Study On Formation Mechanism Of Interface In Of Dissimilar Joining Of Aluminum-Steel

With microstructure evolution mechanism analysis problems in interface of the aluminum and steel welding process, the pulsed double electrode-gas metal arc welding（Pulsed DE-GMAW） was puttd forward to weld aluminum and galvanized steel. Establish a numerical model of its multi-phase and multi-orientation, based on the advantages of the model Monte Carlo（MC） and Cellular Automata（CA）, and assisted by experimental analysis to verify this modelOn the basis of the Monte Carlo simulation of grain growth method, crystal nucleation and growth activated factor are put forward. The preferential growth orientation factor is put forward, preferred orientation factor effect using the CA method, namely, to establish double MC grid model. The activated factor is used to establish a lattice coordinate tracking method. The process of crystal nucleation from the liquid phase to growing up in the continuous simulation was studied. The change of the solid fraction and the grain size were counted in the process of simulation by means of lattice tracking. The results showed that the established model can reflect the grain nucleation and the growing process very well, the number of solid-phase fraction can be accurately counted and the appearance of change in grain size can be accurately reached by using the lattice tracking method, the change of the solid fraction and the Monte Carlo step meet the S type curve in the process of simulation, the grain growth index was 0.477, the index was relatively close to the theoretical value 0.5.Using the double grid MC model simulation the interface microstructure of aluminum/steel Pulsed DE- GMAW welding, the temperature based on the thermal cycle curve for the actual welding process, establishment the one-dimensional unsteady diffusion model of Fe, Al elements, and simulation study on the growth process of Fe₂A_l5 and FeAl3 in the interface. The results showed that the Fe₂A_l5 grain first nucleation in the aluminum and steel initial interface, and soon towards the aluminum side growth into a continuous layer on the interface. Then the Fe₂A_l5 grain growth present the steel side "strip". The FeAl3 grain nucleation in the aluminum side with the weld temperature lowering and it growth presents "needle". The FeAl3 more sensitive for the welding heat input comparison as Fe₂A_l5, and the Fe₂A_l5 generation on the interface is greater than the FeAl3.Combined with the special structure of crystal Fe₂A_l5 and its crystal structure has been physical and geometric abstraction. Th vacancy diffusion mechanism of Fe₂A_l5 crystal growth is put forward, and establish spatial orientation growth model. Using the two-layer gridding MC model simulation studies Fe₂A_l5 crystal growth process. The simulation results show that the model for simulation was employed to simulate the growth process of different crystal orientation, and the angle between the c-axis oriented and nucleation-interface had an effect on the crystal growth shape. With the different nucleation orientation of crystal, the crystal growth existed obvious competitive advantage, and then the competitive was most obvious when the angle between the c-axis oriented and nucleation-interface was 90°. Thus, Fe₂A_l5 intermetallic compounds layer was present and it was tongue-like distributed. By changing the element concentration of Fe₂A_l5 growth interface, the Fe₂A_l5 intermetallic compounds layer was flat plane. The simulation results were in agreement with the experimental results. During aluminum-steel welding process, the growth shape of Fe₂A_l5 intermetallic compounds was related to the c-axis orientation of crystal, and the alloy element concentration of the Fe₂A_l5 intermetallic compounds growth had a greatly effect on the shape and thickness of the Fe₂A_l5 intermetallic compounds layer.In order to study the correctness of the simulation study, the Electron Backscattered Diffraction（EBSD） has been used to study the shape, orientation and size of crystal in the interface, and analyzed the effects of heat input on the growth morphology. Studies have shown that the crystal c axis of Fe₂A_l5 is growth priority and the crystal in the interface "strip" shaped form. Thermal input mainly influence the size of crystal growth, the crystal orientation only very low heat input cases had effect.Heat input on the steel side crystal of secondary grew up and the size of the aluminum side of grain has a certain influence on positive correlation.The Gibbs- markov random field is put forward to exploratory research the migration behavior of zinc element on the interface by numerical simulation. To explore the show that migration behavior of zinc element is obvious on welding the initial stage. The zinc element exist long-range migration toward the steel side when Fe₂A_l5 crystal on the interface growthed cambium-like. The content of zinc element has influence form of zinc element in interface.