FINITE ELEMENT ANALYSIS OF TEMPERATURE FIELD IN LASER plus GMAW HYBRID WELDING FOR T-JOINT OF ALUMINUM ALLOY

T-welded structures of aluminum alloy are increasingly used in automotive, railway vehicles, aerospace and bridges. However, compared with the simple joint, the T-joint of aluminum alloy is more difficultly welded due to its complex temperature distribution and fluid flow mode in the weld pool. Whether using laser welding or the conventional arc welding process, aluminum alloy T-wleded joint is more prone to welding defects such as crack, pore, undercutting, joint softening, and so on. As a promising joining technology, laser+gas metal are welding (laser+GMAW) hybrid welding not only combines the advantages of laser welding with those of GMAW, but also overcomes their shortcomings, thus having great potential to achieve high efficiency and high quality welding of aluminum alloy T-joint. So far, however, there is a lack of fundamental investagations involving mathematical modelling and understanding of the hybrid welding process of aluminum alloy T-joint. As key factors determining the weld quality, thermal field has a significant influence on microstructure and properties of T-welded joint. In this work, using the numerical simulation method, the temperature distribution in laser+GMAW hybrid welding of aluminum alloy T-joint was studied. Considering the influence of joint form on welding heat flux, an adaptive combined volumetric heat source model for laser+GMAW hybrid welding for T-joint is developed based on macroscopic mechanism of heat transfer. The arc heat flux and heat content of overheated droplet are described using an double ellipsoid body heat source model, and the laser power is regarded as peak density exponentially increasing conic body distribution. To take into account the effect of inclination of welding gun on heat flow distribution in T-joint welding, the heat source model is rotated by way of coordinate transformation, thus deducing the formula of combined heat source model suitable to hybrid welding for T-joint. The built model is used to calculate the geometry and dimensions in laser+GMAW hybrid both sided welding for T-joint of aluminum alloy under different welding conditons, and the simulated resluts agree well with the experimental ones, which indicates the accuracy and applicability of the combined model. Besides, the thermal cycles at different positions in hybrid welding for T-joint of aluminum alloy are computed, and the characteristics of the thermal cycles are analyzed, which will lay the foundation for prediction of microstructure and properties of welded joint.