| Galvanized steel can play an anodic protection for base steel in corrosive environment, so the life of the parts can significantly extended. AISI304stainless steel has excellent corrosion resistance, formability and weldability. The compound structure combined with galvanized steel as inner reinforced plate and AISI304stainless steel as the surface can take full advantage of merits of the two steels, where the stainless steel surface keeps smooth while the strength of composite structure increases.The traditional processes of attaching galvanized steel and AISI304stainless steel are resistance spot welding and bonding. As to the resistance spot welding, there are some problems-such as visible scars on the back surface of the stainless steel, deformation and large defects in resistance spot welding, so it is difficult to achieve high-quality connectivity, and the appearance of product reduces. As to the bonding method, there are some problems such as low intensity, easy to aging, inefficient and environmental pollution and so on. Therefore, how to realize the appearance of surface of stainless steel keeping smooth is a current focus.Many types of materials can achieve the connection by laser welding, and laser welding has more advantages than traditional welding process. Especially as to homogeneous or heterogeneous alloy sheets in the aviation and automotive industry, the welding joints by laser have high quality.The galvanized steel and AISI304stainless steel were lap-welded by a pulsed-Nd:YAG laser in this article. The macro-morphology, weld penetration and shear strength of the joint were investigated in different processing parameters, then the optimal parameters were got. The distribution of the microstructure and microhardness of the joint in optimum parameters were analyzed. The numerical simulation of the laser welding process was performed, and the temperature distribution, welding heat cycle curve and pool shape were obtained. In order to validate the model, the melting isotherm of the temperature and macro-morphology of the weld’s cross-section were compared. At last the key problems such as defects and behavior of zinc during laser welding process were analyzed. The results are listed as follows: (1) In the experiments of the lap-joint laser welding, the weld joint is of good surface quality and the shear strength reaches its work requirement at the same time. The optimum welding parameters are I=350A, V=100mm/min, ΔF=-1mm, f=4Hz, W=10ms, and there is no weld trace on the back surface of AISI304stainless steel. Martensitic phase transformation occurs in the center of the welded seam, so the microstructure of the welded seam is martensite and residual austenite, and close to the side of galvanized sheet, there is a small amount of pearlite. The micro structures of HAZ close to the side of galvanized steel are ferrite, pearlite and a small amount of martensite, and close to the side of AISI304stainless steel is austenite, a small amount of δ-ferrite and martensite.(2) In the numerical simulation, a nonlinear transient heat conduction analysis of the process was performed by Ansys software. The temperature field is compatible with the experiment. The actual morphology of cross-section and the shape of the molten pool by simulating are approximately the same.(3) The main defects are the pores and cracks in the laser welding joint of galvanized steel and stainless steel. Side-blowing protective gas and keeping a gap between galvanized steel and stainless steel are good solutions to prevent the generation of defects effectively. So the impact of zinc in laser welding minimized. |
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