Faying Surface Research Articles

Burnishing treatment of the faying surface of the pipe flange

Burnishing treatment of the faying surface of the pipe flange

Study and Applications of Dynamic Resistance Profiles During Resistance Spot Welding of Coated Hot-Stamping Steels

This work compares the role of press hardened steel coating type (Al-Si and GA) on resistance spot welding by analyzing the dynamic resistance curves measured during the weld cycles of the respective materials. It was seen that the dynamic resistance profiles for GA- and Al-Si-coated steels are similar. But the GA specimens exhibited higher resistance than Al-Si-coated specimens in the as-received condition, while the Al-Si-coated specimens exhibited higher resistance after hot stamping. From the early stages of the dynamic resistance profiles, data were obtained and applied for computing the values of components of resistances associated with the different coatings since each coating exhibits characteristic value at the early stages. The results revealed that at the start of the welding cycle, the resistance of the electrode/sheet interface was significantly higher than that of the faying surface or the bulk resistance regardless of whether the steel was Al-Si- or GA-coated. The possible uses of these resistance values in studying welding current requirement and electrode tip life were discussed.

Friction stir spot fusion welding of low-carbon steel to aluminum alloy

Dissimilar lap joints for a low carbon steel (SS400) sheet with thickness of 2mm on a 6061-T6 Al alloy sheet with thickness of 5mm or 10mm were created by a process called friction stir spot fusion welding (FSSFW) using an assembly-embedded rod (AER) tool under a downward force of 12kN and a rotational speed of 1200rpm at different dwell times. The Al alloy sheet was melted at the central area of the faying surface, so that two IMC layers were formed at this surface and identified as Fe2Al5 and Fe4Al13, as detected by XRD and SEM images. The IMC thickness increased along with dwell time, but its increment rate became slower for IMC thickness larger than 25μm. The failure load increased along with the IMC thickness, but the failure load decreased quickly for IMC thickness larger than 17μm. It was able to achieve 18–22kN for the thickness of the IMC layer in the range of 6–17μm for a dwell time from 35–55s. The larger the crack was, the smaller the failure load.

Fatigue life predictions for riveted lap joints

A semi-empirical fatigue life prediction model for riveted lap joints representative of the aircraft fuselage skin connections is developed. The effect of the interference fit between the rivet and the hole is taken into account utilizing fatigue test results for 2024-T3 Alclad aluminium alloy coupons with an open and filled hole. The effect of contact surface friction is considered based on comparisons between the fatigue lives of lap joints from 2024-T3 Alclad sheets and universal rivets with the Alclad contact surface and the fatigue lives of similar joints with the Teflon interfoil which eliminates friction between the sheets. Dependencies between coefficients incorporated into the model to account for the above mentioned effects and several quantities related to the amount of rivet squeezing, and thus representative of the riveting process, are provided. The fatigue life is assumed to be controlled by the local stress amplitude at the critical location of a joint. Analyses of the fatigue test results for the 2024-T3 riveted joints prove that the local stress estimated using the superposition approach can adequately represent the combined effect of the applied loading, interference between the rivet and the hole and faying surface friction condition on the fatigue life. The adequacy of the proposed model is substantiated by a good agreement between the fatigue lives predicted and observed for lap joints from D16 aluminium alloy sheets and round head rivets.

아연도금강판 겹치기 용접부에 대한 2패스 레이저용접 적용성 연구

During laser overlap welding of galvanized steel sheets, explosion of weld pool by the high pressure zinc vapor induces weld defects like porosity and blowhole. In this study, laser 2-pass welding was implemented to prevent the weld defects. Through the 1st pass welding, zinc layers on the faying surfaces were removed when proper heat input was applied. Excessive heat input could result in explosion even during the 1st pass welding and insufficient heat input could not remove enough region of zinc layer for the 2nd pass welding. Coating weights of and were considered and for both cases sound welds without weld defects could be achieved. In spite of 2-pass welding, softening of weld and heat affected zone was not observed and Zn coating was not diluted into the weld metal.

Analysis of Residual Stresses Induced by Riveting Process and Fatigue Life Prediction

Residual stress induced by riveting process is critical to the fatigue life of riveted structures. A residual stress model is proposed to predict the residual stress distribution after riveting process. In the residual stress model, the radial pressure at the hole boundary is obtained, and the strain hardening effect of the rivet material is taken into consideration. The other characteristic of the model is that the solution of radial and circumferential residual stresses is extended to include an unfree springback process by using a springback coefficient. The residual stresses on the faying surface with various parameters, such as the height of the rivet drive head, the hole diameter, and the material property, are predicted with the residual stress model. The residual stresses calculated by the model are employed in the fatigue life prediction using the multi-axial fatigue criterion. The predicted results of the fatigue life show a good agreement with the experimental data. The investigation in this paper can help the residual stress prediction of riveted joints and improve the awareness of the effect of the residual stress on the fatigue behavior of riveted structures.

On microstructure and strength properties of microwave welded Inconel 718/ stainless steel (SS-316L)

Microstructure and mechanical properties of microwave welded Inconel 718/ austenitic stainless steel (SS-316L) were investigated in this work. Principles of microwave hybrid heating were effectively applied for joining of Inconel 718/SS-316L using Inconel 718 powder as an interfacing layer between the candidate surfaces. Experiments were carried out in a thermally insulating box placed inside an industrial microwave applicator for a duration of 600 s. The microwave-induced dissimilar welds were characterized using X-ray diffraction, field emission scanning electron microscope, microhardness tester, and universal testing machine. The X-ray diffraction study of the fusion zone showed the presence of various carbides and intermetallics. Microstructural study revealed metallurgical bonding between the two faying surfaces with no sign of interfacial cracking. The elemental analysis of the welded zone confirms dilution of Inconel 718 powder across the joint interface during microwave hybrid heating. The average microhardness on the joint interface was observed to be 230 ± 5 HV; the average porosity was monitored to be 0.94%. The average ultimate tensile strength of the microwave welds was monitored as 517.5 MPa with 18.18% elongation. The fractography study reveals a mixed mode of failure of the joints during tensile testing.

Microstructure and Properties of W–Cu Composite/Fe-Based Powder Alloy Vacuum Brazed Joint with Different Filler Metals

Abstract W–Cu composite and Fe-based powder alloy were brazed with filler metals of Ag–Cu and Cu–Mn–Co alloys in a vacuum furnace. Both of filler metals can join W–Cu composite with Fe-based powder alloy directly in the experiment process. Microstructure, distribution of elements and fracture morphology were observed and analyzed using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) methods, and phase composition of bonding area was analyzed by X-ray diffraction (XRD). The obtained results indicated that the smooth faying surface and dense microstructure of brazed joint were formed and the primary microstructure of brazing seam were, respectively, Ag(Cu) solid solution and Cu(Mn) solid solution, which ensured forming the stable connection of brazed joint. The bending strength of Ag-based and Cu-based brazed joint can, respectively, reach to 317 and 704 MPa, where fracture showed a typical ductile fracture characteristic. The fracture of Cu-based brazed joint located at brazing seam area, and the fracture of Ag-based brazed joint occurred in Fe-based powder alloy side.

Superior dissimilar adhesive joint of mild steel and aluminium using UDM processed epoxy based TiO2 nano-filler composite adhesive

Abstract Characteristics of the lap joints of mechanically and chemically treated faying surface of dissimilar metals (Mild Steel and Aluminium) prepared by using UDM processed TiO 2 -epoxy nano composite adhesive was investigated. Influence of the extent of TiO 2 nano (25–35 nm) particle reinforcement (5, 10 and 15 wt%) in the composite adhesive on the improvement of tensile lap shear strength of the adhesive joints has been studied. Effect of bond line thickness of the adhesive in lap joints of the differently treated faying surfaces of the dissimilar metals on lap shear strength of the joints has also been studied. The joints of 10 wt% TiO 2 nano-filler content epoxy adhesive shows maximum lap shear strength of the joints. Its lap shear strength was also studied at elevated temperatures in the range of 100–250 °C. In order to establish the potentials of nano composite adhesive to relatively improve the properties of the joint, the lap shear strength of the adhesive joint of neat epoxy adhesive was also studied and compared.

Effect of parameters on local stress field in single-lap bolted joints with the interference fit

From the interference fit bolt installation to tensile loading stage in single-lap joint with a hi-lock bolt, the stress and strain fields were studied experimentally and numerically. A three-dimensional finite element model was generated to simulate the experimental setup, which was validated using the experimental data. The fatigue behavior of the bolted joint is influenced by the local stress fields on the faying surface near the holes in single-lap joints. Therefore, with the aim to improve design awareness, the effects of the parameters on the local stress fields were investigated by means of finite element simulation. With an increase in the interference fit size, the occurred position of the maximum stress values on the upper plate faying surface moves away from the hole edge gradually. As the clamping force or friction coefficient increases, the position of larger stress area is changed to the side of bearing load from the transverse direction. The lap geometry of the bolted joint as well as the amplitude of tensile load has apparent impact on the maximum stress value.

Effect of load transfer by friction on the fatigue behaviour of riveted lap joints

An experimental investigation of load transmission throughout a riveted lap joint is presented with a focus on the role of friction. The main objective was to generate results to be utilized in a semi-empirical model for predicting the fatigue life of riveted joints, which is being developed by the authors. The test variables accounted for in the experiments were the rivet squeeze force and the faying surface condition. Triple-row riveted lap joint coupons of aluminium alloy 2024-T3 Alclad sheets intended to be a simple representation of longitudinal connections in the aircraft fuselage skin structure were assembled with two different rivet squeeze forces. For either force half of the joints had a thin Teflon interfoil in the overlap area in order to minimize friction between the sheets. Friction measurements reveal that, contrary to the friction coefficient between the Alclad mating surfaces, the friction coefficient between the Teflon and Alclad contact surfaces is considerably lower and does not increase with the cycle number.A convenient method of the determination of load transmission throughout a lap joint is proposed utilizing measurements by strain gauges mounted on only outer surfaces of the overlapping sheets supplemented by the secondary bending analysis according to a simple theoretical model. The results obtained indicate that the effect of the squeeze force and the faying surface condition on axial forces in the overlapping sheets is quantitatively insignificant. It is noted that an analytical procedure commonly used to compute axial forces in the sheets of joints with mechanical fasteners considerably underestimates load transfer by the critical, outer rivet rows.Comparative fatigue tests on the riveted coupons with the Teflon interlayer and without such a layer reveal superior fatigue lives of the former. These results demonstrate, contrary to the prevailing opinion, an overall detrimental influence of frictional load transfer at applied stress values representative of those experienced in service by lap splices of the aircraft fuselage.Post-failure examinations of the riveted joints provide evidence that the crack initiation locations and crack paths depend on the test variables and the stress level. For the uncoated joints, the effect of the squeeze force and applied load on the area of fretted regions around the rivet holes was noted, whilst the total roughness heights did not exhibit such a dependency.It is shown that the present and reported in other works experimental results on the effect of coatings on the fatigue performance of riveted joints cannot be explained based on FE stress analyses available in the literature due to simplifications involved in modelling the faying surface condition. A major conclusion of the present work is that because of the extremely complex determinants of frictional load transfer, its effect on the fatigue behaviour of riveted joints can only be predicted using a semi-empirical approach.

Microstructural and mechanical performance of ultrasonic spot welded Al–Cu joints for various surface conditions

The ultrasonic metal welding (USMW) offers a potential solution to join highly thermal conductivity dissimilar materials like aluminium and copper. In this work, the effects of different welding parameters and surface conditions like lubricated, normal, electrolytic polished and emery polished are investigated to obtain the maximum mechanical strengths of the weld joints. The results show that tensile shear and T-peel failure loads increased with weld time and reached the highest value of 1550.48N and 370.46N, respectively. It is also observed that these joint strengths decreased with the increase of surface roughness because of the disappearance of relative motion between the sheets. Thus, the temperature that is obtained from emery paper condition is the lowest among all the four surface conditions. Meanwhile, the maximum interface temperature obtained when the ethanol droplet is added to the faying surface. This is to say, a substantial plastic deformation is observed at the welded region due to this high temperature of 375°C and thus, it facilitates the rupture of the oxide film. From the microstructural analysis, a dimple pattern is noticed in the welding zone, indicating an expansion of weld area and grain refinement has been taken place due to the adhesion of ethanol. Similarly, the microhardness study also revealed that there is no formation of the large heat affected zone in USMW. An average microhardness of HV 88.45 is observed for the joint which is quite high than other solid state welding processes.

Fatigue Life Prediction for Overlap Friction Stir Linear Welds of Magnesium Alloys

This work was undertaken to analyze the stress/strain state at the critical sites in friction stir welded specimens and, further, to assess the fatigue strength of friction stir welded specimens with conventional fatigue life prediction approaches. Elastoplastic and elastic finite-element stress/strain analyses were carried out for friction-stir-linear-welded (FSLW) specimens made of magnesium alloys. The calculated stress/strain at the periphery of the weld nugget was used to evaluate the fatigue life with local life prediction approaches. First, elastoplastic finite-element models were built according to experimental specimen profiles. Fatigue life prediction was conducted with Morrow's modified Manson–Coffin (MC) damage equation and the Smith–Watson–Topper (SWT) damage equation, respectively, for different specimens under different loading cases. Life prediction results showed that both equations can to some extent give reasonable results, especially within a low-cycle fatigue life regime, with the SWT damage equation giving more conservative results. As for high-cycle life, predicted results were much longer and scattered for both methods. Shell element elastic models were then used to calculate the structural stress at the periphery of the weld nuggets. The correlation between structural stress amplitude and experimental life showed the appropriateness of the structural stress fatigue evaluation for friction stir welds. The effect of the notches at the periphery of the faying surface on life prediction was further discussed.

Optimization of Parameters of Friction Stir Welding OG AA-6061

Friction-stir welding (FSW) is a solid-state joining process that uses a third body tool to join two faying surfaces. Frictional heat between the welding tool and the work pieces causes the latter to soften without reaching the melting point, allowing the tool to traverse along the weld line. It then mechanically intermixes the two pieces of metal at the place of joint; the softened metal can be joined using mechanical pressure (which is applied by the tool), much like joining clay or dough [1]. In this project, universal horizontal Milling Machine is used to weld the parts together. The parts being welded are made up of similar materials i.e. Aluminum alloy of 6061 grade. The rotational speed is varied from 1200 rpm to 1500 rpm while the welding speed is kept constant at 25 mm/min. The dimensions of the parts are (100mmx50mmx6mm) which are welded to form a butt joint. The effect of different tool pin profiles on the quality of the welded joint is also studied for welding. Different tool pin profiles considered are threaded, taper and cylindrical. The tools are manufactured on a Lathe machine. After the parts are welded, various practical tests are performed on the welded parts that include the tensile strength, microstructure study and the micro-hardness test. The experimental results proved that the highest tensile strength of the welded joint i.e., 81.073 N/mm2 was achieved with the threaded tool profile at speed 900 rpm with feed 25 mm/min and the highest hardness value of 267HV was achieved with the round tool profile at 1500 rpm and feed of 25 mm/min.

Управление линейной сваркой трением

Linear friction welding is a relatively new method of joining materials. It is a solid state joining technique, in which significant heat is generated at the faying surfaces of two components under a certain combination of pressure, amplitude and frequency of the relative linear motion. In particular one process, linear friction welding, can be used to join of complex profiles. The linear friction welding process is extremely fast, the whole process could last for several seconds and the control of energy and time parameters is only possible in automatic mode. This paper describes a control system of the linear friction welding mashine. The system is based on a servo-hydraulic testing machine "Schenck", computer and a microcontroller. The linear friction welding cycle consists of compressing two samples to be welded, turning on and off vibrations at a given frequency and amplitude and creation of forging force. The key elements of the welding machine are vibration and compression hydraulic cylinders. The control system synchronizes these hydraulic cylinders and ensures that the linear friction machine operates during the whole welding cycle automatically with pre specified parameters. The control systems of hydraulic cylinders are interconnected and connected with computer via microcontroller. The changes in the burn-off and the friction force are recorded in real time. Desirable levels of precision of the burn-off and the strength of the joint are achieved. We performed several experiments with different materials.

Effect of process parameters on microstructure and mechanical behaviors of friction stir linear welded aluminum to magnesium

The microstructure and lap-shear behaviors of friction stir linear welded wrought Al alloy AA6022-T4 to cast Mg alloy AM60B joints were examined. A process window was developed to initially identify the potential process conditions. Multitudes of welds were produced by varying the tool rotation rate and tool traverse speed. Welds produced at 1500 revolutions per minute (rpm) tool rotation rate and either 50mm/min or 75mm/min tool traverse speed displayed the highest quasi-static failure load of ~3.3kN per 30mm wide lap-shear specimens. Analysis of cross sections of untested coupons indicated that the welds made at these optimum welding parameters had negligible microvoids and displayed a favorable weld geometry for the cold lap and hook features at the faying surface, compared to welds produced using other process parameters. Cross sections of the tested coupons indicated that the dominant crack initiated on the advancing side and progressed through the weld nugget, which consists of intermetallic compounds (IMC). This study demonstrates the feasibility of welding wrought Al and cast Mg alloy via friction stir linear welding with promising lap-shear strength results.

Characteristics of Friction Welding Between Solid Bar of 6061 Al Alloy and Pipe of Al-Si12CuNi Al Cast Alloy

This paper describes the characteristics of friction welding between a solid bar of 6061 Al alloy and a pipe of Al-Si12CuNi (AC8A) Al cast alloy. When the joint was made by a continuous drive friction welding machine (conventional method), the AC8A portion of the joint showed heavy deformation and the AA6061 showed minimal deformation. In particular, the joint could not be successfully made with following conditions, because AC8A pipe side crushed due to insufficient friction heat or high pressure: a short friction time such as 0.3 s, high friction pressure such as 100 MPa, or high forge pressure such as 150 MPa. The heavy deformation of AC8A side was caused by increasing friction torque during braking. To prevent braking deformation until rotation stops, a joint was made by a continuous drive friction welding machine that has an electromagnetic clutch. When the clutch was released, the relative speed between both specimens simultaneously decreased to zero. When the joint was made with friction pressure of 25 MPa, friction time of 0.3 s, and forge pressure of 125 MPa, the joining could be successfully achieved and that had approximately 16% efficiency. In addition, when the joint was made with friction pressure of 25 MPa, friction time of 0.7 s, and forge pressure of 125 MPa, it had approximately 54% efficiency. However, all joints showed the fracture between the traveled weld interface and the AC8A side, because the weld interface traveled in the longitudinal direction of AC8A side from the first contacted position of both weld faying surfaces. Hence, it was clarified that the friction welding between a solid bar of AA6061 and a cast pipe of AC8A was not desirable since the traveling phenomena of the weld interface were caused by the combination of the shapes of the friction welding specimens.

Application of Pre-heating to Improve the Consistency and Quality in AA5052 Resistance Spot Welding

Making consistent resistance spot welds of aluminum alloy with good quality and at high volume has several obstacles in automotive industry. One of the difficult issues arises from the presence of a tough non-conducting oxide film on the aluminum sheet surface. The oxide film develops over time and often is non-uniform across the surface of the aluminum alloy sheet, which makes the contact resistance characteristics irregular at the faying interface during welding. The consistency in quality of the final spot welds is therefore problematic to control. To suppress the effect of the irregular oxide film on the spot weld quality, application of a pre-heating treatment in the welding schedule for aluminum alloy 5052 is investigated in this present work. The current level of the pre-heating required to reduce the scatter of the contact resistance at the W/W (workpiece-to-workpiece) faying interface is quantified experimentally. The results indicate that the contact resistance at the W/W faying interface with a pre-heating treatment becomes much consistent and can be reduced by two orders of magnitude. Having the uncertain variation of the contact resistance at the W/W faying surface virtually reduced or removed, the quality of the spot welds in terms of the peak load and nugget diameter is examined and shows a great improvement. The proposed method may provide a robust method for high-volume spot welding of aluminum alloy sheets in auto industry.

Cold Metal Transfer Spot Joining of AA6061-T6 to Galvanized DP590 Under Different Modes

In order to meet the upcoming regulations on greenhouse gas emissions, aluminum use in the automotive industry is increasing. However, this increase is now seen as part of a multimaterial strategy. Consequently, dissimilar material joints are a reality, which poses significant challenges to conventional fusion joining processes. To address this issue, cold metal transfer (CMT) spot welding process was developed in the current study to join aluminum alloy AA6061-T6 as the top sheet to hot dip galvanized (HDG) advanced high strength steel (AHSS) DP590 as the bottom sheet. Three different welding modes, i.e., direct welding (DW) mode, plug welding (PW) mode, and edge plug welding (EPW) mode were proposed and investigated. The DW mode, having no predrilled hole in the aluminum top sheet, required concentrated heat input to melt through the Al top sheet and resulted in a severe tearing fracture, shrinkage voids, and uneven intermetallic compounds (IMC) layer along the faying surface, leading to poor joint properties. Welding with the predrilled hole, PW mode, required significantly less heat input and led to greatly reduced, albeit uneven, IMC layer thickness. However, it was found that the EPW mode could homogenize the welding heat input into the hole and thus produce the most stable welding process and best joint quality. This led to joints having an excellent joint morphology characterized by the thinnest IMC layer and consequently, best mechanical performance among the three modes.

Reconstruction of fatigue crack growth in AA2024-T3 and AA2198-T8 fastened lap joints

This paper presents a comparative study on the fatigue behavior of a typical third generation Aluminum–Lithium alloy, AA2198-T8, to that of a traditional aerospace aluminum–copper alloy, AA2024-T3 with a focus on developing a methodology for reconstructing the crack growth history. Fatigue testing was conducted using a lap joint configuration designed to induce large amounts of secondary bending for the purpose of accentuating any unique behaviors in these two material systems. Fatigue fracture surface morphology was examined in order to determine the effect of alloying and loading direction relative to plate rolling direction on fatigue crack growth behavior. Crack initiation sites occurred in the vicinity of the fastener hole, at multiple sites along the faying surface, yielding crack tunneling in all specimens, prior to the ductile catastrophic fracture. The fracture surface morphologies in the two alloys were markedly different: the AA2024-T3 exhibited substantial meandering fracture surface, with localized fatigue crack progressing along multiple directions and at different rates. The AA2198-T8 alloy exhibited more uniform but shallower fatigue striations, with numerous micro and macro interlaminar cracks. Crack growth rate (da/dN) measurements along the width, thickness and the striation ridge lines indicated that the latter provides the most reliable results in terms of estimating fatigue crack initiation cycle, crack initiation site, and crack growth rate.