attention for multi-metal structure design,while intrinsic sluggish diffusion kinetics of HEA confines diffusion-controlled interfacial reactions and makes it challenging to establish robust metallurgical bonding.This study investigated welding of FeCoCrNiMn HEA to commercial AZ31 as a model combination to pioneer thisfield.Interfacial phase separation phenomenon was observed,with the diffusion accelerated by in-situ engineering a submicron-scale thick(∼400–500 nm)HEA nearby the interface into nanocrystalline-structure during friction stir welding.Abundant grain boundaries generated in this nanocrystalline-interlayer serve as diffusion short-circuits and energetically preferred nucleation-sites,which promoted Al in AZ31 to diffuse into HEA and triggered quick separation into body-centered cubic AlNi-type and tetragonal FeCr-type intermetallics.HEA and AZ31 were thus metallurgically bonded by these interfacial intermetallics.The joint shows exceptional strength in tensile lap-shear testing with fracture largely occurred within AZ31 rather than right along interface as commonly reported previously for dissimilar joints.
文摘The effects of tungsten inert gas arc-assisted friction stir welding(TIG-FSW)on the microstructure,tensile properties and corrosion resistance of AA6016 and AA2519 alloys lap joints were investigated by means of optical microscope,scanning electron microscope,tensile test at room temperature,corrosion immersion tests and electrochemical measurements.The results show that the introduction of TIG arc during FSW process results in a more uniform microstructure of the joint with no tunnel hole defects.Furthermore,it enhances tensile strength and elongation of the joint with increased rates of 11.5%and 50.0%,respectively;meanwhile,the corrosion current density and largest corrosion depth are decreased with reduction rates of 78.2%and 45.7%,respectively.TIG-FSW can promote flow,contact and diffusion of materials,thus improving microstructure of the joint.Additionally,it reduces the size and number of secondary phase particles.Consequently,these factors contribute to the higher tensile properties and corrosion resistance of the joints.
基金supported by the National Natural Science Foundation of China(No.U23A20538)the Fundamental Research Funds for the Universities of Liaoning Province,Shenyang U40 Outstanding Youth Foundation(No.RC230864)+1 种基金the Foundation of CAS Henan Industrial Technology Innovation&Incubation Center(No.2024110)the Natural Science Foundation of Liaoning Province(No.2023-BS-016)。
文摘Interlayer friction stir processing(FSP)has been proved to be an efective method of enhancing the mechanical properties of wire arc-directed energy deposited(WA-DED)samples.However,the original deposition structure was still retained in the FSP-WA-DED component besides the processed zone(PZ),thus forming a composite structure.Considering the material utilization and practical service process of the deposited component,more attention should be paid on this special composite structure,but the relevant investigation has not been carried out.In this study,an Al–Mg–Sc alloy was prepared by WA-DED with interlayer FSP treatment,and the composite structure was frstly investigated.Almost all of the pores were eliminated under the pressure efect from the tool shoulder.The grains were further refned with an average size of about 1.2μm in the PZ.Though no severe plastic deformation was involved in the retained WA-DED deposition zone,comparable tensile properties with the PZ sample were obtained in the composite structure.Low ultimate tensile strength(UTS)of 289 MPa and elongation of 3.2%were achieved in the WA-DED sample.After interlayer FSP treatment,the UTS and elongation of the PZ samples were signifcantly increased to 443 MPa and 16.3%,while those in the composite structure remained at relatively high levels of 410 MPa and 13.5%,respectively.Meanwhile,a high fatigue strength of 180 and 130 MPa was obtained in the PZ and composite structure samples,which was clearly higher than that of the WA-DED sample(100 MPa).It is concluded that the defects in traditional WA-DED process can be eliminated in the composite structure after interlayer FSP treatment,resulting in enhanced tensile and fatigue properties,which provides an efective method of improving the mechanical properties of the WA-DED sample.
基金supported by the National Natural Science Foundation of China(No.52075330)the Interdisciplinary Program of Shanghai Jiao Tong University(No.YG2019QNA15)the Foundation of National Facility for Translational Medicine(Shanghai)(No.TMSK-2020-107)。
文摘Thickness of the intermetallic compounds(IMC)layer at the interface has a significant effect on the mechanical properties of Mg/Al dissimilar joints.However,the thickness of IMC layer can be only obtained by metallurgical microscopy,which is destructive and has to break down the weld.Therefore,it is crucial to find a reliable approach that can non-destructively predict the thickness of IMC layer in practical application.In the current study,Mg alloy and Al alloy were friction stir butt welded(FSW)under different tool rotation speeds(TRS)to obtain different thicknesses of IMC layers.As the TRS increased from 400 rpm to 1000 rpm,thickness of the IMC layer increased from 0.4μm to 1.3μm,the peak welding temperatures increased from 259℃to 402℃,and the Z-axis downforces decreased from10.5 kN to 3.2 k N during welding process.Higher TRS would generally induce higher welding heat input,which promotes the growth of the IMC layer and the softening of base materials.The IMC layer formed through solid-state diffusion and transformation instead of eutectic reaction according to the welding temperature history and interfacial microstructure,and its evolution process was clearly observed by plan view.In order to incorporate the effect of dramatic change of welding temperature which is the characteristic feature of FSW,Psd Voigt function was used to fit the welding temperature histories.A new prediction formula was then established to predict thicknesses of IMC layers with considering sharp welding temperature change.Predicted thicknesses gave good agreement with measured thicknesses obtained experimentally under different welding parameters,which confirmed the accuracy and reliability of the new prediction formula.Based on this prediction formula,the time period of temperature higher than 200℃during welding was found critical for the thickening of interfacial IMC layers.
基金financially supported by the National Natural Science Foundation of China(No.52105373)the China Scholarship Council(No.202106020094).
文摘Ti-10V-2Fe-3Al alloy with fine-grainedβphases was fabricated by friction stir processing with opti-mized processing parameters.The superplastic behavior of the specimens was investigated by tensile deformation at different strain rates and temperatures,and an optimal superplastic elongation of 634%was achieved at 700℃ and 3×10^(-4)/s.An annealing treatment at 650℃ for 60 min showed a mi-crostructure withαprecipitates distributed in theβmatrix in the friction stir specimen.Such pre-heat treatment improves the superplasticity of the specimen,achieving an elongation of up to 807%at 750℃ and 3×10^(-4)/s.The influences of tensile temperatures and strain rates on the microstructural evolution,such as grain size variation,grain morphology,and phase transformations,were discussed.The super-plastic deformation behavior of fine-grained Ti-10V-2Fe-3Al alloy is controlled by grain boundary sliding and accompanied by dynamic phase transformation and recrystallization.
基金supported by the PHC-Tassili program No.24MDU114。
文摘The difference in the microstructure,texture in the stir zone(SZ)of the AZ31(Mg-3 Al-1 Zn,wt.%)alloy after friction stir welding(FSW)and subsequent annealing at 400℃for 1 h was characterized by scanning electron microscopy(SEM)with electron backscatter diffraction(EBSD)measurements at the surface and core regions.The findings indicate that FSW produced grain refinement where the mean grain size decreases from 19μm(base metal)to 5.1 and 3.5μm at the surface and core regions,respectively.The c-axis of the grains at the surface region was aligned with the normal direction(<0001>//ND)due to the additional strain of the tool shoulder.In contrast,the core region shows a typical shear texture,where the c-axis tends to be oriented parallel to the welding direction(<0001>//WD).The Vickers microhardness mapping across the SZ revealed that the core region was soften than the surface region due to the dynamic recrystallization and texture weakening.The microstructure of the SZ remains principally deformed after annealing treatment except for the development of massive Mg_(17)Al_(12)precipitates and the abnormal grain growth of a few grains with<11-20>//WD orientation at the upper side of the surface region.The c-axis of the grains at the surface region was tilted about 10°toward WD,while an inclined<0001>//WD orientation about 30°from WD was developed at the core region.Consequently,the distribution of microhardness values across the SZ was more heterogeneous than the FSW sample.The results were discussed in the light of grain boundary misorientation,dislocation density and the pinning effect of Mg_(17)Al_(12)precipitates.Additionally,Schmid factor analysis was used to examine the activation of the basal slip mode to characterize the associated mechanical response.
基金supported by the funding from the Shi Changxu Innovation Center for Advanced Materials(No.SCXKFJJ202210)the National Natural Science Foundation of China(No.52271043)+2 种基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2021193)the Liaoning Province Excellent Youth Foundation(No.2024JH3/10200021)the Liaoning Revitalization Talents Program(No.XLYC2403094).
文摘For a long time,the conventional superplastic forming temperature for Ti alloys is generally too high(~900-920℃),which leads to too long production cycles,heavy surface oxidation,and property reduction.In this study,an ultrafine bimodal microstructure,consisting of ultrafine equiaxed microstructure(0.66μm)and 43.3%lamellar microstructure,was achieved in the Ti-6Al-4V alloy by friction stir processing(FSP).The low-temperature superplastic behavior and deformation mechanism of the FSP Ti-6Al-4V alloy were investigated at temperatures of 550-675℃and strain rates ranging from 1×10^(−4)to 3×10^(−3)s^(−1).The FSP alloy exhibited superplastic elongations of>200%at the temperature range from 550 to 650℃,and an optimal superplastic elongation of 611%was achieved at 625℃and 1×10^(−4)s^(−1).This is the first time to report the low-temperature superplasticity of the bimodal microstructure in Ti alloys.Grain boundary sliding was identified as the dominant deformation mechanism,which was effectively accommodated by the comprehensive effect of dislocation-inducedβphase precipitation and dynamic spheroidization of the lamellar structure.This study provides a novel insight into the low-temperature superplastic deformation behavior of the bimodal microstructure.
基金supported by the National Natural Science Foundation of China(Nos.52201119,52371108,52203295)the Joint Fund of Henan Science and Technology R&D Plan of China(242103810056)Frontier Exploration Project of Longmen Laboratory,China(LMQYTSKT014).
文摘In this study,friction stir processing(FSP)was employed to modify the as-cast Mg-14Gd-0.6Ce-0.5Zr alloy,and the effects of texture evolution and distribution of second phases on mechanical properties were systematically investigated.The results show that friction stir processing effectively refined the coarse Mg_(5)Gd phases into nanoscale second phases uniformly distributed along grain boundaries.The synergistic effect of texture weakening and second phases refinement significantly enhanced the tensile strength and elongation of the FSP-1000-120 alloy to 302.1 MPa and 18.3%,respectively,representing increases of 20.8%and 281.3%compared to the as-cast alloy.The as-cast alloy has a lower corrosion rate in the initial stage due to fewer micro-galvanic corrosion sites.However,the uniform distribution of the second phase in the FSP-treated(FSPed)alloy contributes to the formation of a more complete and dense corrosion product film.After 120 h of immersion,the as-cast alloy forms deep pits due to the continuous dissolution at the second phase-matrix interface,with the average corrosion rate increasing from 0.31 to 0.47 mL/cm^(2)/h.The long-term corrosion rates of FSP-1000-60,FSP-1000-120,and FSP-1200-120 samples are stable at 0.36,0.43,and 0.50 mL/cm^(2)/h,respectively.Research reveals that FSP regulates texture and second phase distribution to achieve synergistic strengthening of alloy strength plasticity,and the homogenization of second phase distribution is a key factor in improving the long-term corrosion resistance of alloys.
基金the financial support from the National Natural Science Foundation of China(22078058)。
文摘Fractal theory provides a new strategy for equipment design.In this work,we propose a novel H-like fractal(HLF)impeller to improve the uniformity of the distribution of hydrodynamics in stirred tanks.The impellers are constructed by replacing two vertical blades or four legs with two or four H-like subblades by fractal iterations,respectively.Flow characteristics including velocity and turbulent kinetic energy(TKE)distributions,vortices,power number,are predicted by large eddy simulation.Compared with Rushton turbine(RT)impeller when H/T=1(or dual RTs when H/T=1.5,triple RTs when H/T=2),the HLF impeller can produce a flow field with more uniform distributions of larger velocities and TKE level.The impeller with more fractal iteration times can further improve the distribution uniformity of hydrodynamics in the case of high H/T.Power analysis shows that this is mainly due to the improved energy utilization efficiency by the fractal structure design.
