Influence Of Ultrasonic Impact Treatment On Residual Stress Of Aluminum Alloy Welding And Its Finite Element Analysis

Ultrasonic impact treatment (UIT) is classified as surface plastic deformationenhancement techniques. It can be used for the improvement of the fatigue and stresscorrosion crack performance by reducing welding residual tensile stress and generatingcompressive stress. Most studies reported on UIT mainly focus on the stress state or theperformance comparison before and after treatment. However, there is little research aboutthe optimization of the processing effect and other fields. In this study, the influence ofdifferent treatment parameters on the stress state of the Aluminum alloy6061thin weldedsample has been researched. Also, the UIT process has been analysed by means of the finiteelement software ANSYS.By varying different impact times, speeds, zones and types of working head, the effectof the UIT on the welding residual stress state has been studied. The results indicate thatthe welding residual stresses reduce after UIT on the weld, weld toes or heat-affected zones.The tensile residual stresses at and nearby the weld gradually decrease and be compressiveat the beginning of the treatment. After proper processing time, the compressive stresses getsaturated. With the extension of the impact time or the decrease of the impact speed, thecompressive stresses diminish. The impact speed has greater influence on the stress statethan the impact time. Compared with the weld and double surfaces treated, the compressivestress region near the weld becomes larger with UIT on heat-affected zone. One-pintreatment has greater efficiency than three-pin treatment.Based on thermal elastic-plastic theory, the welding stress field is simulated usingthermal-structure indirect coupling and the welding temperature field simulation result asloads. The simulation result of the welding stress field can reflect the stress state changeprocess in welding. The finite element analyse of UIT conducts the welding residual stressas initial stress state, and employs displacement load. The simulation result of ultrasonicsingle impact shows that macroscopic deformation degree increases gradually, more andmore plastic deformation induced and makes the stress level of material higher in dynamicprocess. After the load killed, the stress level of material somewhat reduces. The simulationresult of ultrasonic continuation impact shows that the stress at the impact zone decreasegreatly with the increase of the load. To obtain a more accurate simulation result, the load selected should be higher than the displacement of the impact zone center after the actualUIT process.