Research On Microscopic Mechanism Of Ultrasonic Eliminating Aluminum Alloy Welding Residual Stres

The existence of welding residual stress would lead to descend of the fatigue strength of the welding structure directly. It will not only affect the dimension stability of the welding parts seriously, but it could also cause destructive impacts to many properties of materials. The methods of being used to eliminate residual stress become more and more mature and diversified. Base on the deficiencies of the traditional elimination methods, a new method of eliminating residual stress has been put forward--ultrasonic impacting method. Until now, this method has been used successfully in some engineering projects in domestic. This paper will make a research of microscopic mechanism of eliminating aluminum alloy welding residual stress by ultrasonic impact.On the base of introducing the reasons of the welding residual stress and the methods of eliminating it, the paper takes6061aluminum alloy plates that is provided by Changchun railway vehicle Co., LTD as research object, through the finite element numerical simulates the welding process of aluminum alloy, determines the best impact frequency and the best impact position of eliminating welding residual stress by ultrasonic impact. It analyzes the microscopic mechanism of eliminating aluminum alloy welding residual stress by ultrasonic impact. Accomplishes the test experiment of the residual stress data that before and after ultrasonic impacting by X ray diffraction (XRD). Through the experiment of transmission electron microscope, it verifies the correctness of the microscopic mechanism of eliminating aluminum alloy welding residual stress by ultrasonic impact.The experimental results show that:measure the residual stress data that before and after ultrasonic impacting by X ray diffraction, through analyzing the impact effect of the three groups of materials, it proves that the eliminated effect of ultrasonic impacting is better than that of traditional eliminating methods when the residual stress of the materials that its distance to the surface is shorter than3mm. The transmission electron microscope experiment shows that after ultrasonic impacting treatment, the dislocation of grains slips in the role of shear stress. Some yielding dislocations move from the position that with high-energy to a new one that with lower-energy. The total energy of the dislocations reduces, and the density of dislocations increases greatly. The dislocations become smaller and more uniform, that releases the residual stress directly.Not only the effect that eliminated by ultrasonic impacting technique is higher1-2times than traditional methods, but it has many other advantages, such as:security, energy saving, environmental protection and so on. This makes the ultrasonic impacting technique have wide development space in the field of application in the future.