| Tungsten insert gas (TIG) welding is widely employed in welding of aluminum, but the low welding efficiency and welding defects such as cracks and pores limit its application in aluminum alloys. Early ultrasonic wave has been introduced by our group into the aluminum welding process. The experiment results have showed that the introduction of ultrasonic in aluminum alloys welding can increase efficiency and improve the microstructures and performances of the weld. In order to explore the contribution of ultrasonic to the weld pool in Ultrasonic TIG hybrid welding (U-TIG), In the paper, The propagation and attenuation of ultrasonic wave in argon and arc space were studied, the arc characteristics and weld processes in aluminum alloy U-TIG welding were analyzed, finally the role of ultrasonic wave in weld pool was discussed.First the propagation characteristics of ultrasonic in argon gas and the arc space were analyzed. The research has indicated the ultrasonic energy in argon atmosphere mainly is affected by the transmitting height and the nozzle height, while shielding gas flow rate has little effect. Compared with the argon gas atmosphere, the ultrasonic wave has a severe propagation in the arc space. Arc length and current are also the factors of the propagation of ultrasonic energy. The high-speed camera was employed to observe the arc morphology and the compression in hybrid weld. The stronger of ultrasonic energy, the more obvious of the arc compression, furthermore the introduction of ultrasound in weld can improve the stability of current zero-crossing.For 2219 aluminum alloy, plate bead experiments were carried out. The ultrasonic effects on weld formation, depth to width ratio, microstructures were studied under different welding parameters. The results have indicated that U-TIG weld penetration increases significantly, weld fusion zone is narrower, and the pore defects are decreasing .The best matching experimental parameters is obtained for butt welding, which is the transmitter height of 30mm corresponding to the nozzle height of 11mm.On this basis of bead experiments, for the 2219 aluminum alloy U-TIG butt welding processes with and without filler wire were carried out, The research priority was the effects of transmitter height and the ultrasonic power supply voltage on microstructures and mechanical properties in ultrasonic AC TIG hybrid welding. The results have showed that: Compared with the conventional TIG welding, the coarse columnar grain microstructures of weld central zone have changed into fine equiaxed grains, The grains in heat affected zone are significantly refined in U-TIG welding without filler wire, furthermore the highest obtainable tensile strength is 265.7MPa, 5% higher than the TIG joints. With the ultrasonic power increasing, the tensile strength also increases. Compared to TIG welding with filler wire, fusion zone is narrowed down, the tensile strength increases by 2% in U-TIG welding with filler wire, the effect is inferior to U-TIG welding without filler wire.Finally, Fluent finite element software was adopted to analyzed the effects of the changing arc pressure and the acoustic streaming on the weld pool. The U-TIG force distribution significantly accelerates the flow rate; while the existence of acoustic streaming force in weld pool can produce two cycle flows with different directions ,which change the flow patterns of the pool, and promote heat transfer to the pool bottom. The process is favorable to weld structures and composition homogenization... |
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