Microstructures And Mechanical Properties Of Laser Welded Titanium-steel Joints With Different Interlayers

The welding structure of titanium alloy and stainless steel is an important structure widely used in aerospace,marine,power industry,but the welding of titanium alloy and stainless steel belongs to dissimilar metal welding category,due to great differences in physical properties and chemical properties,there are many problems in the welding process,one of the biggest difficulty is how to avoid the formation of brittle Ti-Fe intermetallic compounds.In this paper,pure titanium and 304 stainless steel were used as welding materials.Firstly,pure titanium and stainless steel welded with the same kind of material were studied to determine the appropriate process parameters,and then the dissimilar metal welding without intermediate layer was carried out to study the effect of laser offset on the weld formation.It was found that the weld shaped better when the laser focus offset towards the stainless steel side about 0.5mm.Then,the dissimilar laser welding of titanium and stainless steel was carried out to research the effect of vanadium interlayer,copper interlayer and copper-vanadium composite interlayer on the microstructures and mechanical properties of the welds.It was difficult to prevent the contact between Ti and Fe due to the good compatibility of vanadium,titanium and iron when the 0.5mmV intermediate layer was used.More Ti-Fe intermetallic compounds were formed in the weld and the highest hardness value of the weld reached 946.5HV,greatly reducing the plasticity of the weld.0.3mm Cu can not prevent the contact of Ti and Fe,forming Ti-Fe and Ti-Cu intermetallic compounds in the weld,with the strength only 101.4 MPa.With 0.5mm Cu and 0.7mm Cu as interlayer,Cu-based solid solution was formed in the weld and brittle phases dispersed in the solid solution,which could effectively reduce the weakening of brittleness compounds to the weld.When the laser focus was located at the interface between stainless steel and copper,the melting amount of titanium could be reduced and the strength of the joint was increased to 192.4 MPa.When the Fe-Cu-V-Ti joint was formed with the Cu-V composite layer,the composite layer could effectively prevent the Ti element from contacting the Fe element.Ti-Fe and Ti-Cu intermetallic compounds were dispersed in the solid solution when copper-based solid solution and vanadium-based solid solution were formed in the weld with single laser beam.The strength of the joint was 142.4MPa.Two welds were formed with double beam welding,and the second beam partially remelted the weld formed by the first beam.The joint strength came up to 201.9MPa when the first beam focus was located at the vanadium-titanium interface and the second beam at the copper-steel interface.In the reverse order,the strength of the joint was 189.1MPa.Both of the fracture sites were located at the vanadium-titanium interface.