Friction Stir Lap Research Articles

Fractal Dimension Characterization of Joint Surface Morphology on Dissimilar Friction Stir Lap Welding of Al/Mg.

The joint surface of the 1060 aluminum and AZ31 magnesium alloy was prepared through friction stir lap welding (FSLW) under different welding process parameters. The joint surface was characterized three-dimensionally using a three-dimensional (3D) optical profiler, and the coordinate data were obtained. The fractal dimension of the joint surface was calculated by the box-width transformation method using a MATLAB program. Furthermore, the influence of the welding process parameters on the fractal dimension of the joint surface was studied. The response surface model was established based on the principle of central composite design (CCD), and analysis of variance (ANOVA) was carried out to test the accuracy of the response surface. The results showed that the joint surface morphology had fractal characteristics, and the fractal dimension could be used as an index to characterize the quality of the joint surface. The change of the welding process parameters had a great impact on the fractal dimension of the joint surface, the interaction between the parameters was small, and the fitting accuracy of the response surface model was high. The fractal dimension of the joint surface decreased with the increase in the welding and rotational speeds and the effect of the rotational speed was more significant.

Effect of Tilt Angle and Pin Depth on Dissimilar Friction Stir Lap Welded Joints of Aluminum and Steel Alloys.

Automobile, aerospace, and shipbuilding industries are looking for lightweight materials for cost effective manufacturing which demands the welding of dissimilar alloy materials. In this study, the effect of tool rotational speed, welding speed, tilt angle, and pin depth on the weld joint were investigated. Aluminum 5052 and 304 stainless-steel alloys were joined by friction stir welding in a lap configuration. The design of the experiments was based on Taguchi’s orthogonal array for conducting the experiments with four factors and three levels for each factor. The microstructural analysis showed tunnel defects, micro voids, and cracks which formed with 0° and 1.5° tilt angles. The defects were eliminated when the tilt angle increased to 2.5° and a mixed stir zone was formed with intermetallic compounds. The presence of the intermetallic compounds increased with the increase in tilt angle and pin depth which further resulted in obtaining a defect-free weld. Hooks were formed on either side of the weld zone creating a mechanical link for the joint. A Vickers hardness value of HV 635.46 was achieved in the mixed stir zone with 1000 rpm, 20 mm/min, and 4.2 mm pin depth with a tilt angle of 2.5°, which increased by three times compared to the hardness of SS 304 steel. The maximum shear strength achieved with 800 rpm, 40 mm/min, and a 4.3 mm pin depth with a tilt angle of 2.5° was 3.18 kN.

Microstructure and mechanical properties of Al/steel dissimilar welds fabricated by friction surfacing assisted friction stir lap welding

Al/steel dissimilar welds were obtained by friction stir lap welding (FSLW) with an Al interlayer, which was fabricated by friction surfacing (FS). In present study, the tool pin was totally plunged into the Al plate and interlayer without stirring steel, which avoided the tool wear. The Al plate and interlayer were remarkably intermixed as pin length increased. A diffusion layer, instead of the intermetallic layer, was found at the Al/steel interface, indicating the enhanced atomic migration and related interfacial bonding. The maximum failure load of the joints of 2.8kN was reached when the 2.5mm pin tool was used. The heterogeneous microstructure, which was caused by the intermixing, was responsible for the fracture, according to the fracture profiles. Necking and dimples were depicted from the fractographies, indicating that the joints were failed by plastic fracture.

Effective joining of Mg/Ti dissimilar alloys by friction stir lap welding

Abstract Mg/Ti dissimilar alloys were lap welded by friction stir lap welding (FSLW) with the tool pin slightly penetrating into the bottom Ti alloy during the welding process. The joint microstructure, mechanical properties and fracture behavior were systematically investigated. The metallurgical bonding associated with an Al enrichment layer and the mechanical interlocking bonding relying on the pin marks on the bottom Ti alloy surface were formed at the lap interface. Decreasing the welding speed was beneficial to increasing the interfacial bonding strength due to the widened Al enrichment layer and the improved mechanical interlocking resulting from the denser pin marks. When the welding speed decreased to 80 mm/min from 120 mm/min, the fracture location transferred to the upper Mg alloy from the lap interface. The maximum joint tensile-shear strength was 424 N/mm and the joint efficiency reached 89.2 % with respect to the base Mg alloy. FSLW technique provides an effective method to acquire a high-quality joint of Mg/Ti dissimilar alloys.

Effect of Process Parameters on Defect Features and Mechanical Performance of Friction Stir Lap Welded AA6063 and ETP Copper Joints

The effect of process parameters such as tool rotational speed and tool traverse speed on mechanical properties of AA-6063 and ETP Cu lap joint is investigated. At present, Friction Stir Welding is being employed to join dissimilar metals. However, the difference in the physical properties of the base metals makes it difficult to join these metals. The present study investigates the effect of using a compatible intermediate layer on weld strength. Different joint defects and their effect on joint strength has been discussed. The experiments were conducted with tool rotational speed of 800, 1000 and 1200 rpm each and with tool traverse speeds of 10, 15 and 20 mm/min. The dissimilar metals are successfully lap welded with fair tensile strength. The effect of process parameters on weld strength and defect formation is discussed

Friction Stir Lap Welding 0.8-mm-Thick 2024 Aluminum Alloy with the Assistance of Stationary Shoulder

In this work, 0.8-mm-thick 2024 aluminum alloy was friction stir lap welded with the assistance of a stationary shoulder system. The joint surface formation, microstructure and mechanical properties of the welded joints were studied. The results showed that sound joints without defect could be obtained at a wide parameter range because stationary shoulder increased the material flow during welding. The stationary shoulder decreased the joint roughness from 125.5 to 58.9 µm. A thickness reduction of 4% was achieved at a welding speed of 200 mm/min. The joint fabricated by the stationary shoulder system had superior lap shear properties compared to the joint fabricated using the conventional tool. A high failure load of 7440 N was achieved at welding speed of 200 mm/min. The joint presented tensile fracture mode and the fracture morphology showed typical ductile fracture.

Improving the Mechanical Property of Dissimilar Al/Mg Zn‐Added Ultrasound‐Assisted Friction Stir Lap Welding Joint by Back Propagation Neural Network–Gray Wolf Optimization Algorithm

Process parameters of rotating velocity, welding speed, Zn interlayer thickness, and ultrasound power are optimized by the hybrid of back propagation neural network (BPNN) and gray wolf optimization algorithm (GWOA) to obtain a high‐quality Zn‐added ultrasound‐assisted friction stir lap welding joint of 7075‐T6 Al/AZ31B Mg dissimilar alloys. The results state that the prediction accuracy of the trained BPNN model is acceptable. The optimal process parameters combination is obtained by the GWOA which is combined with the trained BPNN. The verification tests are performed under the executable optimal solution, which consists of the rotating velocity of 1054 rpm, the welding speed of 54 mm min−1, the Zn interlayer thickness of 0.05 mm, and the ultrasound power of 1568 W. The tensile shear load of the joint reaches 9.05 kN, and the strength is 11.8% larger than that of the reported optimal joint. The artificial intelligence optimization method of GWOA combined with BPNN can accurately predict and optimize the joint strength, which has great time and economic advantages.

Cladding thick Al plate onto strong steel substrate using a novel process of multilayer-friction stir brazing (ML-FSB)

Friction stir brazing (FSB) using a pinless tool together with a braze was developed to extend bond area over friction stir lap welding. When using a large pinless tool of Ø40 mm to clad 10 mm thick 5083Al plate to 16Mn steel by FSB with Zn braze, the thermomechanical effect was sufficient to achieve wetting on Al side by dissolving Al into molten Zn, but joint could not be formed due to poor wettability on steel side. To enhance mechanical disruption of oxide film on the steel, multilayer FSB (ML-FSB) process was proposed by adding a thin (3 mm thickness) and soft aluminum sheet as interlayer. The first FSB pass created bonding between the thin interlayer and steel substrate with 4.7 μm thick FeAl3 without Zn residue, having 55 MPa shear strength. The second FSB pass created bonding between the thin interlayer and thick 5083Al clad with a diffusion zone with a little Zn, having 50 MPa shear strength. This work provided a new way to fabricate “thick clad” layered composite with “strong substrate”, and suggested that mechanical route for strong substrate and metallurgical route (eutectic reaction) for Al for removing oxide film should be preferential and available in FSB.

Microstructural Evolution and Mechanical Behavior of Friction-Stir-Welded DP1180 Advanced Ultrahigh Strength Steel

Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded Ac3, and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.

Friction stir lap welding of plastic to metal using adjustable tool

An OX horn type interlocking joint of MC Nylon-6 (top sheet) and AMXS6020 Mg alloy (bottom sheet) with satisfactory mechanical properties had been obtained by friction stir lap welding (FSLW) using an adjustable tool. The adjustable tool produced the good surface appearances and mechanical interlocking interfaces with low shoulder rotation speeds and high probe rotation speeds. The Mg alloy around the probe was stirred into the melted MC Nylon-6 zone during the FSLW process to form OX horn shape which bended toward the joint centre. The influences of welding parameters on Mg alloy horns formation, tensile shear strength and fracture morphology were investigated. Mechanical interlocking induced by the Mg alloy horns contributed to the main joining mechanism.

Improving Joint Morphologies and Tensile Strength of Al/Mg Dissimilar Alloys Friction Stir Lap Welding by Changing Zn Interlayer Thickness

The pure Zn foils with different thicknesses (0.02, 0.05, 0.1, 0.2 and 0.3 mm) were selected as interlayers to improve the quality of friction stir lap welding joint of 7075-T6 Al and AZ31B Mg dissimilar alloys. The effects of the interlayer thickness on joint formation, microstructure and tensile strength were analyzed. The results displayed that the maximum length of the boundary between stir zone (SZ) and thermo-mechanically affected zone in lower plate was obtained by the addition of the Zn interlayer with 0.05 mm thickness. The Mg–Zn intermetallic compounds (IMCs) were discontinuously distributed in the SZ, replacing the continuous Al–Mg IMCs. The size of Mg–Zn IMCs increased with the increase in the thickness of the Zn interlayer. The maximum tensile shear strength of 276 N mm−1 was obtained by the addition of 0.05 mm Zn foil, which increased by 45.6% of that of the joint without the Zn foil addition.

Effect of tool tilt angle on strength and microstructural characteristics of friction stir welded lap joints of AA2014-T6 aluminum alloy

Abstract Friction stir welding (FSW) has been extensively adopted to fabricate aluminium alloy joints by incorporating various welding parameters that include welding speed, rotational speed, diameters of shoulder and pin and tool tilt angle. FSW parameters significantly affect the weld strength. Tool tilt angle is one of the significant process parameters among the weld parameters. The present study focused on the effect of tool tilt angle on strength of friction stir lap welding of AA2014-T6 aluminium alloy. The tool tilt angle was varied between 0° and 4° with an equal increment of 1°. Other process parameters were kept constant. Macrostructure and microstructure analysis, microhardness measurement, scanning electron micrograph, transmission electron micrograph and energy dispersive spectroscopy analysis were performed to evaluate the lap shear strength of friction stir lap welded joint. Results proved that, defect-free weld joint was obtained while using a tool tilt angle of 1° to 3°. However, sound joints were welded using a tool tilt angle of 2°, which had the maximum lap shear strength of 14.42 kN and microhardness of HV 132. The joints welded using tool tilt angles of 1° and 3° yielded inferior lap shear strength due to unbalanced material flow in the weld region during FSW.

Effect of Zn-brazed-interface on microstructures and mechanical properties of dissimilar 2A12/AZ31 alloys friction stir lap welds

Abstract To improve the mechanical behavior of dissimilar Al/Mg joints, Zn foil, as a brazing filler, was added to the Al/Mg interface when conducting friction stir lap welding with 2A12/AZ31 alloys. Results showed that new phases, such as Mg0.97Zn0.03, Al0.403Zn0.597 and MgZn2, rather than the continuous brittle Al12Mg17 intermetallic compound (IMC), are formed in the brazing area. At a rotation speed of 375 rpm and a travel speed of 30 mm/min, the tensile shear load of the hybrid joint reached 5.5 kN through a Zn-brazed interface, thereby preventing the formation of the continuous brittle IMC Al12Mg17 and enlarging the overlap bonding area.

Effect of leading ultrasonic vibrations on the welding forces of friction stir lap welding

Influence of leading ultrasonic vibrations on the process forces in the friction stir lap welding of AA 6061-T6 with and without ultrasonic vibrations is investigated at varied welding speeds. The axial force, traverse force, and tool torque in the processes are determined by adopting a recently developed method that uses electrical signals of the servo motors and main spindle AC motor of the friction stir welding machine during the welding process. It is found that the exerted ultrasonic vibrations decrease the welding forces without compromising the mechanical properties of welds. The effect of ultrasonic vibrations on traverse force is more pronounced than that on the tool torque and axial force. Force measurements at different welding speeds indicated that the axial force and traverse force varied significantly with travel speed of tool. Not much difference is found in the tool torque variation. With ultrasonic vibrations, the reduction in welding force in different directions is affected differently by welding speed. The ultrasonic effect on welding forces is found to be governed by the travel speeds of both the tool and workpiece.

Study on Low Axial Load Friction Stir Lap Joining of 6061-T6 and Zinc-Coated Steel

Friction stir lap joining of 6061-T6 and zinc-coated steel was performed using a high rotation speed and small tools with different pin lengths. During the welding process, the average axial force ranged from 0.2 to 1.1 kN, which is smaller than that for conventional friction stir welding. Satisfactory surface formation was achieved using a pinless tool and smaller plunge depth. The highest failure load of 2.26 kN was achieved for a pin length of 0.3 mm, plunge depth of 0.3 mm, and welding speed of 50 mm/min. The specimen fractured at the advance side of the 6061-T6 base metal. A continuous and compact interface layer with a thickness of 5.2 μm was formed. The main component of the intermetallic compound at the interface was Fe4Al13. The intermetallic compound was tightly connected and bound to the steel galvanized sheet and aluminum side.

Dissimilar friction stir lap welding of AA 6082 - Mg AZ31: Force analysis and microstructure evolution

AA6082 T6 and MgAZ31 were successfully friction stir lap joined under various regimes of tool rotational and welding speeds. Force evolution as well microstructural evolution have been presented and discussed within the paper. All joints are characterized by the presence of three main metallurgical zones: nugget zone (NZ), dynamic recrystallized zone (DRZ) and interpenetrating feature zone (IPF). Furthermore, intermetallic compounds like Al12Mg17 and Al3Mg2 have been detected inside the NZ. The results of the forces analysis showed a non-univocal trend of the force components respect to the process parameters due to contrasting phenomena dictating material hardening and softening in the investigated processing window.

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.

Corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding in alkaline solution

This study was done to evaluate the nugget zone (NZ) corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding (FSLW) in a solution of 0.015 mol/L borax (pH 9.3). To this end, dissimilar copper/ brass plates were welded with two dissimilar heat inputs (low and high) during the welding procedure. The high and low heat inputs were conducted with 710 r/min, 16 mm/min and 450 r/min, 25 mm/min, respectively. Using open circuit potential (OCP) measurements, electrochemical impedance spectroscopy (EIS) and Tafel polarization tests, the electrochemical behavior of the specimens in borate buffer solution was assessed. With the help of scanning electron microscope (SEM), the morphology of welded specimen surfaces was examined after immersion in the test solution. According to the results, the NZ grain size and resistance improvement reduced due to the nugget zone corrosion with a decreased heat input. The results obtained from Tafel polarization and EIS indicated the improved corrosion behavior of the welded specimen NZ with a decrease in the heat input during the welding process unlike the copper and brass metals. Furthermore, an increased heat input during the welding process shows a reduction in the conditions for forming the passive films with higher protection behavior.

Effect of reverse dual rotation process on properties of friction stir welding of AA7075 to AISI304

Abstract The friction stir lap welding of AISI304 stainless steel to AA7075 aluminium alloy was investigated using the conventional friction stir welding (C-FSW) and the reverse dual rotation friction stir welding (DR-FSW) processes. In order to reduce the heat input, a dual rotation tool with a lower shoulder rotating speed was used. The results showed that both processes provide welds with excellent appearance and free of internal defects. The use of the DR-FSW process with the tool shoulder rotating reversely at low speed results in larger grain refinement in the nugget and less change in the microstructure of the aluminium alloy than using the C-FSW. The use of DR-FSW process at low speed of rotation allows to reduce the amount of intermetallic compounds in the welding interface, but does not prevent their formation. Although DR-FSW welding exhibits tensile strength superior to that achieved with the conventional process (C-FSW), both exhibit brittle behaviour with fracture at the weld interface.

Investing Tensile Strength of Aluminium Alloy 6061 for Multi Line Friction Stir Lap Welding

Investing Tensile Strength of Aluminium Alloy 6061 for Multi Line Friction Stir Lap Welding