Welded Lap Joints Research Articles

Achievement of superb-strength lap joint via opposite-directions flowing friction stir lap welding of 2024 aluminum alloys

It is common for the rotating pin largely plunging into lower sheet to break up lap interface of Friction Stir Lap Welding (FSLW) joint, but the unavoidable up-bending morphology of hook outside Nugget Zone (NZ) largely reduces the joint bearing ability. Based on the novel Opposite-directions Flowing FSLW (OF-FSLW) by the self-developed rotating tool with an X-shaped right-left thread pin, the 2024 aluminum alloys lap joint was successfully welded in this study. The migration law of lap interface during welding was investigated by the experimental and numerical methods, and then how the rotating pin and its rotating velocity affect the formation and strength of OF-FSLW joint was further analyzed. The results show that the Material Concentrated Zone (MCZ) which formed above the original lap interface made the hook bend downward, the NZ greatly enlarged and the beginning part of cold lap compressed and thickened, thereby heightening the joint bearing ability. For the OF-FSLW joint, its maximum tensile strength was 403 MPa, and the corresponding joint efficiency of 90.8% was an incredible and superb value for the 2000 series heat-treatment strengthened aluminum alloys friction stir welded joint. The OF-FSLW technology by the rotating tool with an X-shaped right-left thread pin is proven to be a greatly effective approach for manufacturing the aluminum alloys lap joint with superb strength.

Fatigue assessment on 7075/2A12 aluminum alloy friction stir welding lap joints

Fatigue assessment on 7075/2A12 aluminum alloy friction stir welding lap joints

Effect of swinging laser on porosity, microstructure, and mechanical properties of laser welded aluminum alloy joints with different lap forms

Oscillating and conventional linear laser welding were conducted to enhance the bonding strength of dissimilar aluminum alloys. The effect of lap joint configuration on porosity, microstructure, and mechanical properties of laser-welded dissimilar aluminum alloy joints was investigated. It was found that the solidification rate of the melt pool was the dominant factor in the difference in porosity for oscillating laser-welded joints with different lap joint configurations. The main precipitated phase in welds with different lap joint configurations was eutectic Si, and the proportion of eutectic Si was higher in oscillating laser welds than in linear laser welds. The elemental distribution in oscillating laser welds was more uniform. The strengthening mechanism for tensile shear strength of oscillating laser welded lap joints was analyzed. The improved tensile shear strength and elongation were attributed to the reduced porosity and solid solution strengthening for the oscillating laser welding. The tensile strengths of the two lap types of oscillating laser welded joints increased by 25.1 MPa and 34.5 MPa, and the elongation increased by 0.7% and 4.5%.

The use of nonlinear guided-wave features for detection and assessment of intermetallic compounds within dissimilar joints – an experimental investigation

Abstract Welding dissimilar materials is widely employed in industrial construction and manufacturing to enhance cost-effectiveness and performance, often utilizing non-fusion methods like solid-state and high-energy beam welding. However, a significant challenge is the formation of intermetallic compounds (IMCs) at the joint interface, which can weaken the bond and increase brittleness, leading to hidden internal cracks. Nonlinear ultrasound detection methods are employed as advanced, non-destructive testing techniques for early damage inspection in various materials. This research investigates the assessment of the thickness of the intermetallic layer within dissimilar joints using non-linear ultrasound-wave features. Numerical and experimental investigations were performed using four friction stir welding (FSW) lap joints, between AA5052-H32 aluminum and ASTM 516-70 steel, with various intermetallic thicknesses. The methodology involved examining the generation of second-order harmonic frequency by exciting Lamb waves (LW) at specific frequencies. To determine the necessary LWs' excitation frequency, synchronism, and non-zero power flux conditions were employed. The collected signals were measured and analyzed in the time and frequency domains to understand the behavior of the non-linear parameter β′ with the thickness of the intermetallic layer. The results show that β′ changes in a linear manner with the thickness of the intermetallic compound layer (several micrometers in thickness). This provides strong evidence that nonlinear LW features are sensitive to microstructural variations in the FSW joints, which enables them to effectively evaluate their strength.

Stress Concentration Modelling on Resistance Spot Welding Lap Joint of Steel ASS316L and Titanium Ti-6Al-4V with Variable Weld Geometries

This research is a finite element simulation on resistance spot welding (RSW) process between dissimilar sheet metals consist of Titanium alloy, Ti-6Al-4V and Austenitic Stainless Steel (ASS) 316L. The problem statement was inability to visualize the stress concentration profile over weld nugget joint when Titanium alloy and steel welded with variable electrode geometry of circle, triangle, square and hexagon. To determine the best geometry for best weld with lowest maximum stress concentration. The methodology of simulation was tensile-shear test using SOLIDWORKS software. The tensile-stress load of 664.09 N was applied across all 4 different weld geometries. The result for the lowest magnitude of maximum stress 180.6 MPa was on circle weld geometry. Triangle geometry registered highest stress concentration of 219.6 MPa. This proves that most common weld geometry used in industry was circle. Even for dissimilar material joint the result supports that circle weld geometry as the best geometry. Keywords: Resistance spot welding (RSW), stress concentration, weld nugget, weld geometry.

Tensile analysis of loop joints with different overlap lengths

ABSTRACT In order to achieve rapid bridge construction, on-site wet joint joining techniques for prefabricated bridge decks are commonly used. The primary method involves mainly lap welding, but this form poses some drawbacks such as difficult lap jointing of two steel bars and a hefty welding workload. To address these issues, this study conducts model experiments on the unwelded structure of loop joints. We compare and analyze the displacement, crack distribution, crack development process, and strain variability of loop joints across three different overlap lengths, along with one type of straight bar lap-welded wet joints. It is observed that, despite the comparable ultimate tensile capacity of loop joints with the main rib to that of the welded wet joint with the main rib, the failure mode varies, and the crack direction changes with the overlap length. From a structural stress perspective, if the U-bar of the loop joint meets a specific overlap length, the wet joint adequately fulfills stress requirements and can be applied in practical engineering.

Fatigue life evaluation of laser welded lap joints of dissimilar aluminum alloys

Abstract Constant amplitude fatigue tests were conducted on 6061/7075 dissimilar aluminum alloy laser welded lap specimens, as well as weld line cross-section hardness measurements. The fatigue test results show that the specimens exhibit multiple fracture modes that exit near the weld seam. The microhardness data on weld line cross-section from 7075 side to 6061 side display a sharp change and the softening phenomenon is serious. The hardness variation in heat affected zone of laser welding is very shallow, and its hardness is close to that of the base material. It was found that there are slag inclusions and pores in the weld seam when observing the fatigue fracture surface using SEM, and a small amount of secondary cracks were generated. However, stress concentration plays a dominant role in causing specimen fracture under fatigue loading, rather than welding defects. Defective specimens are found to have higher fatigue strength. The fatigue life prediction results obtained by the notch stress method and the hot spot stress method are both conservative and fall within two factor lines. The hot spot stress method has relatively higher accuracy for life prediction. The accuracy of both methods in predicting life is influenced by the location of the fracture.

Effect of stirring time on the quality of aluminum-steel lap joints of friction stir spot welding

AA6061 aluminum alloy sheet and TRIP steel plate were welded by friction stir spot welding using a tungsten-based hard alloy stirring head, and the effect of stirring time on the formation and connection strength of spot welded lap joints was studied. The results showed that as the stirring time increased from 0 s to 7 s, all spot welded joints formed well, and the size of the hooks appearing in the stirring needle’s action area gradually increased. The connection strength of the joint gradually increases with the increase of stirring time. When the stirring time is 5 seconds, it reaches a maximum value. At this time, when the stirring time is increased, the joint strength decreases significantly. The strength of the joint is influenced by the size of the bending hook and the formation of intermetallic compounds.

Enhanced formation quality and tensile shear load of 7B04 aluminum alloys lap joint by impacting flow friction stir lap welding

Avoiding the upward-bending hook is a highly pressing and challenging task in the field of similar aluminum alloys friction stir lap welding (FSLW). To enhance formation quality and then obtain the welded lap joint with high tensile shear load, a novel impacting flow FSLW (IF-FSLW) process based on the X-shape reverse-threaded pin was proposed in this study. Three welding tools with different tool geometry parameters were developed to analyze how the locations of the materials accumulated zone (MAZ) influenced the joint formation and the joint loading capacity, and 7B04 aluminum alloys were chosen as research subject. Results showed that the horizontally-impacting and vertically-impacting effects of MAZ on and above the original lap interface made the hook respectively present the forky structure at the end and the downward-bending morphology, and the horizontally-impacting effect of MAZ made the stir zone (SZ) have a protruding morphology near the MAZ. Under the tensile fracture mode, the IF-FSLW joint under configuration A had a greatly heightened tensile shear load under the combined actions of the downward-bending hook and the enlarged SZ. The tensile shear load of IF-FSLW joint reached 8.62 kN/mm under the reasonable combination of tool geometry parameters and welding process parameters. The IF-FSLW process by the X-shape reverse-threaded pin provides an effective way to obtain a superb-strength lap joint of aluminum alloys.

Effect of the Energy Director Material on the Structure and Properties of Ultrasonic Welded Lap Joints of PEI Plates with CF Fabric/PEI Prepreg

To estimate the possibility of using both low-melting TecaPEI and neat PEI films as energy directors (EDs) for ultrasonic welding (USW) of carbon fiber (CF) fabric–polyetherimide (PEI) laminates, some patterns of structure formation and mechanical properties of their lap joints were investigated by varying the process parameters. The experiment was planned by the Taguchi method with the L9 orthogonal matrix. Based on the obtained results, USW parameters were optimized accounting for maintaining the structural integrity of the joined components and improving their functional characteristics. The use of the low-melting EDTecaPEI film enabled US-welding the laminates with minimal damage to the fusion zone, and the achieved lap shear strength (LSS) values of ~7.6 MPa were low. The use of EDSolverPEI excluded thermal degradation of the components as well as damage to the fusion zone, and improved LSS values to 21 MPa. With the use of digital image correlation (DIC) and computed tomography (CT) techniques, the structural factors affecting the deformation behavior of the USW lap joints were justified. A scheme was proposed that established the relationship between structural factors and the deformation response of the USW lap joints under static tension. The TecaPEI film can be used in USW procedures when very high interlayer adhesion properties are not on demand.

Evolution of interfacial phases between Al alloy and high entropy alloy during annealing

While the interfacial phases between Al and high-entropy alloy (HEA) share the same types as that between Al and steel, it has been found previously that the thermal stability of the Al-HEA interfacial phases is significantly higher than that of the Al-steel interfacial phases. To further elucidate the reason for the exceptional thermal stability of Al-HEA interfacial phases, this study investigated the evolution of the interfacial phases formed between Al alloy and FeCoCrNiMn HEA during annealing. An Al-FeCoCrNiMn thin film diffusion couple was extracted from a friction stir lap welding (FSLW) joint by focused ion beam and then annealed at 400 °C. An amorphous layer is formed initially at the interface due to the high strain rate deformation during FSLW. The amorphous layer remained even after prolonged annealing at 400 °C (∼0.72 Tm of Al alloy) for 60 min with very limited thickening (from 50 nm to 55 nm), showing remarkable thermal stability at the relatively high temperature. Al13Fe4-type intermetallic compound (IMC) with the Fe site occupied by Fe, Co, Cr, Ni and Mn first nucleates at the interface between Al alloy and amorphous layer. With the annealing time extended to 180 min, the amorphous layer is partially transformed into Al5Fe2-type IMC. The rate constant for the thickening of the reaction layer at the Al/FeCoCrNiMn interface is 0.03 μm∙min1/2, which is much smaller than (only 0.02 times) that at the Al/steel interface under similar annealing condition. The high thermal stability of Al-HEA interfacial layer is thus attributed to the slow kinetics in crystallization of the initially formed amorphous layer, the barrier effect of amorphous layer for interdiffusion, and the reduced diffusivity inside of IMCs caused by significant fluctuations in lattice potential energy due to high-density doping with HEA elements. This finding provides new insights into the fabrication of thermally stable Al-HEA hybrid structures suitable for service conditions involving high-temperature exposure.

Effect of welding speed on mechanical properties of dissimilar friction stir lap-joint welding between AA6061 and C1100 copper

Nowadays, renewable energy such as wind and solar energy can be employed for marine application to enhance clean and green technology. So, using battery is necessary to apply power for ship activities. To contribute sustainable development, optimizing structure in electric transmission such as bimetal connector Cu-Al is necessary to improve joint quality. This study focused the influence of welding parameters on the quality of the lap-joint between AA6061 aluminum alloy and C1100 copper. Experimental results indicate that the welding interface was sensitive to welding speed. Some welding defect was found in the joint such as tunnel and hook defects. The highest tensile strength produced by the welding speed of 200 mm/min was approximately 1100 N. In all experimental regimes, the weld zone structure, hardness distribution, tensile strength, fracture location, and local deformation were analyzed and discussed in detail. Keywords: Friction stir welding, microstructure, mechanical properties, hardness

Impact of Welding Parameters in the Porosity of a Dissimilar Welded Lap Joint of CP800-XPF1000 Steel Weldment by GMAW-P

The use of the orthogonal array L4 allows a determination of the effect between the welding parameters peak current (Ip), background current (Ib) and frequency (f) on the porosities in a dissimilar welded lap joint of CP800 and XPF1000 steel weldment by the gas metal arc welding process with the transfer pulsed mode. According to the results, modifications in the welding parameters affect the heat input during welding. A heat input higher than 0.30 KJ/mm generates up to 0.32% porosity in the weld metal, while a heat input lower than 0.25 KJ/mm generates up to 28% porosity in the weld metal. The variation in heat input generated by the process allowed the observation of the final microstructure of the welded joints and the effect of mechanical properties such as hardness because the results show values of hardness from 300 Hv to 400 Hv in the heat affected zone (HAZ).

Evaluation of Welded Lap Joints Using Ultrasonic Guided Waves.

Welded lap joints play a vital role in a wide range of engineering structures such as pipelines, storage tanks, pressure vessels, and ship hulls. This study aims to investigate the propagation of ultrasonic guided waves in steel welded lap joints for the baseline-free inspection of joint defects using the mode conversion of Lamb waves. The finite element method was used to simulate a single lap joint with common defects such as corrosion and disbonding. To identify the propagating wave modes, a wavenumber-frequency analysis was conducted using the 2D fast Fourier transform. The power loss of the transmitted modes was also determined to identify damage in the lap joints. The results indicate that the A0 incident in pristine conditions experienced significant transmission losses of about 9.5 dB compared to an attenuation of 2.8 dB for the S0 incident. The presence of corrosion was found to reduce these transmission losses by more than 28%. In contrast, introducing disbonding in the lap joint increased the transmission loss of the S0 incident, while a negligible loss was observed for the A0 incident. The mode-converted S0 (MC-S) and mode-converted A0 (MC-A0) incidents were found to exhibit a unique sensitivity to the presence of corrosion and disbonding. The results indicate that MC-S0 and MC-A0 as well as Lamb mode incidents interact differently in terms of corrosion and disbonding, providing a means to identify damage without relying on baseline signals.

Enhancement of mechanical properties and corrosion resistance in laser lap welding joint of zirconium R60702 by forced water-cooling

A comparison was conducted on the microstructure, mechanical properties, and corrosion resistance of the fusion zone (FZ) in Zr R60702 laser lap joints prepared under air-cooled and water-cooled conditions. The results reveal that the upper and lower regions of the FZ in the welded joint consist of dendritic structure and α′ martensite, respectively. When water-cooled forced cooling is applied, α′ martensite emerges in the upper region of the FZ, with a few dendrites exhibiting an isoaxial distribution. Furthermore, the α′ martensite in the lower region becomes noticeably refined. The utilization of water-cooling triggers multiple strengthening mechanisms that, through synergistic interactions, enhance the microhardness, strength, and plasticity of the welded joints. The improved corrosion resistance within the FZ of the welded joint is attributed to the formation of a more stable passivation film.

A NEW TYPE OF PLUG-IN FRICTION-STIR LAP WELDING BASED ON THE 6061-T6 ALUMINUM ALLOY

In this study a new type of plug-in friction-stir lap welding (PFSLW) is proposed to prepare welded joints based on 4-mm-thick 6061-T6 aluminum alloy sheet. The differences in the cross-sectional morphology, microstructure, cross-sectional hardness and shear properties between the PFSLW joint and the normal friction-stir lap-welding (FSLW) joint are discussed. The results show that the cross-sectional morphology of the PFSLW joint has undergone changes. The PFSLW joint has a mechanical interlocking structure on the advancing side that is beneficial to the connection strength of the joint. The grain structure differs at the boundary between the thermo-mechanically affected zone (TMAZ) and the heat-affected zone (HAZ), and the PFSLW joints show a more pronounced bending deformation of the grain organization near the boundary. The microhardness of PFSLW joints was increased in the TMAZ and HAZ areas, and the lowest hardness is further away from the center of the weld. The failure load of the PFSLW joint has been improved, the microcracks part of the PFSLW joint has a ridge-like structure. In addition, the actual welding width of PFSLW joints was improved.

Al heat affected zone-less resistance element welded lap joints of Al alloy and 1 GPa class steel: Transition of microstructure and fracture with heat transfer

In this study, Al joint systems without heat-affected zones (HAZ) were developed on Al/Fe alloy lap joints fabricated by resistance element welding (REW). The robustness of the joints with and without HAZs was quantitatively evaluated to consider another side effect in REW Al/Fe alloy systems. Compared to conventional REW, removing the Al HAZ not only alters the steel properties, but also reduces the work hardening of the Al alloy due to the difference in the distinct heat transfer paths. Furthermore, the presence of Al HAZ significantly influenced the hardness characteristics of the molten steel portion. In the cold wall configuration without Al HAZ, hardness values exceeding those of the hot wall by approximately 100 Hv or more were observed. At a welding current of 10.5 kA, the hot wall configuration demonstrated an approximate 30 % increase in tensile shear load and a 66 % increase in displacement compared to the cold wall configuration without HAZ. In the cold wall conditions, interfacial failure (IF) was not attributed to microstructural disparities but was linked to the formation of an inherent notch root when S20C melted due to the absence of Al HAZ. Contrary to previous reports, the presence of HAZ in Al alloys results the production of tough steel through REW.

Improvement of electrical and mechanical properties of laser welded lap joints via dimensional optimization

With the proliferation of electric drivetrains, the development and optimization of joining techniques for the fabrication of battery packs became a prime manufacturing topic. Decreasing the electrical resistance and increasing the mechanical strength of the welds at the individual cell level are of great importance not only for productivity and efficiency but also for safety and sustainability purposes. Lasers offer an advanced, highly automatable solution for battery cell joining. Usually, the optimization focuses on the laser parameters or the scanning speed. However, the most widespread battery welding geometry, the so-called lap geometry, allows alternative possibilities for joint property optimization. The novelty of our approach is that we focus on systematic experimental investigation of the effects of dimensional parameters and the layout of the weld pattern. Systematic experiments reveal that the shape and size of the weld area have substantial effect on the properties of the laser welded joint. Our results prove that a rather substantial gain can be achieved in both the electrical and mechanical properties when the weld consists of at least two parallel bead segments. We also show that it is beneficial by both means if the segments have the greatest individual length and placed apart at the maximum feasible distance. The orientation of the straight segments affects the mechanical and electrical behavior differently: strongest welds consist of weld segments oriented in parallel, while the smallest resistance can be achieved using segments oriented perpendicular to the direction of current flow, respectively.

Effect of Ni interlayer on interfacial microstructure and fatigue behavior of friction stir lap welded 6061 aluminum alloy and QP1180 steel

In this work, the interfacial microstructure and fatigue properties of friction stir lap welding (FSLW) joint of 6061 aluminum (Al) alloy and QP1180 steel with a Ni interlayer were characterized, and the effects of Ni on the intermetallic compounds (IMCs) evolution and fatigue behavior were revealed. The results show that an Al-Ni transition layer with a thickness of ∼ 200 nm appears at the interface of Al-Ni-Fe joint. No Al-Fe IMC is formed in the joint, because the Ni interlayer effectively blocks the reaction between Al alloy and steel. The fatigue strength of Al-Ni-Fe joint is 50 % higher than that of Al-Fe joint. The failure modes of Al-Fe joints are affected by the load levels. The joint breaks at the interface at high load levels, while the joint tends to break along the thickness direction of Al plate at low load levels. After adding Ni interlayer, the joint breaks along the thickness direction of Al plate at both high and low load levels. Based on the theoretical calculation, all Al-Fe IMCs exhibit brittleness, and most of Al-Ni IMCs exhibit toughness. Hence, Al-Ni phases effectively prevent crack propagation by enhancing the interface bonding strength of Al alloy and steel, and improve the fatigue strength of joint.

Comprehensive influence of silane layer and interfacial thermo-mechanical effect on joining mechanism of silane pretreated Al/CFRP FSLW joint: FEA and experiment

Al/CFRP composite structure has the advantage of lightweight and high specific strength, making it a promising material for aviation, railway, and automotive applications. Silane coupling pretreatment is a chemical surface pretreatment method that can improve the mechanical properties of the Al/CFRP friction stir lap welding (FSLW) joint. To further investigate the strengthening mechanism of silane-treated Al/CFRP FSLW joint, a 6061-T6 Al/CF-PA66 FSLW experiment was carried out and the finite element analysis (FEA) was used. The thermophysical properties of semi-crystalline resin during the welding process were also considered. The joining mechanism of silane surface pretreated Al/CFRP FSLW joints was further revealed by comparing the changes in interface morphology, temperature, stress, and mechanical properties. The results indicated that the silane coupling agent forms a silane film by an Al-O-Si chemical bond at the interface. The silane film can enhance the Al/CFRP interface's tightness and reduce interfacial defects. The FSLW process affected the joint morphology and mechanical properties through interfacial temperature and stress, which were decided by welding parameters and thermophysical properties of the resin. By adjusting the thermal-mechanical effect of the Al/CFRP interface, defects can be reduced and the joining force can be improved. According to the analysis of interfacial chemical bonds and mechanical properties, the introduction of silane film enhances the hydrogen bond between Al and resin and thus enhances the mechanical properties of the interface. This study provides a new method for revealing the strengthening mechanism of silane-pretreated FSLW Al/CFRP joint.