Ultrasonic Assisted Friction Stir Welding Research Articles

Numerical investigation of heat generation and plastic deformation in ultrasonic assisted friction stir welding

In ultrasonic assisted friction stir welding (UaFSW) system, the ultrasonic vibration is exerted onto the tool radially, and can achieve synchronously thermo-mechanical action with the tool. A mathematical model is established to investigate the coupled “acoustic action-heat generation-plastic deformation” behaviors in UaFSW. The ultrasonic stress work is considered to revise both the constitutive equation and the slip rate. In UaFSW the ultrasound vibrates along the welding direction and the peak acoustic pressures at both leading and trailing sides enhance the material plastic flow there. It is found that the ultrasound increase the percentage of viscous dissipation heat in the total heat generation. It is the acoustic softening effect, not the supplemented ultrasonic energy, which plays a dominate role in UaFSW. The numerical results are compared and experimentally verified with the thermal cycle at typical positions and the cross section of weld zone respectively.

Effects of ultrasonic assisted friction stir welding on flow behavior, microstructure and mechanical properties of 7N01-T4 aluminum alloy joints

Conventional friction stir welding (FSW) and ultrasonic assisted friction stir welding (UAFSW) were employed to weld 6-mm thick 7N01-T4 aluminum alloy plates. Weld forming characteristics and material flow behavior in these two different welding processes were studied and compared. Ultrasonic vibration was applied directly on the weld in axial direction through the welding tool. Metal flow behavior, microstructure characteristics in the nugget zone (NZ) and evolution of the mechanical properties of naturally aged joints were studied. Results show that the ultrasonic vibration can significantly increase the welding speed of defect-free welded joint. At the rotation speed of 1200 rpm, the UAFSW can produce defect-free welded joints at a welding speed that is 50% higher than that of the conventional FSW. Ultrasonic vibrations can also improve surface quality of the joints and reduce axial force by 9%. Moreover, ultrasonic vibrations significantly increase the volume of the pin-driven zone (PDZ) and decrease the thickness of the transition zone (TZ). The number of subgrains and deformed grains resulting from the UAFSW is higher than that from the FSW. By increase the strain level and strain gradient in the NZ, the ultrasonic vibrations can refine the grains. Ultrasonic energy is the most at the top of the NZ, and gradually reduces along the thickness of the plate. The difference in strengths between the FSW and the UAFSW joints after post-weld natural aging (PWNA) is small. However, the elongation of the UAFSW is 8.8% higher than that of the FSW (PWNA for 4320 h). Fracture surface observation demonstrates that all the specimens fail by ductile fracture, and the fracture position of the UAFSW joint changes from HAZ (PWNA for 120 h) to NZ (PWNA for 720 and 4320 h).

Effect of ultrasonic assisted friction stir welding on microstructure and mechanical properties of AZ91−C magnesium alloy

Abstract The influence of ultrasonic vibrations on microstructure and mechanical properties of the AZ91−C magnesium alloy after ultrasonic assisted friction stir welding (UaFSW) in comparison with conventional friction stir welding (FSW) was investigated. The FSW was applied at the rotational speed of 1400 r/min and welding speed of 40 mm/min and no defects were observed. Using the same welding parameters, the process was carried out with inducing ultrasonic vibrations to the weld line at the amplitude of 15 µm. The microstructure of the specimens was observed with optical and scanning electron microscopy. The results indicate that a very fine microstructure is obtained in UaFSW with respect to that of conventional FSW. Moreover, β-Mg17Al12 coarse dendrites are segregated to very fine and partly spherical particles that homogeneously distribute in α-Mg matrix. This remarkably-modified morphology of microstructure attributed to severe plastic deformation comes from ultrasonic vibration and friction stirring effect. Tensile and hardness tests were performed to evaluate the mechanical properties of the welds. According to the results, the vibration greatly improves the mechanical properties of the conventional FSW joint. The tensile strength and hardness are increased from 195 MPa and HV 79 in conventional FSW to 225 MPa and HV 87 in UaFSW, respectively.

A general strategy for the reliable joining of Al/Ti dissimilar alloys via ultrasonic assisted friction stir welding

Ultrasonic assisted friction stir welding (UaFSW) was used to join 6061-T6 aluminum and Ti6Al4V alloys. A small plunge depth endowed with the low heat input was used and the sound joints without obvious thickness reduction were achieved. A diffusion-type bonding without the intermetallic compounds layer was observed at the joint interface. The ultrasonic improved the diffusion thickness and decreased the average size of grains and titanium alloy fragments. A hook-like structure was formed at the bottom interface of the UaFSW joint, which improved the bonding length and the mechanical interlocking. The microhardness of the stir zone was increased because of the further grain refinement induced by ultrasonic. The maximum tensile strength of the UaFSW joint was 236 MPa, which reached 85% of the base 6061-T6 alloy.

Residual stress, tensile strength, and macrostructure investigations on ultrasonic assisted friction stir welding of AA 6061-T6

In recent decades, ultrasonic vibrations are used in manufacturing processes because they can improve tool life, material performance, and quality. One of them which can be integrated with ultrasonic vibrations is friction stir welding called ultrasonic assisted friction stir welding. In previous studies, the effect of ultrasonic vibrations on the mechanical, metallurgical, and thermal properties was investigated and there is not any residual stress investigations on ultrasonic assisted friction stir welding. Since residual stress plays an important role in performance and stability of components, the influence of ultrasonic power on the longitudinal residual stress in friction stir welding is investigated in this work. In spite of residual stress, tensile strength and quality of weldment were investigated as complementary terms to ensure successful performance of ultrasonic assisted friction stir welding. The findings indicated that high-frequency vibrations with power of 200 W can reduce the maximum tensile residual stress about 45% and significantly increase tensile strength. Also, ultrasonic vibrations prevent defect such has voids and tunnel in weld zone due to peening effect in ultrasonic assisted friction stir welding.

Joining of magnesium and aluminum alloys via ultrasonic assisted friction stir welding at low temperature

Intermetallic compounds (IMCs) formed in the stir zone (SZ) of dissimilar friction stir welded aluminum/magnesium (Al/Mg) joint always deteriorate tensile properties. Joining of 6061-T6 Al and AZ31B Mg alloys via ultrasonic assisted friction stir welding (UaFSW) at low temperature was performed to reduce the disadvantages caused by IMCs. A sound Al/Mg joint with smooth surface was obtained based on the stationary shoulder at a high welding speed of 80 mm/min, rotational velocity of 1000 rpm, and ultrasonic power of 1400 W due to the improvement of material flow caused by ultrasonic, indicating the success of low-temperature welding. Meanwhile, joining interface, characterized by the IMCs, was attributed to inter diffusion caused by severe plastic deformation from ultrasonic and friction stirring. The tensile strength and elongation of the Al/Mg joint reached 134 MPa and 1.5%, respectively. The IMCs containing Al2Mg3 formed in the SZ was the main reason of tensile fracture, and then resulted in cleavage fracture. The present study suggests that UaFSW has feasible and potential to join Al/Mg alloys at low temperature, which provides a significant reference for welding joint of dissimilar materials with the IMCs.

Improving tensile properties of Al/Mg joint by smashing intermetallic compounds via ultrasonic-assisted stationary shoulder friction stir welding

Continuous intermetallic compounds (IMCs) at the nugget zone (NZ) of dissimilar friction stir welded Al/Mg joint easily become crack initiation and propagation path, deteriorating mechanical properties. To reduce or eliminate the disadvantages induced by the continuous IMCs, ultrasonic-assisted friction stir welding (UaFSW) based on stationary shoulder system was employed to join 6061-T6 aluminum alloy and AZ31B magnesium alloy. Defect-free joint without the shoulder marks was obtained under the synergistic effect of the stationary shoulder and the ultrasonic. Vibration and acoustic streaming induced by the ultrasonic broke the continuous IMCs layer near the thermo-mechanically affected zone (TMAZ) of advancing side (AS) into pieces or particles. Facture path from the short Al/Mg interface near the TMAZ at the AS of the conventional joint was changed to the long Al/Mg interface at the retreating side (RS) of the UaFSW joint, improving tensile properties. Maximum values of tensile strength and elongation of the UaFSW joint were 152.4 MPa and 1.9%, which were 17 MPa and 0.8% higher than those of the conventional joint, respectively.

A practical strategy for improving the weldability of ultra-thin Al/Mg sheets by ultrasonic-assisted friction stir welding

ABSTRACTIn order to enhance the weldable thickness and tensile properties of dissimilar ultra-thin Al/Mg alloy sheets, ultrasonic-assisted friction stir welding (UaFSW) was performed. The addition of ultrasonic produces three benefits. First, a sound joint with smooth surface appearance was achieved. Next, weldable thickness and mixing degree of Al/Mg alloys were improved based on better material flow. Finally, continuous intermetallic compound (IMC) layer in the conventional joint was broken into small pieces, delaying crack propagation. Maximum tensile strength of the UaFSW joint reached 130 MPa, which was much more higher than 102 MPa of the conventional joint. It is concluded that UaFSW has a huge potential to join dissimilar alloys, especially those with the formation of IMCs.

The influence of bending mode ultrasonic-assisted friction stir welding of Al-6061-T6 alloy on residual stress, welding force and macrostructure

Residual stress can affect the properties and performance of materials. Since it is an important factor in all welding processes, either fusion welding or friction stir welding, thus, novel complementary methods should be integrated with friction stir welding for reduction of residual stress. In this work, a hybrid method was introduced called bending mode ultrasonic-assisted friction stir welding (BM-UAFSW) and its effect under various vibration amplitudes was investigated on the longitudinal residual stress in a cross-section area of 3 mm and thickness of 5 mm AA6061-T6 plates using contour method. The findings indicated that BM-UAFSW can decrease the maximum longitudinal residual stress by up to 24% in relation with the conventional FSW. In addition, the reaction forces along tool axis and macrostructure observation were provided to illustrate the effect of high-frequency bending mode ultrasonic vibrations on the welding force and welding quality. All the results suggest that BM-UAFSW with amplitude of 2 and 3 μm provides the best outcome for the welding of 3 and 5 mm thick joints, respectively.

Structural Phase Evolution in Ultrasonic-Assisted Friction Stir Welded 2195 Aluminum Alloy Joints

The authors examined the structural and phase state of fixed joints produced by method of friction stir welding (FSW) and ultrasonic-assisted friction stir welding (UAFSW) from extruded profile of aluminum alloy AA2195. In order to identify the role of ultrasonic application in the course of welding, such characteristics, as volume fraction and average size of secondary particles are compared in the base material and stir zones of FSW and UAFSW joints. By applying the methods of SEM and TEM analysis, researchers established the complex character of phase transitions as a result of ultrasonic application.

Ultrasonic-assisted aging in friction stir welding on Al-Cu-Li-Mg aluminum alloy

Friction stir welding (FSW) on Al-Cu-Li-Mg aluminum alloy V-1469 (AA2195) has been carried out to find out the effect of ultrasonic energy on the microstructural evolution of the welded metal. It was found that ultrasonic-assisted FSW (UAFSW) reduced the recrystallized grain size in the stirring zone (SZ), facilitated strain-induced dissolution of both soluble and insoluble intermetallic precipitates, and enhanced solid solution grain recrystallization and precipitation of coherent metastable phases.

Test analysis for ultrasonic assisted friction stir welding of aircraft skin aluminium alloy

Test analysis for ultrasonic assisted friction stir welding of aircraft skin aluminium alloy

Recent Developments for Ultrasonic-Assisted Friction Stir Welding: Joining, Testing, Corrosion - an Overview

Due to the steadily increasing demand on innovative manufacturing processes, modern lightweight construction concepts become more and more important. Especially joints of dissimilar metals offer a variety of advantages due to their high potential for lightweight construction. The focus of the investigations was Al/Mg-joints. Friction Stir Welding (FSW) is an efficient process to realize high strength joints between these materials in ductile condition. Furthermore, for a simultaneous transmission of power ultrasound during the FSW-process (US-FSW) a positive effect on the achievable tensile strength of the Al/Mg-joints was proven.In the present work the industrial used die cast alloys EN AC-48000 (AlSi12CuNiMg) and AZ80 (MgAl8Zn) were joined by a machining center modified especially for Ultrasound Supported Friction Stir Welding. The appearing welding zone and the formation of intermetallic phases under the influence of power ultrasound were examined in particular. In order to identify optimal process parameters extensive preliminary process analyzes have been carried out. Following this, an ultrasound-induced more intensive stirring of the joining zone and as a result of this a considerably modified intermetallic zone was detected. At the same time an increase of the tensile strength of about 25% for US-FSW-joints and for fatigue an up to three times higher number of cycles to failure in comparison to a conventional welding process was observed. Moreover, detailed corrosion analyzes have shown that especially the welding zone was influenced by the corrosive attack. To expand and deepen the knowledge of the US-FSW-process further material combinations such as Ti/Steel and Al/Steel will be considered in future.

Effect of Ultrasonic Application during Friction Stir Welding on Microstructure and Properties of AA2024 Fixed Joints

Microstructure and mechanical properties of aluminum alloy 2024 fixed joint produced by ultrasonic assisted friction stir welding are described. Tensile strength, microhardness, grain size and zone area are measured and compared with ones of joint produced without ultrasonic vibration. Analyzing this data authors make conclusion about ultrasonic vibration effect on friction stir welding joint quality.

Determining influence of ultrasonic-assisted friction stir welding parameters on mechanical and tribological properties of AA6061 joints

In recent years, ultrasonic vibration has been integrated with various types of manufacturing processes, and researchers reported enhancement of the process efficiency while applying this method. In the present study, a vertical high-frequency vibration is applied on friction stir tool to determine its effects on tensile strength and formability (as characteristics of mechanical properties) as well as surface quality and sliding wear rate (as characteristics of tribological properties) of the welded AA6061. L9 Taguchi design was used to conduct the experiments and analyze effect of factors on mentioned quality characteristics. The four major parameters are ultrasonic power, tool rotary speed, traverse speed, and axial force. Also, the optimal welding conditions to maximize the tensile strength and formability and minimize the surface roughness and sliding wear rate were identified using grey relational analysis and reported here. Results indicated that the vibration power is a most significant factor having positive influence on both mechanical and tribological properties of welded samples.

A study of the temperature field during ultrasonic-assisted friction-stir welding

Ultrasonic-assisted friction-stir welding is a new solid-state metal welding technology, based on friction-stir welding, in which weld performance is improved through application of ultrasound during welding. In this study, a model for the temperature field in 1.8 mm 2024 aluminum alloy is built based on computational fluid dynamics and elastic-plastic mechanics theory. Result show the impact of the ultrasound’s vibrations on the temperature field is less obvious at lower welding speeds. However, at higher welding speeds, it can provide the additional heat to keep sufficient welding temperature. The numerical results are compared with optical micrographs in order to validate the numerical models. Good agreement is obtained.