Spectroscopic studies on laser induced plume of aluminum alloys

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The paper describes the features and characteristics of plume induced in the pulsed YAG laser welding of Al-Mg alloys in air and Argon atmospheres. Compared with plumes of steel, stainless steel, Titanium, etc., the dynamic behavior of Al-Mg alloys plume is very unstable and this instability is closely related to the unstable motion of key-hole during laser irradiation. The shape of key-hole fluctuates both in size and shape and its fluctuation period was about 450 μs. This instability has been estimated to be caused by the evaporation phenomena of metals with different boiling points and latent heats of vaporization. Therefore, the authors have conducted the spectroscopic analysis of laser induced Al-Mg alloys plume. In the air environment, the identified spectra are atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg line, as well as strong molecular spectra of AlO, MgO and AlH. It has been confirmed that the resonant lines of Al and Mg are strongly self-absorbed, in particular in the vicinity of pool surface. The self-absorption of atomic Mg line is more eminent in alloys containing higher Mg. These facts have shown that the laser induced plume is relatively a low temperature and high density metallic vapor. The intensities of molecular spectra of AlO and MgO are different each other depending on the power density of laser beam. Under the low power density condition, the MgO band spectrum is predominant in intensity, while the AlO spectrum became much stronger in higher power density. In Argon atmosphere MgO and AlO spectra vanish, but AlH spectrum is detected. The Hydrogen source is presumably the Hydrogen solved in the base metal, adsorbed water on the surface oxide layer or H2 and H2O in the shielding gas. The time average plume temperature at 1 mm high above the surface is determined by the Boltzmann plot and the obtained electron temperature is 3,280 ± 150 K. The electron number density, which has been determined by measuring the relative intensities of the spectral lines of atomic and singly ionized Magnesium, is 1.85 × 10191/m3.The paper describes the features and characteristics of plume induced in the pulsed YAG laser welding of Al-Mg alloys in air and Argon atmospheres. Compared with plumes of steel, stainless steel, Titanium, etc., the dynamic behavior of Al-Mg alloys plume is very unstable and this instability is closely related to the unstable motion of key-hole during laser irradiation. The shape of key-hole fluctuates both in size and shape and its fluctuation period was about 450 μs. This instability has been estimated to be caused by the evaporation phenomena of metals with different boiling points and latent heats of vaporization. Therefore, the authors have conducted the spectroscopic analysis of laser induced Al-Mg alloys plume. In the air environment, the identified spectra are atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg line, as well as strong molecular spectra of AlO, MgO and AlH. It has been confirmed that the resonant lines of Al and Mg are strongly self-absorbed, in particular in the v...