| With the continuous improvement of the society, the security and energy consumption saving of the industrial products are the focused issues nowadays. Therefore, the products need to be reduced their weight. However, aluminum alloy has the characteristic of low density, high specific strength and good abrasive resistance which is widely used in the aerospace and transportation, etc. Welding in the aluminum alloy components processing and manufacturing occupies a decisive position. Nevertheless, there are many defects in the welding joints of aluminum alloy which seriously limit the application field of welding parts of aluminum alloy in the industry. There are several methods to weld aluminum alloy, and the tungsten inert gas(TIG) welding has the characteristics of good adaptation, easy operation and low cost that has a wide application range. But the TIG also has the problems of shallow depth of fusion and low welding efficiency. The proposed ultrasonic assisted TIG(U-TIG) method can improve the disadvantages of the conventional TIG, and it has the unique advantage in welding aluminum alloy.The U-TIG welding torch is the major part in the U-TIG method. The welding torch directly decides the welding results. At present, the U-TIG welding torch is not enough perfect. For this reason, the welding torch had designed and optimized again to realize the integration and practical application. The corresponding tests were conducted on the welding torch and the results showed that the welding torch can work stably and reliably. And the optimum radiation height of this welding torch was confirmed. Sound field condition in the space between the amplitude transformer and workpiece surface was simulated with the finite element software COMSOL. The distribution characteristics of the acoustic pressure and acoustic radiation force were simulated.The welding arc was shot by the high-speed camera. Compared with the conventional TIG arc, the U-TIG arc contracts and the light of the arc brightens. Besides, it’s the first time to observe that the hybrid arc has a phenomenon of periodic bounce. Furthermore, the arc was measured by the current and voltage sensors and the results showed that the voltage of the arc increases due to the adding ultrasonic. And the arc thermal efficiency is improved. The main reason of these phenomena produced in the hybrid arc is that ultrasonic radiation force affects the motion state of the arc plasma.The 2195-T8 Al-Li alloy was welded with the conventional TIG and U-TIG. The results of microstructure in joints showed that there was mainly the eutectic structure of α-Al and θ-Al2 Cu phase in the weld zone. There were obvious shrinkage cavities in the weld zone of conventional TIG while the microstructure in the weld zone of U-TIG was more compact as a result of ultrasonic vibration to the molten pool. There was specific equiaxed fine grain zone existing in the Al-Li alloy in the fusion zone. The equiaxed fine grain zone was apt to form in the U-TIG process so that this microstructure was more obvious in the joint. The source of joint fracture is that the coarse grain in the heat affected zone and hard-brittle eutectic structure which distributed like nets. The mechanics performance testing showed that the strength coefficient and the percentage elongation were increased because of the adding ultrasonic. The soften phenomenon weakens in the joint of U-TIG tested by the Vickers hardness. Moreover, the heat affected zone is narrow and accordingly the mechanical property is good.Finally, welding work on the aluminum tubes of small diameter and big diameter was done. The formations of welding joints are perfect and the joints comply with relevant standard requirement. |
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