Study On Temperature Field And Flow Field Of Aluminum Alloy Oscillating Laser Welding Molten Pool

Aluminum alloy laser welding is prone to problems such as poor weld formation,porosity,etc.It has been regarded as a poor weldable material in laser welding.With the development of beam forming technology,the oscillating laser welding technology has become more and more mature.In order to solve these problems,the above problems can be improved to a great extent by increasing the area of the heat source and enhancing the stirring effect on the molten pool through beam oscillation.At present,the research work on the oscillating laser welding is mainly focused on the welding process,and there are few reports on the mechanism of heat and mass transfer in the molten pool.In this paper,for the oscillating laser self-melting and filler wire welding method,based on the Flow 3D numerical simulation platform,numerical simulations of the molten pool thermal heading and flow field characteristics in the oscillating laser welding process are provided,which provide theoretical basis for process optimization and regulation of weld microstructure and performance.In this paper,the 5A06 aluminum alloy is used as the material to establish the heat flux coupling model of laser oscillating welding.The true VOF method is used to track the free surface of the molten pool,and the effects of back pressure,surface tension and buoyancy are considered.Firstly,the characteristics of the thermal and flow fields of the welding pool are compared and analyzed when the laser beam moves in different directions such as the normal movement,vertical oscillation,and circular oscillation.Combined with the experimental results,it is proved that the circular oscillating path can be used to obtain better fluidity molten pool,and then get better weld formation and lower porosity.Further,based on the circular oscillating laser welding method,through the combination of numerical simulation and experimental results,the effects of the parameters such as the oscillating amplitude,the oscillating frequency,and the welding speed on the flow field in the molten pool thermal field,the morphology of the weld,and the porosity were systematically studied.The results show that with the increase of the oscillating amplitude,the depth-width ratio of the weld pool is obviously reduced and the stability of the weld pool is enhanced.With the increase of the oscillating frequency,the direction of the liquid flow in the molten pool will change greatly,and the main vortex inside the weld pool will be horizontal.When changing to the vertical direction,the surface of the weld is better shaped and the porosity is significantly reduced.Under oscillating welding conditions,increasing the welding speed will reduce the depth and width of the weld pool,but it will have little effect on the porosity of the weld.Finally,the heat flow coupling calculation model for the oscillating laser filler wire welding is established.The filling process of the welding wire is fitted as the momentum source term in the calculation domain.The influence of the welding wire filling on the thermal and flow fields in the molten pool is analyzed.Compared with the changes of conventional laser filler wire welding,the influence of wire feed speed on the weld pool characteristics of the oscillating laser filler wire was further studied.The results show that with the increase of wire feeding speed,the convection phenomenon in the molten pool is gradually reduced,and the stability of the molten pool is improved.