Numerical Simulation Of Heat Flow Coupling In Weld Pool Of High Strength Aluminum Alloy By Dual-spot Laser Welding

With the development of aerospace industry in China,high-strength aluminium alloy has become the focus of attention and research.Laser welding is widely used in high-strength aluminium alloy as a welding technology with high precision and efficiency.However,in actual welding,traditional single-spot laser welding of high-strength aluminium alloy has certain limitations:hot cracks,pore,reduced strength of welded joints,hard to weld thick plates and other defects.It is found that dual-spot laser welding can improve the welding quality of high-strength aluminium alloy welding and solve the limitation of welding assembly accuracy.However,the current research on dual-spot laser welding mainly focuses on the comparison of single-spot and dual-spot welding characteristics and weld quality.There is little research on dual-spot welding mechanism.It is often unclear to infer the welding mechanism from the final weld quality.Therefore,in this paper,FLUENT software is used to analyze the temperature field and flow field of high-strength aluminium alloy dual-spot laser welding pool by numerical simulation method in order to reveal the flow characteristics of the dual-spot laser welding process of high-strength aluminum alloys and provide theoretical basis for welding parameter formulation and optimization.Firstly,a three-dimensional transient numerical model of heat-flow coupling in high-strength aluminum alloy dual-spot laser welding pool was established.The welding mode is deeppenetration welding,the melt flow mode is laminar flow and the dual-spot laser heat source is Gauss double-rotating body heat source.Secondary development of FLUENT software,laser heat source,vapor impulse P_r,surface tension Pσ,buoyancy F_B and source term in control equation are written as UDF and loaded into corresponding module.Then,the influence laws of dual-spot focal length,welding speed and laser power on temperature field and flow field in the molten pool of dual-spot laser welding were studied by controlling single variable.The results show that with the increase of bifocal length,the peak temperature of temperature field decreases,the flow rate increases but the flow area decreases,and the single keyhole gradually changes into double-keyhole in the molten pool.With the increase of welding speed,the peak temperature and flow rate of the flow field decrease,the shape of the temperature field changes,the flow field moves towards the back end of the molten pool,the width and length of the swirl current decrease,and the convection phenomenon decreases.With the laser power increases,the peak temperature and flow rate increase,the temperature field increases clockwise along the X-Y diagonal direction,the flow field expands towards the rear of the weldment and the growth rate slows down.The penetration depth,width and area of molten pool are inversely proportional to the change of dual-spot focal length and welding speed and directly proportional to the change of laser power.Moreover,the three all appeared the turning point that affected the penetration depth,the weld width and the pool area.Finally,the dual-spot laser welding test on high-strength aluminium alloy A7075 is carried out,and the sectional morphology of the simulated weld is compared with that of the tested weld by the method of morphological comparison of the fusion line.It is found that the morphological contour of the weld fusion line agrees well,which verifies the accuracy of the mathematical model.