| Aluminum alloy(Al)and steel composite structure can reduce the structural weight and optimize the structural design,which can make full use of the excellent properties of the properties of material.Because of the large difference in physical properties and chemical compatibility between Al and steel,residual stress and deformation inevitably occur,which have the serious influence on the dimensional accuracy and the mechanical properties of the joint.With the continuous improvement of calculation technology and numerical analysis methods,numerical simulation had become an effective method to predict and analysized the welding residual stress and deformation.Based on the aluminum alloy/steel MIG arc brazing-fusion welding experiments,a thermo-elastic-plastic finite element calculation model was developed,which is suitable for the brazing-fusion welding process of dissimilar materials.In order to reveal the stress evolution and residual stress distribution of brazed interface,numerical simulation was applied to analyze the temperature distribution and stress-strain behavior of the brazed interface between aluminum alloy weld and steel.The welding process was optimized by changing welding heat process using numerical calculation methods,which provides guidance for practical engineering applications.A three-dimensional finite element numerical model of MIG arc brazing-fusion welding was established for overlap joint of Al/steel.In the model,the physical process of the brazing-fusion welding process,the joint geometry,the nonlinearity of the material and the boundary conditions were considered.An asymmetric four-ellipse heat source model was established,fased on the influence of welding speed,torch inclination on heat flux in welding direction and the asymmetry of arc.The thermo-mechanical sequential coupling method was used to calculate the temperature field,stress field and deformation of 1-mm-thick 5052 Al alloy plate and 2-mm-thick hot-dip galvanized steel(SGCC+ Z 120)plate at different heat input.The thermal cycle curve and blind-hole method was used to verify the accuracy of the model.The MIG arc brazing-fusion welding thermal process of Al alloy/steel was analysed by the microstructure of the intermetallic compounds layer in the brazed interface.The results show that the peak temperature and high temperature residence time of the molten pool also increase with the welding heat input being increased.The high temperature range of the brazed interface is about 621-758 0 C at Q = 592 J/cm.The interface reaction time is about 1.0 s,which is corresponding to the thickness of IMCs layer about 0.568 μm and the IMCs interface relatively flat.When the heat input reaches up to 1071 J/cm,the high temperature range at the brazed interface is about 621-986 ℃,the interfacial reaction time was about 1.8 s,and the thickness of the IMCs layer is increased to 2.548 μm.The IMCs layer becomes sharper.The IMCs layer of the steel side at brazed interface becomes undulating,due to the increase of peak temperature and the prolongation of the high temperature residence time.With the increase of galvanized steel thickness,heat was transferred quickly,the peak temperature of brazed interface and the range of high temperature zone were decreased.The distribution of Welding residual stress was particularly complex due to asymmetry of material properties,heat distribution,and structural.At the Al alloy side of the brazed interface,the tensile stress of weld zone reaches the yield strength of the Al alloy.The transverse residual stress on the galvanized steel side of the brazed interface was a left-right asymmetric M-shaped distribution;the transverse residual stress had a compressive stress peak of 320 MPa at the central region.Longitudinal residual stress shows a W-shaped distribution,and there is a small wave trough in the welding zone.The tensile stress in the weld zone was about 160 MPa.Due to the difference of welding thermal process in different regions of end effect.the distribution of Three-dimensional residual stresses in the initiation and end zone is different from that in the middle zone.In addition,the reverse bending of the Al cancels out the compressive stress on the upper surface and superimposes the tensile stress on the lower surface.There was a large residual stress difference between the two sides of the brazed interface.The distribution of residual stress difference between the two sides of the brazed interface was same under different welding heat input.The residual stress difference in the transverse and longitudinal direction was n-shaped distribution.The residual stress difference in the thickness direction was stable in a small value in the central area of the brazing interface,tension in the root area and compression in the weld toe.With increasing welding heat input,the peak stress in the central area of brazing interface increases.There was a negative correlation between the shear strength of the brazing interface and the residual stress difference of the brazing interface.The residual stress difference at the brazing interface and the morphology of intermetallic compound layer affecte the bonding strength of the fusion-brazing joint.The maximum shear strength was 75 MPa.With the increases of heat input,the morphology of intermetallic compound layer changed and the residual stress difference at the interface increases.Therefore,the shear strength of the joint decreases,which was about 12 MPa at Q=1071 J/cm.The distribution of welding residual stress of the brazing interface was generally same as that at different initial temperatures.The pre-weld preheating optimization effects on the weldment were not obvious without considering the improvement of the spreadability of the weld metal.The increases of the thickness of the galvanized steel plate reduces the overall temperature difference of the workpiece.The high stress range of the galvanized steel side and the deformation of the Al alloy decrease with the increases of the galvanrzed steel plate thickness,which plays a certain role in regulating the residual stress of the whole weldment. |
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