Effect Of Real Time Ultrasonic Impact Treatment On Welding Residual Stress, Deformation And Microstructure Property

Along with the uneven heating and cooling processes in welding, the residual stress and deformation was produced during soldering processes. After welding, both the organization and the performance of the work piece was changed to be uneven. Residual stress and deformation may cause the deformation of the work piece and reducing the strength of the weldment etc. With the poor uniformity of the organization, the joints were considered as the weakest part of the whole weld structures. Reducing the residual stress and deformation, and improving the microstructure properties of the joints is the ways to improve the weld ability.The real-time ultrasonic impact is a method, newly proposed, which can not only reduce welding residual stress and deformation but also improve the uniformity of the weldments’ organization. During the welding process, ultrasonic shock was carried on the back of the weld. Positive tensile plastic deformation was produced so as to reduce the welding deformation and residual stress. And the vibration caused by the ultrasonic impact may play an important role in improving the organization and the performance.The welding process can be divided into four different temperature ranges by different distances from the axis of the arc: the pool area, the brittle temperature zone, high temperature plastic zone and the elastic-plastic transition region. Firstly, based on the elastic-plastic mechanics theory and the rules of stress and deformation during the welding process, the theoretical model of reducing the stress and deformation by real-time ultrasonic impact was established. According to the model, a micro-bending of the weld was produced during the real-time ultrasonic impact, resulting in the introduction of the front seam tensile plastic deformation. After ultrasonic impact was removed, the residual tensile plastic deformation occurred to offset some of the weld shrinkage during the process of weld springback, so that the weld shrinkage decreases. Because the yield of the weld, the residual stress also decreases. Meanwhile, the greater the ultrasonic power was, the more obvious the reduction of the residual stress and deformation was. Also, the welding stress was reduced remarkably when the ultrasonic impact was applied on the elastic-plastic transition temperature zone; while, applied in the brittle zone, the welding deformation reduced a lot.By applying two different power ultrasonic impact in different temperature ranges on6mm plate, experiments were conducted, and experimental data was analyzed. The results of the analysis concluded that, it is most significant to reduce the residual stress when the high-power ultrasound was impact in elastic plastic transition temperature zone, and it is reduced the most deformation when the high-power ultrasonic was impact in the high temperature brittle zone. This is consistent with the theoretical analysis. Meanwhile, effect of ultrasonic impact on microstructure properties of the weld was explored, the results show that it is most influence when the ultrasonic impact was impacted under welding pool, it show columnar crystals weakening, the equiaxed grain generated and grain refinement.When ultrasound impact was applied on5mm plate with the power of800W, the grains were coarsened due to the large degree of superheat and the intense ultrasonic shock. Applied on the tail of the bath, a crystalline cracks was generated. In the butt experiment of12mm plates, the ultrasonic impact were added at different distances from the arc axis. It was at5mm away from the arc the ultrasonic impact applied that grain sizes were refined and the toughness, hardness and strength of the weld were improved.