Study On Welding Charicatics And Mechanism Of Energy Interaction During Laser-TIG Double-Side Welding For Aluminum Alloys

Laser welding of aluminum alloys faces the problems of high reflectivity, high thermal conductivity and high thermal diffusivity, and heavy porosity formation in the weld metal. To solve these problems, a novel technology of laser-arc double-side welding was developed. On the one hand, it attempts to improve the characteristics of laser welding by the arc heating, such as the stability of keyhole, improvement of welding quality, decrease of porosity. On the other hand, it tries to reform the stability of the arc by the laser heating. Due to the combination heating of laser beam and TIG arc on the opposites of workpiece, the joining of high efficiency and good quality for aluminum alloy can be realized, such as the increase of energy utilizing efficiency for the laser and the arc, the improvement of welding quality and the decrease of cost.In the experiments, the plates of 4mm thick 5A06 aluminum alloy were used as the workpiece material. The experiments were carried out by combining a CO2 laser equipment and an inverter argon arc welding machine. The characteristics of laser-TIG double-side welding (LTDSW) for aluminum alloys were investigated, including welding technology, appearance of the welds and the decrease of defects. The microstructure and mechanical properties of the welds was analyzed under the typical energy matching of the laser and the arc. The control method of cross-sectional profile was put forward, and the welding parameters were optimized. At the same time, aiming at the adaptability of the LTDSW process, the experiments of aluminum alloy butt joint, dissimilar thickness butt joint were pursued, and the application foreground of this method was explored on the thick and thin plates for aluminum alloys.To understand the physics property and interaction of the arc and the laser in the LTDSW process, the arc shapes and its current-voltage characteristics were investigated systemically by signal picking system and image processing technology. The influence of the specific heat transfer for laser keyhole welding on the characteristics of the arc was investigated, and its mechanism was analyzed in the LTDSW process. The local high temperature zone of laser keyhole heating was validated as the reason of arc constriction, the decrease in the voltage, the improvement of process stability. The transformation rule of arc energy effect was explored under various experimental conditions. The transformation rule and cause of laser-induced plasma behavior were analyzed. All the investigations can provide for the experimental data and theory base to analyse the heat transfer of the process.According to the conditions of threshold power density and temperature on the formation of laser keyhole, an adaptive numerical model for examining and simulating the heat transfer process is developed, including the mode of close keyhole penetration and the mode of open keyhole penetration. The temperature fields of the process were calculated with finite element method. The characteristics of heat transfer, the forming process of keyhole and molten pool were investigated by FEM analysis. Utilizing the adaptive heat source model, the transformation rule of the welding formation, the conditions of critical penetration and the open keyhole full penetration were calculated under different welding velocity and plate thickness.At last, from the theory, experiment and numerical simulation point of view, the mechanisms of enhancing penetration and increasing heat efficiency were explored in the LTDSW process. The main causes of increasing heat efficiency were proved as in turn: the formation of heat-congregated region, the increase of keyhole depth and the convergence of the arc. The transformation rules of the melting efficiency were investigated under different experimental conditions. The optimal energy matching and position conditions of the laser and the arc were put forward.