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A three-dimensional (3D) numerical model with the volume of fluid method is developed for high-speed variable polarity gas tungsten arc welding (VP-GTAW) of aluminum alloys. It predicts the thermal flow field in the weld pool, the weld pool surface deformation, and solidified bead geometry during VP-GTAW in successive welding passes. Verification of the numerical model was performed by comparing the calculated results with metallography of welded cross-sections. The prediction showed reasonable accuracy in predicting weld bead geometry. The prediction average relative errors of the bead width and depth of penetration are less than 7%. The deformed weld pool surface, the fluid flow in the weld pool, and maximum fluid temperature in the workpiece based on the developed model, are discussed in detail. The effects of welding speed and pulse frequency on surface depression are studied. The results show that the maximum fluid temperature is closely correlated to the welding speed and pulse frequency. Further, the upper and lower limit of maximum fluid temperature would provide a clue by which the surface depression and the pitch of humps may be recognized. An increase in welding speed will lead to the increase of the pitch of humps, but the reverse is true in the pulse frequency. These detailed physical insights facilitate the prediction of welding surface defects in the high-speed VP-GTAW of aluminum alloy.

Effects of Welding Speed and Pulse Frequency on Surface Depression in Variable Polarity Gas Tungsten Arc Welding of Aluminum Alloy