Study On The Mechanism Of Oscillating Laser And TIG Composite Filler Wire Welding And Porosity Suppression Of Titanium Alloy

Titanium alloy owns the features of lesser density,high specific strength,good corrosion resistance,etc,and is widely used in aerospace and other fields.At present,TIG and MIG are still the main welding methods for titanium alloys,but these welding methods have some problems such as limited penetration capacity,low process progress and uncontrollable heat input.Laser welding keyhole is unstable,easy to produce porosities,affect the joint performance.Versus regular laser welding,the laser swings to prevent the keyhole instability.The oscillating laser is combined with TIG,and the superposition of the coupling input source energy fields makes the energy efficient coupling,which can improve the melting efficiency and reduce the porosity defects.To explore suitable for aerospace field with new connection technology of titanium alloy,this paper select aircraft exhaust duct in TC4 titanium alloy as the object,to carry out the oscillating laser and experimental study on the composite TIG welding process,to explore the weld and weld porosity and species distribution,the joint effects of organizational performance,reveal the laser oscillation inhibition mechanism of porosity.It is expected to provide a new idea and theoretical basis for the application of oscillating laser and TIG composite welding of titanium alloy.In order to determine the oscillating parameters of oscillating laser welding,the influences of oscillating trajectory,oscillating frequency and oscillating amplitude on the weld surface,cross section shape and porosity were firstly explored.It is found that there is an optimal oscillating process parameter interval,beyond which defects such as uneven surface,bite edge and splash appear on the welding seam,and the penetration depth decreases obviously,while the porosity of the welding seam increases obviously.With TIG as the main welding heat source,the laser and TIG arc oscillating laser-TIG composite welding was carried out.It was found that under the combined action of the two heat sources,the weld surface had higher brightness,the distribution of fish scales was compact,and the transition between the weld center and both sides of the weld was gentle.The coupling between the two heat sources energy increased the width of the weld.Comparing the size and types of weld porosities,joint microstructure,microhardness and tensile strength before and after the oscillating of laser heat source,it is found that the stability of keyhole is improved and the process type porosities are reduced when the oscillating of laser heat source.In addition,the oscillating laser plays a role in refining the grain,forming fine and dispersed needle-like ? 'martensite,which significantly improves the mechanical properties of the weld.Second,by high speed camera,the metal vapor/plasma before and after laser oscillation,fluctuation characteristics of keyhole,found that the laser heat source,to reduce the height of metal vapor/plasma,brightness is reduced,show obvious cyclical changes,metal vapor/plasma area of low level fluctuations,welding stability;Compared with conventional laser,the opening diameter of the keyhole generated by swinging laser increased,and the size of the aperture changed little with time,indicating that the keyhole was stable.In addition,the oscillating laser molten pool flows in an orderly manner,and there is no backflow phenomenon.Finally,the inhibitory mechanism of porosity in titanium alloy oscillating laser and TIG composite welding is discussed.It is considered that the oscillating of laser heat source has the stirring effect on welding pool,and the movement path of oscillating laser overlaps,resulting in the remelting effect on solidified weld,which leads to the existence of liquid metal for a long time,so as to win more time for bubbles to float up in the welding pool and avoid the incomplete escape porosities in the welding pool.In addition,the oscillating laser increases the keyhole opening area,improves the keyhole stability,and reduces the production of process porosities caused by keyhole collapse.