Temperature Field Studies And Joint Properties On Ultrasonic Assisted Friction Stir Welding Of Aluminum Alloy

Abstract:With the development of science and technology, aluminum alloy is widely used in the field of aerospace, military, and civilian industry. Friction stir welding (FSW) as a solid-phase welding technology, which can effectively avoid the defects such as cracks, porosity and become the preferred welding technology of aluminum alloy welding. Friction stir welding but also exist some limitations, in this paper, on the basis of the aluminium alloy friction stir welding, ultrasonic is imported into the process, namely the ultrasonic assisted friction stir welding (UAFSW), to study the effect of ultrasonic in welding process.In this paper, with the Ansys finite element software,2024-T4aluminum alloy three-dimensional heat transfer model of FSW and20kHz,25kHz UAFSW were established, to analyzing their temperature field distribution under the condition of the same welding speed and rotational speed, found that ultrasonic import can lower the temperature of the weld forming during the process of welding,20kHz UAFSW peak temperature is lower than FSW’s, and25kHz UAFSW peak temperature slightly lower than20kHz’s. Finally, with infrared thermal imager to measure the whole welding process, verified the correctness of the models.1.8mm thick2024-T4aluminum alloy is adoped in the experiment and appropriate welding parameters of aluminum alloy sheets are explored through a large number of ultrasonic assisted friction stir welding experiments. Some comparative experimints were done between ultrasonic assisted friction stir welding and friction stir welding, the results showed that there is obvious difference in the macro micro of weld surface between FSW and UAFSW, the latter is more than the former rules of level off, the texture is more clear.UAFSW joint performance is superior to FSW, and25kHz UAFSW joint performance is better than20kHz UAFSW joint. Experimental results show that20kHz UAFSW joint average tensile strength is higher than the FSW’s about20Mpa under the same welding parameters, and25kHz UAFSW’s is higher than20kHz UAFSW’s about5Mpa, and25kHz joint has the best elongation, the highest hardness. Within three days after welding, the UAFSW joint is more lively than FSW’s, and less corrosion resistance; With the passage of time, the corrosion resistance difference gradually disappear, converge in around15days after welding. Metallographic microstructure show that the25kHz UAFSW joint welding nuclear area grain is most small, which also has uniform organization and the highest hardness, the20kHz UAFSW joint is less better than25kHz UAFSW’s, the FSW joint welding nuclear area grain is most relatively bulky,and hardness is lowest.Experimental results show that ultrasound play a certain positive effects on the weld quality,which can enhance the flow of the metal around mixing head, reduce the friction resistance, inhibit the formation of defects, achieve the effects of grain refinement so as to enhanced mechanical properties, and improved weld quality, with the increase of ultrasonic frequency, the positive role and the effect was more obvious.