Numerical investigation of surface roughness formation under alternating current gas tungsten arc welding

Surface roughness is a critical factor influencing weld quality and mechanical performance in aluminum arc welding. This study presents a Multiphysics simulation of surface ripple formation during gas tungsten arc welding (GTAW) under alternating current (AC). A two-dimensional transient model is developed using COMSOL Multiphysics 6.0, incorporating fluid flow, heat transfer, electromagnetics (EM), and phase transition. The influence of alternating electrode polarity on molten-pool flow and surface deformation is analyzed. Results show that thermocapillary convection dominates the surface flow, whereas the electrocapillary force exhibits periodic variation with current polarity and remains minor in magnitude compared with the thermocapillary force. Time-dependent ripple amplitude and pitch are evaluated using scale analysis and validated against experimental data. The model also reveals a finite response lag between surface velocity and ripple growth, attributed to thermal and capillary inertia. The findings provide physical insights for controlling weld surface morphology and optimizing AC-GTAW parameters in applications such as additive manufacturing, laser remelting, and precision surface processing, where molten-pool transport is dominated by thermocapillary convection rather than keyhole or vapor-recoil-driven dynamics.