Study On Spectral Characteristics Of Plasma In Laser Welding And Laser-Arc Hybrid Welding Of Al Alloys With Beam Oscillation

Beam oscillation could optimize the plasma behaviors and change the energy transfer characteristics in both laser welding and laser-arc hybrid welding,which improves the metallurgical behaviors of molten pool.Thus the application of oscillating laser is an effective way to enhance the welding quality of aluminum alloys.However,the studies on the effects of beam oscillation on the spectral characteristics of plasma in both laser welding and laser-arc hybrid welding are seldom.In the current study,the effects of oscillation amplitude and frequency on the spectral characteristics of plasma in both laser welding and laser-arc hybrid welding are discussed.The main results are as follows.The typical spectrum of laser oscillating welding of aluminum alloy mainly concentrates in the range of 300-600 nm,including Mg atomic spectral line,Mg ionic spectral line and Al atomic spectral line.The average spectral intensity of Mg I 518.36nm atomic spectral line is used to characterize the plasma intensity in laser welding because beam oscillation has a significant influence on it during laser oscillating welding.The Mg? 279.76nm ionic spectral line is used to characterize the effects of beam oscillation on the laser-arc interactions because it occurs in the laser irradiation zone during hybrid welding,and its spectral line intensity at peak current is about 21 times larger than that of none-oscillating hybrid welding.In laser welding,increasing oscillation amplitude or frequency decreases the plasma spectral intensity and electron density,and simultaneously lessens weld penetration because the beam oscillation reduces local energy density and action time and hinders the continuous increasing plasma density.The electron temperature decreases with the increase of oscillation amplitude,but is not influenced by the oscillation frequency.When the oscillation amplitude increases from 0.5 to 3mm,the spectral intensity and electron density both decrease by 18%,and the electron temperature reduced by 10%.When the oscillation frequency increases from 50 to 500Hz,the spectral intensity and electron density reduces by 19%and 21%respectively,but the electron temperature maintains at about 5500K.In laser-arc hybrid welding,the beam oscillation strengthens the interactions between laser-induced plasma and arc plasma,which is characterized by the increase of the intensity of Mg? 279.76nm ionic spectral line,but it is not consistent to the electron temperature and density.The oscillation amplitude has a greater effect on spectral intensity than the oscillation frequency in arc center zone.When the oscillation amplitude increases from 0.3 to 1.0mm,the spectral intensity reaches the maximum of2.31×10~4counts,which increases by 83%than that of the none-oscillating welding.It then reduces,which indicates decreasing laser-arc interactions.When the oscillation frequency increases from 10 to 200Hz,the spectral intensity quickly increases to 2.36×10~4 counts and then keeps stable,which increases by 87% than that of the none-oscillation welding.The differences in spectral intensity between arc center zone and Laser irradiation zone based on the Mg? 279.76 nm ionic spectral line can be used as an effective way to characterize the laser-arc interactions in hybrid welding with beam oscillation.As the oscillating amplitude or frequency increases,the beam scanning area and velocity both increase,and the difference between spectral intensity decreases,which indicates that the laser-arc interactions become more and more intense.Besides,the particle exchange between laser-induced plasma and arc plasma is getting stronger and the entire plasma in hybrid welding becomes more and more uniform.