Research On Dual Laser Welding Of Dissimilar Titanium Alloys

Ti₂AlNb alloy is a new class of titanium intermetallic alloy developed in the process of researching on Ti₃ Al for higher strength and toughness.It has high specific strength,fracture toughness,high temperature strength and creep resistance,etc.Some components made of this alloy have been used in the field of aerospace.However it is easy to generate single B2 phase in the weld when using laser beam welding which causes low tensile strength.In order to solve this problem,this paper uses dual laser beam welding to improve the phase composition and tensile strength.This research has theoretical significance and actual application value for dual laser welding of dissimilar titanium alloys.In this paper,the alloys of Ti-22Al-25 Nb and TA15 which were 2mm thick were welded by continuous laser beam welding.The appearances,microstructure and properties of welded joint under single or dual beam welding were compared.Influences of welding parameters on appearances,microstructure and properties under dual laser beam welding were explored.Results showed that,in the selected welding parameters,the cross section shape of weld zone was like cup-cone under single or dual laser beam welding.Front weld width of dual laser beam welding was wider than that of single mode,back weld width of dual laser beam welding was narrower than that of single mode,ratio of front and back weld width under dual laser beam welding was bigger than that of single mode.Weld of both single and dual laser beam welding consisted of plane crystal and cellular dendrite,size of the cellular dendrite under dual laser beam welding was larger.In the mode of single laser beam,the weld only consisted of B2 and the fracture located at the weld,the morphology was quasi-cleavage fracture.In the mode of dual laser beam,the weld contained B2 and O.Micro-hardness of the weld under dual laser beam was higher than that of single laser beam.The fracture also located at the weld,but the tensile strength and elongation were both increased.The morphology was dimple fracture.In the mode of dual laser beam,the weld only consisted of B2 when the power was lower or the welding speed was higher.The content of O increased with the increase of laser power or the decrease of welding speed.The interaction between light spot spacing and power ratio was obvious in the mode of dual laser beam and both of them had a great influence on the width of the back weld.In the selected welding parameters,when the light spot spacing and power ratio varied,the weld contained B2 and O.With the increasing of light spot spacing or the approaching of power ratio,the content of O increased.Both micro-hardness in the weld zone and tensile strength increased with the content of O raised.Only when the power ratio was 50:50 and the light spot spacing was 0.54 mm,part of the weld was not penetrated,the room temperature tensile strength obviously decreased.