Characterization of plastic deformation and material flow in ultrasonic vibration enhanced friction stir welding
Material flow and plastic deformation in ultrasonic vibration enhanced friction stir welding are visualized by employing a special marker material and welding procedure. Based on the results, three methods are developed to evaluate the volume of deformed material, the material flow velocity and the strain/strain rate, and the effect of ultrasonic vibration on the plastic deformation and material flow around the tool is characterized.
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Cited by (162)
Effect of material position and tool offset on the microstructure and mechanical properties of friction stir welded AA7075/AZ31B with ultrasonic assistance
2024, Journal of Manufacturing ProcessesThe primary focus of this study is to analyze how changes in material position and tool offset affect the microstructure and mechanical properties of dissimilar alloys (AA7075/AZ31B) joints. The study specifically examines these effects in normal and ultrasonic-assisted friction stir welded (UVaFSW) aluminum and magnesium-based joints. The experiment showed that the sound weld was achieved only when the AA7075 plate was placed on the advancing side (AS). The metallographic analysis showed that the use of ultrasonic vibration increased the flow of material in the nugget zone (NZ) and improved the length of interpenetration at the interface. Moreover, the intermetallic compound (IMC) layer thickness decreased throughout the interface during UVaFSW, improving joint strength. The maximum ultimate tensile strength was obtained at 1 mm tool-off condition for UVaFSW, i.e., 112.40 ± 7.24 MPa. Ultrasonic vibrations reduced the IMC thickness by up to 78 % at the middle of the joint interface. The fracture surface showed the ductile fracture mode in the case of UVaFSW compared to the FSW process. The current study establishes the framework for optimizing and controlling the welding process of dissimilar AA7075/AZ31B alloys, which possess considerable potential for use in the aviation industry.
Mechanism of ultrasonic effects on thermal-stress field in Cu/Al-FSW process
2024, International Journal of Mechanical SciencesThis paper examined the mechanism of ultrasonic depressive effects on Al/Cu intermetallic compounds (IMCs) during friction stir welding (FSW) process by combining numerical simulations and macro/microstructural evolution analyses. The coupling process of ultrasonic field and the multienergy field for Al/Cu-FSW was simulated for the first time. The ultrasonic mechanisms of the acoustic thermal effect, acoustic anti-friction effect and acoustic softening were considered in the constitutive model and thermal-stress boundary conditions. Based on our research, ultrasonic vibration (UV) could homogenize the Al/Cu plastic difference and the Al/Cu rheological properties in the mixed zone. The modeling results showed that the difference in flow stress between Al and Cu was reduced on the two sides of the weld. The gradient of the phase-volume fraction in the weld cross section was reduced under UV, which reduced the power of Al/Cu interdiffusion and inhibited the generation of IMCs via diffusion. In addition, the acoustic softening and antifriction effects reduced the contact interfacial heat flux and the peak temperature. The heat generation within the nugget zone decreased by approximately 12.8 %. The UV reduced the absolute value of the effective heat of formation (EHF) for Al2Cu and Al4Cu9, which indicated that ultrasound could inhibit the generation of IMCs to some extent. The decrease of heat and concentration gradient weakened the atomic diffusion and growth rate of IMCs. Therefore, the SEM images of the Al/Cu interfaces showed that the total thickness of the Al/Cu-IMCs decreased by approximately 30.5 %, the distribution of IMCs was more uniform, and the boundaries were straighter under ultrasonic effects. Under ultrasonic action, more fine Cu particles entered the Al side, and the Cu particles were scattered, showing a dispersed distribution. Furthermore, acoustic softening enhanced the plastic flow and increased the number of layered staggered structures at the Al/Cu interface, which enhanced the mechanical interlocking of the Al/Cu composite. The tensile strength improved 21.3 % under the ultrasonic treatment.
Characteristics and mechanical properties of retractable pin-tool friction stir welded joints of A356-alloy LPDC hollow hubs
2024, Materials CharacterizationTo produce high-performance noise- and weight-reducing A356-alloy hollow hubs, hub-rims and hubcaps were prepared separately through low-pressure die casting and joined together through retractable pin-tool friction stir welding (RPT-FSW). The effects of the pin retraction speed (6–37.5 mm/min) on the microstructural and mechanical properties were analysed. The results showed that the stirred zone (SZ) could be divided into a double stirred zone (DSZ) and single stirred zone (SSZ) within the pin retraction region. During the pin retraction stage, the DSZ underwent severe deformation and had a longer high-temperature duration, had larger recrystallised grains after the second dynamic recrystallisation, and had a finer and denser β'′ phase after dissolution and re-precipitation. In contrast, the SSZ underwent static recovery due to the low processing temperature, resulting in less-coarsened original recrystallised grains accompanied by much coarsened original β'′ precipitates. The combination of severer deformation and higher temperature resulted in coarser nanoscale Si precipitations in the DSZ than in the SSZ. Statistical data showed that β'′ precipitates dominated the variation in strength in the RPT-FSW region. As slow pin retraction and a long thermal experience coarsened the β'′ precipitates, a U-type Vickers hardness distribution instead of a W-type Vickers hardness distribution formed in the SSZ. This distribution degraded the service performance of the RPT-FSW joints. An appropriately high pin retraction speed improved the strength of the RPT-FSW joints and the fatigue life of the A356-alloy hollow hubs.
Thermomechanical behavior and microstructural characteristics of 7055 aluminum alloy during friction stirring welding
2024, Materials Today CommunicationsThis study employed a viscoplastic finite element model and re-meshing technique to investigate the thermomechanical response of 7055 aluminum alloy during friction stir welding (FSW). The stirring pin rotates at 800–1200 rpm and moves at 80–120 mm/min (i.e., welding speed) during the FSW process. The temperature field and viscoplastic flow were mathematically modeled based on a computational solid mechanics method and predicted by a three-dimensional coupled thermomechanical numerical simulation. To validate the simulation results, real-time temperature measurements at the welded joint were acquired via thermocouples embedded in the plate prior to the welding process. Additionally, optical microscopy and electron backscatter diffraction techniques were used to examine the metallographic structure and grain orientation of the welds, respectively. The results revealed a temperature difference of 5–10 ℃ between the advancing and retreating sides of the plate. The material on the advancing side was extruded upward in a circular motion and eventually reached the surface. Meanwhile, the material on the retreating side moved half a revolution around the pin and remained at the original depth of the plate. Complete dynamic recrystallization occurred in the weld nugget, resulting in the formation of fine equiaxed grains with random orientation. In the thermomechanically affected zone, the proximity to the weld nugget was associated with an increased proportion of high-angle grain boundaries and recrystallized structures. Simultaneously, the intensity of the deformation texture decreased, while the recrystallized texture showed an initial strengthening followed by a subsequent weakening. This comprehensive investigation contributes to a deeper understanding of the thermomechanical behavior and metallographic characterization of 7055 aluminum alloy during the FSW process.
Gradient process parameter optimization in additive friction stir deposition of aluminum alloys
2024, International Journal of Machine Tools and ManufactureAs one of the most novel additive manufacturing methods, currently selection and optimization of processing parameters in additive friction stir deposition (AFSD) have mainly relied on experiments and subsequent characterization of microstructural and mechanical properties. Such approaches are both time- and resource-consuming. Therefore, an ultrasound elastography enhanced gradient process parameter optimization method was applied in the present work to obtain a window of optimized processing parameters for AFSD processing of aluminum alloy by varying both rotational and linear deposition speeds. The quality of AFSD processed layer was investigated for physical nature of surface, dynamic elastic modulus, and microstructural aspects in cross-sections of the deposited layer. The efficiency in exploring process parameters was significantly enhanced by implementing a high-throughput screening experimental design based on application of gradient process parameters and continuous ultrasound elastographs. In addition, the applied ultrasonic elastography technique assisted in evaluating the homogeneity in microstructure and mechanical properties of AFSD sample over the entire gradients of the process parameters. The techniques adopted in current work can be further extended to identify suitable parameters for AFSD fabrication of components with desired mechanical properties such as hardness, fatigue, etc.
Numerical and experimental study on the thermal process during additive friction stir deposition
2024, CIRP Journal of Manufacturing Science and TechnologyAdditive friction stir deposition (AFSD) is a solid state coating process as well as a developing solid state additive manufacturing technology. AFSD has numerous advantages over friction surfacing coating technology. However, extensive research has demonstrated that a relationship between microstructure and mechanical properties exists at present. On the other hand, a few research focus on temperature field evolution.The temperature field during AFSD is examined in this paper using a combined experimental-numerical approach. According to characterizations of AFSD thermal process, AFSD was classified into friction preheating stages and steady deposition stages. The friction preheating model and the steady deposition heat model are both established. The experiment is carried out to confirm the temperature difference between the simulation and the experiment, where experimental and numerical results correspond well. The AFSD process parameters include rotational speed, feed speed, and deposition rate. The purpose of this research is to examine the effect of process parameters on heat input during the production of aluminum alloy coating by AFSD. The results shows that rotational speed is a critical element that influences heat input. Overall, the comparisons of experimental and numerical results show that the numerical model's accuracy is satisfactory, and the effect of process parameters on heat input was thoroughly investigated.