Study On Controlling Of Welding Stress And Distortion For Aluminum Alloy By Welding With Trailing Ultrasonic Vibration

Contrapose the problems of large welding distortion for aluminum alloy sheet.From the view of mechanical perspective, a new method of welding with trailingultrasonic vibration to control the welding residual stress and deformation ofaluminum alloy sheet is put forward. During the welding process, a vibration force isapplied along the thickness direction of the weldment using power ultrasound, and theposition of the vibration force has a certain distance behind the molten pool. Thedevice moves with welding heat source and vibrates the metal which is in the state ofcondensing and shrinkage, which will produce longitudinal plastic extension andcompensate for the compressive plastic strain in the heating process. The shrinkage ofweld will be reduced, and then reducing the transient stress in welding process andthe welding deformation in the end.Finite element numerical simulation and experimental study are considered to study.ultrasonic vibration force is chosen as power sources. According to the theory ofcontrolling welding residual stress, welding with trailing ultrasonic vibrationequipment is designed and self-developed based upon perspective of longitudinalresidual stress of thin plate welding, which could meet all experiment conditions.Based on finite element numerical simulation analysis, thermal-mechanicalcoupling model of aluminum alloy sheet welding with trailing ultrasonic vibration isbuilt using MARC software. Temperature field and stress field in different conditionof welding process are calculated, the maximum residual stress is263Mpa, which iscorrect, the result verifies the reliability of the model. The optimal weldingparameters and the best distance between vibrating position and heat source in theoryare obtained, and the scope of effective vibration is determined.Welding experiments with LY12aluminum alloy plate as specimen, the size is320mm×200mm×2mm, are conducted on self-developed device, and residual stressof plate after welding are measured. The test results show that when the distancebetween vibrating point and heat source is22mm, longitudinal residual tensile stress in middle cross-section reduced from282.4MPa of conventional welding to60.6MPa. The maximum compressive residual stress reduced from-83.3MPa to-27MPa, the descend range is67.6%, the average compressive stress is-15.1MPa,which is below critical buckling stress of the plate. The buckling deformation isdisappeared entirely, and the maximum deflection of plate edges dropped from8.66mm to0.9mm. There are good agreements between test results and simulationresults.Microstructure and mechanical properties of LY12plate welded joint in differentwelding conditions are compared. The result shows that while vibrating metal inplastic zone with ultrasonic energy of high frequency pulse power, the characteristicsof vibration welding is taken into account, which will improve crystalline forms ofweld metal, break the thick branch crystal, refine the microstructure of weld metal,and change crystalline direction of crystal grain. The organizations tend to be moreuniform. The tensile strength, alongation and hardness of welding joint are greatlyimproved when compared to conventional welding.