| The connection between aluminum alloy and steel is a key research field of heterogeneous materials,and the connection between aluminum alloy and steel is in great demand of engineering applications.Due to the huge difference in physical and chemical properties of aluminum/steel,it is easy to produce brittle compounds and other welding problems,which is an important problem for researchers to solve.In this paper,the intermetallic compound can be effectively controlled through MIG brazing to change the welding heat input and other processes,so as to realize the effective welding of aluminum alloy and steel.Meanwhile,further research is carried out by combining the process with simulation,which has important practical engineering significance.Aluminum alloy of the MIG brazing is selected for the 1.5 mm thick and 2 mm thick galvanized steel lap welding,filling welding wire ER4043 wire is 1.2 mm.The different welding process parameters on the weld and the influence law of microstructure performance,analyzed different welding process on the welding joint the influence of the thickness of the intermetallic compound,and under the different welding heat input interface layer organization discussed the mechanism of the formation process.At the same time,the finite element model of MIG brazing heat source was established,the influence of welding temperature field on the thickness of the interface layer was calculated,the thickness of intermetallic compound was predicted,and the results of simulation calculation and test were compared and verified.The experimental results show that the MIG brazing joint in this experiment achieves a good connection.When the welding current is 55A and the welding speed is 55-60cm/min,the weld is formed beautifully,producing fish-scale stacking stripes,and no pores,spatter and other defects.The structure of soldering joint can be divided into fusion zone,zinc-rich zone,interface zone and weld zone.The microstructure of zinc-rich zone is relatively large.Si film and al-Zn eutectic structure are found at the grain boundary of the weld zone.Obviously,the growth direction of the fusion line and grain is 90 degrees,and the microstructure of grain is relatively large near the brazing interface.With the increase of welding current,the thickness of the interface layer gradually increases,and the thickness of the intermetallic compound is between 2-8um.The morphology of the interface layer gradually changes from a flat strip to a"saw-toothed" shaped compound,and finally forms a dense "needle-like" dendrite.The intermetallic compound layer of the brazing interface layer is FeAl3 near the aluminum alloy side and Fe2Al5 phase near the steel side.The microhardness test results show that:the microhardness of the weld of aluminum alloy is the lowest,the hardness of the intermetallic compound is obviously higher than that of the zinc-rich zone,the fusion zone and the weld zone,and the maximum value can reach 600HV.In the tensile test,all brazing joints broke at the interface between aluminum and galvanized steel,which belongs to the brittle fracture mode.It is beneficial to improve the mechanical properties of the joint by increasing the tilt Angle of the worktable appropriately.The tensile strength can reach 227N/mm under the best welding technology.The side section of aluminum alloy is mainly composed of Al5Fe2Zn0.5 and FeAl3.When the wetting angle ratio is between 0.3 to 0.65 and the welding current is 55A-65A,the tensile strength values are in the higher range.The finite element method was used to simulate the temperature field of MIG brazing of 6060 aluminum alloy/galvanized steel.Considering the influence of interface width,interface reaction time and galvanized layer on the temperature field,a double ellipsoidal heat source model was established.The results showed that the heat source model was in line with the practical lap welding test.The cross section morphology of welding seam and the simulation results are verified,and the calculated results are basically in agreement with the test results.It can be seen from the temperature field that the temperature band range of aluminum alloy and steel side is not uniform due to the difference of physical properties.The actual evaporation width of galvanized layer on the back of welding plate and the temperature band width calculated by simulation were verified and compared.The width difference was only about 1mm,which was within the normal error range.According to the interface reaction characteristic relation obtained by simulation calculation and test comparison,as the welding heat input increases,the interface temperature increases gradually,the interface reaction time increases,and the interface layer thickness also increases. |
