【作者】 曾杰；

【导师】 曾晓雁；

【作者基本信息】 华中科技大学 ， 光学工程， 2019， 硕士

【摘要】 激光束振荡扫描行为能够影响激光焊接和激光-电弧复合焊接的等离子体行为、改变能量传递特性,进而改善熔池冶金行为,是提升铝合金焊缝质量的有效手段。但是有关光束扫描行为对激光焊接/复合焊接等离子体光谱特性影响的研究相对缺乏。为此,本文系统研究了圆形光束扫描振幅(半径)和频率对AA6082铝合金激光焊接和激光-电弧复合焊接等离子体光谱特性的影响规律。主要结果如下:振荡扫描激光焊接和复合焊接的光谱谱线都主要集中在300-600nm波段,由Mg原子谱线、Mg离子谱线及Al原子谱线构成。扫描行为对MgⅠ 518.36nm原子谱线影响最为显著,将其平均光谱强度作为表征激光焊接等离子体强度的特征参量。扫描复合焊接的激光辐照区有MgⅡ 279.76nm离子谱线,峰值电流下其谱线强度比无扫描增加了约20倍,表明激光束扫描能够增强激光-电弧相互作用,因此可以用MgⅡ 279.76nm谱线强度来表征激光束扫描对两种热源之间相互作用的影响程度。激光焊接时,由于光束扫描行为降低了局部区域能量密度和作用时间,阻碍了光致等离子体的持续增强,因此增大扫描振幅或频率都会减少等离子体光谱强度和电子密度,同时降低焊缝熔深,但是电子温度仅随着扫描振幅的增加而减少,基本不受扫描频率的影响。当扫描振幅从0.5mm增加到3mm时,等离子体光谱强度和电子密度都减少18%,电子温度降低10%;当扫描频率从50Hz增加到500Hz时,光谱强度和电子密度分别减少19%和21%,电子温度则稳定在5500K左右。激光-电弧复合焊接时,激光束扫描行为能够增强光致等离子体和电弧等离子体之间的粒子交换,促进两者的相互作用,主要表现为MgⅡ 279.76nm谱线强度的增强,和电子温度、电子密度没有直接的对应关系。对于电弧中心区而言,扫描振幅对光谱强度影响更大。当扫描振幅由0.3mm增加到1mm时,光谱强度达到最大,为2.31×10~4counts,比无扫描焊接提高83%,随后逐渐降低,意味着激光-电弧相互作用程度减弱。当扫描频率由10Hz增加到200Hz时,光谱强度快速增加至2.36×10~4counts,比无扫描焊接提高87%,然后保持稳定。基于MgⅡ 279.76nm谱线的电弧中心区和激光辐照区光谱强度的差值可以作为表征扫描复合焊接激光-电弧相互作用程度的有效手段。数据表明随着扫描振幅或频率的增加,光束扫描范围和速度增大,光谱强度差值不断减小,意味着激光-电弧相互作用程度越来越大,光致等离子体和电弧等离子体之间的粒子交换越来越强烈,两者的融合越来越充分,整个复合焊接等离子体越来越均匀。更多还原

【Abstract】 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 MgⅡ 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 MgⅡ 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 MgⅡ 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.更多还原