| The weight loss of automobile bodies has become a hot research direction in the current improvement of automobile technology.The application of aluminum,magnesium and other alloys in automobiles inevitably involves the connection between the two.The paper focuses on the laser welding of aluminum and magnesium alloy lap joints.For the problem of brittle compound phase,it is of great theoretical significance and practical application to select the topic of the intermediate layer and the welding process parameters on the aluminum/magnesium laser welding structure performance.In this paper,6061 aluminum alloy and AZ31 B magnesium alloy sheets are taken as the research object,with the original intention of improving the strength of magnesium/aluminum dissimilar alloy joints,high melting point Ti and Ni interlayers are selected,and the lap welding method above magnesium and aluminum is used to study Ti,Effect of Ni interlayer on laser welding joints of dissimilar metals of aluminum and magnesium.Using metallographic microscope,microhardness tester,environmental scanning electron microscope,XRD diffractometer and electronic universal testing machine,etc.,to study the influence of interlayer on the microstructure and mechanical properties of magnesium/aluminum welded joints,while using COMSOL numerical simulation and MS software First-principles calculation,from the perspective of energy transfer and metallurgy,combined with the temperature field distribution,discusses the connection mechanism of magnesium/aluminum welded joints after adding Ti and Ni interlayers.The main conclusions of the paper are as follows:(1)Based on the selection and design of the intermediate layer,two intermediate layers with similar melting points,Ti and Ni,were selected for auxiliary welding.After adding Ti and Ni intermediate layers,the shape of the molten pool changes from "V" shape to "glass shape",which is manifested by the widening of the upper molten pool and the more rounded edges,and the effective contact area of ??the molten pool and the base metal becoming wider.The experimental results show that after adding the Ni interlayer,an effective IMC intermediate layer is formed at the joint interface,which completely suppresses the generation of brittle compounds of magnesium and aluminum,and connects the magnesium and aluminum substrates in a bidirectional manner in the form of a bridge,while the addition of the Ti interlayer is not An effective IMC intermediate layer is formed at the interface,which affects the effective connection of the welded joint.(2)The laser welding process parameters with Ni foil as the intermediate layer were optimized as laser power 1450 W,welding speed 1200mm/min,Ni foil thickness0.2mm,and the resulting joint wire strength was 78.9N/mm.The intermetallic compound at the joint interface affects the shear performance of the joint,and the reasonable control of the formation of the mesophase compounds Al Ni and Al3 Ni is the key to improving the mechanical properties of the magnesium/aluminum joint.After the Ni interlayer is added,the Ni-Al mesophase is preferentially formed,and Al Ni The mesophase is easier to form than the Al3 Ni mesophase.(3)The COMSOL Multiphysics software is used to simulate the temperature field of the molten pool,and the Gaussian heat source is used to load,combined with the temperature field and flow field,to simulate the temperature field of the magnesium/aluminum laser welding joint is reasonable and feasible.Through comparative analysis of the temperature field distribution of the magnesium/aluminum welded joint before and after adding the interlayer,it is found that the presence of Ni foil has a heat insulation effect,which is helpful for the bidirectional metallurgical combination of the intermediate layer and the substrate.The simulation results are consistent with the experimental results. |
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