A review of linear friction welding of Ni -based superalloys

Ni-based superalloys are one of the most important materials employed in high-temperature applications within the aerospace and nuclear energy industries and in gas turbines due to their excellent corrosion,radiation,fatigue resistance,and high-temperature strength.Linear friction welding(LFW)is a new joining technology with near-net-forming characteristics that can be used for the manu-facture and repair of a wide range of aerospace components.This paper reviews published works on LFW of Ni-based superalloys with the aim of understanding the characteristics of frictional heat generation and extrusion deformation,microstructures,mechanical proper-ties,flash morphology,residual stresses,creep,and fatigue of Ni-based superalloy weldments produced with LFW to enable future optim-um utilization of the LFW process.

Finite element analysis of the effect of micro-pore defect on linear friction welding of medium carbon steel

Micro-pore is a very common material defect. In the present paper, the temperature fields of medium carbon steel joints with and without micro-pore defect during linear friction welding （LFW） were investigated by using finite element method. The effect of micro-pore defect on the axial shortening of joints during LFW was examined. The x- and y-direction displacements of micro-pore during the LFW process were also studied. In addition, the shape of micro-pore after LFW was observed. The heat conducted from the weld inteace to the specimen interior. The fluctuation range of the temperature curves for the joint with micro-pore is larger than that without micro-pore. Position of micro-pore changes with the change of the friction time. The circular shape of micro-pore becomes oval after welding.

Numerical analysis of joint temperature evolution during friction stir welding based on plastic deformation heat

3D numerical model for friction stir welding （FSW） was developed by using ABAQUS software considering the plastic deformation heat. Effects of the rotation and welding speeds on the temperature field of FSW 2024-73 aluminum alloy were systematicaUy investigated. The temperature measurement was performed to validate the reliability of the model. The simulation results are in good agreement with the experiments. Results show that changing the rotation speed has no influence on the time for reaching the peak temperature at certain point in the workpiece at a constant welding speed. While increasing the welding speed has significant effect on the time for reaching the peak temperature but the value of peak temperature changes little.

Detection and analysis of basic variables during linear friction welding of GH4169 superalloy

By monitoring the line voltage and current of the driving motor during linear friction welding （ LFW） of GH4169 superalloy, the frictional power of the rubbing interface between two components to be joined was detected. The data was recorded by a data acquisition card and processed by the LabVIEW software. By analyzing the evolution of frictional power, the joint formation mechanism was discussed. The curves of the measured basic variables （frictional power, axial shortening, interfacial temperature and axial pressure） reflected the characteristics of the LFW process and offered an effective way for welding parameter optimization.

Study on deformation and microstructure characterizations of mild steel joints by continuous drive friction welding

Macro-deformation characteristics of continuous drive friction welded mild steel joints were examined by using one deformable workpiece （objective） and the other undeformable one （rigid）. The microstructure evolution and hardness change across the joint were studied. The results show that the axial shortening and radial increment of joints increase with increasing the frictiou time at l 200 rpm. The cementite particles of pearlites in the weld center are uniformly distributed on the ferrite matrix, while the cementites of the pearlite in the thermal-mechanically affected zone are broken and discontinuously dispersed in the pearlite. The hardness decreases rapidly from the weld center to the parent metal under the coupled effects of heat and deformation during the rapid heating and cooling processes.

Stress-strain characteristics of linear friction welding of TC11 and TC17 alloys

Abstract Transient stress and strain fields of dissimilar titanium alloys （TCll and TC17 ） joint during linear friction welding （ LFW） were investigated by a two-dimensional model with ABAQUS/Explicit. The results showed that in the X-axis, the maximum compressive stress of 850 MPa occurred in the center zone of friction interface , and the maximum tensile stress of 190 MPa distributed at the flash; in the Y-axis, the maximum compressive stress of 1 261 MPa located at the junction region between the welding fixture and edge of the specimen, and the maximum tensile stress of 320 MPa distributed in the connecting portion between the flash and edge of the specimen. In addition, areas of plastic strain increased gradually during welding process. In the X-axis, tensile strain mainly existed at the heads of the specimens; in the Y-axis, compressive strain mainly occurred at the heads of the specimens.

Computational analysis of linear friction welding process and micromechanical modeling of deformation behavior for medium carbon steel

Finite element simulation of linear friction welding(LFW) medium carbon steel was carried out using the ABAQUS software. A two-dimensional(2D) coupled thermo-mechanical model was established. First, the temperature fields of medium carbon steel during LFW process were investigated. And then, the Mises stress and the 1st, 2nd and 3rd principal stresses fields' evolution of the steel during LFW process were studied. The deformation behavior of LFW carbon steel was analyzed by using micromechanics model based on ABAQUS with Python code. The Lode parameter was expressed using the Mohr stress circle and it was investigated in detail.

Analysis of local microstructure and strengthening mechanisms in adjustable-gap bobbin tool friction stir welds of Al-Mg

The bobbin tool friction stir welding process was used to join 6 mm thick 5A06 aluminum alloy plates.Optical microscope was used to characterize the microstructure.The electron backscatter diffraction(EBSD)identified the effect of non-homogeneous microstructure on the tensile properties.It was observed that the grain size in the top of the stir zone(SZ)is smaller than that in the centre region.The lowest ratio of recrystallization and density of the geometrically-necessary dislocations(GNDs)in the SZ was found in the middle near the thermo-mechanically affected zone(TMAZ)being 22%and 1.15×10^(−13) m^(−2),respectively.The texture strength of the heat-affected zone(HAZ)is the largest,followed by that in the SZ,with the lowest being in the TMAZ.There were additional interfaces developed which contributed to the strengthening mechanism,and their effect on tensile strength was analysed.The tensile tests identified the weakest part in the joint at the interfaces,and the specific reduction value is about 93 MPa.

Effect of heat treatment on the microstructure and mechanical properties of structural steel–mild steel composite plates fabricated by explosion welding

Two dissimilar steel plates,structural steel and mild steel,were joined by explosion welding to form a composite.The composite was then heat-treated by quenching at 840℃ for 30 min followed by tempering at 200℃ for 3 h.The microstructure was investigated under an optical microscope and a scanning electron microscope.The mechanical properties were measured using Vickers microhardness and Charpy impact tests.The results show a deformed interface with typical wave features at the welding zone,but no defects were observed.Moreover,the ferrite in the parent plate in the weld zone was elongated due to the strong plastic deformation from the explosion.After heat treatment,the hardness of the flyer plate(structural steel)was over HV0.2800,while that of the parent plate(mild steel)was HV0.2200.The increase in hardness was due to the presence of martensite.Moreover,the average impact energy was increased from 18.5 to 44.0 J following heat treatment;this is because of the formation of recrystallized grains at the weld interface,which is due to the dynamic recovery and local recrystallization,and the strong elemental diffusion that occurred between the two plates.

Neural network prediction of the shunt current in resistance spot welding

An error back propagation （BP） neural network prediction model was established for the shunt current compensation in series resistance spot welding. The input variables for the neural network consist of the resistivity of the material, the thickness of workpiece and the spot spacing, and the shunt rate is outputted. A simplified calculation for the shunt rate was presented based on the feature of the constant-current resistance spot welding and the variation of the resistance in resistance spot welding process, and then the data generated by simplified calculation were used to train and adjust the neural network model. The neural network model proposed was used to predict the shunt rate in the spot welding of 20# mlid steel （in Chinese classification） （in 2. 0 mm thickness） and 10# mild steel （in 1.5 mm and 1.0 mm thickness）. The maximum relative prediction errors are, respectively, 2. 83%, 1.77% and 3.67%. Shunt current compensation experiments were peoCormed based on the neural network prediction model proposed to check the diameter difference of nuggets. Experimental results show that maximum nugget diameter deviation is less than 4% for both 10# and 20# mlid steels with spot spacing of 30 mm and 50 mm.

Defects of friction stir welded 1060 aluminum alloy and their effects on joint tensile property

9. 6 mm thick 1060-H24 aluminum alloy plates were friction stir welded and the influencing factors on groove and tunnel defects were examined. Results show that the welding speed range for achieving a groove-free joint is enlarged with increasing the rotating speed. The tunnel size decreases with decreasing the welding speed under the same rotating speed. Excessive or insufficient shoulder plunge depth will cause defective joints. At a relatively low rotating speed and high welding speed, the tool having a larger shoulder diameter has a larger range of processing parameters to obtain a groove-free joint. Moreover, the tensile fracture behaviors of the defective and defect-free samples are different.

Recent progress in corrosion protection of friction stir welded high-strength aluminum alloy joints

Friction stir welding （FSW） has been widely used in many industries, with which high-strength aluminum alloys can be well joined. However, the corrosion resistance of FSW high-strength Al alloy joints is relatively poor, which limits their industrial applications. The joints shall be protected against corrosion. In this review, therefore, the current status and development of corrosion protection for FSW high-strength Al alloy joints are presented. Particular emphasis has been given to different protection methods ： lowering heat input, post-weld heat treatment, surface modification and spray coatings. Finally, opportunities are identified for further research and development in corrosion protection of FSW high-strength Al alloy joints.

Multi-scale analyses of phase transformation mechanisms and hardness in linear friction welded Ti17(a+β)/Ti17(β)dissimilar titanium alloy joint

The Ti17(a+β)-Ti17(β)dual alloy-dual property blisk produced using Linear Friction Welding(LFW)is considered as high-performance component in advanced aeroengine.However,up to now,microstructure evolution and relationship between microstructure and micro mechanical properties of LFWed Ti17(a+β)/Ti17(β)dissimilar joint have not been thoroughly revealed.In this work,complex analyses of the phase transformation mechanisms of the joint are conducted,and phase transformations in individual zones are correlated to their microhardness and nanohardness.Results reveal that a dissolution occurs under high temperatures encountered during LFW,which reduces microhardness of the joint to that of Ti17(a+β)and Ti17(β).In ThermoMechanically Affected Zone of Ti17(a+β)(TMAZ-(a+β))side joint,a large number of nanocrystalline a phases form with different orientations.This microstructure strengthens significantly by fine grains which balances partial softening effect of a dissolution,and increases nanohardness of a phase and microhardness of TMAZ-(a+β).Superlattice metastableβphase precipitates from metastableβin Weld Zone(WZ)during quick cooling following welding,because of short-range diffusion migration of solute atoms,especiallyβstabilizing elements Mo and Cr.The precipitation of the superlattice metastableβphase results in precipitation strengthening,which in turn increases nanohardness of metastableβand microhardness in WZ.

Strengthening mechanism and forming control of linear friction welded GH4169 alloy joints

Numerical simulation and experimental research on Linear Friction Welding(LFW) for GH4169 superalloy were carried out. Based on the joint microstructure and mechanical properties,a suitable welding process was determined, which provided an important theoretical basis for the manufacture and repair of aeroengine components such as the superalloy blisk. The results show that the joint strain rate gradually increases with the increase of welding frequency, and the deformation resistance of the thermoplastic metal increases in the welding process, resulting in the interface thermoplastic metal not being extruded in time to form a flash, so the joint shortening amount gradually decreases. The thermoplastic metal in the center of the welding surface is kept at high welding temperature for a long time, resulting in the decrease of the joint strength. The microhardness of the joint shows a “W” distribution perpendicular to the weld, and most of the joints break in the Thermo-Mechanically Affected Zone(TMAZ) with high tensile strength and low elongation.When the welding area is increased without changing the aspect ratio of the welding surface, the interface peak temperature increases gradually, and the joint shortening amount decreases with the increase of the welding interface size.

Through-thickness heterogeneity in creep properties of friction stir welding 7B50-T7451 aluminum alloy thick plate joint:Experiments and modeling

Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW)joints was investigated.Creep tests for three slices of the FSW joint were conducted at the temperature of 150-200℃ and applied stress of 60-225 MPa.The theta projection method was used to predict creep curves and minimum creep rate.The results show that the minimum creep rate increases and creep rupture life decreases with the increase of creep temperature and applied stress.Creep properties of the FSW joint deteriorate along the thickness direction from the top to the bottom.The threshold stress of all three slices of the FSW joint decreases with the increase of creep temperature and even disappears at 200℃ for the bottom slice.Creep activation energy approaches the activation energy of the lattice self-diffusion of aluminum.The value of true stress exponent for different slices is approximately equal to three.The predominant creep mechanism of the FSW joint is dislocation viscous glide by lattice self-diffusion.What is more,a constitutive model is established based on the theta method to accurately describe creep behavior ofdifferent slices of the FSW joint.

Investigation on the process parameters of TIG-welded aluminum alloy through mechanical and microstructural characterization

Multi-pass TIG welding was conducted on plates(15×300×180 mm^(3))of aluminum alloy Al-5083 that usually serves as the component material in structural applications such as cryogenics and chemical processing industries.Porosity formation and solidification cracking are the most common defects when TIG welding Al-5083 alloy,which is sensitive to the welding heat input.In the experiment,the heat input was varied from 0.89 kJ/mm to 5 kJ/mm designed by the combination of welding torch travel speed and welding current.Tensile,micro-Vicker hardness and Charpy impact tests were executed to witness the impetus response of heat input on the mechanical properties of the joints.Radiographic inspection was performed to assess the joint’s quality and welding defects.The results show that all the specimens displayed inferior mechanical properties as compared to the base alloy.It was established that porosity was progressively abridged by the increase of heat input.The results also clinched that the use of medium heat input(1-2 kJ/mm)offered the best mechanical properties by eradicating welding defects,in which only about 18.26% of strength was lost.The yield strength of all the welded specimens remained unaffected indica ted no influence of heat input.Partially melted zone(PMZ)width also affected by heat input,which became widened with the increase of heat input.The grain size of PMZ was found to be coarser than the respective grain size in the fusion zone.Charpy impact testing revealed that the absorbed energy by low heat input specimen(welded at high speed)was greater than that of high heat input(welded at low speed)because of low porosity and the formation of equiaxed grains which induce better impact toughness.Cryogenic(-196℃)impact testing was also performed and the results corroborate that impact properties under the cryogenic environment revealed no appreciable change after welding at designated heat input.Finally,Macro and micro fractured surfaces of tensile and impact specimens were analyzed using Stereo and Scanning Electron Microscopy(SEM),which have supported the experimental findings.

Evolution mechanism of the interfacial reaction layers in the joints of diffusion bonded Mo and Al foils

Mo foil （10 -20 μm in thickness） and Al foil （20 -60 μLm in thickness） were vacuum diffusion bonded at 600 - 640 ~C under 20 MPa for 54 min - 6 h. The joints were examined by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） to study the evolution mechanism of the reaction layers. The results show that Al atoms diffuse into Mo grain boundaries and form reaction products as Mo3Al8, MoAl4 , MoAl5 and MoAl12. The surface oxide film is eroded by the growths of the reaction products that plow into the lamellar texture of Mo grain boundaries. Mo3Al8 layer grows by ＂taking root＂ downwards and transforms into MoAl4 and MoAl5 phases upwards by absorbing Al atoms. MoAl12 layer grows up from MoAl5 layer in the same way. When the supplement of Al atoms ceases, MoAl12 transforms reversely into MoAl5 and MoAl5 into MoAl4 via the loss of Al atoms. However, MoAl4 continues to precipitate from Mo3Als layer. At last, there are MoAl4 and Mo3Al8 remained on the joint interface.

On conversion of plastic work to heat during plastic deformation of tin-lead alloy and mild steel

The temperature rise caused by plastic deformation during the quick upsetting of tin-lead alloy and mild steel was investigated via experiments and numerical simulations aiming at a better understanding of the heat generation mechanism in friction welding. The results show that the compression amount and deformation temperature influence significantly the temperature rise during the upsetting of tin-lead alloy. The temperature rise increases with increasing the compression but decreases with increasing the deformation temperature. The simulation results are in good agreement with the experimental inspection for Sn63A alloy. The simulation results of mild steel present a similar tendency with tin-lead alloy. Moreover, the temperature rise of mild steel at elevated temperatures is comparable to that of tin-lead alloy at low temperatures.

A New Spot Welding Technique for Fuselage

High strength aluminum alloys(series 2XXX and 7XXX)are kinds of precipitation-hardening alloys,which have been widely applied in manufacturing of fuselage for their high strength-to-weight ratio,good fatigue performance and damage tolerance[1-2].These structures mostly adopt lap joint.The traditional joining methods include riveting and bolting,which cost weight-increase and inefficiency.These disadvantages could be overcome by a new joining technique—friction stir spot welding(FSSW)developed from friction stir welding(FSW).However,after wel-ding,FSSW normally leaves the workpiece with a keyhole,which decreases mechanical properties and corrosion resistance of the joint.To fill the keyhole,refill friction stir spot welding(RFSSW,Refill-FSSW)was invented by GKSS in 1999.GKSS designs a special welding tool for RFSSW,consisting of pin,sleeve and clamping ring,which are precisely assembled with indepen-dent driving systems[3].In a typical RFSSW process,the pin and sleeve move in opposite direction at a given speed ratio.Approximately,the speeds are set inverse proportional to their cross-sectional area.In 2011,GKSS performed RFSSW on aluminum alloy and obtained the joint with good strength.Thereafter,RFSSW was highlighted in research,which was expected to apply in fuselage manufacturing and to replace the traditional joining methods.

Interfacial microstructure and properties of YG11C/42CrMo joint brazed with BCu64MnNi filler metal

Brazing hard alloy to high strength steel, incomplete atomic diffusion and excessive brittle reaction product precipitation at the faying interface are usually suffered because of incomplete understanding the process of the initial interface disappearing and diffusion layer forming and evolving. In this paper , hard alloy YG11C （ WC-11wt. %Co） and high strength steel 42CrMo were picked up as base metals and BCu64MnNi as filler metal to clarify the interfacial microstrncture evolution. The process parameters of dwell time were set as 30 s, 60 s, 120 s, and 300 s and braze temperature were set as 950 ℃, 970 ℃, 990 ℃, 1 010 ℃, the effect of which on the evolution of interfacial microstructure, tensile strength, integrated with fracture morphology analysis, were conducted. The results showed that increasing brazing temperature from 950 ℃ to 970 ℃, no signifwant difference existed in the joint interface, whereas brazed at 990 ℃, the binder phase erosion occurred, i. e. the liquid filler metal etched into Co binder phase of WC-Co base metal, which caused WC particles debonding from the base metal surface and formed an micro-anisotropic zone.. Increase temperature to 1 010 ℃, severe binder erosion happened so as to micropores appear. Through the parameters optimization, the tensile strength can reach to the maximum 589 MPa at temperature of 970 ℃. The dwell time showed similar effect on tensile strength because longer dwell time also caused erosion and porosity owing to long-time diffusion and reaction.