Lap Joint Configuration Research Articles

Dissimilar Laser Beam Welding of Titanium to Stainless Steel Using Pure Niobium as Filler Material in Lap Joint Configuration

In the present investigation, commercially pure titanium is welded to AISI 316L stainless steel by intermixing niobium as filler material in a lap joint configuration. For this purpose, a pulsed Nd:YAG laser with various pulse durations and pulse peak powers is employed to obtain different mixing conditions for the materials. It will be demonstrated that, despite the implementation of the filler material, the weld seams are characterized by a high affinity for cracking, which in turn can be attributed to the formation of hard intermetallic compounds. Nevertheless, utilization of optimized process parameters can yield crack-free specimens in a reproducible manner through equable intermixing of otherwise critical alloy elements. Lap-shear forces of up to 140 N can be achieved with a single weld seam measuring 2.5 mm in length. By increasing the joint area with four adjacent weld seams, maximum loads up to 320 N are attained, thus exceeding the yield strength of the applied stainless steel. Considering the biocompatibility of the niobium filler material used, this work provides the foundation for this dissimilar material combination to be implemented in future medical technology applications.

Effect of interfacial thermal history on bonding mechanism of laser assisted joining of QP980-CFRTP with adjustable flat-top rectangular laser beam

Carbon fiber reinforced thermoplastic composite (CFRTP) - metal hybrid structures, which have been increasingly used in the industry, can significantly reduce structure weight and energy consumption. In this paper, an adjustable flat-top rectangular diode laser beam was used as a heat source to join the quenched and portioned QP980 steel and CFRTP in a lap joint configuration. Compared to conventional laser beam scanning process in the literatures, the rectangular laser beam provides a relatively uniform temperature distribution at interface. The relationship between interfacial thermal history and the joint performance was explored. Experimental results showed that thermal history had a significant impact on interfacial chemical compositions and the formation of joint defects via affecting the resin state, resulting in change of the joint fracture behaviors. Furthermore, higher interfacial temperature and sufficient heating/holding time contributed to the complete melting and diffusing of resin matrix on QP980 surface, filling the micro pores of the interface, and promoting the chemical bonding between QP980 and CFRTP. On this basis, a novel strategy to achieve excellent interfacial bonding via adjusting the interfacial thermal history was proposed to produce a high-quality joint with the peak load higher than 10 kN and the shear strength of 22 MPa.

Using a non-linear mixed model behavior of CZM to predict the damage in single lap bonded joint with Bi-composite graded materials

The present work is a numerical prediction based initially on a reliable model validated by experiments under the same conditions used as ours with new concepts in Bi-composite plates. A system formulation approach of the adhesive in ductile and nonlinear damage behavior is used in this analysis This ductility is developed by the CZM technique implemented using the MATLAB program in ABAQUS computer code. For a numerical prediction of the ductile behavior of the adhesive, the CZM model is an extension of the pure modes (I and II) previously characterized in block by tests. This extension is trapezoidal in increasing stresses of the adhesive in its behavior law. The single lap joint configuration allows us to stress the glue joint to mixed-mode loading. The resistance of the assembled structures remains conditioned by the behavior of the adhesive until it is damaged and the rigidity of the attached plates. Therefore, our objective in this work is to cause the plasticization damage of the adhesive at different responses and levels. For this, the bi-composite graduation in concept and in graduation index largely plays the role of evaluation parameters. In order to test the adequacy for a good resistance, three different concepts of graduation in Bi-composite were proposed such as: concept1-concept1, concept2-concept2, and simple concept-simple concept. By these two cases of assemblies, these concepts have the advantage of having different assembly possibilities, The proposed concepts of graduated bi-composite plates showed an overcapacity of resistance on the assembly. The latter becomes important in the adequacy of concept of these assembled plates. Similarly, the results show that different responses and levels cause the damage by effect of these concepts.

The role of filler wire and scanning strategy in laser welding of difficult-to-weld aluminum alloys

AbstractLaser welding of dissimilar aluminum alloys has gained interest over recent years, especially for the production of lightweight components. Pore and crack formation is one of the most critical factors to be taken into consideration for such applications, in particular when one or more parts are produced by die casting or additive manufacturing (AM). Current laser systems offer several methods for defect reduction and process control, while optimized process strategies must be correlated to key factors influencing welding outcomes. In light of these aspects, the current paper investigates the welding of AA6082 sheets with AlSi10Mg parts produced by AM in a lap-joint configuration typical of battery housings in the e-mobility industry. Both laser welding with and without filler wire are investigated, along with the potential advantages of using a wobbling scanning strategy, in order to understand the impact of process strategies on weld bead quality. The importance of process parameter optimization is highlighted for all of the employed strategies, with special emphasis on defects, weld bead chemical composition, joint morphology, and dilution between the materials involved. The findings demonstrate that by introducing filler wire and employing active wobbling, highly reflective alloys can be welded correctly (porosity below 1%, equivalent ultimate strength up to 204 MPa) with good tolerance to variations in process parameters, while filler wire can be excluded in high-productivity welding where linear scanning is employed and detailed optimization of process parameters is performed (porosity below 2%, equivalent ultimate strength up to 190 MPa).

Fundamental study of blue wavelength laser for welding low thickness dissimilar Cu and steel materials

The present study reports on the application of blue wavelength (450 nm), continuous wave laser welding of Ni-coated copper to mild steel in lap joint configuration. The laser power was varied from 1 kW to 1.5 kW in incremental steps of 0.1 kW whilst the welding speed was kept constant at 6 m/min. Metallographic examination of the weld samples revealed that the weld penetration and width strongly correlated to the laser power, the characteristic of a stable welding process due to the high absorption of the blue wavelength laser. No substantial cracks or a large number of porosities were observed in the welds. The mechanical properties of the weld samples were characterized through tensile testing and microhardness measurements to establish the microstructure property relationship. The maximum tensile strength measured for specified weld geometries was 649 N with corresponding weld efficiency of 91%. The higher-strength welds showed a tensile fracture in the heat-affected zone (HAZ) of Cu, at the periphery of weld nuggets while lower-strength welds showed interfacial fracture due to the lack of fusion. In samples made with sufficient penetration the joint strength was controlled by the HAZ rather than the joint microstructure. A significant increase in the microhardness was measured inside the weld nugget compared to the parent materials, attributed to the formation of Cu-Fe composite microstructure owing to the inter-mixing of Cu and Fe during welding. The highest microhardness was observed in the HAZ of the mild steel due to martensitic microstructure formation in this region.

Dissimilar joining of titanium to aluminum using friction stir welding process and weld joint characterization

Abstract The present investigation studies the solid-state joining of difficult-to-weld aerospace materials such as titanium alloy (Ti6Al4V, ELI) and pure aluminum. Due to the wide difference in thermo-mechanical properties, it was a challenging task to establish a dissimilar metal joint. The friction stir welding process with a conically shaped tungsten carbide tool was used in the present investigation to join the dissimilar titanium alloy and aluminum in the lap joint configuration. After a series of pilot experiments, the optimum test conditions to produce the defect-free joint are spindle speed of 1200 rpm, feed rate of 40 mm min−1, tool tilt angle of 1°, and 1 mm tool offset towards the aluminum side. The results show that a good joint was achieved with a maximum joint strength of 89 MPa. The dissimilar joints are characterized by macrostructure, microstructure, microhardness, and scanning electron microscopic analysis.

Modelling and optimization of laser welding of Al2024 aluminium alloy

PurposeAluminium alloys can be used as lightweight and high-strength materials in combination with the technology of laser beam welding, an efficient joining method, in the manufacturing of automotive parts. The purposes of this paper are to conduct laser welding experiments with Al2024 in the lap joint configuration, model the laser welding process parameters of Al2024 alloys and use propounded models to optimize the process parameters.Design/methodology/approachLaser welding of Al2024 alloy has been conducted in the lap joint configuration. Then, the influences of explanatory variables (laser peak power, scanning speed and frequency) on outcome variables (weld width [WW], throat length [TL] and breaking load [BL]) have been investigated with Poisson regression analysis of the data set derived from experimentation. Thereafter, a multi-objective genetic algorithm (MOGA) has been used using MATLAB to find the optimum solutions. The effects of various input process parameters on the responses have also been analysed using response surface plots.FindingsThe promulgated statistical models, derived with Poisson regression analysis, are evinced to be well-fit ones using the analysis of deviance approach. Pareto fronts have been used to demonstrate the optimization results, and the maximized load-bearing capacity is computed to be 1,263 N, whereas the compromised WW and TL are 714 µm and 760 µm, respectively.Originality/valueThis work of conducting laser welding of lap joint of Al2024 alloy incorporating the Taguchi method and optimizing the input process parameters with the promulgated statistical models proffers a neoteric perspective that can be useful to the manufacturing industry.

Effect of heat input on corrosion behavior of automotive zinc-coated steel joint

Abstract Lately, coated steel sheets have replaced bare steel in the automotive sectors due to their corrosion protection. Among them, zinc-coated high strength interstitial free (HIF) steel is widely used due to its durability, formability, good surface finish, impact resistance, and corrosion resistance. However, joining galvannealed (GA) steel using conventional fusion welding processes is challenging as it results in porosity and potentially harmful fumes. To overcome these challenges, this work uses a pulse MIG (metal inert gas) brazing technique to join the HIF-GA steel sheet with a lap joint configuration utilizing Cu-Si base filler wire (CuSi3Mn1) in an argon atmosphere. The study aims to evaluate the effect of heat input on bead geometry and Zn degradation in MIG brazed joints by adjusting the current from 40 to 60 A and brazing speed from 400 to 500 mm min−1. It is observed that the heat input is inversely proportional to the wetting angle and directly proportional to the bead width, leg length, and cross-sectional area. Heat input influences Zn degradation on both the front (at the toe) and back sides of the lap joint. The corrosion behavior of joints is studied using an electrochemical test (in 3.5% NaCl solution) and a salt spray test (in 5% NaCl solution). Further, the Zn degradation is analyzed with EDS line scanning to understand the corrosion resistance of the MIG brazed joints. A potentiostatic polarization study is also conducted to determine the corrosion rate using a Tafel plot. It is found that the lowest corrosion rate in base metal (BM) increased from 0.88 to 12.26 mm year−1 with the increase in heat input from 61 to 113 J mm−1.

Effect of hygrothermal and thermal aging on the fatigue and static strength of mechanical and hybrid single lap joint

In this study, the effect of hygrothermal (in tap water at 53 °C for 20 days) and thermal (53 °C for 20 days) ageing on the mechanical (OB) and hybrid (HBB) joints with similar (AL/AL and CFRP/CFRP) and dissimilar (AL/CFRP) adherends, is investigated on single lap joint (SLJ) configuration. Three- point bending strength of the un-aged, aged joints were measured and compared for static and fatigue testing at different load levels (50, 60, and 70 % of static load level) of 16 Hz frequency. The results showed that HBB-CFRP/CFRP SLJs has the highest bending strength. Both the thermal and hygrothermal aging showed to have a noticeable effect on the static bending properties of the SLJs with similar and dissimilar adherends. Al/CFRP had the longest fatigue life between the OB samples while CFRP/CFRP had the longest fatigue life in the HBB SLJs. The load percent and aging both reduce the number of cycles to failure and change the mode of failure of the joints.

Achieving excellent interfacial bonding of QP980 steel to CFRTP by laser joining via carbon fiber reinforced mechanical anchorage

Carbon fiber reinforced thermoplastic composites (CFRTP)-metal hybrid structures can significantly reduce weight and cost while maintaining good performance. In this paper, a diode laser was used to join QP980 steel-CFRTP at a lap joint configuration. Furthermore, an ultrafast laser ablation process was used to produce periodic micro-groove structures on the surface of QP980 in order to generate mechanical anchors and improve QP980-CFRTP interfacial bonding performance. The relationship between the shear strength of QP980-CFRTP joints and laser heat input as well as QP980 surface micro-groove depth were evaluated. It was found that both heat input and micro-groove depth significantly affected the state of resin near the bonding interface. The suitable heat input and the micro-groove depth produced the optimized mechanical anchorage structures without the formation of the pores and porosities. Furthermore, a new method was proposed to significantly improve the joint performance where the orientation of fiber and the micro-grooves were intentionally designated as the same and perpendicular to loading direction in order to form carbon fiber reinforced interfacial mechanical anchorage structures. By optimized heat input, micro-groove depth and orientation, the peak load of the joint was dramatically improved by 515% compared with that without laser ablation treatment.

Significance of underwater friction stir welding on the weld integrity of thin sheets of aluminum (AA1050-O) and brass (CuZn34) joints

Classical friction stir welding (C-FSW), because of its solid-state joining nature, offers several benefits over traditional fusion welding for joining dissimilar materials. C-FSW conducted in open air, are affected by several weld flaws and thick Intermetallic Compounds (IMCs) that reduce the weld joint quality. In this study, FSW of thin sheets of aluminum alloy (AA1050-O) and brass (CuZn34) in lap joint configuration was performed in air and underwater. The main objective of this study was to investigate the feasibility of underwater-FSW (UW-FSW) for obtaining aluminum and brass (Al-Brass) joints at different values of shoulder plunge depth (SPD) and tool rotational speed (N). To determine the effect of welding temperature at different values of SPD and N on the formation of weld joints, K-type thermocouples were used. Underwater welding reduced the welding temperature and thermal cycle time. The optical images of C-FSW joints revealed the presence of kissing bonds, wavy patterns, cracks, tunnels, and void defects. In UW-FSW, the faster cooling rate significantly reduced these weld flaws. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used for the microstructural characterization. EBSD and TEM results show fine microstructure and precipitates in UW-FSW specimens. The X-ray diffraction results demonstrated that the weld joint interface primarily consisted of Al-Cu & Cu-Zn IMCs in the form of Al4Cu9, Al2Cu, AlCu3, AlCu4, CuZn5, and Cu5Zn8. The amount of IMCs was less in the joints produced by UW-FSW. The obtained results were used to understand the variation in the weld strength of C-FSW and UW-FSW joints at different values of SPD and N. To further evaluate the interface of the Al-Brass weld joint, energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) were employed. EDS confirmed the presence of brass fragments in the stirred zone of aluminum substrate. TEM and SEM images illustrated fine precipitates and formation of thin IMC layers in UW-FSW. The tensile test result shows that the UW-FSW remarkably improved the joint strength. The percentage increase in the joint tensile strength for UW-FSW was found 42%, 30% and 50% higher than C-FSW for lower, medium and high heat input welding conditions. The lower heat input in UW-FSW significantly suppressed the formation of weld flaws and IMCs, which collectively improved the tensile strength of the weld joint.

Service Life Modelling of Single Lap Joint Subjected to Cyclic Bending Load

Bonded joints used in wing sections and frames of aircraft structures are mostly exposed to cyclic loadings instead of static ones during their services. Bending types of dynamic loadings are mostly encountered. In this study, the fatigue response of a single lap joint (SLJ) exposed to bending loading was studied with the developed advanced finite-element (FE) model. The cohesive zone model describing the behaviour of the adhesive layer used the damage mechanism, where static and fatigue damages were linked to each other; i.e., the total damage was accumulated because of material deterioration and cyclic plastic separation. This enabled us to predict the fatigue characteristics including the finite fatigue life, crack propagation rate using Paris law. The model was implemented via a user-defined UMAT subroutine offered in ABAQUS-Standard. The numerical model was validated by experiments available in the literature. The fatigue performance of an SLJ subjected to bending loading was investigated for different lap joint configurations. A smaller bending load, a thicker adherend or a longer overlap length (OL) led to enhanced fatigue life. For instance, the fatigue life was observed to increase up to 50 times for a 66% increase in OL.

Direction-independent laser-GMA hybrid welding with coaxial wire feed and annular beam

Conventional laser gas metal arc hybrid welding (LB-GMA hybrid welding) is used as an efficient joining process in several high-tech steel processing production facilities. However, the use of the LB-GMA hybrid welding is often limited to the joining of linear weld seams as the welding process has a preferred welding direction due to lateral positioning of the laser beam and welding wire electrode. Reorienting the welding direction, therefore, often results in weld defects since changing the welding direction also requires a geometric manipulation of the GMA torch in relation to the laser beam optics. This means a considerable additional effort that is necessary if this efficient welding process is to be used for geometrically complex weld seam contours. Furthermore, the conventional LB-GMA hybrid welding process has a high adjustment complexity. Within this work, a direction-independent laser GMA hybrid welding head with an annular beam and coaxial wire feed is used. The annular laser beam with homogenous intensity profile is formed by a special processing head, split and reassembled around the coaxial wire. Due to the coaxial arrangement of the wire electrode to the annular beam, the hybrid process is in theory direction independent. As a result, there should not be any irregularities in the weld seam, when the welding direction is changed. The annular beam considerably reduces the complexity of adjustment and improves reproducibility. The focus of this work is to qualify the process for joining geometrically complex weld contours and to investigate possible advantages of the directional independence of the coaxial LB-GMA hybrid welding process. For this purpose, fillet welds in lap joint configuration with a sheet thickness of 2 mm each at different weld contours (different direction changes, corners, radii) are discussed. By performing a DoE-based sensitivity analysis, influencing factors on the quality of the generated weld are analysed.

Friction stir welding for manufacturing of a light weight combat aircraft structure

Abstract This paper aims to validate the viability of friction stir welding process (FSW) to join high strength aerospace grade AA2014-T6 aluminium alloy for manufacturing light-weight combat aircraft (LCA) structure as a replacement to riveting process. FSW is used to overcome the heat input-related problems in fusion welding of AA2014-T6 aluminium alloy such as coarse grain fusion zone microstructure, softening in HAZ and lower joint efficiency. The 2 mm thick AA2014-T6 aluminium alloy sheets were used as the base material (BM). Friction stir butt (FBW) and friction stir lap (FLP) joints were developed, and its performance was compared with double cover riveted butt (DRB) joint in butt (RBJ) and lap (RLJ) joint configuration. Results showed that the load-carrying capability of FSW joints is greater than the riveted joints. The superior load-carrying capacities of FBW and FLW joints refers to evolution of refined grains and strengthening precipitates in stirred zone (SZ), which ensures superior metallurgical bonding between the joining surfaces. The riveted joints disclosed inferior load-carrying capacities due to the lack of metallurgical connection between the joining surfaces.

Quasi-Continuous Wave Pulsed Laser Welding of Copper Lap Joints Using Spatial Beam Oscillation.

Laser beam welding of copper (Cu) using near-infrared radiation is extremely challenging due to its high thermal conductivity and large laser reflectivity. In the present study, the challenges and benefits of using spatial beam oscillation during quasi-continuous wave (QCW) pulsed laser beam welding of 0.4 mm Cu to 1 mm Cu in lap joint configuration are presented. This work demonstrates how laser beam oscillating parameters can be used to control the laser weld quality and laser weld dimensions for Cu-Cu joining. Compared to a non-oscillated laser beam, welds made using laser beam oscillation showed fewer spatters, porosities, and better surface quality. Four levels of oscillating amplitudes (0.2 mm, 0.4 mm, 0.6 mm, and 0.8 mm) and oscillating frequencies (100 Hz, 200 Hz, 300 Hz, and 400 Hz) were compared to reveal the effect of beam oscillation parameters. The weld width was mainly controlled by oscillating amplitude, while weld penetration was affected by both oscillating amplitude and frequency. As the oscillating amplitude increased, the weld width increased while the weld penetration decreased. Increasing the oscillating frequency reduced the weld penetration but had a negligible effect on the weld width. The maximum tensile force of approximately 1944 N was achieved for the joint with a high width-to-depth ratio with an oscillating amplitude of 0.8 mm and an oscillating frequency of 200 Hz.

Modeling of Probeless Friction Stir Spot Welding of AA2024/AISI304 Steel Lap Joint.

In the present study, AA2024 aluminum alloy and AISI304 stainless steel were welded in a lap joint configuration by Probeless Friction Stir Spot Welding (P-FSSW) with a flat surface tool. A full factorial DOE plan was performed. The effect of the tool force (4900, 7350 N) and rotational speed (500, 1000, 1500, 2000 RPM) was analyzed regarding the microstructure and microhardness study. A two-dimensional arbitrary Eulerian-Lagrangian FEM model was used to clarify the temperature distribution and material flow within the welds. The experimental results for the weld microstructures were used to validate the temperature field of the numerical model. The results showed that the tool rotation speed had an extensive influence on the heat generation, whereas the load force mainly acted on the material flow.

The Effect of Resistance Spot Welding Parameters on Microstructure and Strength of DP800 Steel Joints Using Response Surface Methodology

Abstract The main objective of this paper is to analyze the direct and interaction effect of resistance spot welding (RSW) parameters on microstructure and strength of DP800 steel joints using response surface methodology (RSM). The DP800 steel sheets were spot welded in straight lap and cross lap joint configuration using RSW. The relationship between the RSW parameters, tensile shear fracture load (TSFL) and nugget zone hardness (NZH) was established employing statistical regression analysis and validated using Analysis of Variance (ANOVA). The DP800 steel joints made using welding current of 5.0 kA, electrode pressure of 4.0 MPa, and welding time of 1.50 s displayed maximum STRAIGHT-TSFL of 21.7 kN, CROSS-TSFL of 17.65 kN, and NZH of 589 HV0.5 respectively.

Brittle failure of laterally loaded self-tapping screw connections for cross-laminated timber structures

The performance of structural timber connections is of utmost importance since they control the global response of the building. A ductile failure mechanism on the global scale is desirable, especially in the design of structures in seismic areas, where dissipative components in which ductile failure modes need to be ensured are considered. Therefore, the knowledge of possible brittle failure modes of connections is crucial. The paper investigates the brittle failures of laterally loaded dowel-type connections in cross-laminated timber subjected to tensile load in a lap joint configuration through experimental investigations and analytical estimations. A set of 13 different test series has been performed with fully threaded self-tapping screws of 8 mm diameter and different lengths (40 to 100 mm) in cross-laminated timber composed of 3 or 5 layers (layer thickness range from 20 to 40 mm), giving rise to the activation of different brittle failure modes at different depths. Plug shear was among the most typically observed failure modes. A previously proposed model for the brittle capacity was applied to the tested connections at the characteristic level. As shown by the performed statistical analysis, the existing model is not reliable and mainly unconservative. A very low performance is observed (CCC = 0.299), but with a good correlation (c = 0.750) for the tests in the parallel direction. Further research work is required to improve the current model predictions and to gain a better understanding of the underlying resisting mechanisms.

Application of machine learning approaches to predict joint strength of friction stir welded aluminium alloy 7475 and PPS polymer hybrid joint

Vehicle weight has been a critical concern in the aerospace and automobile industries for decades. Integrating dissimilar aluminium and polymer hybrid structures is beneficial for weight reduction without affecting structural performance. In the present work, aluminium alloy 7475 and polyphenylene sulfide (PPS) sheets were joined using the friction stir welding (FSW) technology in lap joint configuration. A series of FSW experiments have been performed by the design matrix developed using response surface methodology. Tensile lap shear strength (TLS) is calculated for each experimental run. In this study, an attempt has been made to assess the potential of machine learning algorithms to predict the TLS of the joint. It was found that the support vector machine (SVM) model with RBF kernel was the most effective for predicting the TLS. Furthermore, FSW process parameters are optimized by means of the desirability approach. The optimal set to attain maximum TLS is identified as the tilt angle of 2°, welding speed of 5.12 mm/min and tool rotational speed of 1185.92 r/min. Finally, a confirmation test was performed to validate the optimal set and the adequacy of the developed SVM model. From the confirmation test, the error percentage between experimental and prediction values is less than 5%. Metallographic analysis revealed that the joining mechanism is the macro and micromechanical interlocking assisted by chemical bonding.

CMT welding-brazing of al/steel dissimilar materials using cycle-step mode

Cycle step (CS) process is an advanced mode in cold metal transfer (CMT) welding technology, in which allows to set both the numbers of individual droplets and the pause time between cycles. This novel mode enables a reduced weld heat input and exhibits clear-rippled beads with high degree of reproducibility and high tolerance for workpiece gaps. In the present study, the CMT-CS process was used for welding-brazing of AA5052 aluminum alloy to galvanized low carbon steel with Al-5Si filler wire. A visually acceptable weld with clear fish-scale ripples was successfully obtained in a lap joint configuration. The influence of CMT cycle and interval time on the weld heat input, weld morphology, microstructure and mechanical properties of aluminum/steel dissimilar joints was explored. The results showed that the increase of CMT cycles led to the increase of weld heat input and it in turn increased the braze width and deceased the contact angle; while, the increase of interval time resulted in the decrease of weld heat input and it increased the weld spot spacing and decreased the density of the fish-scale ripples. The change of CMT cycle and interval time had very limited impact on the phase composition of the interfacial reaction layer. The joint strength basically increased with the increased CMT cycle; while, it increased first then deceased with the increased interval time. Two kinds of fracture modes were observed, namely interfacial shear failure and fusion zone failure. The bending angle decreased with the increase of weld heat input.