Friction stir welding [FSW） has achieved remarkable success in the joining and processing of aluminium alloys and other softer structural alloys. Conventional FSW, however, has not been entirely successful in the joi...Friction stir welding [FSW） has achieved remarkable success in the joining and processing of aluminium alloys and other softer structural alloys. Conventional FSW, however, has not been entirely successful in the joining, processing and manufacturing of different desired materials essential to meet the sophis- ticated green globe requirements. Through the efforts of improving the process and transferring the existing friction stir knowledge base to other advanced applications, several friction stir based daughter technologies have emerged over the timeline, A few among these technologies are well developed while others are under the process of emergence. Beginning with a broad classification of the scattered fric- tions stir based technologies into two categories, welding and processing, it appears now time to know, compile and review these to enable their rapid access for reference and academia. In this review article, the friction stir based technologies classified under the categol^J of welding are those applied for join- ing of materials while the remnant are labeled as friction stir processing （FSP） technologies. This review article presents an overview of four general aspects of both the developed and the developing friction stir based technologies, their associated process parameters, metallurgical features of their products and their feasibility and application to various materials. The lesser known and emerging technologies have been emphasized.展开更多
In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-...In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced.Compared to the previous as-cast microstructure,the grain size was reduced from more than 1 mm to around 4μm within 3 s by a single process cycle.The compressive yield strength was increased by 350%while the ultimate compressive strength by 53%.According to the established material flow behaviors by“tracer material”,the plastic material was transported by shear deformation.From the base material to the rod,the material experienced three stages,i.e.deformation by the tool,upward flow with additional tilt,followed by upward transportation.The microstructural evolution was revealed by“stop-action”technique.The microstructural development at regions adjacent to the rod is mainly controlled by twinning,dynamic recrystallization(DRX)as well as particle stimulated nucleation,while that within the rod is related to DRX combined with grain growth.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
We proposed a new technique route of directional solidification for the manufacture of super slab.A 7-t laboratory-scale thick slab was casted and characterised for trial.To further understand the process,the evolutio...We proposed a new technique route of directional solidification for the manufacture of super slab.A 7-t laboratory-scale thick slab was casted and characterised for trial.To further understand the process,the evolution of the multiple physical fields during the directional solidification was simulated and verified.Similar to the convectional ingot casting,a negative segregated cone of equiaxed grains was formed at the bottom,and a seriously positive segregated region was formed beneath the top surface of the slab.Specific measures on the lateral walls,base plate,and free surface were strongly recommended to ensure that the slab is relatively directionally casted.A water-cooling copper base plate accelerates the solidification rate and the columnar growth along the vertical direction.It inhibits the sedimentation of equiaxed grains and enlarges the columnar zone.Based on the simulation analysis,it can be concluded that the directional solidification technique route is promising to manufacture super slab with lower segregation level,and less porosities and inclusions.展开更多
Constrained Friction Processing(CFP),a novel friction-based technique,has been developed to efficiently process fine-grained magnesium(Mg)rods,expanding the potential applications of biodegradable Mg alloys in medical...Constrained Friction Processing(CFP),a novel friction-based technique,has been developed to efficiently process fine-grained magnesium(Mg)rods,expanding the potential applications of biodegradable Mg alloys in medical implants.This study investigates the enhancement of mechanical properties through the implementation of multiple pass CFP(MP-CFP)in comparison to the conventional single pass CFP.The results reveal a substantial improvement in compressive yield strength(CYS),ultimate compressive strength,and failure plastic strain by 11%,28%,and 66%,respectively.A comprehensive analysis of material evolution during processing and the effects of the final microstructure on mechanical properties was conducted.The intricate material flow behavior during the final plunge stage of MP-CFP results in a reduced intensity of local basal texture and macrotexture.The diminished intensity of basal texture,combined with a low geometrical compatibility factor at the top of the rod after MP-CFP,effectively impedes slip transfer across grain boundaries.This leads to a local strain gradient along the compression direction,ultimately contributing to the observed enhancement in mechanical properties.The Mg-0.5Zn0.3Ca(wt.%)alloy,after texture modification by MP-CFP,exhibits a competitive CYS compared with other traditional methods,highlighting the promising application potential of MP-CFP.展开更多
Complete understanding of the evolution behaviors of the microstructures and intermetallic compounds(IMCs)along the interface materials flow path in friction stir welding(FSW)of dissimilar Al to Mg alloys is of great ...Complete understanding of the evolution behaviors of the microstructures and intermetallic compounds(IMCs)along the interface materials flow path in friction stir welding(FSW)of dissimilar Al to Mg alloys is of great significance.In this study,conventional FSW and ultrasonic vibration enhanced FSW(UVeFSW)experiments of Al/Mg alloys were performed,and the instantaneous evolution features of the interface materials around the tool were"frozen"by using the"sudden stop"and simultaneous cooling techniques.The microstructures and IMCs formation at different locations around the exit hole were observed and characterized by scanning electron microscope,energy dispersive spectrometer and transmission elec-tron microscope.It was found that before the materials started to deposit near the back of the tool,“IMC+Mg+IMC+Al”multilayer microstructure and simple IMC layer with(β+γ)sequentially emerged on the Al/Mg interface.With the application of ultrasonic vibration,the multi-layered interface structure only appeared at the middle stage of materials flow around the pin,and ultrasonic vibration just began to play a suppression role on the growth of two sub-layers IMC at a position where the materials deposit.With assistance of ultrasonic vibration in UVeFSW,the tool drove a larger volume of Mg alloy to move toward the retreating side,and the final IMCs thickness was thinner than that in FSW.展开更多
It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional frict...It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding.Thus,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed.It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMC)layer is formed at the Al/Cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the joint.With the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface.The maximum tensile strength and elongation of Al/Cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/min.In addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides.The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.展开更多
The tool with polygonal pin profile has been widely employed in friction stir welding(FSW) of aluminum, but there is hardly an effective optimization methodology existed as the thermomechanical characteristics affecte...The tool with polygonal pin profile has been widely employed in friction stir welding(FSW) of aluminum, but there is hardly an effective optimization methodology existed as the thermomechanical characteristics affected by pins with various flats number have not been understood comprehensively. Therefore, the present work employs a 3-dimensional computational fluid dynamics(CFD) model to have an integrated observation of the FSW process with the effect of polygonal pin profiles. Both the heat generation modes due to contact friction at the tool–workpiece interface and volumetric viscous dissipation in the vicinity of the tool are considered. The model is utilized to give a quantitative analysis of the heat generation, temperature distribution, plastic material flow and welding loads during the FSW process for various tools with polygonal pin profiles, as well as a variety of shoulder diameters, welding speeds and tool rotation speeds. The calculated results of thermal cycles, tool torques and joint cross sections for some typical polygonal pins and welding parameters are all found to be compared well with the experimental ones, which demonstrates the feasibility and applicability of the present numerical model. Particularly, a methodology is developed for the optimization of the flats number by identifying the torque components in both parallel and vertical direction of the pin-side flat region. The results show that the optimized pin flats number increases with increasing tool rotation speed, while the influence of both welding speed and shoulder diameter can be supposed to be insignificant. Moreover, the dependability of the optimized results is also discussed by considering wear tendency and service life of the pin for multiple welding conditions.展开更多
The Al alloy and carbon fiber reinforced polymer(CFRP)hybrid structures,incorporating the performance advantages of the two materials,have been attracting more attention in high-end manufacturing fields.In the current...The Al alloy and carbon fiber reinforced polymer(CFRP)hybrid structures,incorporating the performance advantages of the two materials,have been attracting more attention in high-end manufacturing fields.In the current investigation,the flat friction spot joining(FSJ)was employed in joining the AA6061-T6 alloy and CFRP sheets.The significance of temperature distribution in influencing joint quality was highlighted through analyzing interface microstructural features,weld defect formation as well as fractography.To understand the role of thermal energy generation and conduction in the process comprehensively,a 3D thermal-mechanical coupling finite element model was established.The interfacial temperature was characterized by an uneven distribution behavior due to the inhomogeneous heat distribution.The peak temperatures on the top surface and Al alloy to CFRP interface at 1500 rpm rotational speed with 0.1 mm/s plunging speed were 498℃and 489°C,respectively.The peak interface temperature was reduced to286℃at 250 rpm,which produced an extremely small melted area.Compared with the plunging speed,rotational speed was found to be the predominant parameter for determining the joint property,which could be optimized to simultaneously realize the avoidance of thermal decomposition of CFRP,the sufficient melting duration time,and the wide enough melted area.Simulated thermal histories and melted area profiles were in agreement with experimental ones.The findings could be utilized to provide some feasible guidance for process optimization of dissimilar FSJ of metals and composites.展开更多
Al-Cu-Li alloy is a huge potential alloy for aerospace industry due to its low density and excellent comprehensive performances.In this study,the microstructures and mechanical properties of a novel cast Al-Cu-Li allo...Al-Cu-Li alloy is a huge potential alloy for aerospace industry due to its low density and excellent comprehensive performances.In this study,the microstructures and mechanical properties of a novel cast Al-Cu-Li alloy during the heat treatment were investigated.Results showed that most of the secondary phases along grain boundaries in as-cast state were dissolved into the Al matrix after homogenization and solution treatment,while the Cu-rich phases were slightly segregated once again on grain boundaries after aging.A relatively good combination of strength and ductility(average ultimate tensile strength of 430 MPa and elongation of 8.9%)was obtained after natural aging.Transmission electron microscopy(TEM)results revealed that there was a complicated precipitate distribution in this cast alloy after natural aging.Compared with the similar alloys which introduced dislocations before aging,the density of T1(Al_(2)CuLi)phases was decreased but the size was increased.The low volume fraction of d0 phase,medium density of needle-shaped precipitates and relativity narrow precipitates-free zone with varying widths near grain boundary are the reasons accounting for the improvement of performances.展开更多
Short circuit transfer involves bridging between the consumable electrode and the weld pool, associated with variations of electrical parameters which characterize the change of molten metal bridge state and are very ...Short circuit transfer involves bridging between the consumable electrode and the weld pool, associated with variations of electrical parameters which characterize the change of molten metal bridge state and are very important for the control of .spatter. In this paper, electrical process parameters and short circuit transfer images were simultaneously recorded with a LabView-based synchronous sensing and visualizing system. The arc^bridge resistance and derivatives of welding current, arc voltage and arc resistance at various instants were calculated by means of offline analysis of the welding current, arc voltage and droplet images. Parameters and their feature values indicating the onset of short circuit and the oncoming necking-down of molten metal bridge were determined. Using the calculated feature values, bridge-state-feedback control for .short circuit transfer was realized with a spatter rate less than 0. 25%.展开更多
The Editor-in-Chief has retracted this article [1] because Figures 11 and 12 appear to be identical with Figures 3 and 4respectively from a previously published article [2].Sehrish MUKHTAR,Waqas ASGHAR,Zubair BUTT,Zah...The Editor-in-Chief has retracted this article [1] because Figures 11 and 12 appear to be identical with Figures 3 and 4respectively from a previously published article [2].Sehrish MUKHTAR,Waqas ASGHAR,Zubair BUTT,Zaheer ABBAS,Mudaser ULLAH and Rana ATTA-UR-REHMAN did not respond to correspondence about this retraction.展开更多
An atomic diffusion model is developed to predict the thickness of intermetallic compounds(IMCs)at the interface of aluminum/magnesium alloys in dissimilar friction stir welding.Both the temperature and the strain rat...An atomic diffusion model is developed to predict the thickness of intermetallic compounds(IMCs)at the interface of aluminum/magnesium alloys in dissimilar friction stir welding.Both the temperature and the strain rate associated with dislocation density at the checking point are used to determine the diffusion coefficients.The variations of the diffusion coefficients and the thickness of IMCs are quantitatively analyzed at selected characteristic time instants during welding process.It is found that the dislocation density can increase the diffusion coefficient and plays a dominant role in the IMCs formation during the plastic deformation stage.Especially in magnesium alloy and Al12Mg17,the diffusion coefficient is increased by two orders of magnitude or even nearly three orders of magnitude by considering the dislocation density.The temperature is the main influencing factor after the end of plastic deformation.The model is validated by comparing the predicted thickness of IMCs with the experimentally measured results.展开更多
Joining dissimilar Mg/Cu alloys was still an intractable problem because of the excessive intermetallic compounds(IMCs)and poor mechanical properties using conventional welding methods.In the present study,friction st...Joining dissimilar Mg/Cu alloys was still an intractable problem because of the excessive intermetallic compounds(IMCs)and poor mechanical properties using conventional welding methods.In the present study,friction stir welding was employed for the butt joining of dissimilar AZ31B Mg-alloy and T2 pure Cu plates.Defect-free Mg/Cu joints were obtained with Mg-RS and Cu-AS configuration,at a welding speed of 50 mm/min and tool rotating speeds of 325 r/min,625 r/min and 925 r/min.At the joining interface,both Mg_(2)Cu and MgCu_(2) IMC phases were observed,with a clear,uniform and continuous IMCs layer composed of two sub-layers,layer-A of Mg+Mg_(2)Cu and layer-B of Mg_(2)Cu+MgCu_(2).The maximum ultimate tensile strength of the Mg/Cu friction stir welding joint reached 130 MPa at 925 r/min due to enhanced mechanical interlocking between Mg and Cu,as well as sufficient metallurgical bonding at the joining interface with an IMCs layer thickness in the range of 1.0-2.0μm.展开更多
The momentum of strong backward flowing melt jet and the thermal action from transferred droplets are two dominating factors affecting the formation of humping bead in high speed gas metal arc welding （GMAW）. Approp...The momentum of strong backward flowing melt jet and the thermal action from transferred droplets are two dominating factors affecting the formation of humping bead in high speed gas metal arc welding （GMAW）. Appropriate describing the influ- ence of the distribution mode of droplet heat content in the weld pool is essential to understand the physical mechanism of humping bead formation. Based on the exper- imental results, four kinds of droplet heat content distribution modes are proposed and employed to calculate the transient evolution of the temperature field and weld pool during high speed GMAW process. Through making comparison of predicted and measured weld bead dimensions, a suitable and adaptive distribution mode of droplet heat content is found, i.e., droplet heat content is distributed in bottom layer of gouging region at the front of weld pool, and is averagely distributed in the whole layer at the rear of weld pool. The proposed mode is also validated by experimental observation of the weld pool images and measured by geometric dimensions of the weld bead.展开更多
Stainless steel(SS)grade 316L is used for orthopedic implants due to its biocompatibility;yet the effort should be done to minimize the carcinogenic and inflammatory effects related to SS 316L implants.In this researc...Stainless steel(SS)grade 316L is used for orthopedic implants due to its biocompatibility;yet the effort should be done to minimize the carcinogenic and inflammatory effects related to SS 316L implants.In this research,aluminide coating of Al–Si alloy on SS 316L is characterized by using optical microscopy,energy dispersive spectroscopy(EDS),nano-indentation and corrosion testing technique.Hot dip aluminizing process is used to coat the SS 316L specimens at 765°C for 2 min immersion time.Half of the specimens are also diffusion treated in a Muffle furnace at 550°C for 4 h to produce diffused specimens of SS 316L.Microstructural examination shows the formation of flat coating/substrate interface due to Si addition.EDS analysis confirms the formation of complex intermetallic at the coating/substrate interface which finally results in increasing the hardness and corrosion resistance properties of coating.展开更多
Zn-based biodegradable metals(BMs)are regarded as revolutionary biomaterials for bone implants.However,their clinical application is limited by insufficient mechanical properties,delayed in vivo degradation,and overdo...Zn-based biodegradable metals(BMs)are regarded as revolutionary biomaterials for bone implants.However,their clinical application is limited by insufficient mechanical properties,delayed in vivo degradation,and overdose-induced Zn^(2+)toxicity.Herein,innovative multi-material additive manufacturing(MMAM)is deployed to construct a Zn/titanium(Ti)hetero-structured composite.The biodegradation and biofunction of Zn exhibited intriguing characteristics in composites.A potential difference of about 300 mV naturally existed between Zn and Ti.This natural potential difference triggered galvanic coupling corrosion,resulting in 2.7 times accelerated degradation of Zn.The excess release of Zn^(2+)induced by accelerated degradation enhanced the antibacterial function.A voltage signal generated by the natural potential difference also promoted in vitro osteogenic differentiation through activating the PI3K-Akt signaling pathway,and inhibited the toxicity of overdose Zn^(2+)in vivo,significantly improving bone regeneration.Furthermore,MMAM technology allows for the specific region deployment of components.In the future,Ti and Zn could be respectively deployed in the primary and non-loadbearing regions of bone implants by structural designs,thereby achieving a functionally graded application to overcome the insufficient mechanical properties of Zn-based BMs.This work clarifies the functional optimization mechanism for multimetal bone implants,which possibly breaks the application dilemma of Zn-based BMs.展开更多
In this study,a wire oscillating laser additive manufacturing(O-WLAM)process was used to deposit 2319 aluminum alloy samples.The optimization of the deposition process parameters made it possible to obtain samples wit...In this study,a wire oscillating laser additive manufacturing(O-WLAM)process was used to deposit 2319 aluminum alloy samples.The optimization of the deposition process parameters made it possible to obtain samples with smooth surfaces and extremely low porosities.The effects of the deposition parameters on the formability and evolution of the microstructure and mechanical properties before and after heat treatment were studied.The oscillating laser deposition of 2319 aluminum alloy,especially the circular oscillation mode,significantly reduced the porosity and improved the process stability and formability compared with non-oscillating laser deposition.There were clear boundaries between the deposition units in the deposition state,the interior of which was dominated by columnar crystals with many rod-and point-shaped precipitates.After the heat treatment,theθphase was significantly dissolved.The residual dot-and rod-shapedθ'phases were dispersedly distributed,exhibiting an obvious precipitation-hardening effect.The samples in the as-deposited state had a tensile strength of 245–265 MPa,an elongation of approximately 12.6%,and an 87 HV microhardness.After heat treatment at 530°C for 20 h and aging at 175°C for 18 h,the tensile strength,elongation,and microhardness reached 425–440 MPa,approximately 10%,and 153 HV,respectively.The performance improved significantly without significant anisotropy.Compared with the samples produced by wire arc additive manufacturing(WAAM),the tensile strength increased by approximately 10%,and the strength and microhardness were significantly improved.展开更多
基金financial support on this work from the National Natural Science Foundation of China(Grant Nos.51475272 and 51550110501)Shandong University for the Postdoctoral fellowship
文摘Friction stir welding [FSW） has achieved remarkable success in the joining and processing of aluminium alloys and other softer structural alloys. Conventional FSW, however, has not been entirely successful in the joining, processing and manufacturing of different desired materials essential to meet the sophis- ticated green globe requirements. Through the efforts of improving the process and transferring the existing friction stir knowledge base to other advanced applications, several friction stir based daughter technologies have emerged over the timeline, A few among these technologies are well developed while others are under the process of emergence. Beginning with a broad classification of the scattered fric- tions stir based technologies into two categories, welding and processing, it appears now time to know, compile and review these to enable their rapid access for reference and academia. In this review article, the friction stir based technologies classified under the categol^J of welding are those applied for join- ing of materials while the remnant are labeled as friction stir processing （FSP） technologies. This review article presents an overview of four general aspects of both the developed and the developing friction stir based technologies, their associated process parameters, metallurgical features of their products and their feasibility and application to various materials. The lesser known and emerging technologies have been emphasized.
基金the China Scholarship Council for the award of fellowship and funding(No.202006230137)。
文摘In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced.Compared to the previous as-cast microstructure,the grain size was reduced from more than 1 mm to around 4μm within 3 s by a single process cycle.The compressive yield strength was increased by 350%while the ultimate compressive strength by 53%.According to the established material flow behaviors by“tracer material”,the plastic material was transported by shear deformation.From the base material to the rod,the material experienced three stages,i.e.deformation by the tool,upward flow with additional tilt,followed by upward transportation.The microstructural evolution was revealed by“stop-action”technique.The microstructural development at regions adjacent to the rod is mainly controlled by twinning,dynamic recrystallization(DRX)as well as particle stimulated nucleation,while that within the rod is related to DRX combined with grain growth.
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%.
基金the National Natural Science Foundation of China(No.52074182)Joint Funds of the National Natural Science Foundation of China(No.U23A20612).
文摘We proposed a new technique route of directional solidification for the manufacture of super slab.A 7-t laboratory-scale thick slab was casted and characterised for trial.To further understand the process,the evolution of the multiple physical fields during the directional solidification was simulated and verified.Similar to the convectional ingot casting,a negative segregated cone of equiaxed grains was formed at the bottom,and a seriously positive segregated region was formed beneath the top surface of the slab.Specific measures on the lateral walls,base plate,and free surface were strongly recommended to ensure that the slab is relatively directionally casted.A water-cooling copper base plate accelerates the solidification rate and the columnar growth along the vertical direction.It inhibits the sedimentation of equiaxed grains and enlarges the columnar zone.Based on the simulation analysis,it can be concluded that the directional solidification technique route is promising to manufacture super slab with lower segregation level,and less porosities and inclusions.
基金Ting Chen thanks the China Scholarship Council for the Award of a Fellowship(No.202006230137)Benjamin Klusemann ac-knowledges funding by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-project number 544306307+1 种基金Banglong Fu acknowledge the financial support of the National Natural Science Foundation of China(Grant No.52405386)State Key Laboratory of Precision Welding&Joining of Materials and Structures(Grant No.MSWJ-24M13).
文摘Constrained Friction Processing(CFP),a novel friction-based technique,has been developed to efficiently process fine-grained magnesium(Mg)rods,expanding the potential applications of biodegradable Mg alloys in medical implants.This study investigates the enhancement of mechanical properties through the implementation of multiple pass CFP(MP-CFP)in comparison to the conventional single pass CFP.The results reveal a substantial improvement in compressive yield strength(CYS),ultimate compressive strength,and failure plastic strain by 11%,28%,and 66%,respectively.A comprehensive analysis of material evolution during processing and the effects of the final microstructure on mechanical properties was conducted.The intricate material flow behavior during the final plunge stage of MP-CFP results in a reduced intensity of local basal texture and macrotexture.The diminished intensity of basal texture,combined with a low geometrical compatibility factor at the top of the rod after MP-CFP,effectively impedes slip transfer across grain boundaries.This leads to a local strain gradient along the compression direction,ultimately contributing to the observed enhancement in mechanical properties.The Mg-0.5Zn0.3Ca(wt.%)alloy,after texture modification by MP-CFP,exhibits a competitive CYS compared with other traditional methods,highlighting the promising application potential of MP-CFP.
基金This work was financially supported by the National Natural Science Foundation of China(No.52035005).
文摘Complete understanding of the evolution behaviors of the microstructures and intermetallic compounds(IMCs)along the interface materials flow path in friction stir welding(FSW)of dissimilar Al to Mg alloys is of great significance.In this study,conventional FSW and ultrasonic vibration enhanced FSW(UVeFSW)experiments of Al/Mg alloys were performed,and the instantaneous evolution features of the interface materials around the tool were"frozen"by using the"sudden stop"and simultaneous cooling techniques.The microstructures and IMCs formation at different locations around the exit hole were observed and characterized by scanning electron microscope,energy dispersive spectrometer and transmission elec-tron microscope.It was found that before the materials started to deposit near the back of the tool,“IMC+Mg+IMC+Al”multilayer microstructure and simple IMC layer with(β+γ)sequentially emerged on the Al/Mg interface.With the application of ultrasonic vibration,the multi-layered interface structure only appeared at the middle stage of materials flow around the pin,and ultrasonic vibration just began to play a suppression role on the growth of two sub-layers IMC at a position where the materials deposit.With assistance of ultrasonic vibration in UVeFSW,the tool drove a larger volume of Mg alloy to move toward the retreating side,and the final IMCs thickness was thinner than that in FSW.
基金financially supported by the National Natural Science Foundation of China(No.51905309)the Science and Technology Planning Project of State Grid Henan Electric Power Company(No.52170220009Y)。
文摘It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding.Thus,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed.It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMC)layer is formed at the Al/Cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the joint.With the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface.The maximum tensile strength and elongation of Al/Cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/min.In addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides.The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52005297 and 52035005)the Fundamental Research Funds of Shandong University(Grant No.2019GN003)。
文摘The tool with polygonal pin profile has been widely employed in friction stir welding(FSW) of aluminum, but there is hardly an effective optimization methodology existed as the thermomechanical characteristics affected by pins with various flats number have not been understood comprehensively. Therefore, the present work employs a 3-dimensional computational fluid dynamics(CFD) model to have an integrated observation of the FSW process with the effect of polygonal pin profiles. Both the heat generation modes due to contact friction at the tool–workpiece interface and volumetric viscous dissipation in the vicinity of the tool are considered. The model is utilized to give a quantitative analysis of the heat generation, temperature distribution, plastic material flow and welding loads during the FSW process for various tools with polygonal pin profiles, as well as a variety of shoulder diameters, welding speeds and tool rotation speeds. The calculated results of thermal cycles, tool torques and joint cross sections for some typical polygonal pins and welding parameters are all found to be compared well with the experimental ones, which demonstrates the feasibility and applicability of the present numerical model. Particularly, a methodology is developed for the optimization of the flats number by identifying the torque components in both parallel and vertical direction of the pin-side flat region. The results show that the optimized pin flats number increases with increasing tool rotation speed, while the influence of both welding speed and shoulder diameter can be supposed to be insignificant. Moreover, the dependability of the optimized results is also discussed by considering wear tendency and service life of the pin for multiple welding conditions.
基金financially supported by the New Energy and Industrial Technology Development Organization(NEDO)under the"Innovation Structural Materials Project(Future Pioneering Projects)"。
文摘The Al alloy and carbon fiber reinforced polymer(CFRP)hybrid structures,incorporating the performance advantages of the two materials,have been attracting more attention in high-end manufacturing fields.In the current investigation,the flat friction spot joining(FSJ)was employed in joining the AA6061-T6 alloy and CFRP sheets.The significance of temperature distribution in influencing joint quality was highlighted through analyzing interface microstructural features,weld defect formation as well as fractography.To understand the role of thermal energy generation and conduction in the process comprehensively,a 3D thermal-mechanical coupling finite element model was established.The interfacial temperature was characterized by an uneven distribution behavior due to the inhomogeneous heat distribution.The peak temperatures on the top surface and Al alloy to CFRP interface at 1500 rpm rotational speed with 0.1 mm/s plunging speed were 498℃and 489°C,respectively.The peak interface temperature was reduced to286℃at 250 rpm,which produced an extremely small melted area.Compared with the plunging speed,rotational speed was found to be the predominant parameter for determining the joint property,which could be optimized to simultaneously realize the avoidance of thermal decomposition of CFRP,the sufficient melting duration time,and the wide enough melted area.Simulated thermal histories and melted area profiles were in agreement with experimental ones.The findings could be utilized to provide some feasible guidance for process optimization of dissimilar FSJ of metals and composites.
基金the Key Research and Development Project of Shandong Province(No.2018CXGC0403)。
文摘Al-Cu-Li alloy is a huge potential alloy for aerospace industry due to its low density and excellent comprehensive performances.In this study,the microstructures and mechanical properties of a novel cast Al-Cu-Li alloy during the heat treatment were investigated.Results showed that most of the secondary phases along grain boundaries in as-cast state were dissolved into the Al matrix after homogenization and solution treatment,while the Cu-rich phases were slightly segregated once again on grain boundaries after aging.A relatively good combination of strength and ductility(average ultimate tensile strength of 430 MPa and elongation of 8.9%)was obtained after natural aging.Transmission electron microscopy(TEM)results revealed that there was a complicated precipitate distribution in this cast alloy after natural aging.Compared with the similar alloys which introduced dislocations before aging,the density of T1(Al_(2)CuLi)phases was decreased but the size was increased.The low volume fraction of d0 phase,medium density of needle-shaped precipitates and relativity narrow precipitates-free zone with varying widths near grain boundary are the reasons accounting for the improvement of performances.
基金This work is supported by Shandong Natural Science Foundation （ Key Project） under contract No. ZR2010EZ005.
文摘Short circuit transfer involves bridging between the consumable electrode and the weld pool, associated with variations of electrical parameters which characterize the change of molten metal bridge state and are very important for the control of .spatter. In this paper, electrical process parameters and short circuit transfer images were simultaneously recorded with a LabView-based synchronous sensing and visualizing system. The arc^bridge resistance and derivatives of welding current, arc voltage and arc resistance at various instants were calculated by means of offline analysis of the welding current, arc voltage and droplet images. Parameters and their feature values indicating the onset of short circuit and the oncoming necking-down of molten metal bridge were determined. Using the calculated feature values, bridge-state-feedback control for .short circuit transfer was realized with a spatter rate less than 0. 25%.
文摘The Editor-in-Chief has retracted this article [1] because Figures 11 and 12 appear to be identical with Figures 3 and 4respectively from a previously published article [2].Sehrish MUKHTAR,Waqas ASGHAR,Zubair BUTT,Zaheer ABBAS,Mudaser ULLAH and Rana ATTA-UR-REHMAN did not respond to correspondence about this retraction.
基金the National Natural Science Foundation of China(Grant Nos.52035005 and 51475272)。
文摘An atomic diffusion model is developed to predict the thickness of intermetallic compounds(IMCs)at the interface of aluminum/magnesium alloys in dissimilar friction stir welding.Both the temperature and the strain rate associated with dislocation density at the checking point are used to determine the diffusion coefficients.The variations of the diffusion coefficients and the thickness of IMCs are quantitatively analyzed at selected characteristic time instants during welding process.It is found that the dislocation density can increase the diffusion coefficient and plays a dominant role in the IMCs formation during the plastic deformation stage.Especially in magnesium alloy and Al12Mg17,the diffusion coefficient is increased by two orders of magnitude or even nearly three orders of magnitude by considering the dislocation density.The temperature is the main influencing factor after the end of plastic deformation.The model is validated by comparing the predicted thickness of IMCs with the experimentally measured results.
基金the financial support of the National Natural Science Foundation of China(Grant Nos.52005297 and 52035005)the Key Research and Development Program of Shandong Province(Grant No.2021ZLGX01).
文摘Joining dissimilar Mg/Cu alloys was still an intractable problem because of the excessive intermetallic compounds(IMCs)and poor mechanical properties using conventional welding methods.In the present study,friction stir welding was employed for the butt joining of dissimilar AZ31B Mg-alloy and T2 pure Cu plates.Defect-free Mg/Cu joints were obtained with Mg-RS and Cu-AS configuration,at a welding speed of 50 mm/min and tool rotating speeds of 325 r/min,625 r/min and 925 r/min.At the joining interface,both Mg_(2)Cu and MgCu_(2) IMC phases were observed,with a clear,uniform and continuous IMCs layer composed of two sub-layers,layer-A of Mg+Mg_(2)Cu and layer-B of Mg_(2)Cu+MgCu_(2).The maximum ultimate tensile strength of the Mg/Cu friction stir welding joint reached 130 MPa at 925 r/min due to enhanced mechanical interlocking between Mg and Cu,as well as sufficient metallurgical bonding at the joining interface with an IMCs layer thickness in the range of 1.0-2.0μm.
基金supported by the project from the State Key Laboratory for Advanced Welding & Joining at Harbin Institute of Technology (No.09005)
文摘The momentum of strong backward flowing melt jet and the thermal action from transferred droplets are two dominating factors affecting the formation of humping bead in high speed gas metal arc welding （GMAW）. Appropriate describing the influ- ence of the distribution mode of droplet heat content in the weld pool is essential to understand the physical mechanism of humping bead formation. Based on the exper- imental results, four kinds of droplet heat content distribution modes are proposed and employed to calculate the transient evolution of the temperature field and weld pool during high speed GMAW process. Through making comparison of predicted and measured weld bead dimensions, a suitable and adaptive distribution mode of droplet heat content is found, i.e., droplet heat content is distributed in bottom layer of gouging region at the front of weld pool, and is averagely distributed in the whole layer at the rear of weld pool. The proposed mode is also validated by experimental observation of the weld pool images and measured by geometric dimensions of the weld bead.
基金sponsored and funded by Metallurgy and Materials Engineering Department,College of Engineering and Emerging Technologies, University of the Punjab (grant no.PU/ASR&TD/ RG-348 dated 26-1-2012)
文摘Stainless steel(SS)grade 316L is used for orthopedic implants due to its biocompatibility;yet the effort should be done to minimize the carcinogenic and inflammatory effects related to SS 316L implants.In this research,aluminide coating of Al–Si alloy on SS 316L is characterized by using optical microscopy,energy dispersive spectroscopy(EDS),nano-indentation and corrosion testing technique.Hot dip aluminizing process is used to coat the SS 316L specimens at 765°C for 2 min immersion time.Half of the specimens are also diffusion treated in a Muffle furnace at 550°C for 4 h to produce diffused specimens of SS 316L.Microstructural examination shows the formation of flat coating/substrate interface due to Si addition.EDS analysis confirms the formation of complex intermetallic at the coating/substrate interface which finally results in increasing the hardness and corrosion resistance properties of coating.
基金funded by National Key Research and Development Program of China(2022YFB4600302)National Natural Science Foundation of China(52104368,82151312,82272493)+4 种基金Fundamental Research Funds for the Central Universities(FRF-IDRY-23-011)Beijing Natural Science Foundation(L222110,L212066)Beijing Science Nova Program(20220484155)Capital’s Funds for Health Improvement and Research(CFH 2024-2-5051)Autonomous Innovation Science Foundation of the Fourth Medical Center of PLA General Hospital(2024-4ZX-MS-15).
文摘Zn-based biodegradable metals(BMs)are regarded as revolutionary biomaterials for bone implants.However,their clinical application is limited by insufficient mechanical properties,delayed in vivo degradation,and overdose-induced Zn^(2+)toxicity.Herein,innovative multi-material additive manufacturing(MMAM)is deployed to construct a Zn/titanium(Ti)hetero-structured composite.The biodegradation and biofunction of Zn exhibited intriguing characteristics in composites.A potential difference of about 300 mV naturally existed between Zn and Ti.This natural potential difference triggered galvanic coupling corrosion,resulting in 2.7 times accelerated degradation of Zn.The excess release of Zn^(2+)induced by accelerated degradation enhanced the antibacterial function.A voltage signal generated by the natural potential difference also promoted in vitro osteogenic differentiation through activating the PI3K-Akt signaling pathway,and inhibited the toxicity of overdose Zn^(2+)in vivo,significantly improving bone regeneration.Furthermore,MMAM technology allows for the specific region deployment of components.In the future,Ti and Zn could be respectively deployed in the primary and non-loadbearing regions of bone implants by structural designs,thereby achieving a functionally graded application to overcome the insufficient mechanical properties of Zn-based BMs.This work clarifies the functional optimization mechanism for multimetal bone implants,which possibly breaks the application dilemma of Zn-based BMs.
基金National Natural Science Foundation of China(Grant No.52175370).
文摘In this study,a wire oscillating laser additive manufacturing(O-WLAM)process was used to deposit 2319 aluminum alloy samples.The optimization of the deposition process parameters made it possible to obtain samples with smooth surfaces and extremely low porosities.The effects of the deposition parameters on the formability and evolution of the microstructure and mechanical properties before and after heat treatment were studied.The oscillating laser deposition of 2319 aluminum alloy,especially the circular oscillation mode,significantly reduced the porosity and improved the process stability and formability compared with non-oscillating laser deposition.There were clear boundaries between the deposition units in the deposition state,the interior of which was dominated by columnar crystals with many rod-and point-shaped precipitates.After the heat treatment,theθphase was significantly dissolved.The residual dot-and rod-shapedθ'phases were dispersedly distributed,exhibiting an obvious precipitation-hardening effect.The samples in the as-deposited state had a tensile strength of 245–265 MPa,an elongation of approximately 12.6%,and an 87 HV microhardness.After heat treatment at 530°C for 20 h and aging at 175°C for 18 h,the tensile strength,elongation,and microhardness reached 425–440 MPa,approximately 10%,and 153 HV,respectively.The performance improved significantly without significant anisotropy.Compared with the samples produced by wire arc additive manufacturing(WAAM),the tensile strength increased by approximately 10%,and the strength and microhardness were significantly improved.
