Friction Stir Lap Welding Research Articles

Improved Mechanical Properties of SUS304/AA5083 Dissimilar Joint by Laser Ablation Pretreatment in Vortex- Friction Stir Lap Welding

To obtain a high-quality Al/steel dissimilar joint, a micro-groove-assisted vortex-friction stir lap welding (MG-VFSLW) process was developed. Through prefabricating micro-grooves on the steel plate surface by laser ablation, high-quality mechanical interlock and metallurgical bonding were obtained simultaneously in the MG-VFSLW process. The weld formation, interface microstructure, mechanical properties, and failure mode in MG-VFSLW were studied by comparing them with those in VFSLW. The results showed that a line load of the AA5083/SUS304 dissimilar joint up to 485.9 N/mm was obtained by MG-VFSLW, which is 40.1% higher than that in VFSLW. Remarkable intermetallic compound layers and cracks were found in VFSLW. The cracks were closely related to the oxides on the interface. However, in MG-VFSLW, cross-riveting aluminum rivets and steel rivets were formed on the interface due to the micro-grooves and flashes made by the laser ablation. Good metallurgical bonding was also formed between AA5083 and SUS304. No remarkable intermetallic compound layers and cracks occurred. During the tensile shear tests, the aluminum rivets were cut off and some dimples and tear ridges existed on the fracture surface. In short, the high strength of the Al/steel lap joint in MG-VFSLW was attributed to the high-quality mechanical interlock and metallurgical bonding.

Strengthening characteristic and mechanism of AlCoCrFeNi high-entropy alloy particles for Al-Cu dissimilar friction stir lap welded joint

Regarding the light-weight welding application, the strategy of non-tool penetration into lower hard sheet is considered as a promising dissimilar friction stir lap welding (FSLW) process for restriction of tool wear and reduction of welding force. In order to further improve the mechanical properties of the lap joint for such a case, AlCoCrFeNi high-entropy alloy (HEA) particles were selected as reinforcement for the Al-Cu dissimilar FSLW. A novel approach to incorporating HEA particles into lap weld, where a HEA particle-reinforced Al matrix was pre-prepared by FSLW, was proposed to prevent the overflow of particles from weld effectively during Al-Cu FSLW. The strengthening characteristic and mechanism of the HEA particles were systematically explored in this paper. Microstructural analyses indicate that the spherical HEA particles with large size contribute to the grain refinement via particle-stimulated nucleation mechanism, furthermore, nanoscale particles (Al3Ni and Al13Fe4) are formed adjacent to the HEA particles in the Al matrix. The induced grain refinement strengthening and secondary phase strengthening by the HEA particles are responsible for the significant improvement in the mechanical properties of Al-Cu lap joint. This study provides a technological approach and a theoretical foundation for the high-quality dissimilar FSLW used in light-weight manufacturing field.

Achievement of high-quality joints and regulation of intermetallic compounds in ultrasonic vibration enhanced friction stir lap welding of aluminum/steel

The lap joints of 6061-T6 aluminum alloy/Q235 steel were obtained by conventional friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW). The weld forming characteristics and microstructure differences of the joints with or without ultrasonic were compared and analyzed, and the effects of acoustic energy on the mechanical properties and intermetallic compounds (IMCs) layer of the joints were revealed. The results showed that ultrasonic vibrations could effectively improve the weld surface forming quality, increase the volume of plastic flow materials, significantly improve the welding speed of defect-free joints and expand the welding process window. The additional ultrasonic vibration can refine the grain structure of the weld nugget zone and the thermo-mechanically affected zone, improve the mechanical properties of the lap joints, and change the joint's fracture position and fracture mechanism. The assistance of acoustic can significantly enhance the mechanical interlocking ability of the center of the lap interface and change the type and thickness of the IMCs layer.

Influence of welding environment on joint characteristics of friction stir lap welded AA7475-PPS polymer hybrid joints

This study explores the impact of air and underwater welding environments during friction stir lap welding (FSLW) of AA7475 and Polyphenylene-sulfide (PPS) polymer dissimilar materials. Response surface methodology-based desirability function approach was used to identify the optimal FSLW process parameter set in an underwater environment. The joint characteristics, such as microstructure, mechanical properties of the joints, and physicochemical changes in the polymer with the air and underwater FSLW, were compared. The maximum tensile lap shear strength was attained as 12 MPa and 19 MPa in the air and underwater weld environment, respectively. Microstructural examination revealed that the bonding mechanism in FSLWed hybrid joint in both weld environment conditions is macro/micromechanical interlocking. Based on the findings of a Differential Scanning Calorimetry study, the FSLW technique causes the loss of crystallinity in the polymer. The study found that the welding environment significantly impacted air voids formation, tensile characteristics, and loss of crystallinity in polymers.

Friction stir lap welding between A6061/SPC270 thin sheets using welding tool with scroll shoulder

Dissimilar materials welding between A6061 and SPC270 thin sheets was performed through friction stir lap welding and the effects of welding tool shape and clearance were investigated. The welding process was carried out on the 3-axis vertical machining center without tilt angle, using welding tools with flat or scroll shoulder surfaces. The highest tensile shear strength of 208.2 MPa using the flat shoulder was achieved under tool rotation speed of 2000 rpm and welding speed of 500 mm/min. Groove-like defects were found at the advancing side of this welding joint, which was thought to be caused by the deficiency of plastic material flow. Scroll shoulder improved the plastic material flow of aluminum alloys and weld surface without defects. However, cavities were formed in joints welding with a clearance of 0.1 mm near the interface between A6061 and SPC270. Reduction of clearance suppressed the formation of cavities and tensile shear strength of 217.9 MPa was achieved with the clearance of 0 mm. The welding interface was observed by SEM and TEM for microstructure investigation. Welding interface temperature during FSLW was measured and the factors for welding strength variation were also discussed in this paper.

Interface structure and mechanical properties of Fe/Al dissimilar lap joints formed by friction stir welding using an adjustable tool

Friction stir welding (FSW) of aluminum alloy and steel using an adjustable tool was carried out, which can effectively control the thickness and uniformity of the IMC layer. The continuous and uniform IMC layer as thin as about 0.4 µm was obtained, owing to the strong material flow introduced by the adjustable probe. The strength of the welded joints increased as the thickness of the IMC layer decreased in the range of 0.9 µm to 0.4 µm. However, when the thickness of the IMC layer was below 0.4 µm, it became nonuniform and discontinuous, decreasing the joint properties. In this study, a high-strength Fe/Al dissimilar lap FSW joint was obtained, ascribed to the more uniform and continuous thin IMC layer.

Acoustic effect on the joint quality and process of friction stir lap welding of aluminum to steel

To gain a high strength-to-weight ratio and economic viability for multiple industrial applications, the Al and steel need to be joined successfully. In the present work, we used conventional friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW) techniques to obtain high-strength industrial-grade dissimilar joints of Al and steel. The effects of acoustic energy on the joint quality and welding process were investigated. Macrographs of the joints revealed that ultrasonic vibrations could effectively promote the material flow and increase the mixing degree and width of the Al/steel interface. Steel strips' fragmentation and intermixing with the Al substrate were enhanced under ultrasonic effects. The tool torque, axial force, and spindle power were significantly decreased with ultrasonic vibration. Acoustic assistance was found beneficial to increase the joints’ failure load and change the fracture mechanism. The microhardness of acoustically treated regions was found to be higher compared to its counterparts. The thinning of the brittle intermetallic compounds (IMCs) layer at the interface of the UVeFSW joint was caused by decreased peak temperature during welding. In UVeFSW, when the welding speed was 50 mm/min, the maximum failure load of the joint was obtained under the joint action of the macro interlocks (interface zone), the thinner IMCs layer, and the micro interlocks (laminated structure). When the welding speed was 100 mm/min, the failure load of the joint was improved by 25.8% compared with conventional FSW.

The microstructure and mechanical properties of aluminum/steel welded joint by FSLW

Friction stir lap welding experiments between 6061 aluminum alloy and DP590 dual-phase steel plates were carried out. The effects of welding parameters and the addition of Cu foil interlayers with 0–0.3 mm thickness on the microstructures and mechanical properties of the lap joints were investigated. The shear strength of the joint reached the maximum value of 5337 N and showed a mixed ductile-brittle fracture mode when the welding speed, the rotating speed, and the thickness of the Cu foil intermediate layer were set to 80 mm/min, 900 rpm, and 0.1 mm, respectively. The plastic Al2Cu and AlCu intermetallic compounds formed through Al and Cu reaction at the aluminium alloy/steel interface play a beneficial role in the Cu-added joint strength.

Influence of welding parameters on the interface temperature field of TC4 titanium alloys/304 stainless steel friction stir lap joints

Abstract The welding parameters optimization of TC4 titanium alloys/304 stainless steel (TC4/304 SS) by friction stir lap welding (FSLW) based on orthogonal test was researched. The results show that when the rotating speed was constant, the area of the high temperature zone and the peak temperature decreased with the increase of the traversing speed; when the traversing speed was constant, the area of the high temperature zone and the peak temperature increased with the increasing rotating speed. Among them, under the condition of low heat input, the interface temperature was about 912 °C, the material at the interface cannot fully react, and there was no formation of a large amount of brittle and hard intermetallic compounds; under the condition of medium heat input, the interface temperature was about 930 °C, this temperature caused a large amount of brittle and hard intermetallic compounds at the interface; under high heat input, the interface temperature was about 975 °C, a large number of intermetallic compounds were not formed at the interface.

A novel seal-flow multi-vortex friction stir lap welding of metal to polymer matrix composites

The friction stir lap welding (FSLW) of metal to polymer is a challenging work due to the unavoidable polymer overflowing. Facing this problem, a novel seal-flow multi-vortex friction stir lap welding (SM-FSLW) technology based on the subversively-designed multi-step pin was put forward. Choosing 7075 aluminum alloy and short glass fiber-reinforced polyether ether ketone (PEEK) as research subjects, the welding temperature, material flow, formation and tensile shear strength of dissimilar materials lap joint under the SM-FSLW were studied and compared with those under traditional FSLW based on the conical pin. The multi-step pin rather than the conical pin effectively hindered the polymer overflowing due to the formation of vortexes by the step, thereby attaining a joint with a smooth surface. Compared with traditional FSLW, the SM-FSLW obtained the higher welding temperature, the more violent material flow and the larger area with high flow velocity, thereby producing the macro-mechanical and micro-mechanical interlockings and then heightening the joint loading capacity. The tensile shear strength of lap joint under SM-FSLW was 27.8% higher than that under traditional FSLW. The SM-FSLW technology using the multi-step pin provides an effective way on obtaining a heterogeneous lap joint of metal to polymer with the excellent formation and high strength.

Similar and dissimilar lap friction stir welding of titanium alloys: on the elimination of the hook defect

Similar and dissimilar lap friction stir welding of titanium alloys: on the elimination of the hook defect

Research on formation analysis of Al-Mg-Si alloy FSLW process in aerospace technology

Regarding traditional fusion welding challenges, this research will illustrate the impact of the combined welding parameter for the friction stir lap welding (FSLW) process for two Al-Mg-Si Al-alloy plate joints. Firstly, the oxide film on the surface of the workpiece was polished, and the surface was cleaned with absolute ethyl alcohol. Secondly, the sheets were fixed on a particular fixture. The “FSW-3LM-4012” machine was used to employ the welding process. The stir tool rotated counter-clockwise, and the “welding direction” was parallel to the “rolling-direction” of the base material. The width of the overlapped area of the upper and lower sheets was 50 mm. Finally, the result was optimized by cross-sectional analysis, fracture path analysis, microhardness analysis, and surface morphology analysis. It is evident that under the optimal value (1597.4 rpm-173.7 mm/min-0.124 mm) of the three applied welding parameters (WP), the heat input is the smallest, the grain size in the weld zone is the finest, and the effect of fine-grain strengthening is most apparent. As a result, the microhardness is the best. The research has practical implications for the FSLW process in modern aerospace and automobile company.

Effect of tool pin length on interfacial behaviors and mechanical properties of friction stir-welded lap joints of 430/304 stainless steels

In this study, the effect of tool pin length on friction stir lap welding of 430 and 304 stainless steels has been investigated. The thermal history of interface was measured by thermocouple. The interfacial macro- and micro-structures under different tool pin lengths were analyzed via optical microscope and scanning electron microscope. Also, tensile shear tests were carried out to evaluate the strength of the lap joint. The results show that increasing the pin length from 0.5 to 1.3 mm increases the peak temperature of the interface, which has a significant effect on diffusion layer formation and hook geometry. The fracture mode of the joints shifts from shear fracture to tensile fracture with the increase of the pin insertion depth. When the pin length is 1.0 mm, i.e., a slight penetration into the 304 plate, the joint presents a maximum failure load of 2.86 kN. The findings reveal that the effective top plate thickness (Teff) used to describe the hook geometry is an important factor determining the joint strength and fracture mode.

Effect of tool tilt angle on microstructure, mechanical properties and fracture behavior of dissimilar friction stir lap welding joint of SiCp/ZL101 and ZL101

In order to achieve the lightweight goal of urban rail train braking system, friction stir lap welding (FSLW) was used to weld SiCp/ZL101 and ZL101 sheets to prepare a new type of brake disc material. The effects of different tool tilt angles (TTAs) on microstructure and mechanical properties of the welding joints were systematically studied. The TTA had a significant effect on the microstructure and defect formation of the dissimilar FSLW joints. There were tunnel defects under the advancing side at 1° and 2°. Internal defect-free weld structures were formed at 3° and 3.5°. A large number of dislocations caused by plastic deformation remained in the microstructure of the weld region at 1° and 2°, and the transformation of the microstructure of the weld region at 3° and 3.5° was dominated by dynamic recovery and dynamic recrystallization. The distribution of SiC particles in the nugget area was uniform, and the grains were obviously refined. With the increase of the TTA, the average grain size of the nugget area increased, the average size of the SiC particles decreased, and the average hardness of the nugget area increased. The four samples all formed a transition zone with good metallurgical bonding at the welding interface. The shear strength of the welding joints increased first and then decreased with the increase of the TTA. In the absence of welding defects, the shear strength reached the best level of 130.71 MPa at 3°. Both shear and tensile fractures were ductile fractures.

Friction stir lap joining techniques effects on microstructure and tensile properties of high-strength automotive steel top hat sections

Dual Phase (DP) steel, a type of Advanced High Strength Steel (AHSS) with a thickness of 1.7 mm, is used to fabricate single-hat components that are then joined to the base plate using two friction stir welding processes: friction stir lap welding (FSLW) and friction stir spot lap welding (FSSLW). It is difficult to join this assembly using fusion welding techniques. The welding variables for the FSLW process, tool rotation speed (TRS), tool traverse speed (TTS), and plunge depth (PD), were optimized using the design of an experiments-based response surface method by experimentally measured tensile shear failure load (TFL) of top hat assembly. For the FSSLW process, the welding variable TTS was replaced by dwell time (DT). Peak temperature, microstructure at different zones, microhardness mapping, and energy absorption capacity of both processes were evaluated under optimal welding conditions. For both processes, the stir zone and the heat-affected zone had the highest and lowest microhardness, which can be correlated with the level of martensite tempering, martensite lath spacing, polygonal ferrite volume, and precipitated carbides. Under optimum welding conditions, the TSL and energy absorption of FSLW joints were 14 kN and 170 J, respectively, which is 20% and 47 higher than the TSL and energy absorption of FSSLW joints.

Friction Stir Lap Welding of Inconel 625 and a High Strength Steel

The joining of dissimilar hard metals such as high-strength steel and nickel-based alloy is required for shipbuilding and offshore applications to enhance the strength, fracture toughness, and corrosion resistance of the exposed parts. However, the joining of these dissimilar alloys has remained a major challenge due to the limited solubility of Fe and Ni in each other, which commonly results in the formation of brittle intermetallic compounds. We present here a novel investigation on the joining of overlapped nickel-based alloy 625 and marine-grade GL E36 steel plates by friction stir lap welding (FSLW). The interface microstructure and its influence on joint strength are rigorously tested. The main bonding mechanism is found to be the mechanical mixing of Fe and Ni along the interface. The interface thermal cycles are computed by a three-dimensional numerical heat transfer model and their effects on the microstructure are examined. Multiple micro tensile specimens are extracted from the stir zone to examine the through-thickness variation in the stir zone properties. The welded joint is characterized further by evaluating the interface microhardness distribution, lap-shear strength, and surface residual stresses.

Friction stir lap welding between A6061/SPC270 thin sheets using welding tool with scroll shoulder

Friction stir lap welding between A6061/SPC270 thin sheets using welding tool with scroll shoulder

Prediction of the temperature recorded in lap joint at during the friction stir welding

The objective of the present work is the modelling of parameters influencing the temperature during friction stir lap welding. The area of physical understanding is the influence of the tool pin geometry and material on the temperature field, microstructural refinement, resulting material flow, and the influence of flow variations on the subsequent mechanical properties of FSW butt lap joints in aluminium 3003 Alloy. The results obtained allowed us to propose a mathematical model to study the interactions between different factors. Thus, it was shown that the most influential parameters are respectively the rotational speed and weld speed.

Friction stir lap welding of AZ31 and TC4: Mechanical properties and bonding mechanism

Friction stir lap welding of AZ31 and TC4: Mechanical properties and bonding mechanism

Determining material model parameters by optimization for temperature controlled friction stir additive manufacturing

Friction stir additive manufacturing (FSAM) is a novel process with the potential of being used for efficiently fabricating large aircraft structures. It is based on the repeated stacking and friction stir lap welding of metal sheets. Recent studies have reported that temperature-related defects occur in the upper layers of the builds, which are explained by changed thermal conditions. The temperatures during fabrication can be calculated by a digital twin of the process. A precise material model is necessary for this purpose. This paper presents and discusses several strategies used to determine Johnson-Cook material model parameters for the aerospace aluminum alloy EN AW-7075. Using only the process data of two welding experiments, suitable material model parameters (C of -0.14161, m of 0.66863) were determined by solving an optimization problem. For these parameters, the mean absolute temperature error was less than or equal to 4.07 K for unknown test data. The method therefore enables the inline calculation and control of the welding temperature during FSAM, thus ensuring stable thermal conditions and high-quality parts.