| In the automotive industry, when light materials are considered to reduce vehicleweight, the connection of steel and aluminum must be taken into account. Steel andaluminum are different in physical and chemical properties, and the solid solubility ofthem is very low, so some FeAl brittle intermetallic compounds will form there,which will obviously influence on welding quality. In the process of laserwelding-brazing, the welding heat source only melts the aluminum, while steelmaintains the solid state or melts little. The weld pool solidifies and forms goodsoldering, which relies on the good spreading property of liquid aluminum on solidsteel and the thermal diffusion in the contact area of liquid aluminum and solid steelin welding pool. Laser welding-brazing is the most effective process to inhibit orreduce FeAl brittle intermetallic compounds.6016aluminum alloy and zinc-coated steel which used in vehicles body are takenas an object of study in this paper. By means of the techniques of numericalsimulation, the impact of changes of process parameters on the weld pool shape andweld penetration is studied during laser welding-brazing. Moreover, based onartificial neural network, a method of optimizing the parameters of laserwelding-brazing process is explored. Besides, the verification tests of thealuminum/steel laser welding-brazing are developed, and the weld morphology,microstructure of welding joints in all regions, microhardness, major elementdistribution and material composition are analyzed. The results are expected toprovide important theoretical guidance and technical support for laser welding ofmulti-material vehicle body.A mathematical model of weld pool in laser welding-brazing of aluminum andsteel is established. A calculation program is designed according to the quasi-steadystate condition of welding pool shape. The solid-liquid phase interface is used todescribe the welding pool shape. The distribution of geometry shape of welding poolis obtained based on the calculation of solid-liquid interface and liquid-vaporinterface of laser welding-brazing. In addition, the influence of changes of processparameters on welding shape is studied.A numerical model of the temperature field for laser welding-brazing isestablished. And a small step moving heat source is used to simulate the continuous irradiation of laser beam. Besides, a user-defined horizontal distribution Gaussianheat source model is loaded in ProCAST software by VC++program. Based oncalculation of temperature field for laser welding-brazing, welding penetrations underdifferent process parameters are obtained. And then, the influence of change ofprocess parameters to welding penetrations is studied.Orthogonal simulate experiments are designed based on BP artificial neuralnetwork. This network is trained by the sample of welding penetrations underdifferent process parameters. The nonlinear mapping relationship between weldingpenetrations and welding process parameters such as welding power, welding speedand defocusing amount, is obtained. And welding penetrations under differentwelding process parameters are simulated and predictedBased on simulations of molten pool and welding penetrations, with fiber laser,verification tests of laser welding-brazing of6016aluminum alloy and zinc coatedsteel under optimized process parameters are carried out. Welding specimen are testedby horizontal metallographic microscopy (HMM), scanning electron microscope(SEM) and X-ray diffraction (XRD). When the welding laser power ranges from1600W to1800W, welding speed is30millimeter per second, and the defocusingamount is0millimeter, welding seam is formed well. There is no obvious cracks,holes and other defects. And a step-like structure appears in the area of welding seam.In this area, there is a clear boundary between steel and aluminum. The interface isformed by the wetting, filling and spreading functions of liqu id aluminum on steelbase material. In the concave region, steel and aluminum fuse well, the mixing area ofFe element and Al element is very wide, there is no obvious FeAl brittle intermetalliccompound, and the main reason for interface binding is thermal diffusion between Feand Al. |
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