Welded Lap Joints Research Articles

Friction stir lap welding of Al to Mg assisted by ultrasound and a Zn interlayer

The friction stir lap welding (FSLW) joints of Al/Mg dissimilar alloys presented better formation and higher tensile shear strength when the Mg alloy was selected as the upper plate. Compared with Zn-added FSLW, the Zn-added FSLW assisted by ultrasound further enlarged the effective lap width, improved the mechanical interlocking and attained the finer disperse Mg-Zn intermetallic compounds in the stir zone. The maximum tensile shear strength of the joint assisted by ultrasound and a Zn interlayer reached 268 N/mm. This hybrid process with the ultrasound and the Zn interlayer provides a new method to obtain a high-quality Al/Mg dissimilar welding joint.

Nondestructive detection of defects in friction stir welded lap joints using computed tomography

Based on computed tomography (CT), a method is developed for nondestructive detection of defects in friction stir welded (FSW) joints. Plates of AA6061-T6 and AA1050 are welded to produce short lap welds. Utilized is spindle speed of 1600 RPM and fifteen different tool feeds ranging from 25 to 1000 mm/min (dubbed welded cases #1 to #15). These joints are CT-scanned and DICOM images are produced for digitally sectioned zones within the welded joints. To demarcate metallic zones from defects, a threshold cutoff value for Hounsfield Unit (HU) is needed to create 2D segmented masks determining the periphery between metal pixels from air pixels. Otsu's thresholding selection method from grey-level histograms is utilized for this purpose. These cutoff values are found to vary slightly from one welded joint to another. From the 2D masks, 3D representations of the welded joints revealed the shapes, locations, and volumes of the detected defects. Cross-sectioning of welds is employed as a destructive test to corroborate the locations and areas of CT-detected defects. The results of the defect area analysis from the CT-scans are compared to the results from optical images obtained by computer vision (CV) in a pixel-based analysis.

Reducing Intermetallic Compounds of Mg/Al Joint in Friction Stir Lap Welding

To reduce intermetallic compounds (IMCs) of Al12Mg17 and Al3Mg2 in Mg/Al friction stir lap welding joint, pin tip was plunged into the lower sheet at a small distance. Results showed that at a fixed welding speed of 50 mm/min, sound joints were obtained using rotating speeds from 750 to 500 rpm, and the IMCs zones were rather small. Cracks easily appeared inside IMCs inside onion ring and at lap interface. Therefore, reducing the IMC was beneficial for reducing the crack. Joint lap shear stress firstly increased and then decreased with decrease in the rotating speed. The maximum shear stress of 50.2 MPa was attained at a rotating speed of 500 rpm because of reduced IMC.

AZ31B/7075-T6 alloys friction stir lap welding with a zinc interlayer

Pure zinc foil was selected as an interlayer to improve the strength of the AZ31B Mg/7075-T6 Al dissimilar alloys friction stir lap welding joint. Compared with the conventional lap joint, the joint with the zinc interlayer has a higher effective sheet thickness, a larger effective lap width and a wider stir zone. The dispersed Mg-Zn intermetallic compounds are achieved instead of the continuous Mg-Al intermetallic compounds, improving the tensile shear load. The maximum fracture load of the joint with the zinc interlayer reaches 6.6 K N at the rotating velocity of 1000 rpm.

Dependence of Load Angle on Static Strength of Resistance Spot Welded Lap Joint under Combined Load Test

Dependence of Load Angle on Static Strength of Resistance Spot Welded Lap Joint under Combined Load Test

Shear Strength and Fracture Location of Dissimilar A6063 Aluminum Alloy and SUS430 Stainless Steel Lap Joint

In this paper, friction stir welding (FSW) was used to weld the dissimilar A6063 Aluminum/SUS430 stainless steel lap joint with various parameter setting in a welding process. The setting included a rotating speed between 125-750 rpm, a welding speed between the 25-175 mm/min and 0-5 degrees of tool tilted angle. The welded lap joints were systematically examined in regard of the tensile-shear strength, the fracture path, and microstructure. The experimental results were concluded as follows. The decrease in the welding heat input generated from the low rotating speed and the high welding resulted in decreasing of the shear strength. A degree of a tool tilted angle affected a shear strength, and a change in the strength came from the different rate in material combination at the joint interface. The increase in a tensile-shear strength occurred for specimens produced in 0-2 degrees of a tool tilted angle while 3-5 degrees affected in decreasing. The highest shear strength of 11,870 N was obtained when the lap joint was produced by the rotating speed of 500 rpm, the welding speed of 50 mm/min and the tool tilted angle at 2 degrees. The fracture path found in the specimen with the maximum shear strength was located in the Al stirred zone, not in the joint interface.

Interface Behavior and Lap Shear Properties of the 7075-T6 Al FSLW Joint Using a Tip-Threaded Pin

For the purpose of reducing the hook and increasing the effective sheet thickness of the friction stir lap welding joint, a tip-threaded pin was used to weld 3 mm-thick 7075-T6 aluminum alloy in this work. Material flow behavior, joint formation mechanism and lap shear properties of the lap joints were mainly discussed. Results showed that when using the tip-threaded pin, lap joint with nearly aequilate stir zone (SZ) along thickness and rather flat hooks were obtained. When using high rotating speeds, the width of the lower SZ exceeded that of the middle SZ. A void, which resulted from the material loss near the lap interface, was observed at the same time. With increasing the rotating speed, the lap shear failure load of the joint initially increased and then decreased, while the fracture mode changed from tensile fracture to shear fracture mode. The maximum failure load of 17661 N was attained for the joint without void at 850 rpm.

Calculation of welding tool pin width for friction stir welding of thin overlapping sheets

The fabrication friction stir welded lap joints with Al 7075-T6 sheets is examined with a wide range of tool pin geometries and dimensions while comparing microstructures, bonded area geometry, hardness, and fracture load during overlap shear testing. The tool pin geometry and features significantly affected the hook geometry and thus weld strength and failure mode. A hook feature is prone to forming when a larger diameter or helical threaded tool pins are used and is shown to deteriorate overlap shear fracture load by reducing the bonded ligament in the upper sheet. This hook feature can be controlled by removing the helical threads on the tool pin and replacing these with concentric grooves. The overlap shear fracture load is controlled by a combination of the sheet thickness, the width of the bonded area, and extent of the hook feature. These factors are captured in a model which was shown to provide good predictions of the fracture load and can be used to select tool pin sizes for varying overlapping sheet thicknesses.

Effect of pin length and welding speed on lap joint quality of friction stir welded dissimilar aluminum alloys

Hook and cold lap are the key factors which can affect the friction stir lap welding (FSLW) joint performance. Pin length has also an important effect on the morphologies of the hook and cold lap. Joints of AA7075 and AA2024 which are frequently used in aircraft structural elements mainly adopt lap joint configuration. The effect of pin length on dissimilar AA7075 and AA2024 lap joints has not been reported. Current paper intends to provide some further insights on this subject by discussing the relations among pin length, welding speed, and the corresponding tensile shear strength. It is interesting to find that the joint with high strength can be obtained when the harder material is placed as the upper sheet.

Numerical study of the influence of gap between plates on weld pool formation in arc spot welding process

Arc spot welding is a low heat input process that it is suitable for lap joint welding of thin plates. In a typical arc spot welding process, a controlled short-circuit transfer process, such as cold metal transfer, is used to control the weld pool and/or the heat input to the base metal. In this study, the arc spot welding process is modeled in two dimensions to clarify the metal transfer and weld pool phenomena during the process. In this model, the arc plasma is not calculated and a pseudo arc is set as the conductor of current between the wire and the base metal; the heat input from the arc plasma is given by a simplified heat input model. Droplet formation, droplet transfer, and weld pool formation are included in the proposed model, and the influence of the welding conditions is investigated numerically. First, welding parameters, such as current and the wire feeding speed, are obtained from experimental observation as the input parameters of the model. The calculation result of the weld shape shows good agreement with the experimental result with adjustment of the heat input parameters. The influence of the gap between thin plates is investigated numerically. When a gap exists between the plates, the weld shape differs from that without a gap, and the numerical result is similar to the experimental result. This result shows that the heat conduction between the plates strongly affects the weld shape.

Influence of variable processing conditions on the quasi-static and dynamic behaviors of resistance spot welded aluminum 6061-T6 sheets

The mechanical properties of the weld regions of a 6061-T6 resistance spot welded lap joint are determined. The change in mechanical properties resulting from RSW are linked to the changes observed in the microstructure. Processing currents and strain rates are varied to probe the effects of processing temperature at strain rates from 10−3 to 103 s−1. Results show that material strength decreases within the heat affected zone (HAZ) and fusion zone due to precipitate dispersion. Further, decreased ductility results at quasi-static strain rates from accelerated crack growth arising near voids formed during weld formation, but the short time scale at higher strain rates limits the ability for crack growth from these voids allowing the material to exhibit higher ductility. Overall, significant changes in the mechanical behavior across the weld resulting from a change in microstructure congruent with precipitate dispersion are apparent for all processing conditions.

On the Characteristics of Friction Stir Welding Lap Joint of Magnesium and Aluminum

On the Characteristics of Friction Stir Welding Lap Joint of Magnesium and Aluminum

EFFECT OF WELDING PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR LAP WELDED JOINTS FOR SIMILAR ALUMINUM ALLOYS (AA1100-H112 & AA6061-T6)

Friction stir welding (FSW) is a solid state welding used for joining similar and dissimilar aluminum alloys which are hard to weld by conventional fusion welding processes. In this study friction stir lap welding (FSLW) Joints are made for similar aluminum alloys (AA1100 to AA1100) and(AA6061to AA6061) sheets of 3mm thickness and those alloys have low to medium strength and have difference in melting temperature and other physical properties.FSLW processes were carried out by conventional technique. The friction stir lap welding of similar aluminum alloys was carried out by varying the welding parameters, such as tool rotation speeds (1000, 1250 and 1600pm) and travel speeds (35, 75 and 100mm) and pin length of ( 5.4 mm) with using cylindrical threaded pin geometry or profile. Many tests and inspections were performed such as X-Ray radiographic and tensile shear test .Microhardness and microstructure observations by using optical and SEM were carried out at the best welding parameters. The above tests were used to evaluate the weld quality and joint efficiency under different welding parameters. The best welding parameters appeared in FSLW were 1250rpm and travel speed 100 mm/min. It was found that higher hardness value was (94.38HV) for 6061-T6 and 49HV for 1100-H112 in stir zone for both FSLW joints of AA6061-T6 and AA1100-H112 and that decrease toward the HAZ and base metals of AA1100 and AA6061.

CFD를 이용한 티타늄 박판 레이저 용접 퍼징장치의 성능예측에 관한 연구

As titanium generally combines with oxygen at high temperatures to form a brittle region, the performance of a purging device for shielding welds in titanium welding is an important factor. Therefore, this study is focused on investigating the performance of a purging device. The nozzle length is changed using CFD (Computational Fluid Dynamics) to confirm the shielding performance of the purging device, and the shielding performance is predicted by the volume fraction of the shielding gas at laser beam focus. Next, the quality of the primary welding workpiece is checked. In addition, a hardness test and a tensile test are conducted to confirm the change in mechanical properties according to the nozzle length. A comparison of the calculated and measured results confirmed that a good weld can be obtained when the laser beam focus is more than 67% shielded in the lap-joint welding of a titanium thin plate.

Improving interface morphology and shear failure load of friction stir lap welding by changing material concentrated zone location

The morphology of lap interface is the key factor to affect the tensile properties of friction stir lap welding (FSLW) joint. Choosing the pin length as research object, effects of material concentrated zone (MCZ) location on interface morphology and shear failure load of FSLW joint were mainly investigated. Based on 2024-T4 aluminum alloy with 3 mm thickness, four tools were discussed, whose pin lengths are respectively 2, 3, 4, and 5 mm. Material flow models of four different tools are established to explain how MCZ locations over, on, and below lap interfaces influence the formation of hook and cold lap morphology. For both configurations A and B of FSLW joint, lap shear failure load curves changing with pin length exhibit a “N” shape under the special rotating speed varying from 850 to 1000 rpm. The highest lap shear load of 25,665.34 N is attained under the pin length of 3 mm and the rotating speed of 850 rpm. The typical shear and tensile fracture modes are found and the fracture morphologies present ductile fracture.

Dependence of Load Angle on Static Strength of Resistance Spot Welded Lap Joint in Combined Load Test

Dependence of Load Angle on Static Strength of Resistance Spot Welded Lap Joint in Combined Load Test

Computer analysis of thermal phenomena and deformation in lap joint welded by a laser beam

Laser welding technology is applied to many types of welded joints. The determination of the influence of technological parameters on the properties of resulting joint is a significant problem for technologists. Numerical estimation of the shape of the weld and its deformation is important in the initial stage of construction design. The paper concerns computer analysis of thermal and mechanical phenomena in laser welded lap joint made of austenitic steel. Three dimensional discrete model of analyzed lap joint is created in Abaqus FEA engineering software. Numerical analysis takes into account temperature dependent thermomechanical properties of austenitic steel. The movable heat source power distribution is modelled using Gaussian distribution. Computational model takes into account the gap between the joined plates. Temperature distribution in analysed joints is presented on the basis of performed numerical simulations. The shape and size of the fusion zone as well as deformation of the joint are estimated.

Investigation on Different Type of Defects, Temperature Variation and Mechanical Properties of Friction Stir Welded Lap joint of Aluminum Alloy 6101-T6

This paper is focused on the effect of friction stir welding parameters i.e. traverse speed and rotational speed on the quality of the weld. The defects formation such as tunneling defect, kissing defect and interface lifting defect arises due to these parameters were investigated. The experiment was performed on the vertical milling machine with a threaded probe tool designed according to the machine. The samples were welded at different rotational and traverse speeds and different type of defects was analyzed. Three levels of parameters have been chosen were 355 rpm, 500 rpm, 710 rpm and 16mm/min, 25mm/min, 40mm/min rotational speeds and traverse speeds respectively The weld morphology was analyzed using optical microscopy and field effect scanning electron microscopy (FESEM). The effect of heat due to temperature distribution was also studied. Two plates of same material i.e. Aluminum alloy AA6101-T6 having different thickness of 3mm and 5mm respectively were selected for this experimental study. The tensile shear test was performed to find the type and cause of failure during the test. The composition of material after and before the welding was compared using the Energy dispersive X-ray spectroscopy (EDX) analysis.

RETRACTED: Investigation of ductile fracture behavior of lap-welded joints with 460 MPa steel

Fractures in welded connections usually occurred at Earthquake. The lap-welded joints are an important type of welded connections in high strength steel structures. In this article, the ductile fracture behavior of lap-welded joints has been studied experimentally and numerically with 460 MPa steel. A series of coupon tests were used to determine two corresponding weld materials (ER55-D2 and ER55-G) mechanical properties. Two micromechanics models (void growth model and stress-modified critical strain models) had been calibrated by circumferentially notched tension specimens and calculated the fracture parameters numerically, which had been applied in predicting in five lap-welded joints. The experimental study showed that the fracture mode of 460 MPa lap-welded joints exhibited plastic damage under the tension tests. Numerical analysis of the fracture parameters also showed that the ductile fracture behavior of lap-welded joint with ER55-G was better. The study establishes an accurate numerical model for analyzing the ductile fracture behavior of Q460 high strength steel lap-welded joints that is applicable in predicting the fracture failure of welded steel structures.

Analysis of hot cracking during lap joint laser welding processes using the melting state-based thermomechanical modeling approach

Although lap joint laser welding is in great demand in practice, very limited numerical studies have been performed to investigate the hot cracking behavior in this welding configuration. This is because the traditional numerical methods are ineffective in simulating lap joint welding processes, which requires consideration of the discontinuous thermomechanical fields across the metal sheet interface prior to joining and the complicated contact conditions that evolve with material phase transitions during the welding process. The aim of the present study is to introduce a new irreversible melting state variable into the thermomechanical coupled computational model to account for the melting state effects on the mechanical and thermal properties at the welding interfaces. Under this framework, the calculation of thermal conductance and frictional coefficient depends on both temperature and the melting state variable. This allows the proper thermal and mechanical contact conditions to be captured at various melting states during the whole welding process. The proposed melting state-based model has been applied to the simulation of lap joint laser welding for the numerical investigation of the critical crack initiation location as well as the influence of various processing parameters on the cracking susceptibility and the cracking mechanism during heating-cooling processes.