Friction Stir Welded Lap Joints Research Articles

Effect of Tool Design and Process Parameters on Lap Joints Made by Right Angle Friction Stir Welding (RAFSW)

In recent decades, friction stir welding (FSW) has attracted extensive attention of academic and industrial sectors as the most considerable development in metal joining processes. FSW lap joint is an interesting alternative for rivets, fusion welds and bonding particularly in the transportation industry. In this paper, the effect of tool design and process parameters on the generated downward axial force and strength of AA6061-T6 lap joints is studied. The welds are made by a low-cost friction stir welding technique at right angle (RAFSW). The studied tool design parameters are shoulder diameter, shoulder groove depth, pin length, pin angle, pin base diameter and pin lead. Moreover, the effect of tool rotational speed, traverse speed, plunge depth and lap joint configuration is evaluated. The Taguchi method is used to design the experiments and artificial neural network (ANN) modeling is applied to predict the plunging force and the strength of the joints. The results indicate that a quality weld can be obtained at low downward axial forces during welding by proper selection of tool design and process parameters. It is identified that one can achieve a quality lap joint at traverse speeds as high as 1400 mm/min and downward axial forces as low as 3.2 kN by a low-cost RAFSW technique.

Evaluation of load-carrying capabilities of friction stir welded, TIG welded and riveted joints of AA2014-T6 aluminium alloy

PurposePresently, the materials used in light combat aircraft structures are aluminium alloys and composites. These structures are joined together through riveted joints. The weight of these rivets for the entire aircraft is nearly one ton. In addition to weight, the riveted connection requires a lot of tools, equipments, fixtures and manpower, which makes it an expensive and time-consuming process. Moreover, Al alloy is also welded using tungsten inert gas (TIG) welding process by proper control of process parameters. This process has limitations such as porosity, alloy segregation and hot cracking. To overcome the above limitations, an alternative technology is required. One such technology is friction stir welding (FSW), which can be successfully applied for welding of aluminium alloy in LCA structures. Therefore, this paper aims to compare the load carrying capabilities of FSW joints with TIG welded and riveted joints.Design/methodology/approachFSW joints and TIG welded joints were fabricated using optimized process parameters, followed by riveted joints using standard shop floor practice in the butt and lap joint configurations.FindingsThe load-carrying capabilities of FSW joints are superior than those of other joints. FSW joints exhibited 75 per cent higher load-carrying capability compared to the riveted joints and TIG-welded joints.Practical implicationsFrom this investigation, it is inferred that the FSW joint is suitable for the replacement of riveted joints in LCA and TIG-welded joints.Originality/valueFriction stir butt joints exhibited 75 per cent higher load-carrying capability than riveted butt joints. Friction stir welded lap joints showed 70 per cent higher load-carrying capability than the riveted lap joints. Friction stir butt joints yielded 41 per cent higher breaking load capabilities than the TIG-welded butt joints. Moreover, Friction stir lap weld joints have 57 per cent more load-carrying capabilities than the TIG-welded lap joints.

Microstructures and Properties of Friction Stir Welded Al-Cu Lap Joints

Friction stir welded lap joints of 5083 aluminum alloy plates with thickness of 2mm and T2 pure copper plates with thickness of 3mm were prepared, and the microstructures and properties of lap joints were investigated. The results showed that Al and Cu interdiffusion occurred at the interface of the lap joints, the grains in the stir zone of Al were refined and the microhardness increased sharply. The joint of Cu can be divided into four parts, including the nugget zone (NZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM). Using the optimum welding parameters (rotation speed of 900rpm and welding speed of 100mm/min), the lap joints were well formed. There were fewer welding defects and the average shear tensile force reached 3.155KN. Also, the ductile-brittle hybrid fracture occurred at the transitional zone of the advancing side of the Al plates. XRD results showed that intermetallic compounds (IMCS) mainly composed of Al2Cu and AlCu4 were produced in the interface of the lap joints during welding.

Evaluation on Microstructures and Mechanical Properties in Friction Stir Welded Lap Joints of Invar 42/SS 400

This study evaluated the microstructures and mechanical properties of friction stir welded lap joints. Invar 42 and SS 400 as experimental materials were selected, and friction stir welding was carried out at tool rotation speed of 200 rpm and welding speed of 100 mm/min. Applying the friction stir welding was notably effective to reduce the grain size of the stir zone, consequently, the average grain size of Invar 42 was reduced from 11.5 μm in the base material to 6.4 μm in the stir zone. Joint interface between Invar 42 and SS 400 showed a sound weld without voids and cracks, and the intermetallic compounds with Ll₂ type in lap joint interface were partially formed with size of 100 nm. Also, the hook, along the Invar 42 from SS 400, was formed at advancing side, which directly affected an increase in peel strength.

Mechanical Properties Optimization of Friction Stir Welded Lap Joints in Aluminium Alloy

This work focuses on the influence of the rotational and travel speed on the strength of AA 2024 T3 friction stir welded lap joints. Tensile tests were carried out on minispecimens extracted from different welding zones. A central composite design was applied to identify the relative importance of the variable factors’ effects and their interaction on yield/ultimate strength and elongation for both the heat affected-zone (HAZ) and nugget zone. Surface methods and gradient algorithms were used to optimize the yield strength of the joints. Shear and microhardness tests were executed to achieve a more complete mechanical characterization.

Improving mechanical properties of composite/metal friction stir lap welding joints via a taper-screwed pin with triple facets

Material flow rates at the horizontal and vertical directions were markedly increased by a taper-screwed pin with triple facets. A stationary shoulder could prevent plasticized materials overflowing out of the weld and make them backflow into the nugget zone, achieving good surface integrity. The short carbon fiber-reinforced poly-ether-ether-ketone and the AA2060-T8 were tightly joined, and the carbon fibers were dispersedly distributed at the nugget zone, which attributed to the effective load transfer effects and then improved the joint strength. The tensile shear strength reached 18 MPa. The combination of the stationary shoulder tool system and plunging the taper-screwed pin with triple facets into the composite was feasible and effective to improving mechanical properties of composite/metal friction stir lap welding joints.

Influence of Rotation Speed on Microstructure and Mechanical Properties of Friction Stir Lap Welded Joints of AA 6061 and Ti6Al4V Alloys

Three-mm-thick AA 6061 plate and 2-mm-thick Ti6Al4V plate were friction stir lap welded using a W-Re pin tool. Defect-free joints were obtained at various rotation speeds ranging from 800 to 1400 rpm with a constant welding speed of 100 mm/min. The influence of rotation speed on the microstructure and mechanical properties of the Al/Ti friction stir lap welding (FSLW) joints was investigated. At low rotation speed within 1000 rpm, the obtained joint has no obvious mechanical Al/Ti intermixing at the interface. However, a significant mechanical mixture of Al and Ti alloys accompanied by hooks could be found in the joint welded at a rotation speed over 1000 rpm. Only diffusion layer was observed in the joint obtained at low rotation speed. Further, IMCs could be found in the Al/Ti mixture and hook when the rotation speed increased to 1400 rpm. The highest microhardness was measured at the interface due to the formation of IMCs. The tensile shear load of the welded joints reached the maximum at 1000 rpm and the specimens failed along the interface during the test.

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.

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.

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.

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.

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.

Effect of Thread and Rotating Speed on Material Flow Behavior and Mechanical Properties of Friction Stir Lap Welding Joints

This study focused on the effects of thread on hook and cold lap formation, lap shear property and impact toughness of alclad 2024-T4 friction stir lap welding (FSLW) joints. Except the traditional threaded pin tool (TR-tool), three new tools with different thread locations and orientations were designed. Results showed that thread significantly affected hook, cold lap morphologies and lap shear properties. The tool with tip-threaded pin (T-tool) fabricated joint with flat hook and cold lap, which resulted in shear fracture mode. The tools with bottom-threaded pin (B-tool) eliminated the hook. The tool with reverse-threaded pin (R-tool) widened the stir zone width. When using configuration A, the joints fabricated by the three new tools showed higher failure loads than the joint fabricated by the TR-tool. The joint using the T-tool owned the optimum impact toughness. This study demonstrated the significance of thread during FSLW and provided a reference to optimize tool geometry.

Interface characteristic and tensile property of friction stir lap welding of dissimilar aircraft 2060-T8 and 2099-T83 Al–Li alloys

Here, to reduce or eliminate the disadvantages induced by traditional riveting or laser welding for joining dissimilar 2060-T8 and 2099-T83 alloys, friction stir lap welding (FSLW) was performed. Sound lap joint featured by the skin of 2060-T8 alloy and the stringer of 2099-T83 alloy was obtained. Under the welding speed of 200 mm/min, the defect-free joint with optimal effective lap width and effective sheet thickness was attained. Tensile properties of the skin of 2060-T8 alloy of all the FSLW joints from 50 to 400 mm/min were not affected by hook or cold lap, which were higher than those by double-sided laser beam welding. The maximum tensile strength of 495.4 MPa and elongation of 10% of the FSLW joint were obtained at the welding speed of 200 mm/min, rotational velocity of 800 rpm, and plunge depth of 0.1 mm, which were equivalent to 93.1 and 80% of the 2060 alloy, respectively.

A study on the effect of cooling on microstructure and mechanical properties of friction stir-welded AA5086 aluminum butt and lap joints

In this paper, the effect of water cooling on mechanical properties and microstructure of AA5086 aluminum joints during friction stir welding is investigated. For doing so, the mechanical and microstructural behavior of samples welded both in air and in water was analyzed. Tests were performed involving both butt and lap welds and the results were compared. The effect of rotational speed at constant feed rate of 50 mm/min and changing rotational speed ranging from 250 to 1250 r/min was investigated. The results showed a significant change in the tensile behavior of the butt-welded specimens due to water cooling. In addition, welding was performed at constant spindle speed of 800 r/min and various traverse speeds (25 mm/min to 80 mm/min) to determine the effect of feed rate. The strength increases at first, but then decreases dramatically along with the feed rate which is due to the occurrence of a groove defect. Results showed some generally positive impacts of water cooling which are discussed in terms of tensile results, hardness distributions and microstructure analysis.

Friction stir weld-bonding defect inspection using phased array ultrasonic testing

Weight reduction is an important driver of the aerospace industry, which encourages the development of lightweight joining techniques to substitute rivet joints. Friction stir welding (FSW) is a solid-state process that enables the production of lighter joints with a small performance reduction compared to the base material properties. Increasing the FSW lap joint performance is an important concern. Friction stir weld bonding is a hybrid joining technology that combines FSW and adhesive bonding in order to increase the mechanical properties of FSW lap joints. FSW and hybrid lap joints were produced, using 2-mm-thick AA6082-T6 plates and a 0.2-mm-thick adhesive layer. Defect detection using the non-destructive test, phased array ultrasonic testing (PAUT), has been made. Microscopic observations were performed in order to validate the phased array ultrasonic testing results. Lap shear strength tests were carried out to quantify the joint’s quality. PAUT inspection successfully detected non-welded specimens but was not able to distinguish specimens with major hook defects from specimens correctly weld bonded with small hook defects.