Friction Stir Lap Research Articles

Crack initiation and propagation behavior of dissimilar interface with intermetallic compound layer in Al/steel joint using coupled multiscale mechanical testing

We demonstrate multiscale mechanical testing using miniature and microscale tensile tests to elucidate the crack initiation and propagation behaviors corresponding to interfacial nanostructures in dissimilar joints of 6061 aluminum alloy and 304 stainless steel. The initial nucleation and subsequent growth of intermetallic compounds (IMCs) can be controlled by heat treatment after friction stir lap welding. The miniature tensile tests exhibited the relationship between the joint strength and IMC layer thickness with changes in the fracture location. Microscale tensile testing using a single edge-notch tension geometry initiates the crack and subsequent propagations near the interface, which helps identify the crack initiation site and understand the dependence of the local strength on the type of IMCs. Crack deviation behavior toward the Al side, attributed to the difference of local strength, is confirmed by in situ observations, which indicated that continuous failure can easily occur within the grown IMCs, particularly in macroscale joints. It was concluded that the crack propagation is controlled by the local crack deviation toward metal matrix, which tends to occur for the dissimilar interface with thin IMC layer. This miniature/microscale tensile testing approach is expected to clarify the essential relationship between the interfacial microstructure and the fracture behavior.

Microstructure and texture evolution of friction stir lap welded dissimilar multi‑aluminum stack

This work investigates the microstructural evolution of a dissimilar multiple‑aluminum alloy stack (AA7055, AA7055, AA6022) produced by friction stir lap welding (FSLW). A through-thickness analyses of grain orientation map, grain size and distribution, strain distribution, and texture evolution by electron backscattered diffraction-based characterization technique were performed. Two different welding parameters (combination of tool rotation and traverse speed) were used to study the effects of the welding parameters on these microstructural characteristics. The study shows that higher welding speed and higher rotation speed of the FSLW tool yield finer grains. FSLW resulted in shear texture formation in the weld regions due to high welding speeds. This texture development in the nugget zone is consistent with shear deformation, and (111) pole figures show ideal shear texture components. The Stir Zone (SZ) exhibits shear texture (A/A ̅ and B/B ̅ components), consistent with other shear-assisted processes. Recrystallization mechanisms observed are CDRX in SZ and DDRX in TMAZ (Thermo-Mechanically Affected Zone). Interface analysis reveals the presence of oxide layers between different aluminum sheets, affecting joint mechanical performance. The mechanical property of the lap welded joints was presented in terms of microhardness distribution across the weld cross section. Slightly higher hardness in higher speed welding setup was observed throughout the SZ and AA6022 layer, indicating greater grain refinement and uniform grain structure distribution.

The microstructure and mechanical properties of aluminum/steel welded joint with Ni foil interlayers by FSLW

Friction stir lap welding experiments between 6061 aluminum alloy plate and DP590 dual-phase steel plate were carried out. The effects of welding parameters and addition of Ni foil interlayers with different thickness on the microstructures and mechanical properties of the lap joints were investigated. The shear strength of the joint reached the maximum value of 6597 N and showed a mixed ductile-brittle fracture mode when the welding speed, the rotating speed and the thickness of the Ni foil intermediate layer were set to 100 mm/min, 900 rpm and 0.3 mm, respectively. A certain amount of beneficial plastic AlNi and FeNi3 intermetallic compounds are formed through the reaction of Al, Fe and Ni at the aluminum alloy/steel interface.

Investigation on the microstructure and mechanical property of friction stir lap welded acrylonitrile butadiene styrene/polycarbonate produced by double-pin tool

Friction stir lap welding (FSLW) of dissimilar acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) was conducted using a double-pin tool. The formation process of the weld and the influences of rotational speed on the microstructure and mechanical property were investigated. It was found that the weld was generated accompanying with the closure of old cavities in the front of the pins and the simultaneous regeneration of new cavities in the rear of the pins. Annular material flow on the vertical and horizontal directions occurred during FSLW. With the increase of the rotational speed, the PC anchors resulted from the upflow of plasticized PC layer and the shoulder affected zone both enlarged. Microstructure analysis of the weld nugget showed that PC was fragmented into lamellar, columnar, and spherical particles and their dimensions decreased when rotational speed increased. Lap-shear tensile tests showed that the weld strength increased with higher rotational speed and the maximum strength of the weld produced under 800 r/min reached 19.38 MPa, which was comparable to the ABS/PC welds produced by a tapered pin under the optimal parameters. Through the further optimization of such FSLW process, it was potential to join dissimilar polymeric components in future industrial manufacturing field.

Elucidating the process mechanism in Mg-to-Al friction stir lap welding enhanced by ultrasonic vibration

The composite structures/components made by friction stir lap welding (FSLW) of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles. To further improve the joint quality, the ultrasonic vibration (UV) is exerted in FSLW, and the UV enhanced FSLW (UVeFSLW) was developed for making Mg-to-Al dissimilar joints. The numerical analysis and experimental investigation were combined to study the process mechanism in Mg/Al UVeFSLW. An equation related to the temperature and strain rate was derived to calculate the grain size at different locations of the weld nugget zone, and the effect of grain size distribution on the threshold thermal stress was included, so that the prediction accuracy of flow stress was further improved. With such modified constitutive equation, the numerical simulation was conducted to compare the heat generation, temperature profiles and material flow behaviors in Mg/Al UVeFSLW/FSLW processes. It was found that the exerted UV decreased the temperature at two checking points on the tool/workpiece interface from 707/671 K in FSLW to 689/660 K in UVeFSLW, which suppressed the IMCs thickness at Mg-Al interface from 1.7 µm in FSLW to 1.1 µm in UVeFSLW. The exerted UV increased the horizontal materials flow ability, and decreased the upward flow ability, which resulted in the increase of effective sheet thickness/effective lap width from 2.01/3.70 mm in FSLW to 2.04/4.84 mm in UVeFSLW. Therefore, the ultrasonic vibration improved the tensile shear strength of Mg-to-Al lap joints by 18 %.

Interfacial Microstructure Produced during Dissimilar AA6013/Ti-6Al-4V Friction Stir Lap Welding under Zero-Penetration Condition

The purpose of this study was to investigate the interfacial microstructure that was produced during dissimilar friction stir lap welding (FSW) of 6013 aluminum alloy and Ti-6Al-4V. FSW was conducted under a zero-penetration condition, i.e., the welding tool was plunged exclusively into the upper (aluminum) plate of the dissimilar lap joint. To facilitate the interpretation of microstructural processes, finite element modeling (FEM) was applied to evaluate the temperature field within the weld zone. The FEM simulation revealed a very sharp temperature gradient across the dissimilar interface. This effect was attributed to the generation of FSW heat exclusively within the aluminum part and a relatively low thermal conductivity of titanium. The abrupt temperature drop on the titanium side imposed a strict limitation on the diffusion penetration of aluminum and thus resulted in a relatively thin (~0.5 μm) and discontinuous intermetallic compound. Due to the complex chemical composition of the FSWed aluminum alloy, the diffusion processes also involved alloying elements. Consequently, the evolved intermetallic compound had a complicated chemical composition, with the principal elements being aluminum, titanium, silicon, manganese, and magnesium.

Formation and Evolution Mechanism of Intermetallic Compounds of Friction Stir Lap Welded Steel/Aluminum Joints.

Interfacial layers with brittle intermetallic compounds (IMC) greatly influence the performance of steel-aluminum friction stir lap welding (FSLW) joints. Thus, the formation and evolution of IMC between 7075-T6 aluminum alloy and galvanized DP590 steel in steel-aluminum FSLW joints were investigated. An FSLW numerical model was developed using the computational fluid dynamics method to analyze the interface temperature between the aluminum alloy and steel. Scanning electron microscopy (SEM) was conducted to observe the microstructure characterization and measure the IMC thickness. Phases among different joint zones were analyzed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). IMC layer formation was predicted by the effective Gibbs free energy model presented in this paper according to thermodynamic principles. The Monte Carlo method was utilized to predict the thickness of IMC layers. It was found that the IMC layer at the interface of the welded joint is composed of Fe2Al5, FeAl3, and Al-Zn eutectic. The IMC thickness decreased from 4.3 μm to 0.8 μm with the increasing welding speed, which was consistent with the Monte Carlo simulation results.

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.

Formation and fracture characteristics of friction stir lap joint of Alclad 2A12-T42 aluminum alloy at different tilt angles

Formation and fracture characteristics of friction stir lap joint of Alclad 2A12-T42 aluminum alloy at different tilt angles

Study on the process parameters and mechanical properties of FSWed AA7075 to AZ31B alloy

As-cast Mg (AZ31B) -3.0 Nd-0.2 Zn-0.7 Zr (weight %) and AA7075 alloy friction stir lap linear joints were studied for lap-shear behaviours. Several parameters were employed, each with a unique rotation and travel speed, to release the joints. The Al-Mg binary schematic reveals that the eutectic reaction temperature is between 438 °C and 460 °C, suggesting that the peak temperatures for both samples could be greater than these values. This is indicated by the study of the temperature. Aluminium and magnesium alloys contact exhibits ferocious intermixing, resulting in the intermetallic Al3Mg2. The highest tensile shear failure force, which is approximately 2.24 kN, is displayed by welds with rotational speeds of 1000 rpm and travel speeds of 130 mm/min. The value increased by 15% after being heated at 400 °C for 30 min.

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.

Analysis of fatigue strength on friction stir lap weld AA2198 / Ti6Al4V joints

In this research, Friction stirs lap welding (FSLW) of AA2198 (Al4.5Cu1.4 Mg 0.5 Mn) alloy to Ti6Al4V alloy was put through fatigue tests. Even though they could readily pierce the Ti6Al4V plate (dpin > 0) during the melting process, the bottoms of the FSLW pin bottoms (dpin ≈ 0) sought to touch the plate. There was a modest difference between the fatigue range of the AA2198/Ti6Al4V welds and the fatigue limit of the Friction Stir Lap AA2198 to Ti6Al4V welds. The good fatigue strength was found to be mostly attributable to the creation of a very thinner interfacing layer during FSLW, according to the findings. Outside the pin width, there was a significant disparity in distance between the diffusion welds of dpin > 0 and dpin ≈ 0. Welds made with dpin > 0 were found to have a fatigue limit that was comparable to that of welds made with a dpin ≈ 0, even though the mixing stir zone in the dpin > 0 welds was brittle. Varied diffusion-weld widths will have different thermo-mechanical conditions, which will be established.

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.

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.