Microstructure And Properties Of Cu/Ti Laser Welded Joints

The butt joint of Cu/Ti has a wide range of applications in aerospace,electrolytic copper and other industries because of the excellent performance of titanium alloy and copper.In the paper,5mm T2 copper and TA18 titanium alloys were welded by laser welding.The study mainly focused on the weld appearance,organizational characteristics and mechanical properties with the different laser offsets,control the amount and form of the intermetallic compounds.The transition layer V was used to ducuse the form of the intermetallic compounds.The OM?SEM?EDS?XRD?and TEM was used to certified the micristructure and phase composition of the Cu/Ti joint.The mechanical properties of the joints were tested by stretching test and microdimensional hardness test.With the laser focused on the center of the Cu/Ti joint,the amount of intermetallic compounds of Ti₂Cu?TiCu and Ti₂Cu₃ were formed and which reduced the joint strength to only 81MPa,the hardness of joint was between 450-550HV.The organization structure and formation of the intermetallic compounds of the joint could be improved by adjusting the offset of the laser beam.With the laser offset to Ti side 0.15mm,0.3mm,0.45mm,the tensile strength of the joint was gradually improved.When the laser beam offset to Ti side0.45mm,the weld metal was consisted of Ti?s,s?and amount of intermetallic compounds,the tensile strength of the joint was 108MPa.When the laser beam adjusted to Cu side,the intermetallic compounds in the weld metal decreased with the offset distance increased.With laser beam offset to copper side by 0.45 mm,the welded metal and fusion line of Cu side were mainly consisted of the Cu solid solution.The intermetallic layer was formed at the titanium-welded metal interface.The thickness of IMCs was about 25?m and consisted of the Cu solid solution,intermetallic compounds such as TiCu,TiCu₂,Ti₂Cu and Ti₃Cu₄.The tensile strength of butt joints could reach 151MPa,i.e.61%of the tensile strength of the copper base metal.The quasi-cleavage fracture occurred at the IMCs.The metal V with different thickness was filling as the transition layer of the Cu/Ti joint welded by laser.When the thickness of the V is 0.2mm,the proportion of V in the weld metal was very low and the tensile strength is only 84MPa;When the thickness of the V is 0.4mm,the Ti-Cu-V mixed phase and amount of intermetallic compounds Ti₂Cu₃ and TiCu₂ were formed in the weld metal and fusion line of Ti side,there are hardly any intermetallic compounds found in the weld metal near the Cu side.The tensile strength of the joint is greatly increased to 153MPa;When the thickness of the V is 0.6mm,the number of intermetallic compounds in the joint is significantly reduced,there are hardly any intermetallic compounds found in the weld metal near the Cu side.The phase in the fusion line of Ti side is consisted of Ti-Cu-V mixed phase,Ti?s,s?,?TiCu₄ and TiCu_2,the middle of weld metal is mainly consisted of Ti-Cu-V mixed phase substrate and a bit of intermetallic compounds precipitated from the substrate.The hardness of the weld metal is between400HV and 500HV,the tensile strength of the joint is 176MPa,i.e.71%of the tensile strength of the copper base metal.The quasi-cleavage fracture occurred middle of the weld metal.