| Aluminum alloys have the advantages of low density,high specific strength and stiffness,good electrical and thermal conductivity,excellent corrosion resistance and so on.Magnesium alloys have the advantages of high specific strength,good shock absorption,excellent electromagnetic shielding performance and so on.They are the lightest metal structural materials in current industrial applications.If the welding method is used to connect aluminum alloys and magnesium alloys,it can not only give full play to the respective performance advantages of aluminum alloys and magnesium alloys,but also further improve the lightweight level.It has great application potential in the fields of new energy vehicles,aerospace,shipbuilding,national defense and military industry.However,due to the great differences in physical and chemical properties between aluminum alloys and magnesium alloys,it is difficult to obtain welded joints with good performance by traditional welding methods,and it is a great challenge to realize the reliable connection of Al/Mg dissimilar metals.In order to solve the problem of Al/Mg dissimilar metals welding,magnetic pulse welding technology is adopted in this paper.The microstructure evolution of Al/Mg magnetic pulse welded joint interface was systematically studied by OM,SEM,EDS,TEM and other microscopic analysis and mechanical property testing methods.The formation mechanism and bonding mechanism of Al/Mg magnetic pulse welded joint interface were discussed by combining with simulation calculation,and the service performances of Al/Mg magnetic pulse welded joint under different working conditions were explored.The main research results of this paper are as follows:(1)The effects of process parameters on the interface morphology and mechanical properties of Al/Mg magnetic pulse welded joints were studied.The results showed that the characteristic morphology of Al/Mg joint welding zone included transition layer interface,waveform interface and straight interface,and the degree of element diffusion and plastic deformation at different interfaces were different.The Al/Mg dissimilar metal welded joint with higher performance than Al alloy base metal can be obtained by optimizing the process parameters,so that the joint fails at Al alloy base metal.The optimal process parameters for Al/Mg plate welding and Al/Mg pipe welding are 30 k J-1.4mm and 35 k J-1.5mm.(2)The finite element-boundary element coupling model of the macroscopic deformation process of Al/Mg magnetic pulse welding and the smooth particle hydrodynamics fluid dynamics model of the microscopic interface were established,and the changing laws of electromagnetic field and structural field in the welding process were explored.The deformation characteristics of the outer tube were analyzed,and the material flow law at the interface was simulated based on this.The forming mechanism of wave interface was revealed.The results showed that the formation of wave interface of Al/Mg joint was related to the jets.During the process of Al/Mg magnetic pulse welding,a jet was formed at the front end of the collision point due to high-speed collision.The jet periodically oscillates under the action of stress waves to form wave interface.(3)The microstructure evolution characteristics of Al/Mg magnetic pulse welding interface were discussed by combining experiment and simulation.The bonding mechanism and strengthening mechanism of Al/Mg magnetic pulse welding interface were revealed.The results showed that severe plastic deformation and local melting occurred at different characteristic interfaces.There were amorphous bands with a width of about 10 nm and obvious element diffusion and grain refinement phenomena at the interface.It has been revealed that the micro bonding mechanism of Al/Mg magnetic pulse welding interface was a metallurgical bonding caused by the combined effects of plastic deformation,local melting and element diffusion at the interface.(4)The microstructure,properties and failure behavior of Al/Mg magnetic pulse welded joint under fatigue and thermal exposure conditions were studied.The results showed that Al/Mg joints were prone to failure at the impact site of Mg tubes at low stress levels(21.3MPa),while Al/Mg joints turned into failure at the welding interface at high stress levels(28.5-42.7MPa).In the thermal exposure condition,when the thermal exposure temperature below 150 ℃,there was no significant change in interface morphology and no significant decrease in joint properties.When the thermal exposure temperature is higher than 200 ℃,hard and brittle intermetallic compound layer will be formed at the interface of Al/Mg joint,greatly reducing the mechanical properties of the joint.The tensile shear failure mode of Al/Mg joint changed from Al base metal failure to brittle fracture along the intermetallic compound layer. |
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