| Automobile lightweight has become the frontier and hotspot of automobile technology in twenty-first century, the using of lightweight materials has become the inevitable trend of the development of the automobile industry. Dual phase steel and aluminum alloy as good lightweight material have been widely used. It is difficult to obtain high-quality welding joint and easy to generate the brittle Fe-Al intermetallic compound because of the clear difference between physical and chemical properties.To explore a new method of steel/aluminum connection, this paper selects DP590 high strength steel and 6016 aluminum alloy as the research object, the experimental scheme of laser lap welding of steel to aluminum with or without powder addition and metallic vapor/plasma spectrum are designed. By using high speed cameras horizontal, micro spectrometer, metallographic microscope, scanning electron microscope with EDS and EBSD, microcomputer control electronic universal testing machine and other means to study the morphology of welding metallic vapor/plasma, the spectral information of plasma, weld formability, the microstructure of welded joint region, distribution and content of phase, grain size, interface combining situation and mechanical properties of welded joints. To explore the effect of welding process and improve the mechanism of the welding joint performance with powder addition, the research results are expected to provide a new thought of research for automotive dual phase steel/aluminum alloy welding and provide important theoretical and experimental basis for promoting the automotive lightweight.By collecting and analyzing metallic vapor/plasma shape and welding spectra, it is found that the color of metallic vapor/plasma is darker and the shape is scattered without powder addition. With Mn powder addition, the color of metallic vapor/plasma is bright, the relative intensity of spectra and electron density of metallic vapor/plasma is increased. The color of metallic vapor/plasma induced by laser welding with Si powder addition is bright, the relative intensity of spectra and electron density of metallic vapor/plasma is increased. In addition, the metallic vapor/plasma form a certain angle with the surface of welding plate. The particles density of metallic vapor/plasma is increased with powder addition, more particles of Fe and Mn escape from the molten pool during the welding process. It effect the absorption of the laser energy of welding material with powder addition.To get the best weld formability, the fiber laser welding test with Mn or Si powder addition is carried out on the Dual-Phase steel of 1.4mm and the 6016 aluminum alloy of 1.2 mm. The optimized parameters of the welding test are 2000W of the laser power,50 mm/s of the welding speed,+2mm of the focal distances, 15L/min of the Ar gas flow. With powder addition, the weld face is continuous, forming uniform, non-obvious defects. The average shear strength of welding joints in DP steel/aluminum alloy laser welding is improved by adding powder, comparing those without powder addition. With Mn powder addition, the diffusion from the lower Al to the upper steel side is suppressed, and the molten Al remove to the both side of the Al molten pool. Meanwhile, the mixing of Fe and Al in the molten pool is decreased and the size of Fe-Al intermetallic compound in aluminum/steel interface is reduced. Therefore, it can improve the mechanical properties of DP steel/aluminum alloy welding joint with Mn powder addition. With Si powder addition, the welding material absorb more laser energy and the penetration depth of weld metal is increased. Meanwhile, the rheological property of the molten pool is improved and the thickness of the interface layer is reduced. What's more, the interface layer produce Al0.5Fe3Si0.5 which has good ductility. Therefore, it can improve the mechanical properties of DP steel/aluminum alloy welding joint with Si powder addition. |
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