| Bimetallic tubes(also Bi-metal tubes), as a tubular kind of composite materials, combine the excellent properties of the base and clad tube. As compari son to a single metal tube, bi-metal tubes have an advantage in the aspects, such as, less consuming of expensive metals, reduction of cost and extensive capabilities, and thus find themselves to be useful in the industrial fields of petroleum, chemical, nuclear power and cooling. The type and application of bi-metal tubes, however, is greatly limited by the manufacture processing. Recently, due to the restriction of process principle, each kind of the various cladding technologies has its own disadvantage in term of interface quality and environmental protection. A new method, namely magnetic pulse cladding(MPC), is proposed in this study to clad the long metal tubes, which utilizes the magnetic force. Al/Fe bi-metal tubes which include the lined-aluminum steel tube and aluminum-clad steel tube were studied experimentally. Plastic deformation behavior of bi-metal tubes subjected to the progressive magnetic force, microstructure of the MPC interface and its formation mechanism were emphatically investigated. What’s more, molecular dynamic(MD) simulation was conducted to reveal the dynamic mechanism of parent-atom diffusion in the atomic level.According to the structural feature of lined bi-metal tubes, lined-aluminum steel tubes were fabricated via the MPC process by the magnetic tube bulging model. The main processing parameters, such as feeding length, discharging energy and initial radial gap between the base and clad tube, were selected to investigate the effect on the bonding strength. Metallurgical bonding interface can be obtained via employing field shaper in the case of fabrication of the aluminum-clad steel tube.Numerical scheme and finite element model of the cladding of tube-to-tube subjected to the progressive magnetic force were established to investigate the plastic deformation behavior of the aluminum-clad tube. It was revealed that a ripple defect, a bamboo-like shape produced on the outer surface of the clad tube, is a result of inharmonious plastic deformation behavior between the transiti on and non-transition zone. Correspondingly, a method to control the coordination deformation of the clad tube was present, which is realized by modification of the work-zone of the field shaper to fit the configuration of the deformed clad tube.The mechanical property of the 1060Al/20 steel MPC interface was examined. The results show that the coordination deformation of the clad tube plays an important role in the distribution of bonding strength. The region, in which the relative bonding strength(in comparison to the shear strength of the aluminum base tube) can reach to 100%, has an axial length of 50% the length of whole bonding zone. The feature of macro-morphology of the 1060Al/20 steel MPC interface was analyzed to establish the relationship between the mechanical property and microstructure of the MPC interface.Microstructure of the 1060Al/20 steel MPC interface without a transition zone was studied for the first time via TEM observation. The results show that this interface consists of only a disordered interfacial layer with thickness of ~10 nm. The side of the disordered layer is the parent metals. A trip-like nano-sized Fe grain is adjacent to the amorphous layer, and amorphization takes place in the triple junction of the Al grains on the Al side adjacent to the amorphous layer. The composition of the amorphous phase in the triple conjunction of Al grains is in accordance with the base one. The formation mechanism of the amorphous interfacial layer was analyzed from the thermodynamics and kinetics respect. Molecular dynamic(MD) simulation was carried out to investigate the parent atom diffusion and the results show that the interdiffusion interface with a gradient distribution of the base element Al and Fe is a result of the rapid diffusion of Fe atom into the disordered Al matrix.Microstructure of the 1060Al/20 steel MPC interface with a transition zone was also studied by the TEM observation. The results show that the transition zone contains a disordered base phase and ordered but dispersed part icles with superlattice structure. The composition of element O in the disordered phase can reach to 10 at. %. Twinning of the Fe crystal was observed on the 20 steel side, and subgrains were founded on the 1060 aluminum side, while columnar crystals in somewhere region was also observed. Results reveal that the 1060Al/20 steel MPC interface was a kind of fusion interface which experiences fusion and subsequent solidification.According to the feature of the deformation of the Al/Fe contact materials, the jetting and severe shear deformation was simulated by smoothed particle hydrodynamics(SPH) method. A 2D axial symmetry SPH model for the impact collision was established and the physical field was analyzed. The numerical simulation results show that the single inductive heating could not lead to the fusion of the interfacial material, while combined effect of the inductive heating and the severe plastic deformation could result in increasing of the temperature to the melting point of Al base material.By analyzing the SPH numerical simulation and TEM observations of microstructure of fusion MPC interface, it was revealed that the captured jetting is also an incentive for the formation of fusion interface in addition to melting of Al base metal. In the case of 1060Al/20 steel MPC system, the evolution of the diffusion MPC interface into one with a transition zone is triggered by increasing of the external input of energy. The fusion MPC interface with thickness up to several tens of micrometers is a product formed by the joint action of the melting of Al base metal and captured jetting. |
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