Study On The Dissimilar Metal Welding Properties Of Titanium Alloy With Copper Or Steel

TC4 titanium alloy with T2 copper electron beam welding process was studied in this paper.At first,the debugging of electron beam welding parameters was carried out,then the impact of different electron beam offset distance on the mechanical properties of the joint and the phase composition of the joint interface welded by electron beam welding at copper side were analyzed.Furthermore,electron beam welding at copper side for the first time then welding at titanium side for the second time and welding at titanium side for the first time then welding at copper side for the second time were studied on the phase composition and the mechanical properties of the welding joint.Electron beam welding and friction welding process of TC4 titanium with 304 stainless steel by adding copper transition layer was also studied in this paper.The suitable welding parameters were obtained in this research,such as:accelerating voltage 60kV,electron beam 45mA,focusing current 680mA and welding speed 10mm/s,then the plates were welded by adjusting different electron beam offset distance.The experiment results showed that:with the increase of electron beam offset distance,the joint tensile strength increased first and then decreased.The electron beam welding joint welded at copper side was divided into three regions,a very small area of the dendrite at the titanium alloy side,a large area of the dendrite at copper side and the final solidification zone between them.There was a reaction layer with 39?m width near TC4 titanium alloy.In the reaction layer,most of the area was Cu,and near the titanium side there was a intermetallic layer,which was very thin.In the whole welding process,the diffusion distance of Ti element was 23p.m,in the intermetallic layer,there was CuTi,CuTi₂,Cu₄Ti,Cu₂Ti,Cu₃Ti and Ti₃Cu₄ phases.The joint strength was 162MPa,which had a brittle fracture,and there was a large amount of CuTi phase in the fracture surface.The results showed that after welding at the titanium side for the second time,in the reaction layer,the morphology and growth direction of the dendrite had changed greatly,the dendrite attached to the titanium alloy substrate and growed toward to the first weld pool previously almost did not exist,the new dendrite attached to the front of the final solidfacition zone and growed toward to the second weld pool,and a new interface formed.The joint strength of electron beam welding at copper side for the first time then welding at titanium side for the second time by adjusting different beam offset distance was 210MPa,the fracture surface mainly existed CuTi₂ phase,The joint strength of electron beam welding at titanium side for the first time then welding at copper side for the second time was 84MPa.TC4-304SS welding experiment results showed that it was difficult to obtain reliable welding joint without transition layer,using electron beam welded titanium alloy with copper first,then cut at copper side and remain 2cm wide copper,finally,welded copper with stainless steel,in this way,the joint strength could be improved to 196MPa.When the thickness of the copper transition layer added was 0.5mm,with the increase of the friction time,the joint tensile strength increased first and then decreased,the highest strength of the joint was 178MPa,and the fracture occurred at the interface between titanium alloy and copper,at the interface of which existed CuTi phase.