Research On Laser Welding Of Titanium/Steel Dissimilar Metal Based On Hybrid Welding Mechanism

Titanium alloy and stainless steel are widely used metal materials in industrial field.The increasing application of titanium alloy and stainless steel welding in the industrial field has promoted the demand for high-quality welded joints.The two metals often produce highly brittle Ti-Fe intermetallics due to the huge difference in metallurgical properties.For a long time,how to reduce the influence of Ti-Fe intermetallics on joints has become the focus of this research.In addition,industrial field also requires welding methods with high efficiency and low welding conditions.Therefore,in order to reduce the effect of brittle Ti-Fe intermetallics on the quality of joints,this work designs a laser welding method based on the combination of brazing(diffusion welding)and fusion welding.Firstly,the laser welding of Ti alloy/SS using the medium temperature brazing filler metal system was explored.When Ag30Cu Zn silver-based solder is used,the main microstructure of the Ti alloy-SS interface is?-Ti,Ti₂Zn,Ti₂Cu,Ti Zn phase and(Ag,Cu)solid solution,the maximum tensile strength is 130 MPa.When Ag73Cu Zn silver-based solder is used,the main microstructure of the Ti alloy-SS interface is?-Fe,Fe₃Zn₂,Ag Zn₃,Cu₅Zn₈,?-Ti and Ti₂Cu phase,the maximum tensile strength is 129MPa.When Ag30Cu Zn silver-based solder in the case of a large roughness welding surface is used,a relatively thick reaction layer is formed at the widest part of the brazing seam,and a relatively thin reaction layer is formed at the thinnest part of the brazing seam.Next,the laser welding of Ti alloy/SS using a high-temperature brazing filler metal system was explored.When the Nb interlayer was used,the main microstructure of Ti alloy-SS interface is?-Fe,Fe₂Nb phase and(Ti,Cu)solid solution,the maximum tensile strength is 156 MPa.When the V interlayer was used,the main microstructure of Ti alloy-SS interface interface is(?Ti,V),(Fe,V)solid solution and(Fe,V)_?phase,the maximum tensile strength is only 88 MPa.When Monel 400 alloy was added,the main microstructure of the Ti alloy-SS interface is Ni Ti₂,Ti₂Cu,Ti Cu₂,Ni₃Ti,Ni Ti phase and(Cu,Ni)solid solution.No unfusion defects were observed in the diffusion weld,the maximum tensile strength is 132 MPa.By adjusting welding parameters,when the unmelted Monel 400 alloy is retained,the unfused defects in the diffusion weld are eliminated,and the joint strength is increased to 216 MPa.Finally,the laser welding of Ti alloy/SS using bilayer was explored.When the Cu/Ag30Cu Zn bilayer was used,the main microstructure of the Ti alloy-SS interface is Ti Cu₂,Ti₃Cu₄phase and Cu solid solution,the maximum tensile strength is 151MPa.When Nb/Cu bilayer was used,the main microstructure of the Ti alloy-SS interface is(Fe,Cu),(Cu,Nb),(Ti,Nb)solid solution,the maximum tensile strength is 172 MPa.The simulation results of the welding temperature field of titanium alloy and stainless steel show that compared with the simulated thermal cycle curve,the temperature rise and fall are much slower in the actual measurement.The measured temperature(998°C)is 288°C lower than the simulated temperature(1286°C).The simulated temperature of Ti alloy-SS interface is 1286-1412°C.When the power is constant,as the laser offset changes,the temperature of the Ti alloy-SS interface changes sharply,and the optimal offset range for laser diffusion welding is smaller.