Research On CMT + Laser Welding Process Of Titanium-Steel Composite Plate

Metal composites have been widely used in many fields such as petrochemicals,transportation and daily-use cosmetics,due to the excellent comprehensive properties.However,Because of the large differences in the chemical composition and physical properties between the base layer and the cladding layer of the composite material,brittle intermetallic compounds are easily generated during welding,which is difficult in practical applications.In industry,it has always been a research hotspot and difficulty.This paper starts with the problems and limitations in the fusion welding process of titanium-steel dissimilar composites.Firstly,TA2-Q235composite plate are welded by laser-MAG hybrid welding+single laser,laser-MAG hybrid welding+TIG welding,CMT+single Laser welding method.After the analysis of the advantages and disadvantages,it is determined that the CMT double-pass welding+single laser welding method is adopted.The orthogonal design method is used to optimize the process scheme,and the better two-stage process is selected for further follow-up research.The micro-hardness,tensile strength,iMPact energy,micro-shear strength and fracture morphology of the two groups of processes are coMPared;OM,XRD,EBSD technology are used to analyze the microstructure of the joint;The arc behavior,the droplet transition process,and the related electrical signal information during the welding process are analyzed by high-speed camera and oscilloscope electrical signal synchronization acquisition system.The experimental results show that in the first weld of Q235,the hardness value of the weld zone in parameter 1 is 213HV,and the hardness value of the weld zone in parameter 2is 251HV.The hardness value of the weld zone in parameter 1 of Q235 second weld is226HV,and weld zone hardness value in Parameter 2 is 258HV.Weld zone hardness value of TA2 side parameter 1 is 169 HV.The tensile strength of the parameter 1 weld joint is 420MPa,and the tensile strength of the parameter 2 weld joint is 397 MPa,both of which higher than the standard strength 387 MPa.The iMPact energy of parameter 1 weld joint is 112J,and the iMPact energy of parameter 2 weld joint is 85J.The micro-shear strength of the base metal is 436 MPa,the micro-shear strength at the interface of the weld zone is 368 MPa and the micro-shear strength at the interface of the weld zone 2 is 289 MPa.The micro-shear strength at the interface of the two parameters is less than the micro-shear strength of the parent metal.Observing the fracture analysis,the fracture at the interface of parameter 1 is mainly a mixed dimple,and the fracture at the interface of parameter 2 is mainly a cleaved shape fracture;Through the mechanical properties and fracture analysis,it can be concluded that the strength of the welded joint under both parameter parameters is consistent with operating requirement,and the comprehensive mechanical properties of parameter 1 are better than those of parameter 2.The content of brittle compounds in parameter 1 is FeTi:13.9%,Fe₂Ti:17.7%,the total amount of brittle compounds:31.6%.The content of brittle compounds in parameter 2 is FeTi:10.7%,Fe₂Ti:24.3%,and the total number of brittle compounds:35.0%.The grain size of the two sets of parameters is statistically calculated using statistics.The average grain size of FeTi in parameters 1 and 2 are 2.3?m and 15.6?m,respectively.The average grain size of Fe₂Ti in parameters 1 and 2 are 4.9?m,9.7?m.The average grain size of the brittle compound with parameter 1 is smaller than that of parameter 2.The statistical results of the degree of recrystallization show that the recrystallized volume ratio of?-Fe in parameters 1 and 2 are 13.3%and 16.0%,respectively;The volume ratio of FeTi recrystallized in parameters 1 and 2 are 10.7%and 25.4%,respectively;The Fe₂Ti recrystallization volume ratio of parameter 1 and parameter 2 are76.2%,84.4%,respectively.The statistical results of the crystal grain orientation difference reveal that the ratios of?-Fe grain boundary in the range of 2°to 15°are 7.4%and 6.9%and the average misorientation are 24%and 33.2%,respectively;The grain boundary peak of FeTi changes significantly.The proportions in the range of 2 to 15°are 4.2%and 10.3%and the average orientation differences are 26%and 29.2%,respectively;The proportion of Fe₂Ti grain boundaries in the range of 2°to 15°is extremely small.The angle grain boundaries and the small angle ratios are 0.51%and 0.33%and the average misorientation are 53.5%and 56.2%,respectively.The thermal strain analysis results show that the average of residual strains of the?-Fe phase under the two parameters are 2.12 and 2.25,respectively.The average residual strain of the FeTi phase under two parameters are 1.31 and 1.77,respectively.The average residual strains of Fe₂Ti phase under the two parameters are 0.86and 1.20.The average residual strain of?-Ti phase under the two parameters is 1.48 and 2.25,respectively.Droplet transfer form is observed by the high-speed camera and the 60A,130A,180A electrical signals are collected by the oscilloscopes,the results show that in 60A current state,the droplets show a drop of a short-circuit transition form.In the 130A current state,the droplet size and the electrical signal period increases,but the droplet transition pattern does not change.When the current increases to 180A,the current and voltage waveforms of the CMT cause a large change,and the period increases significantly and multiple pulses are generated in one cycle.Droplet transitions change from a single stable short-circuit transition to a short-circuit transition and jet transition.