Analysis On Charicatics During Laser-TIG Double-side Welding For Aluminum Alloys

As a high-efficiency, high-quality, low-cost welding method, laser-arc hybridwelding technology is one of the main research focuses in the hybrid manufacturingtechnology fields in recent years. Although it becomes the consensus that laser-archybrid welding technology can increase the penetration, improve the speed andadaptability of welding effectively, the interaction mechanism of laser and arc has notbeen fully understood until now. It can’t describe the whole process that laser and arcinteract with each other, when laser and arc are in the same side. To solve this problem,this paper uses laser-TIG double-side welding (LTDSW) to join2219aluminum alloy,and measrues the temperature distribution of the arc side with thermocouple, to explorethe physical mechanism of laser-arc hybrid welding interaction.Firstly, a LTDSW welding system was established, and laser-arc interactioncharacteristics were studied from the side of molten pool feature size and thecrystallization behavior. In the hybrid welding process, the added laser can assist arc informing a molten pool effectively, so that improved appearance of arc weld. On thebasis of this, it was studied that how the weld width and penetration changed when laserpower and arc current changed. The crystal morphology is symmetrical and inerraticwhen welded by single heat, but the stir phenomenon in hybrid weld pool led to grainrefinement and isometric crystal grain growing up locally.Then, based on the analysis of the molten pool macro size, it is micro qualitativeanalysed that the difference of grain size and orientation between the hybrid weldingand single heat welding, and the microstructure and mechanical properties of the weldedjoints were studied at the same time， to study laser-arc hybrid welding interaction fromthe view of welded joints properties. Compared to single heat welding, the grainrefinement and the orientation was different in hybrid weld zone, while a lot ofsmall-angle grain boundaries produced. Weld joint was composed of the weld zone(WZ), the solid solution zone (SSZ) and overaged zone (OZ). The second phase in thehybrid weld seam was mainly in granular form, and in the single heat weld seam wasmainly in the mesh form. The hardness of the seams welded by hybrid heat source islower than those welded by single heat source,but the tensile strength of the seamswelded by hybrid heat sourceis higher because the effect of grain refinement causedmore grain boundaries in the weid seam. But hybrid welding has better ductility becauseof less and smaller porosity.Finally, the flow on the molten pool surface was observed through high-speedcamera and the thermal cycle curve was measured by thermocouple, and the causes ofthe differences on grain and microstructure were analysed between the hybrid welding and single heat welding. In the condition that the workpiece was penetrated duringhybrid welding, the molten pool stirred acutely, while the droplet sprayed out from thearc side. The thermal cycle curve forming by laser was narrow and tip in the arc side.The central hot zone was very small and the temperature gradient is great, which led tothe binding of the arc side temperature field.