Study on welding pool behavior and joint mechanical properties of 2195-T8 Al-Li alloy by laser wire filling double-sided welding

Al-Li alloy has become a new generation of aerospace application materials with its advantages of light weight, high strength and corrosion resistance. Compared with other Al-Li alloys, 2195-T8 Al-Li alloy has the best welding performance. Based on the welding demand of liquid rocket tank joint, better joint quality can be gotten with laser wire filling double-sided welding. For the fluid flow and temperature change in the molten pool in the welding process, heat-flow coupling mathematical model is established. By using the method of numerical simulation, the welding process of 2195-T8 Al-Li alloy is studied, and then the joint axial tensile strength test is carried out. The effect of welding speed and wire filling velocity of the molten pool on the flow and heat input is illustrated. The maximum joint strength under different welding parameters is obtained. The results show that under four different welding parameters, the fluid flow trend in the molten pool is basically the same between the first welding side and the second welding side, which is mainly clockwise eddy current on the left side and counterclockwise eddy current on the right side. Increasing welding speed or wire filling speed can improve the forming quality of the molten pool, reduce the heat input of the molten pool, refine the grain represented by columnar crystal in the welding fusion zone, and effectively improve the mechanical properties of the joint. By comparing and analyzing the numerical simulation and experimental results of 4 groups of different welding process parameters, the weld with the best forming quality and the smallest heat input is finally obtained. The axial tensile strength of the joint is up to 426.4 MPa, which is 72.6% of the base metal strength. The corresponding welding speed and wire filling speed are 50 cm/min and 1.8 m/min respectively.