Study On The Behavior And Mechanism Of Molten Pool In Laser Deep Fusion Welding Of Steel/Aluminum Dissimilar Metals

The use of steel/aluminum structural parts on the car body to achieve weight reduction in automobiles has become the forefront and hot spot of current automotive technology.Laser deep fusion welding has the advantages of high energy density and stable welding process,and has become an important connection method for steel/aluminum structural parts,but steel/Aluminum dissimilar metals involve a variety of physical phenomena in the laser deep fusion welding process,the formation of small holes in the molten pool,the treatment of thermodynamic performance parameters in different metal mixing zones,and the mechanism of coupling of solid/liquid/gas polynomial dynamics.It is not clear.In order to understand the distribution of temperature field and the dynamic behavior of the fluid in the molten pool during the welding process of steel/aluminum,DP590 double-phase steel and 6016 aluminum alloy were selected as the research object in this paper.Observe the shape of the weld pool and use the multi-field analysis software Comsol Multiphysics 5.3 to establish a two-dimensional welding model for steel/aluminum dissimilar metal welding,taking into account the back pressure,surface tension and Marangoni convection generated during the welding process.Influencing,the continuous function is used to process the thermodynamic performance parameters of the Fe/lI mixing zone,the level set method is used to capture the free interface of the pinhole,and the level set method in the fluid heat transfer and laminar flow module in the Comsol software is used to simulate the transient of the pinhole.During the formation process,the effects of different welding process parameters and physical driving force on the temperature field and flow behavior of the molten pool were studied.The distribution of the temperature distribution in the bath,pore formation,and energy transfer mechanisms were analyzed.The scanning electron microscope and spectrometer with EBSD and EDS probes were used to study the welding.Phase composition,element distribution,and welding spectrum of joints,discussion of laser deep fusion welding mode and corresponding process conditions FeAI chemical combination,The distribution rule of the powders is analyzed,and the influence mechanisms of the added powders on the microstructure and distribution of the weld joints are analyzed.The results are expected to provide theoretical guidance for the temperature and the regulation of the distribution and distribution of FeAl compounds in the steel/aluminum overlap laser deep fusion joints.In order to obtain the best welding process conditions,the temperature and flow fields of the steel/aluminum joint under different welding power and welding speeds were numerically simulated.The results show that the laser welding is a typical deep penetration welding mode when the laser power is 1300W or more;under the optimum process conditions,namely,the laser power is 2100W,the welding speed is 35mm/s,and the width of the small hole is 1.4mm,and the depth is 2.2mm;numerical simulation results based on the temperature field and flow field of Ti powder added between steel/aluminum layers in laser deep fusion welding mode and found that adding Ti powder can regulate the energy coupling between steel/aluminum and reduce the temperature on both sides of the bath due to temperature The convection caused by the difference reduces the width of the weld zone and the heat-affected zone of the welded joint;compared with the case of the non-added Ti powder,more metal liquid in the molten pool is gasified,and the fluidity of the molten pool is improved;The morphology of the pores was found to be whether Ti powder was added or not.FeAI compounds were mainly distributed on the bottom of the molten pool and on both sides of the lower layer of aluminum.The numerical simulation results were verified by EBSD,EDS energy spectrum and spectral tests.It was found that Ti powder was added and welded joint welding was found.The area of ferrite and martensite increase in the seam area are basically the same as the relative contents of the phases in the base metal zone.The upper double-phase steel is not softened;when the Ti powder is added,the width of the Fe/AI mixing zone in the aluminum side pool is larger than that of the unaddition powder The width of the Fe/AI of the mixing zone,an FeAI compounds mainly in the bottom of the bath and the aluminum lower sides,substantially in line with the numerical simulation results of estimation.