Abstract
This study was undertaken to obtain a fundamental knowledge of pulsed laser welding phenomena, especially evaporation mechanism of different aluminum alloys. The dynamic behavior of Al-Mg alloys plume was very unstable and its fluctuation period was about 450 to 500μs. This instability was closely related to the unstable motion of a keyhole during laser irradiation. It was confirmed that the resonant lines of Al and Mg were strongly self-absorbed, in particular in the vicinity of pool surface. The intensities of molecular spectra of AlO and MgO were different each other depending on the power density of a laser beam. Under the low power density condition, the MgO band spectrum was predominant in intensity, while the AlO spectra became much stronger with an increase in the power density. These behaviors have been attributed to the difference in evaporation phenomena of Al and Mg metals with different boiling points and latent heats of vaporization. The time-averaged plume temperature and electron number density at 1 mm above the surface were determined by spectroscopic methods, and consequently the obtained temperature was 3, 280±150 K and the electron number density was 1.85×1019 1/m3.
