Ultrasonic Assisted Friction Stir Welding Research Articles

Optimization of ultrasonic assisted friction stir welding (UAFSW) of electrical grade AA 6101T-64 and Cu

Optimization of ultrasonic assisted friction stir welding (UAFSW) of electrical grade AA 6101T-64 and Cu

Study on the effects of ultrasonic assistance and external heat dissipation on friction stir welded 7075 aluminum alloy joints

In this paper, conventional friction stir welding (C-FSW), ultrasonic assisted friction stir welding (Ua-FSW) and heat pipe assisted friction stir welding (Ha-FSW) were performed on 4 mm thick 7075 aluminum alloy. The effects of the two different types of assisted technologies on C-FSW were qualitatively compared and analyzed. The microstructure of the joints in the NZ, HAZ and other regions were primarily characterized via SEM-EBSD and TEM, and the strength of the joints were evaluated via the room-temperature tensile properties and microhardness tests. The test results showed that both Ua-FSW and Ha-FSW effectively improved the weld forming, while the surface quality of the joints fabricated by Ha-FSW was better. The acoustic flow effect from ultrasound reduced the temperature gradient, and the heat pipe provided excellent heat dissipation, which well controlled the peak heat and the rate of heat loss throughout FSW, resulting in finer grain sizes after both the Ua-FSW and Ha-FSW processes. EBSD analysis showed that the assistance of two technologies provided a greater effect on TMAZ and HAZ, the stress field generated by ultrasonic vibration favored the formation of subgrains, the heat dissipation of the heat pipe also inhibited the recrystallization, and more subgrains were retained. The assistance of ultrasonic vibration and the heat pipe was mainly in the elongation, especially the joints prepared by the Ha-FSW showed an improvement in elongation by 16.7 % and 33.3 % compared to the Ua-FSW and C-FSW, respectively. This work provides insight into improving welding efficiency and joint performance through modified FSW processes.

Revealing the acoustic effects on heat transfer and material flow in ultrasonic assisted friction stir welding of dissimilar Al/Mg alloys

Development of a reasonable constitutive equation is critical to realize accurate numerical prediction of ultrasonic vibration-assisted friction stir welding (UVaFSW) of dissimilar Al/Mg alloys and deepen the understanding of the synchronous interaction between the ultrasonic vibration exerted on the tool and the tool induced thermo-mechanical behavior. Considering the thermal activation and dislocation evolution mechanisms, the calculation method of acoustic stress work based on the change of dislocation strain energy is redefined, and a modified acoustic-plastic constitutive equation is developed. The modified constitutive equation was applied to the computational fluid dynamics (CFD) model combined with the volume of fluid (VOF) method and quantitative analysis was conducted on the acoustic effects on heat generation, material flow and intermixing in UVaFSW of Al/Mg alloys. The results indicate that the exerted ultrasonic vibration has a little effect on the total heat due to the multiple effects of acoustic softening, acoustic antifriction and additional acoustic heat, but can promote the material flow around the tool and expand the material intermixed region. The experimental research validates the calculated results, and it is indicated that the flow stress and temperature field calculated by the improved constitutive equation have higher accuracy in UVaFSW of Al/Mg alloys.

Unravelling the ultrasonic effect on residual stress and microstructure in dissimilar ultrasonic-assisted friction stir welding of Al/Mg alloys

An in-depth knowledge and understanding of residual stress in dissimilar ultrasonic vibration-assisted friction stir welding (UVaFSW) are crucial for the performance evaluation of multimaterial structure designs; however, extensive research is still lacking. The present study evaluated the residual stress of dissimilar aluminium (Al)/magnesium (Mg) alloy joints produced by traditional FSW and UVaFSW to elucidate the ultrasonic effect mechanism with the aid of process simulation and microstructural evaluation. The weld surficial residual stress measured by X-ray diffraction (XRD) using the cos α method indicated the generation of predominantly compressive stress in UVaFSW welds. In agreement with the XRD measurements, the stress maps evaluated using the contour method (CM) exhibited an expanded compressive stress region and a mitigated tensile stress region in the UVaFSW welds. The Al/Mg interfacial mismatch of thermal expansion led to a tensile stress state on the Mg side and a compressive stress state on the Al side near the Al/Mg interface. The maximum compressive stress in the UVaFSW weld was ∼100 MPa higher than that in the FSW weld. The ultrasonic effect proficiently reduced the layer thicknesses of the intermetallic compounds (IMCs), promoting grain recrystallisation behaviour due to improved material transfer and mixing. Consequently, more homogeneous hardness distributions and improved tensile properties were formed in UVaFSW welds. However, ultrasonic vibration had an insignificant effect on the density of geometrically necessary dislocations and stored strain energy, indicating limited effects on microscopic residual stress in the studied condition. The ultrasonic vibration was found to positively mitigate residual tensile stresses and macroscopic distortion by increasing the temperature and encouraging material mixing within the stirred zone, as well as enhancing the stress interaction of the Al/Mg interface related to thinner IMCs. The UVaFSW has considerable potential to in-process co-optimise residual stress and microstructure for dissimilar Al/Mg welds.

Effect of Ultrasonic Vibration in Friction Stir Welding of 2219 Aluminum Alloy: An Effective Model for Predicting Weld Strength

Friction stir welding (FSW) is today used as a premier solution for joining non-ferrous metals, although there are many limitations in its application. One of the objectives of this study was to propose an innovative welding technique, namely ultrasonic-assisted friction stir welding (UAFSW) with longitudinal ultrasonic vibration applied to the stirring head. In this paper, UAFSW mechanical properties and microstructure analysis were performed to demonstrate that the fluidity of the weld area was improved and the strengthened phase organization was partially preserved, due to the application of ultrasonic vibration. The addition of 1.8 kW of ultrasonic vibration at 1200 rpm and 150 mm/min welding parameters resulted in a 10.5% increase in the tensile strength of the weld. The ultimate tensile strength of 2219 aluminum alloy UAFSW was analyzed and predicted using mathematical modeling and machine learning techniques. A full factorial design method with multiple regression, random forest, and support vector machine was used to validate the experimental results. In predicting the tensile behavior of UAFSW joints, by comparing the evaluation metrics, such as R2, MSE, RMSE, and MAE, it was found that the RF model was 22% and 21% more accurate in the R2 metric compared to other models, and RF was considered as the best performing machine learning method.

ISIM Achievements Regarding Friction Stir Welding in Inert Gas Environment

Friction stir welding (FSW) is an important research direction within ISIM Timisoara. Also within ISIM Timisoara, in addition to the classic FSW welding, processes and methods derived from FSW were also approached. Those processes and methods include friction stir processing (FSP), coatings with functional layers by friction, conventional friction riveting and friction riveting with hybrid effect, hybrid welding methods: TIG assisted friction stir welding FSW-TIG and ultrasonic assisted friction stir welding FSW-US. Recent research were focused on a new method of applying the FSW process, namely friction stir welding in inert gas environment (FSW-IG). Results obtained by ISIM in the field of FSW-IG welding are presented: data / information on solutions for applying inert gas in the welding area, as well as experimental results obtained for FSW-IG welding of DD13 steel, Cu99 copper and AZ31B magnesium alloy respectively. The solutions for providing shielding gas in the welding area were analyzed, verified and validated by experiment. The experimental welding programs generated the necessary data for the development of the FSW-IG welding technologies for the approached materials. By applying FSW-IG welding there was an improvement in the aspect of the welded joints and for some of mechanical characteristics (as the case may be) compared to the application of classic FSW welding. The use of shielding gas also had beneficial effects on the service life of FSW tools.

CT-based detection of material flow in friction stir welding of dissimilar Al/Mg alloys with and without ultrasonic assistance

Comparative experiments of friction stir welding (FSW) of Al/Mg alloys were conducted with and without ultrasonic assistance. The copper powders were preset inside the workpieces as the marker material, and computer tomography technique was employed to obtain the three-dimensional information of material flow around the tool. The top view of copper powders distribution inside the weldments shows that the distribution zones of marker material at the retreating side and the trailing side were all widened by the exerted ultrasonic vibration (UV). The front view and side view of marker material distribution demonstrated that UV also enhanced the vertical material flow. Such detection results are helpful to elucidate the mechanism of ultrasonic-assisted FSW of dissimilar Al/Mg alloys.

Improving the Quality of Dissimilar Al/Steel Butt-Lap Joint via Ultrasonic-Assisted Friction Stir Welding

A dissimilar AA7075/Q235 butt-lap joint was fabricated via ultrasonic-assisted friction stir welding (UaFSW), and the characteristics of the UaFSW joint were investigated systematically. The acoustoplastic effect of the ultrasonic vibration led to the softening of the materials and enhanced the material flow during welding, decreasing the volume of welding defects in the nugget zone of the UaFSW joint. With the help of ultrasonic vibration, a smooth and thin intermetallic compounds (IMCs) layer could generate along the Al/steel interface at the top of nugget zone, which possibly consisted of Al5Fe2 and Al13Fe4 phases. However, the positive effects of the ultrasonic vibration were weakened at low temperatures; consequently, the IMCs layer became discontinuous at the bottom of the nugget zone and the welding defects also formed. The ultrasonic vibration accelerated the dynamic recrystallization and refined the microstructures in the nugget zone due to the increased strain rate and stored energy. As a result, the UaFSW joint exhibited a better mechanical performance in comparison to the FSW joint, and the increment in the peak tensile load/elongation was more than twice. In addition, the UaFSW joint failed in the nugget zone along with the Al/steel interface, and the fracture mode was a mixture of ductile and brittle.

The influence of acoustic antifriction on heat generation and material flow in ultrasonic-assisted friction stir welding

The influence of acoustic antifriction on heat generation and material flow in ultrasonic-assisted friction stir welding

Comparison Study on Welding Temperature and Joint Characteristics of AZ31 Magnesium Alloy by Ultrasonic and Heat Pipe Assisted FSW

As an important factor in friction stir welding (FSW) process, temperature directly affects the microstructures and mechanical properties of welded joints. The present work aims to investigate the welding temperature and joint characteristics of AZ31 magnesium alloy under three FSW conditions: conventional friction stir welding (FSW), ultrasonic assisted friction stir welding (UaFSW), and ultrasonic and heat pipe assisted friction stir welding (UHaFSW), respectively. The results show that the welding temperature distributions and the characteristic of “non-uniformity” are presented in the FSW and UaFSW joints along the welding and horizontal directions. Compared with conventional FSW, UaFSW can effectively balance and improve the non-uniform temperature distribution in the joints, resulting in the significant decreases in the peak temperatures and durations of high temperature. Hence, the grains are refined in the microstructure of the nugget zone in the UHaFSW joints, which enhances their microhardness and tensile properties. Based on these results, it can be concluded that UHaFSW could be an effective method to improve the mechanical properties of AZ31 magnesium alloy welded joints.

Mechanical and Microstructural Evaluation of AA6082-T61 Joints Produced by Ultrasonic Vibration Assisted Friction Stir Welding Process

Continuous improvement in the friction stir welding process (FSW) is still growing to improve the process capabilities and overcome certain drawbacks encountered in the process. Low welding speeds, high welding loads, and high torque needed are the main limitations of this process. Applying ultrasonic vibration is one of the versatile approaches that was proposed to tackle these issues. In this paper, a comparative study between the conventional friction stir welding process (CFSW) and the ultrasonic-assisted friction stir welding process (UAFSW) was conducted. The objective is to evaluate quantitively and qualitatively the influence of ultrasonic vibration waves on the weld surface quality, tensile strength, micro-hardness, microstructure, and weld formation of the joints. The results have demonstrated that ultrasonic vibration waves cause grain refinement action by 23.6% at the stirring zone (SZ) as well as its desirable role in enhancing the mechanical properties by a percentage up to 15% for ultimate tensile strength and eliminating weld defects, especially at high welding speed (120 mm/min). However, no profound effect was found for ultrasonic waves on the grain size in the thermomechanical affected zone (TMAZ) or the heat-affected zone (HAZ). A considerable reduction in the elongation % whether in CFSW or UAFSW compared to that of base metal was detected.

Investigation of mechanical properties of dissimilar joint of Al6063 aluminium alloy and C26000 copper alloy by ultrasonic assisted friction stir welding

An attempt by this experiment has been made to analyse the difference of mechanical properties in welding among Friction Stir Welding (FSW) and Ultrasonic assisted Friction Stir Welding (UAFSW). Dissimilar metals 6063 Aluminium Alloy with C26000 Copper alloy are joined in this experiment. Optimum mechanical properties obtained by FSW and UAFSW by calibrating tool rpm range from 400 to 600 rpm with tool transverse rate from 15 to 25 mm/min were obtained and compared. For UAFSW calibration of tool rpm ranges from 400 to 600 rpm tool transverse rate from 15 to 25 mm/min assisted by ultrasonic frequency ranging from 10 to 14 kHz were used. An improvement in the mechanical property observed by addition of the ultrasonic energy to FSW process and been presented in the paper and the ultrasonic vibration used in the study has been observed to be suitable in the range of 10–14 khz for joining dissimilar material under study. Also, an improvement of mechanical properties from 10 to 25 % been observed by addition of the ultrasonic energy to FSW process. The comparative results of the UTS, YS and elongation were explained and presented for FSW and UAFSW process showing the improvement in the material property due to the addition of Ultrosonic energy.

Influence of ultrasonic vibration on the microstructure and texture evolution of AZ91 magnesium alloy during ultrasonic-assisted friction stir welding

Influence of ultrasonic vibration on the microstructure and texture evolution of AZ91 magnesium alloy during ultrasonic-assisted friction stir welding

Experimental study of tool wears to join Al6026 aluminium alloy by Ultrasonic Assisted Friction Stir welding

Ultrasonic Assisted Friction Stir Welding is being used in various processes to get enhanced value in the welding properties while reducing the tool wear. Using HSS as tool material, 6026 aluminium base plates has been joined by FSW process and Ultrasonic Assisted Friction Stir Welding. In this experimental study, an attempt has been made to obtain the optimum tool wear values by adjusting the rotational speed, transverse speed and frequency in the range of 400 to 600 rpm, 15 to 25 mm/min and 10 to 14 KHz respectively. This paper investigates the tool wear while joining Al6026 aluminium alloy plates using FSW and UAFSW. The specimen samples have been joined by both FSW and UAFSW process and the tool wear has been studied. The difference in the tool wear has been analysed in both FSW and FSW process and results obtained has been presented to advice the utilisation of the ultrasonic vibration with the FSW process to increase tool life. The suitable vibration that can be used in FSW process has also been studied and presented in the paper. A decrease of 25 % in the tool wear has been observed on using the ultrasonic vibration to FSW, which presented that advantage of the ultrasonic energy in the FSW process for industrial utilisation with increased tool life.

Effects of ultrasonic on friction stir Al–Ti welds: a comparative study

ABSTRACT Ultrasonic assisted friction stir welding (UaFSW) and conventional friction stir welding (FSW) were conducted on AA6061 and Ti6Al4V alloys. Smaller waves and larger flashes were obtained by UaFSW with 20 kHZ frequency and 10 μm amplitude ultrasonics, and the stir zone was expanded as compared to the FSW one. Interfacial micro-cracks were eliminated with the ultrasonic assistance while a mixed zone was formed beside the Al/Ti interface, containing Ti fragment and intermetallic precipitates. As a mixed zone formed with ultrasonics, the UaFSW weld showed doubled strength in the lap shear tests, as compared to the FSW weld. Cracks propagated in the mixed zone weld of the UaFSW weld, whereas propagated along the Al/Ti interface for the FSW weld.

Investigation on ultrasonic assisted friction stir welding of aluminum/steel dissimilar alloys

Abstract The extensive use of light metal material such as aluminum has brought about problems in its joining with steel. However, the weak metallurgical bonding between the dissimilar materials and the formation of hard and brittle intermetallic compounds (IMCs) lead to unsatisfactory joint strength. Aiming at achieving high-quality joining of aluminum and steel, 6061-T6 aluminum and 301L steel alloys were lap joined by ultrasonic assisted friction stir lap welding (UaFSLW) in this study. The UaFSLW joints were well formed with uniform flashes and even arc lines. The strong plastic flow of the aluminum material driven by the dual effects of mechanical stirring and ultrasonic vibration inhibited the excessive growth of the Al–Fe IMCs at the lap interface. Thanks to the enhanced metallurgical bonding and the effective control of the layer thickness of IMCs, the tensile load of the UaFSLW joint under 1,800 rpm reached 16.5 kN, which was an increase of 27.9% compared to that of the conventional FSLW joint.

Influences of ultrasonic on friction stir welding of Al/Ti dissimilar alloys under different welding conditions

Ti6Al4V and 6061-T6 Al alloys were joined by ultrasonic-assisted friction stir welding (UAFSW) at different rotational velocities and pin offsets to explore the influencing mechanisms of the ultrasonic. Results indicate that the positive or negative influence of ultrasonic depends on the welding condition. Applying ultrasonic increases the joint tensile strength at 450 rpm ~ 850 rpm rotational velocity and 1.2 mm pin offset because it does not only decreases the void defect and the size of Ti6Al4V fragments but also promotes the diffusion bonding at Al/Ti interface. When a large pin offset of 1.6 mm is used, a thick intermetallic compounds (IMCs) layer is formed at the Al/Ti interface and large Ti6Al4V fragments appear in the stir zone. Applying ultrasonic at the large pin offset induces cracks initiating in the thick IMCs layer and the formation of large void defect in the stir zone. This investigation provides a reference for the reasonable application of UAFSW technique.

The effect of ultrasonic vibration on stress-strain relations during compression tests of aluminum alloys

Complete understanding of ultrasonic interaction with aluminum alloys is essential to promote application of ultrasonic-assisted friction stir welding process in manufacturing industry. In this study, the ultrasonic-assisted compression tests were performed to investigate the effect of ultrasonic vibration on the stress-strain characteristics of AA2024-T3 alloy. At the same time, AA6061-T6 alloy was also tested, and the stress-strain relations for both alloys were compared and analyzed to study the influence of material properties on the variation of stress-strain characteristics under ultrasonic assisted compression. It was found that on the stress-strain curves of AA2024-T3 there are an obvious and transient stress reduction concave point at the beginning of ultrasonic exertion, a hysteresis of stress recovery and a short-term small hardening phenomenon after the ultrasonic exertion stopped. The results laid foundation for process optimization of ultrasonic-assisted friction stir welding of AA2024-T3.

Fatigue Behaviour of 7N01-T4 Aluminium Alloy Welded by Ultrasonic-Assisted Friction Stir Welding

This study investigates the effects of axial ultrasonic vibration on the microstructure evolution, residual stresses distribution and fatigue fracture behaviour of a 7N01-T4 joint, and demonstrates that ultrasonic vibration can significantly promote the flow of plasticised metals, expand the stirred zone (SZ) width and refine the grain size. The longitudinal residual stresses of the joints are dominant, and the peak longitudinal residual stresses of the thermo-mechanically affected zone (TMAZ) on the advancing side (AS) (TMAZ-AS) in the ultrasonic-assisted friction stir welding (UAFSW) joint are 31.5 MPa lower than those in the friction stir welding (FSW) joint. Compared to that of FSW joints, the fatigue strength of UAFSW joints increases by 20 MPa at 107 cycles (stress ratio of R = 0.1). At high-stress levels, crack initiation occurs at the TMAZ-AS, and is mainly attributed to high residual stresses and second-phase particles. At low-stress levels, fatigue cracks are likely to initiate in the transition zone (TZ).

Acoustic induced antifriction and its effect on thermo-mechanical behavior in ultrasonic assisted friction stir welding

The developed ultrasonic assisted friction stir welding (UaFSW) process can reduce the welding load and improve the joint quality, but the interaction mechanism between the exerted ultrasonic vibration and the thermo-mechanical behavior induced by friction stir welding is not yet elucidated. In this study, the classical Norton friction model is modified with the acoustic stress work, and the effect of ultrasonic vibration on the contact state at the tool/workpiece interface is analyzed. The relative velocity between the tool and its adjacent contacting material is taken as one of the main influencing factors to calculate the interfacial friction shear stress. A non-uniform interfacial friction model is combined with the modified constitution equation. And a fully coupled model of UaFSW process is developed to analyze the ultrasonic field, interfacial contact state, heat generation, plastic material flow and heat transfer phenomena. It is found that ultrasound can effectively reduce the interfacial friction stress, and this antifriction effect is more obvious in the welding direction which coincides with ultrasonic vibration. The ultrasound exerted along the radial direction of tool in UaFSW process results in acoustic softening of base material and friction reduction at the tool/material interface. Both effects change the heat generation, material flow and temperature field in UaFSW. Thus, the torque and traverse force are lowered with the ultrasonic induced reduction of interfacial stress, and the high quality of welds are obtained with the improvement of material flow. The model is experimentally validated by comparison of predicted and measured tool torque, heat input and thermal cycles.