| With the development of modern society,resource and environment have been the main factors that limit the development of the society.As the pillar industry,automotive industry release the pressure of resource and environment through energy saving and emission reduction.For the purpose of energy saving and emission reduction,one way is developing new-energy automobile,and another way is the lightweight of vehicle body.To obtain lightweight vehicle body,the common way is the wide use of different kind of materials with high specifi c strength,such as advanced high strength steel(AHSS),aluminum alloy,magnesium alloy,carbon fiber reinforced composite(CFRP),et al.The use of different kind of materials involves a key problem: the welding of dissimilar materials.Due to the signif icant difference in melting point,thermal expansion coefficient among dissimilar materials,it is hard to obtain dissimilar material joint with high strength through tradition fusion welding.In this study,the 5xxx aluminum alloy and high strength steel were welded by magnetic pulse welding(MPW),and the coil and platform for the MPW were developed.The evolution of the wave interface and microstructures during the high-speed impaction was revealed,and the Al-Fe weldability window was also established.As for the fracture mode of the Al-Fe joint under serveral service conditions,the fracture mechanism under dynamic loading conditions were analyzed,and the fatigue fracture mode of the Al-Fe joint was established.Moreover,the degradation of the mechanical properties and corrosion mechanism in corrosion environment were also investigated.The main research contents of this paper were as follows:(1)The FEM-BEM coupled numerical model of the welding process during MPW was established,and the SPH model in the collision point was also established.The deformation rule of the flyer plate and the formation mechanism of the microstructure in the weld were revealed.The SPH model was established based on the dynamic parameters that obtained by the FEM-BEM simulation,and the formation mechanism of the wave interface as well as the distribution rule of the temperature in the interface was revealed,and the formation mechanism of amorphous layer and ultra-fine grain was revealed.(2)The Al-Fe magnetic pulse weldability window was established.The Al-Fe joints with high strength were obtained through various process experiments,and the sizes of the annular weld under different process parameters were obtained.Then the dynamic parameters in the inner side and outer side of the annular weld were obtained by the FEM-BEM simulation,and the dynamic parameters were then used for the establishment of the weldability window.(3)The fracture mechanism of the Al-Fe joint under dynamic loading condition was revealded,and the fatigue fracture mode of the Al-Fe joint was established.The strain rate sensitivity of the Al-Fe joint was proposed through the analysis of the distribution of the strain and the fracture of the Al-Fe weld that suffered high-speed impact loading,and the fracture mechanism of the Al-Fe joint under impact loading was revealed.Moreover,the fatigue fracture mode of the Al-Fe joint was established through the analysis of the fatigue data,and the fatigue life of the Al-Fe joint under different stress levels was predicted,and the reason of the transformation of fracture mode of the Al-Fe joint under different stress levels was revealded.(4)The fracture mode of the Al-Fe joint under corrosion environment was established.The corrosion behavior and degradation of the Al-Fe under salt spray corrosion environment were analyzed,and the fracture mode of the Al-Fe joint during salt spray corrosion environment was established.Moreover,the corrosion behavior in the flat weld interface and transition zone was analyzed,and the reason for the occurrence of galvanic corrosion and stress corrosion in the weld interface was studied,and the corrosion fracture mechanism of the Al-Fe joint was also revealed. |
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