Spectroscopic investigation of laser-induced plasma in CO₂ laser welding aluminum alloys

Laser-induced plasma obtained during the process of CO₂ laser welding aluminum alloys have been studied. Laser-induced plasma occurs in laser welding and reveals important information about technological process. Optical spectrums of laser-induced plasma in CO₂ laser welding 6061 aluminum alloy were measured through PI Acton Research Spectra Pro2500i transient spectrometer. Boltzmann diagrams could be used to calculate the average temperature of laser-induced plasma, which were deduced from MgⅠspectrum lines between 200 and 600 nm. The influence of welding parameters, such as laser power, welding speed, focus position and shielding gas, on laser-induced plasma temperature were investigated separately and the reasons were also discussed. Under the experimental conditions, laser power played little role on laser-induced plasma temperature (6000K) when it exceeded the threshold power of laser penetration welding. The effect rule of welding speeds on laser-induced plasma temperature liked inverted U curve. Laser-induced plasma temperature had been increasing before decreasing when the flow rate of shielding gas was increasing for a given diameter of nozzle. Laser-induced plasma temperature would increase from 500 to 1000K when adding Argon in Helium.