The Research On Micro-structure And Properties Of Titanium Joint By Vacuum Electron Beam Welding

At present,The research is common which concentrate on technique,structure and mechanical properties,especially on the fatigue and tensile properties of the welded joint.It is rare to study on corrosion resistance due to the microstructure change caused by high energy beam welding.The same/dissimilar butt joints of TC4 and TA2 titanium alloy sheets by vacuum electron beam welding were taken as the object in this essay.The visualization of internal temperature field during welding process could be realized and the parameter could be optimized,through sysweld software to simulate welding process.The mechanical properties of the welded joints were studied by microhardness and tensile test.The influence of electrochemical corrosion process and behaviour due to microstructure evolution between base metal,weld zone and joint in Na Cl and HCl solution,which was studied through OM,SEM,EDS,XRD and electrochemical work station methods.The result shows that:Based on Mesh,Heat Input Fitting,Welding wizard and Solver modulars from sysweld software,TA2-TC4 dissimilar titanium alloy during vacuum electron beam welding process could be numerical simulation.A better quality joint could be get,if the composite heat source which consist of two Gaussian heat sources and a spherical heat source is used,high-pressure is 70k V,electron beam current is 21m A,electron beam focus on surface and welding speed is 650～800mm/min.The laboratory test under the same conditions shows high agreement between welding and simulated molten pool parameters,which improves the test efficiency.TC4-TC4 the same kind of titanium alloy joint by vacuum electron beam welding,the weld seam of it is composed ofα’-phase and a fewβ-phase.The content ofα’-phase is 86.1%.The highest micro-hardness is 407HV.Tensile strength of it are about 92%of the base metal.In 0.6mol·L^-1Nacl solution or saturated Na Cl solution,corrosion resistance of the weld seam and the joint are higher than the base metal.When the concentration of Cl^-increases,the corrosion current value(I_corr)and passivation current value（I_p）from weld beam,joint and base metal decrease,which may be due to the migration of electron has be hindered.In1.0mol·L^-1HCl,both of them increased significantly,the corrosion resistance of hydrochloric acid decreased significantly compared with that of Na Cl.With the increase of test time,the impedance of all samples decreases,and tends to be stable after 96h.Pitting corrosion is occurred between the weld and the base metal,selective corrosion is occurred in the joints.TA2-TA2 the same kind of titanium alloy joint by vacuum electron beam welding,the weld beam of it includes serrated structureα-Phase and lathα-Phase.The micro-hardness of weld seam is up to 160HV.The tensile strength of it is 445MPa,equivalent to that of base metal.In different corrosive solution,from high to low,the order of corrosion resistance is,base metal>weld seam>joint.In 1.0mol·L^-1HCl solution,With the increase of test time,the impedance of all samples decrease,pitting occurred on all of them.TA2-TC4 the dissimilar titanium alloy joint by vacuum electron beam welding,The weld seam of it mainly consists of irregularα-phase,α’-phase and fewβ-phase.The ratio ofα+α’phase is 75.9%,β-phase is 23.5%.The highest micro-hardness of the weld seam is392HV.The tensile strength of it is 456 MPa,3.63%higher than that of TA2,about 40%than that of TC4.In 0.6mol·L^-1Na Cl solution,the corrosion resistance of the weld seam is roughly equal to both base metal.In 1.0mol·L^-1HCl solution,the corrosion resistance of the weld is worse than that of the base metal,selective corrosion is occurs on it,the impedance decreases with the test time increased.Due to the segregation of V element,the chemical galvanic cell is formed,which accelerates the growth of the batteryα-phase corrosion.