Friction stir welding(FSW) is a promising welding process that can join age hardenable aluminium alloys with high joint efficiency. However,the thermal cycles experienced by the material to be joined during FSW result...Friction stir welding(FSW) is a promising welding process that can join age hardenable aluminium alloys with high joint efficiency. However,the thermal cycles experienced by the material to be joined during FSW resulted in the deterioration of mechanical properties due to the coarsening and dissolution of strengthening precipitates in the thermo-mechanical affected zone(TMAZ) and heat affected zone(HAZ). Under water friction stir welding(UWFSW) is a variant of FSW process which can maintain low heat input as well as constant heat input along the weld line. The heat conduction and dissipation during UWFSW controls the width of TMAZ and HAZ and also improves the joint properties. In this investigation, an attempt has been made to evaluate the mechanical properties and microstructural characteristics of AA2519-T87 aluminium alloy joints made by FSW and UWFSW processes. Finite element analysis has been used to estimate the temperature distribution and width of TMAZ region in both the joints and the results have been compared with experimental results and subsequently correlated with mechanical properties.? 2016 China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.展开更多
Bead-on-plate friction stir welds were made on P91 alloy with low and high rotational speeds(100 and 1000 RPM) to study their effects on weld microstructural changes and impression creep behavior. Temperatures experie...Bead-on-plate friction stir welds were made on P91 alloy with low and high rotational speeds(100 and 1000 RPM) to study their effects on weld microstructural changes and impression creep behavior. Temperatures experienced by the stir zone were recorded at the weld tool tip. Different zones of welds were characterized for their microstructural changes, hardness and creep behavior(by impression creep tests). The results were compared with submerged arc fusion weld. Studies revealed that the stir zone temperature with 100 RPM was well below A_(c1) temperature of P91 steel while it was above A_(c3) with 1000 RPM. The results suggest that the microstructural degradation in P91 welds can be controlled by low temperature friction stir welding technique.展开更多
The plates of AA5086 aluminium alloy were joined together by friction stir welding at a fixed rotation speed of 1000 r/min various welding speeds ranging from 63 to 100 mm/min.Corrosion behavior of the parent alloy(PA...The plates of AA5086 aluminium alloy were joined together by friction stir welding at a fixed rotation speed of 1000 r/min various welding speeds ranging from 63 to 100 mm/min.Corrosion behavior of the parent alloy(PA),the heat affected zone(HAZ),and the weld nugget zone(WNZ)of the joints were studied in 3.5%(mass fraction)aerated aqueous Na Cl solution by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The corrosion susceptibility of the weldments increases when the welding speed increases to 63 and 100 mm/min.However,the value of corrosion rate in the weldments is lower than that in the PA.Additionally,the corrosion current density increases with increasing the welding speed in the HAZ and the WNZ.On the contrary,the corrosion potential in the WNZ appears more positive than in the HAZ with decreasing the welding speed.The WNZ exhibits higher resistance compared to the HAZ and the PA as the welding speed decreases.The results obtained from the EIS measurements suggest that the weld regions have higher corrosion resistance than the parent alloy.With increasing the welding speed,the distribution and extent of the corroded areas in the WNZ region are lower than those of the HAZ region.In the HAZ region,in addition to the pits in the corroded area,some cracks can be seen around the corroded areas,which confirms that intergranular corrosion is formed in this area.The alkaline localized corrosion and the pitting corrosion are the main corrosion mechanisms in the corroded areas within the weld regions.Crystallographic pits are observed within the weld regions.展开更多
2017 aluminum alloy plates with an ultrafine grained （UFG） structure were produced by equal channel angular processing （ECAP） and then were joined by underwater friction stir welding （underwater FSW）. X-ray diff...2017 aluminum alloy plates with an ultrafine grained （UFG） structure were produced by equal channel angular processing （ECAP） and then were joined by underwater friction stir welding （underwater FSW）. X-ray diffractometer （XRD）, transmission electron microscope （TEM）, scanning electron microscope （SEM） and microhardness tester were adopted to investigate the microstructural and mechanical characteristics of the FSW joint. The results indicate that an ultrafine grained microstructure with the mean grain size of-0.7 Ixm is obtained in the weld nugget by using water cooling. However, The FSW joint exhibits softening compared with the ultrafine grained based material and the heat affected zone （HAZ） has the lowest hardness owing to the coarsening of the strengthening precipitates.展开更多
This study investigates the effect of tool rotational speed(TRS)on particle distribution in nugget zone(NZ)through quantitative approach and its consequences on the mechanical property of friction stir welded joints o...This study investigates the effect of tool rotational speed(TRS)on particle distribution in nugget zone(NZ)through quantitative approach and its consequences on the mechanical property of friction stir welded joints of AA6092/17.5 SiCp-T6 composite.6 mm thick plates are welded at a constant tool tilt angle of 2°and tool traverse speed of 1 mm/s by varying the TRS at 1000 rpm,1500 rpm and 2000 rpm with a taper pin profiled tool.Microstructure analysis shows large quantity of uniformly shaped smaller size SiC particle with lower average particle area which are homogeneously distributed in the NZ.The fragmentation of bigger size particles has been observed because of abrading action of the hard tool and resulting shearing effect and severe stress generation due to the rotation of tool.The particles occupy maximum area in the matrix compared to that of the base material(BM)due to the redistribution of broken particles as an effect of TRS.The migration of particles towards the TMAZ-NZ transition zone has been also encountered at higher TRS(2000 rpm).The microhardness analysis depicts variation in average hardness from top to bottom of the NZ,minimum for 1500 rpm and maximum for 2000 rpm.The impact strength at 1000 rpm and 1500 rpm remains close to that of BM(21.6 J)while 2000 rpm shows the accountable reduction.The maximum joint efficiency has been achieved at 1500 rpm(84%)and minimum at 1000 rpm(68%)under tensile loading.Fractographic analysis shows mixed mode of failure for BM,1000 rpm and 1500 rpm,whereas 2000 rpm shows the brittle mode of failure.展开更多
This study was done to evaluate the nugget zone(NZ)corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding(FSLW)in a solution of 0.015 mol/L borax(pH 9.3).To this end,dissimilar copper...This study was done to evaluate the nugget zone(NZ)corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding(FSLW)in a solution of 0.015 mol/L borax(pH 9.3).To this end,dissimilar copper/brass plates were welded with two dissimilar heat inputs(low and high)during the welding procedure.The high and low heat inputs were conducted with 710 r/min,16 mm/min and 450 r/min,25 mm/min,respectively.Using open circuit potential(OCP)measurements,electrochemical impedance spectroscopy(EIS)and Tafel polarization tests,the electrochemical behavior of the specimens in borate buffer solution was assessed.With the help of scanning electron microscope(SEM),the morphology of welded specimen surfaces was examined after immersion in the test solution.According to the results,the NZ grain size and resistance improvement reduced due to the nugget zone corrosion with a decreased heat input.The results obtained from Tafel polarization and EIS indicated the improved corrosion behavior of the welded specimen NZ with a decrease in the heat input during the welding process unlike the copper and brass metals.Furthermore,an increased heat input during the welding process shows a reduction in the conditions for forming the passive films with higher protection behavior.展开更多
A comparative approach was performed between the response surface method(RSM) and the adaptive neuro-fuzzy inference system(ANFIS) to enhance the tensile properties, including the ultimate tensile strength and the ten...A comparative approach was performed between the response surface method(RSM) and the adaptive neuro-fuzzy inference system(ANFIS) to enhance the tensile properties, including the ultimate tensile strength and the tensile elongation, of friction stir welded age hardenable AA6061 and AA2024 aluminum alloys. The effects of the welding parameters, namely the tool rotational speed, welding speed, axial load and pin profile, on the ultimate tensile strength and the tensile elongation were analyzed using a three-level, four-factor Box-Behnken experimental design. The developed design was utilized to train the ANFIS models. The predictive capabilities of RSM and ANFIS were compared based on the root mean square error, the mean absolute error, and the correlation coefficient based on the obtained data set. The results demonstrate that the developed ANFIS models are more effective than the RSM model.展开更多
The aluminium alloy AA2219(Al—Cu—Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance.Welding is main fabrication method of AA2219 al...The aluminium alloy AA2219(Al—Cu—Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance.Welding is main fabrication method of AA2219 alloy for manufacturing various engineering components.Friction stir welding(FSW) is a recently developed solid state welding process to overcome the problems encountered in fusion welding.This process uses a non-consumable tool to generate frictional heat on the abutting surfaces.The welding parameters,such as tool pin profile,rotational speed,welding speed and axial force,play major role in determining the microstructure and corrosion resistance of welded joint.The main objective of this work is to develop a mathematical model to predict the corrosion resistance of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters.In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions.Dynamic polarization testing was carried out to determine critical pitting potential in millivolt,which is a criteria for measuring corrosion resistance and the data was used in model.Further the response surface method(RSM) was used to develop the model.The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the friction stir welded AA2219 aluminium alloy joints.展开更多
This paper studies the friction stir spot welding of AA2024-T3/AA7075-T6 Al alloys in the ambient and underwater environments by clarifying the nugget features,microstructure,fracture and mechanical properties of the ...This paper studies the friction stir spot welding of AA2024-T3/AA7075-T6 Al alloys in the ambient and underwater environments by clarifying the nugget features,microstructure,fracture and mechanical properties of the joints.The results show that the water-cooling medium exhibits a significant heat absorption capacity in the AA2024-T3/AA7075-T6 welded joint.Nugget features such as stir zone width,circular imprints,average grain sizes,and angular inter-material hooking are reduced by the watercooling effect in the joints.Narrower whitish(intercalated structures)bands are formed in the underwater joints while Mg2Si and Al2CuMg precipitates are formed in the ambient and the underwater welded joints respectively.An increase in tool rotational speed(600e1400 rpm)and plunge depth(0.1 e0.5 mm)increases the tensile-shear force of the welded AA2024-T3/AA7075-T6 joints in both the ambient and underwater environments.The maximum tensile-shear forces of 5900 N and 6700 N were obtained in the ambient and the underwater welds respectively.展开更多
Friction stir welding using the tools with polygonal pins is often found to improve the mechanical strength of weld joint in comparison to the tools with circular pins. However, the impacts of pin profile on the peak ...Friction stir welding using the tools with polygonal pins is often found to improve the mechanical strength of weld joint in comparison to the tools with circular pins. However, the impacts of pin profile on the peak temperature, tool torque and traverse force, and the resultant mechanical stresses experienced by the tool have been rarely reported in a systematic manner. An estimation of the rate of heat generation for the tools with polygonal pins is challenging due to their non-axisymmetric cross-section about the tool axis. A novel methodology is presented to analytically estimate the rate of heat generation for the tools with polygonal pins. A three-dimensional heat transfer analysis of friction stir welding is carried out using finite element method. The computed temperature field from the heat transfer model is used to estimate the torque, traverse force and the mechanical stresses experienced by regular triangular, square, pentagon and hexagon pins following the principles of solid mechanics. The computed results show that the peak temperature experienced by the tool pin increases with the number of pin sides. However, the resultant maximum shear stress experienced by the pin reduces from the triangular to hexagonal pins.展开更多
The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zon...The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zone(NZ)and thermo-mechanical affected zone(TMAZ). Multiple crack sources are developed at the same time, and they merge into large cracks along the boundary line of NZ and TMAZ during the propagation stage. Furthermore, a mutual reinforcement coupling always exists between corrosion and cyclic loading during the initiation and propagation of corrosion fatigue crack. It is necessary to consider the effect of welding residual stress for understanding the mechanism of corrosion fatigue fracture of FSW joints.展开更多
An attempt is made to develop the tools that are capable enough to withstand the shear, impact and thermal forces that occur during friction stir welding of stainless steels. The atmospheric plasma spray and plasma tr...An attempt is made to develop the tools that are capable enough to withstand the shear, impact and thermal forces that occur during friction stir welding of stainless steels. The atmospheric plasma spray and plasma transferred arc hardfacing processes are employed to deposit refractory ceramic based composite coatings on the Inconel 738 alloy. Five different combinations of self-fluxing alloy powder and 60% ceramic reinforcement particulate mixtures are used for coating. The best friction stir welding tool selected based on tool wear analysis is used to fabricate the austenitic stainless steel joints.展开更多
Friction stir welding(FSW) is a novel technique for joining different materials without melting. In FSW the welded components are joined by stirring the plasticized material of the welded edges with a special rotating...Friction stir welding(FSW) is a novel technique for joining different materials without melting. In FSW the welded components are joined by stirring the plasticized material of the welded edges with a special rotating pin plunged into the material and moving along the joint line. From the scientific point of view,the key role of the FSW processes belongs to formation of the special plasticized conditions and activation of physical mechanisms of mixing the materials in such conditions to produce the strong homogeneous weld. But it is still a lack of complete understanding of what are these conditions and mechanisms.This paper is devoted to understanding the mechanisms of material mixing in conditions of FSW based on a computer simulation using particles. The movable cellular automaton method(MCA), which is a representative of the particle methods in mechanics of materials, was used to perform all computations.Usually, material flow including material stirring in FSW is simulated using computational fluid mechanics or smoothed particle hydrodynamics, which assume that the material is a continuum and does not take into account the material structure. MCA considers a material as an ensemble of bonded particles. Breaking of inter-particle bonds and formation of new bonds enables simulation of crack nucleation and healing, as well as mass mixing and micro-welding.The paper consists of two main parts. In the first part, the simulations in 2 D statements are performed to study the dynamics of friction stir welding of duralumin plates and influence of different welding regimes on the features of the material stirring and temperature distribution in the forming welded joints. It is shown that the ratio of the rotational speed to the advancing velocity of the tool has a dramatic effect on the joint quality. A suitable choice of these parameters combined with additional ultrasonic impact could considerably reduce the number of pores and microcracks in the weld without significant overheating of the welded materials.The second part of the paper considers simulation in the 3 D statement. These simulations showed that using tool pins of different shape like a cylinder, cone, or pyramid without a shoulder results in negligible motion of the plasticized material in the direction of workpiece thickness. However, the optimal ratio of the advancing velocity to the rotational speed allows transporting of the stirred material around the tool pin several times and hence producing the joint of good quality.展开更多
The present research introduces a unique concept of scarf joint technique in friction stir welding(FSW) of aluminum alloy AA 6061-T6 plates and an investigation on weld quality.A new joint configuration with two disti...The present research introduces a unique concept of scarf joint technique in friction stir welding(FSW) of aluminum alloy AA 6061-T6 plates and an investigation on weld quality.A new joint configuration with two distinct scarf angles(75°and 60°) was considered in this study.The various aspects of welding were compared with contemporary simple square butt(SSB) joint configuration.Welding was carried out at a constant tool rotation speed(TRS),tool traverse speed(TTS) and tool tilt angle of 1100 rpm,2 mm/s and2°,respectively.The results are analyzed in terms of force and torque distribution,microstructure,macrostructure,and mechanical property perspective for different joint configurations.The study reveals the minimum amount of force and torque at 60°scarf angle joint configuration compared to that of square butt joint configuration.Macro study shows that all the joints were defect-free,and a prominent onion ring was present in the lower portion of the weld nugget(WN).Fine equiaxed grains with a minimum average grain size diameter of 6.82 μm were obtained in the WN of scarf joint configuration(SJC).The maximum ultimate tensile strength(UTS) and maximum average NZ hardness of 267 MPa and83.82 HV0.1were obtained in SJC3 at a scarf angle of 60°.It has been observed from the investigation that the joint efficiency increases from 72.5%(SSB) to 86%(SJC3) at a 60° scarf angle.This unique characteristic may lay an impetus on probable joint strength enhancement technique without increasing the production cost.展开更多
Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relatio...Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relationships were derived to evaluate the MAO coating properties(porosity and hardness) by incorporating very important MAO parameters(current density, inter-electrode distance and oxidation time). MAO parameters were also optimized to achieve coatings with minimum porosity and maximum hardness. Further, the effect of MAO parameters on coating characteristics was analysed. From the results, it is found that the current density has greater influence on the responses than the other two parameters.展开更多
A systematic approach was presented to develop the empirical model for predicting the ultimate tensile strength of AA5083-H111 aluminum alloy which is widely used in ship building industry by incorporating friction st...A systematic approach was presented to develop the empirical model for predicting the ultimate tensile strength of AA5083-H111 aluminum alloy which is widely used in ship building industry by incorporating friction stir welding(FSW) process parameters such as tool rotational speed,welding speed,and axial force.FSW was carried out considering three-factor five-level central composite rotatable design with full replications technique.Response surface methodology(RSM) was applied to developing linear regression model for establishing the relationship between the FSW process parameters and ultimate tensile strength.Analysis of variance(ANOVA) technique was used to check the adequacy of the developed model.The FSW process parameters were also optimized using response surface methodology(RSM) to maximize the ultimate tensile strength.The joint welded at a tool rotational speed of 1 000 r/min,a welding speed of 69 mm/min and an axial force of 1.33 t exhibits higher tensile strength compared with other joints.展开更多
The microstructure and mechanical properties of dissimilar pinless friction stir spot welded joint of2A12aluminum alloy and TC4titanium alloy were evaluated.The results show that the joint of Al/Ti dissimilar alloys c...The microstructure and mechanical properties of dissimilar pinless friction stir spot welded joint of2A12aluminum alloy and TC4titanium alloy were evaluated.The results show that the joint of Al/Ti dissimilar alloys can be successfully attained through pinless friction stir spot welding(FSSW).The joint can be divided into three zones(SZ,TMAZ and HAZ).The microstructure of joint in Al alloy side changes significantly but it basically has no change in Ti alloy side.At the same rotation speed,the maximum load of welded joints gradually rises with the increase in dwell time.At the same dwell time,the maximum load of the welded joint increases with the increase of the rotational speed.In addition,optimal parameters were obtained in this work,and they are rotation speed of1500r/min,plunge speed of30mm/min,plunge depth of0.3mm and dwell time of15s.The fracture mode of welded joints is interfacial shear fracture.The microhardness of the joint on the Al side distributes in a typical“W”type and is symmetry along the weld center,but the distribution of the microhardness on the Ti side has no obvious change.展开更多
Aluminium alloys generally present low weldability by traditional fusion welding process. Development of the friction stir welding （FSW） has provided an alternative improved way of producing aluminium joints in a fa...Aluminium alloys generally present low weldability by traditional fusion welding process. Development of the friction stir welding （FSW） has provided an alternative improved way of producing aluminium joints in a faster and reliable manner. The quality of a weld joint is stalwartly influenced by process parameter used during welding. An approach to develop a mathematical model was studied for predicting and optimizing the process parameters of dissimilar aluminum alloy （AA6351 T6-AA5083 Hlll）joints by incorporating the FSW process parameters such as tool pin profile, tool rotational speed welding speed and axial force. The effects of the FSW process parameters on the ultimate tensile strength （UTS） of friction welded dissimilar joints were discussed. Optimization was carried out to maximize the UTS using response surface methodology （RSM） and the identified optimum FSW welding parameters were reported.展开更多
The application of friction stir welding(FSW) is growing owing to the omission of difficulties in traditional welding processes. In the current investigation, artificial neural network(ANN) technique was employed to p...The application of friction stir welding(FSW) is growing owing to the omission of difficulties in traditional welding processes. In the current investigation, artificial neural network(ANN) technique was employed to predict the microhardness of AA6061 friction stir welded plates. Specimens were welded employing triangular and tapered cylindrical pins. The effects of thread and conical shoulder of each pin profile on the microhardness of welded zone were studied using tow ANNs through the different distances from weld centerline. It is observed that using conical shoulder tools enhances the quality of welded area. Besides, in both pin profiles threaded pins and conical shoulders increase yield strength and ultimate tensile strength. Mean absolute percentage error(MAPE) for train and test data sets did not exceed 5.4% and 7.48%, respectively. Considering the accurate results and acceptable errors in the models' responses, the ANN method can be used to economize material and time.展开更多
Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by f...Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.展开更多
基金the financial support of the Directorate of Extramural Research & Intellectual Property Rights (ER&IPR)Defense Research Development Organization (DRDO)New Delhi through a R&D project no. DRDO-ERIPER/ERIP/ER/0903821/M/01/1404 to carry out this investigation
文摘Friction stir welding(FSW) is a promising welding process that can join age hardenable aluminium alloys with high joint efficiency. However,the thermal cycles experienced by the material to be joined during FSW resulted in the deterioration of mechanical properties due to the coarsening and dissolution of strengthening precipitates in the thermo-mechanical affected zone(TMAZ) and heat affected zone(HAZ). Under water friction stir welding(UWFSW) is a variant of FSW process which can maintain low heat input as well as constant heat input along the weld line. The heat conduction and dissipation during UWFSW controls the width of TMAZ and HAZ and also improves the joint properties. In this investigation, an attempt has been made to evaluate the mechanical properties and microstructural characteristics of AA2519-T87 aluminium alloy joints made by FSW and UWFSW processes. Finite element analysis has been used to estimate the temperature distribution and width of TMAZ region in both the joints and the results have been compared with experimental results and subsequently correlated with mechanical properties.? 2016 China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.
文摘Bead-on-plate friction stir welds were made on P91 alloy with low and high rotational speeds(100 and 1000 RPM) to study their effects on weld microstructural changes and impression creep behavior. Temperatures experienced by the stir zone were recorded at the weld tool tip. Different zones of welds were characterized for their microstructural changes, hardness and creep behavior(by impression creep tests). The results were compared with submerged arc fusion weld. Studies revealed that the stir zone temperature with 100 RPM was well below A_(c1) temperature of P91 steel while it was above A_(c3) with 1000 RPM. The results suggest that the microstructural degradation in P91 welds can be controlled by low temperature friction stir welding technique.
文摘The plates of AA5086 aluminium alloy were joined together by friction stir welding at a fixed rotation speed of 1000 r/min various welding speeds ranging from 63 to 100 mm/min.Corrosion behavior of the parent alloy(PA),the heat affected zone(HAZ),and the weld nugget zone(WNZ)of the joints were studied in 3.5%(mass fraction)aerated aqueous Na Cl solution by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The corrosion susceptibility of the weldments increases when the welding speed increases to 63 and 100 mm/min.However,the value of corrosion rate in the weldments is lower than that in the PA.Additionally,the corrosion current density increases with increasing the welding speed in the HAZ and the WNZ.On the contrary,the corrosion potential in the WNZ appears more positive than in the HAZ with decreasing the welding speed.The WNZ exhibits higher resistance compared to the HAZ and the PA as the welding speed decreases.The results obtained from the EIS measurements suggest that the weld regions have higher corrosion resistance than the parent alloy.With increasing the welding speed,the distribution and extent of the corroded areas in the WNZ region are lower than those of the HAZ region.In the HAZ region,in addition to the pits in the corroded area,some cracks can be seen around the corroded areas,which confirms that intergranular corrosion is formed in this area.The alkaline localized corrosion and the pitting corrosion are the main corrosion mechanisms in the corroded areas within the weld regions.Crystallographic pits are observed within the weld regions.
基金Projects(50774059, 51074119) supported by the National Natural Science Foundation of China
文摘2017 aluminum alloy plates with an ultrafine grained （UFG） structure were produced by equal channel angular processing （ECAP） and then were joined by underwater friction stir welding （underwater FSW）. X-ray diffractometer （XRD）, transmission electron microscope （TEM）, scanning electron microscope （SEM） and microhardness tester were adopted to investigate the microstructural and mechanical characteristics of the FSW joint. The results indicate that an ultrafine grained microstructure with the mean grain size of-0.7 Ixm is obtained in the weld nugget by using water cooling. However, The FSW joint exhibits softening compared with the ultrafine grained based material and the heat affected zone （HAZ） has the lowest hardness owing to the coarsening of the strengthening precipitates.
基金Ministry of Human Resource,Government of India for providing necessary funding through scholarship to carry out the research activities。
文摘This study investigates the effect of tool rotational speed(TRS)on particle distribution in nugget zone(NZ)through quantitative approach and its consequences on the mechanical property of friction stir welded joints of AA6092/17.5 SiCp-T6 composite.6 mm thick plates are welded at a constant tool tilt angle of 2°and tool traverse speed of 1 mm/s by varying the TRS at 1000 rpm,1500 rpm and 2000 rpm with a taper pin profiled tool.Microstructure analysis shows large quantity of uniformly shaped smaller size SiC particle with lower average particle area which are homogeneously distributed in the NZ.The fragmentation of bigger size particles has been observed because of abrading action of the hard tool and resulting shearing effect and severe stress generation due to the rotation of tool.The particles occupy maximum area in the matrix compared to that of the base material(BM)due to the redistribution of broken particles as an effect of TRS.The migration of particles towards the TMAZ-NZ transition zone has been also encountered at higher TRS(2000 rpm).The microhardness analysis depicts variation in average hardness from top to bottom of the NZ,minimum for 1500 rpm and maximum for 2000 rpm.The impact strength at 1000 rpm and 1500 rpm remains close to that of BM(21.6 J)while 2000 rpm shows the accountable reduction.The maximum joint efficiency has been achieved at 1500 rpm(84%)and minimum at 1000 rpm(68%)under tensile loading.Fractographic analysis shows mixed mode of failure for BM,1000 rpm and 1500 rpm,whereas 2000 rpm shows the brittle mode of failure.
文摘This study was done to evaluate the nugget zone(NZ)corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding(FSLW)in a solution of 0.015 mol/L borax(pH 9.3).To this end,dissimilar copper/brass plates were welded with two dissimilar heat inputs(low and high)during the welding procedure.The high and low heat inputs were conducted with 710 r/min,16 mm/min and 450 r/min,25 mm/min,respectively.Using open circuit potential(OCP)measurements,electrochemical impedance spectroscopy(EIS)and Tafel polarization tests,the electrochemical behavior of the specimens in borate buffer solution was assessed.With the help of scanning electron microscope(SEM),the morphology of welded specimen surfaces was examined after immersion in the test solution.According to the results,the NZ grain size and resistance improvement reduced due to the nugget zone corrosion with a decreased heat input.The results obtained from Tafel polarization and EIS indicated the improved corrosion behavior of the welded specimen NZ with a decrease in the heat input during the welding process unlike the copper and brass metals.Furthermore,an increased heat input during the welding process shows a reduction in the conditions for forming the passive films with higher protection behavior.
基金Sri Chandrasekharendra Saraswathi Viswa Maha Vidyalaya, Enathur, Kanchipuram, Tamilnadu for funding this research as a university minor research project
文摘A comparative approach was performed between the response surface method(RSM) and the adaptive neuro-fuzzy inference system(ANFIS) to enhance the tensile properties, including the ultimate tensile strength and the tensile elongation, of friction stir welded age hardenable AA6061 and AA2024 aluminum alloys. The effects of the welding parameters, namely the tool rotational speed, welding speed, axial load and pin profile, on the ultimate tensile strength and the tensile elongation were analyzed using a three-level, four-factor Box-Behnken experimental design. The developed design was utilized to train the ANFIS models. The predictive capabilities of RSM and ANFIS were compared based on the root mean square error, the mean absolute error, and the correlation coefficient based on the obtained data set. The results demonstrate that the developed ANFIS models are more effective than the RSM model.
文摘The aluminium alloy AA2219(Al—Cu—Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance.Welding is main fabrication method of AA2219 alloy for manufacturing various engineering components.Friction stir welding(FSW) is a recently developed solid state welding process to overcome the problems encountered in fusion welding.This process uses a non-consumable tool to generate frictional heat on the abutting surfaces.The welding parameters,such as tool pin profile,rotational speed,welding speed and axial force,play major role in determining the microstructure and corrosion resistance of welded joint.The main objective of this work is to develop a mathematical model to predict the corrosion resistance of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters.In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions.Dynamic polarization testing was carried out to determine critical pitting potential in millivolt,which is a criteria for measuring corrosion resistance and the data was used in model.Further the response surface method(RSM) was used to develop the model.The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the friction stir welded AA2219 aluminium alloy joints.
基金Scientific Research Fund of Hunan Provincial Education Department(No.15C1240)Innovation platform open fund Project(No.16K080).
文摘This paper studies the friction stir spot welding of AA2024-T3/AA7075-T6 Al alloys in the ambient and underwater environments by clarifying the nugget features,microstructure,fracture and mechanical properties of the joints.The results show that the water-cooling medium exhibits a significant heat absorption capacity in the AA2024-T3/AA7075-T6 welded joint.Nugget features such as stir zone width,circular imprints,average grain sizes,and angular inter-material hooking are reduced by the watercooling effect in the joints.Narrower whitish(intercalated structures)bands are formed in the underwater joints while Mg2Si and Al2CuMg precipitates are formed in the ambient and the underwater welded joints respectively.An increase in tool rotational speed(600e1400 rpm)and plunge depth(0.1 e0.5 mm)increases the tensile-shear force of the welded AA2024-T3/AA7075-T6 joints in both the ambient and underwater environments.The maximum tensile-shear forces of 5900 N and 6700 N were obtained in the ambient and the underwater welds respectively.
文摘Friction stir welding using the tools with polygonal pins is often found to improve the mechanical strength of weld joint in comparison to the tools with circular pins. However, the impacts of pin profile on the peak temperature, tool torque and traverse force, and the resultant mechanical stresses experienced by the tool have been rarely reported in a systematic manner. An estimation of the rate of heat generation for the tools with polygonal pins is challenging due to their non-axisymmetric cross-section about the tool axis. A novel methodology is presented to analytically estimate the rate of heat generation for the tools with polygonal pins. A three-dimensional heat transfer analysis of friction stir welding is carried out using finite element method. The computed temperature field from the heat transfer model is used to estimate the torque, traverse force and the mechanical stresses experienced by regular triangular, square, pentagon and hexagon pins following the principles of solid mechanics. The computed results show that the peak temperature experienced by the tool pin increases with the number of pin sides. However, the resultant maximum shear stress experienced by the pin reduces from the triangular to hexagonal pins.
基金Project(KYGYJQZL2204) supported by the Basic Frontier Science and Technology Innovation Project of Army Engineering University of PLA,ChinaProjects(30110010403, 30110030103) supported by the Preliminary Research of Equipment,China。
文摘The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zone(NZ)and thermo-mechanical affected zone(TMAZ). Multiple crack sources are developed at the same time, and they merge into large cracks along the boundary line of NZ and TMAZ during the propagation stage. Furthermore, a mutual reinforcement coupling always exists between corrosion and cyclic loading during the initiation and propagation of corrosion fatigue crack. It is necessary to consider the effect of welding residual stress for understanding the mechanism of corrosion fatigue fracture of FSW joints.
基金the Department of Science and Technology (DST), Government of India for the financial support through Fast Track Scheme for Young Scientists R&D project (SR/FTP/ETA043/2009) to carry out this investigation
文摘An attempt is made to develop the tools that are capable enough to withstand the shear, impact and thermal forces that occur during friction stir welding of stainless steels. The atmospheric plasma spray and plasma transferred arc hardfacing processes are employed to deposit refractory ceramic based composite coatings on the Inconel 738 alloy. Five different combinations of self-fluxing alloy powder and 60% ceramic reinforcement particulate mixtures are used for coating. The best friction stir welding tool selected based on tool wear analysis is used to fabricate the austenitic stainless steel joints.
基金the Russian Fundamental Research Program of the State Academies of Sciencesfor 2013-2020(Priority directionⅢ.23)
文摘Friction stir welding(FSW) is a novel technique for joining different materials without melting. In FSW the welded components are joined by stirring the plasticized material of the welded edges with a special rotating pin plunged into the material and moving along the joint line. From the scientific point of view,the key role of the FSW processes belongs to formation of the special plasticized conditions and activation of physical mechanisms of mixing the materials in such conditions to produce the strong homogeneous weld. But it is still a lack of complete understanding of what are these conditions and mechanisms.This paper is devoted to understanding the mechanisms of material mixing in conditions of FSW based on a computer simulation using particles. The movable cellular automaton method(MCA), which is a representative of the particle methods in mechanics of materials, was used to perform all computations.Usually, material flow including material stirring in FSW is simulated using computational fluid mechanics or smoothed particle hydrodynamics, which assume that the material is a continuum and does not take into account the material structure. MCA considers a material as an ensemble of bonded particles. Breaking of inter-particle bonds and formation of new bonds enables simulation of crack nucleation and healing, as well as mass mixing and micro-welding.The paper consists of two main parts. In the first part, the simulations in 2 D statements are performed to study the dynamics of friction stir welding of duralumin plates and influence of different welding regimes on the features of the material stirring and temperature distribution in the forming welded joints. It is shown that the ratio of the rotational speed to the advancing velocity of the tool has a dramatic effect on the joint quality. A suitable choice of these parameters combined with additional ultrasonic impact could considerably reduce the number of pores and microcracks in the weld without significant overheating of the welded materials.The second part of the paper considers simulation in the 3 D statement. These simulations showed that using tool pins of different shape like a cylinder, cone, or pyramid without a shoulder results in negligible motion of the plasticized material in the direction of workpiece thickness. However, the optimal ratio of the advancing velocity to the rotational speed allows transporting of the stirred material around the tool pin several times and hence producing the joint of good quality.
基金the Ministry of Human Resource and Development,Government of India for providing the financial assistantship in the form of fellowship。
文摘The present research introduces a unique concept of scarf joint technique in friction stir welding(FSW) of aluminum alloy AA 6061-T6 plates and an investigation on weld quality.A new joint configuration with two distinct scarf angles(75°and 60°) was considered in this study.The various aspects of welding were compared with contemporary simple square butt(SSB) joint configuration.Welding was carried out at a constant tool rotation speed(TRS),tool traverse speed(TTS) and tool tilt angle of 1100 rpm,2 mm/s and2°,respectively.The results are analyzed in terms of force and torque distribution,microstructure,macrostructure,and mechanical property perspective for different joint configurations.The study reveals the minimum amount of force and torque at 60°scarf angle joint configuration compared to that of square butt joint configuration.Macro study shows that all the joints were defect-free,and a prominent onion ring was present in the lower portion of the weld nugget(WN).Fine equiaxed grains with a minimum average grain size diameter of 6.82 μm were obtained in the WN of scarf joint configuration(SJC).The maximum ultimate tensile strength(UTS) and maximum average NZ hardness of 267 MPa and83.82 HV0.1were obtained in SJC3 at a scarf angle of 60°.It has been observed from the investigation that the joint efficiency increases from 72.5%(SSB) to 86%(SJC3) at a 60° scarf angle.This unique characteristic may lay an impetus on probable joint strength enhancement technique without increasing the production cost.
基金Council of Scientific and Industrial Research (G8/19901/2013), New Delhi for the financial support provided to conduct this investigation through sponsored project No. 22(0615)/13/EMR-II dated 26.02.2013
文摘Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relationships were derived to evaluate the MAO coating properties(porosity and hardness) by incorporating very important MAO parameters(current density, inter-electrode distance and oxidation time). MAO parameters were also optimized to achieve coatings with minimum porosity and maximum hardness. Further, the effect of MAO parameters on coating characteristics was analysed. From the results, it is found that the current density has greater influence on the responses than the other two parameters.
文摘A systematic approach was presented to develop the empirical model for predicting the ultimate tensile strength of AA5083-H111 aluminum alloy which is widely used in ship building industry by incorporating friction stir welding(FSW) process parameters such as tool rotational speed,welding speed,and axial force.FSW was carried out considering three-factor five-level central composite rotatable design with full replications technique.Response surface methodology(RSM) was applied to developing linear regression model for establishing the relationship between the FSW process parameters and ultimate tensile strength.Analysis of variance(ANOVA) technique was used to check the adequacy of the developed model.The FSW process parameters were also optimized using response surface methodology(RSM) to maximize the ultimate tensile strength.The joint welded at a tool rotational speed of 1 000 r/min,a welding speed of 69 mm/min and an axial force of 1.33 t exhibits higher tensile strength compared with other joints.
基金Projects(51405389,51675435)supported by the National Natural Science Foundation of ChinaProject(3102017ZY005)supported by the Fundamental Research Funds for the Central Universities,China+3 种基金Project(SAST2016043)supported by the Fund of SAST,ChinaProject(20161125002)supported by the Aeronautical Science Foundation of ChinaProject(B08040)supported by the 111 Project,ChinaProjects(2016YFB0701203,2016YFB1100104)supported by the National Key Research and Development Program of China
文摘The microstructure and mechanical properties of dissimilar pinless friction stir spot welded joint of2A12aluminum alloy and TC4titanium alloy were evaluated.The results show that the joint of Al/Ti dissimilar alloys can be successfully attained through pinless friction stir spot welding(FSSW).The joint can be divided into three zones(SZ,TMAZ and HAZ).The microstructure of joint in Al alloy side changes significantly but it basically has no change in Ti alloy side.At the same rotation speed,the maximum load of welded joints gradually rises with the increase in dwell time.At the same dwell time,the maximum load of the welded joint increases with the increase of the rotational speed.In addition,optimal parameters were obtained in this work,and they are rotation speed of1500r/min,plunge speed of30mm/min,plunge depth of0.3mm and dwell time of15s.The fracture mode of welded joints is interfacial shear fracture.The microhardness of the joint on the Al side distributes in a typical“W”type and is symmetry along the weld center,but the distribution of the microhardness on the Ti side has no obvious change.
文摘Aluminium alloys generally present low weldability by traditional fusion welding process. Development of the friction stir welding （FSW） has provided an alternative improved way of producing aluminium joints in a faster and reliable manner. The quality of a weld joint is stalwartly influenced by process parameter used during welding. An approach to develop a mathematical model was studied for predicting and optimizing the process parameters of dissimilar aluminum alloy （AA6351 T6-AA5083 Hlll）joints by incorporating the FSW process parameters such as tool pin profile, tool rotational speed welding speed and axial force. The effects of the FSW process parameters on the ultimate tensile strength （UTS） of friction welded dissimilar joints were discussed. Optimization was carried out to maximize the UTS using response surface methodology （RSM） and the identified optimum FSW welding parameters were reported.
文摘The application of friction stir welding(FSW) is growing owing to the omission of difficulties in traditional welding processes. In the current investigation, artificial neural network(ANN) technique was employed to predict the microhardness of AA6061 friction stir welded plates. Specimens were welded employing triangular and tapered cylindrical pins. The effects of thread and conical shoulder of each pin profile on the microhardness of welded zone were studied using tow ANNs through the different distances from weld centerline. It is observed that using conical shoulder tools enhances the quality of welded area. Besides, in both pin profiles threaded pins and conical shoulders increase yield strength and ultimate tensile strength. Mean absolute percentage error(MAPE) for train and test data sets did not exceed 5.4% and 7.48%, respectively. Considering the accurate results and acceptable errors in the models' responses, the ANN method can be used to economize material and time.
基金Project(2021YFB3400903) supported by the National Key R&D Program of ChinaProject(1053320211480) supported by the Science and Technology Innovation Project of Graduate Students of Central South University,China。
文摘Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.
