Study On Welding Process & Fatigue Properties & Deformation Of Variable Polarity TIG Welded T-joints Of Aluminum Alloy

The production of welded panels reduce the manufacturing costs and improve the efficiency of the overall structure. The variable polarity welded T-joints which have a few defects, good fatigue performance, small deformation is very meaningful.Based on self-melting experimental, the parameters of variable polarity TIG welder were compared. The influence of DCEP current value, duty cycle, DCEN current value, variable polarity frequency on weld penetration, weld width , width of cathode cleaning action were discussed in detail. And the influence of pulse modulation was studied. The results will provide important reference on parameter selection for the T-joints welding process.Macro-defects of T-joints cross section were observed. It was found that the better root penetration was acquired by helium-argon mixture shielding gas. Thus the helium-argon mixture shielding gas is more suitable for backing weld.Six sets of T-joints specimens: T-welded and the peened welded T-specimens by argon shielding gas; T-welded and the peened welded T-specimens by helium-argon mixture shielding gas, base material and peened base material plates were submitted to four point bending fatigue tests .The fatigue strength of base material specimen is 113.7MPa. In comparison, the value of T-welded by argon shielding gas 82.7% of base material and the value of helium-argon mixture shielding gas is 65.12% of base material. The stress concentration factor in the weld toe was computed by ANSYS. Due to the knuckle radius of T-welded by argon shielding gas is larger, the stress concentration factor is smaller. Thus the argon shielding gas is more suitable for cosmetic weld.High value of residual compressive stress formed on T-welded weld toe after ultrasonic peening, while surface pits form, the stress concentration factor increases. In the high stress levels, the residual compressive stress is released. And the stress concentration factor increasing resulted in the poor fatigue performance. The increasing value is lower by helium-argon mixture shielding gas thus in the low stress level, ultrasonic peening is more effectively, the fatigue strength is larger than the corresponding T-welded specimens. While the increasing value is higher by argon shielding gas, ultrasonic peening is not so effectively, the fatigue strength is lower than the corresponding T-welded specimens. For giving full play to the role of ultrasonic peening, peening under load and using larger curvature radius impact needle and surface finishing after the ultrasonic peening.Finite element analysis software ANSYS was used to simulate the welding process. The value of bending deformation and angular deformation is close to the measured value, which verifies the accuracy of the simulation process. The fixture preload should be appropriate to balancing the deformation of the wing plate and web plate.Reasonable arrangement of position welding can ensure the gaps between the wing plate and web plate. The gaps will not shrink too much to reduce the bending deformation of the web. The size of fillet weld at the wing plate should be appropriate in the basic premise of the mechanical properties to reduce the weld cross-sectional area and reduce the heat input.