Research On Cold Metal Transfer Welding Process Of Titanium/Steel Dissimilar Metals

Cold metal transfer(CMT)welding of titanium/steel dissimilar joint was investigated in the thesis to solve the problem that sound joint could be obtained only in a vacuum environment.Lap joint of pure titanium TA2 and low alloy steel 16 MnR together using the CMT technology.Buffer of Cu,Ni,Al were deposited on the 16 MnR steel to reduce generation of intermetallic compounds.The influence on weld quality of each buffer layer was compared to each other.Metallographic microscope,scanning electron microscope(SEM),energy dispersion spectroscopy(EDS)and X-ray diffraction(XRD)were used to analyze the microstructure of the welded joints.And the tensile testing machine and micro-hardness tester were used to test the welding joint.The results show that with filler metal ER4043 or ER5356 titanium and steel could be jointed together by CMT.The welding current was 125 A,the welding speed was 5.3 mm/s and the gas flow rate was 18 L/min.Brittle intermetallic compounds were produced in both titanium joint and steel side.Hardness of the reaction zone was increased.The Intermetallic compound were FeAl3 and TiAl3.Less porosity and thinner intermetallic compound were found in the joint with ER5356.Cu buffer layer could effectively prevent the formation of Fe-Al intermetallic compounds,but the joint was prone to brittle fracture.There was a lot Fe going into the Ni buffer layer during the process of depositing Ni on steel.Both Ni-Al and Fe-Al intermetallic compounds were produced in the boundary between the weld metal and the Ni buffer layer.Hardness of the joint is increased and brittle phases were produced on interface.ER5356 deposited on steel with a small current(Welding current is 76 A,welding speed is 5 mm/s).Strength of the joint was effectively improved with aluminum buffer layer.The joint between the weld and the aluminum alloy buffer layer was fusion welding joint.The joint between the aluminum alloy buffer layer and the steel was brazing joint.Thickness of the Al-Fe intermetallic compound layer was 70~80?m.The shear strength of joint was 31 MPa.