Study On Resistance Spot Welding Between Titanium And Mild Steel With An Insert

Light structural materials and composite structural materials are increasingly being pursued by people.Whether in terms of economy and usability,or in industrial production and practical applications,a single traditional material can not meet the equipment and structural requirements of the material performance.Therefore,two or more composite structure materials in the actual production more and more widely used.As the two commonly used structural materials between the titanium and steel connection has important practical significance.However,due to both titanium and steel in the physical and metallurgical properties are quite different and difficult to achieve effective connection.In view of this,this paper uses titanium and low carbon steel as the research object,its resistance spot welding joint organization,performance research.For comparison,this first study industrial pure titanium / steel resistance spot welding directly connected by optical microscopy,scanning electron microscopy of the microstructure of the nugget joint and a joint line of fracture morphology observation,analysis by XRD ray diffraction The surface of the joint was tested.The effects of welding current,welding time and electrode pressure on the nugget diameter and the shear load of the joint were discussed.The fracture form and fracture position of the joint fracture were observed.In order to suppress the interface reaction metallurgy,this paper by pure niobium and copper industrial pure titanium of low carbon steel resistance spot welding an intermediate dielectric layer,the joint tissues studied Ti / Cu / steel,titanium / Nb / steel Discussion The influence of welding parameters on the nugget diameter and mechanical properties of the joint was observed and analyzed.The maximum shear load Ti / low carbon steel direct resistance spot welded joints only 3.3k N.A nugget formed in the macro-homogeneous titanium / steel are directly welded joint,the joint in the thickness direction toward the titanium side of the nugget.The nuggets are composed of TiFe₂ + α-Fe eutectic structure near the steel side,TiFe columnar grains inside the nugget and TiFe + α-Ti eutectic structure near the titanium side.Direct resistance spot weld joint fracture titanium / steel joint fracture occurs analysis results of the intermetallic compound generated at the interface,joint fracture brittle fracture.When the Cu middle layer is used to weld titanium / steel,the inside of the titanium / Cu / steel joint is cracked and the nugget is made.Near the titanium matrix to produce a thickness of about 15μm FeTi,α-Ti eutectic reaction layer.Near the steel matrix is generated by the thickness of about 10μm α-Fe,TiFe₂ phase reaction layer.The internal organization of the nugget is black and white strip organization.Mainly Ti Fe and TiFe₂ phase.The intermediate layer Nb medium can suppress the diffusion of Ti onto the steel side,but can not suppress the diffusion of Fe onto the titanium side.When Nb is used as the intermediate layer to weld titanium / steel,the steel side melting nets are mainly α-Fe and Fe-Nb intermetallic compounds.And the edge of the titanium side of the nugget formed at the thickness of about 10μm α-Ti and β-Ti band,the inside of the nugget is mainly α-Ti and Fe-Ti intermetallic compounds.The results show that the mechanical properties of the joints are improved when Cu / Nb is used as the intermediate layer to weld titanium / steel.Titanium / Cu / steel joints have a maximum shear load of 4.4 kN and a titanium / Nb / steel joint with a maximum shear load of 4.5 kN.Titanium / steel direct resistance spot welding of the maximum shear load of 4.07 kN.The mechanical properties of the titanium / Cu / steel joint are mainly due to the enhancement of the mechanical properties of the joint by the Cu intermediate layer at the edge of the nugget and the matrix formed by the matrix.The improvement of the mechanical properties of the Ti / Nb / steel joint is mainly due to the decrease of the amount of Fe-Ti intermetallic fusion in the nugget.However,the thickness of the intermetallic compound formed by Fe and Nb suppresses the improvement of the mechanical properties of the joint.